Download A Single Exposure to Particulate or Gaseous Air

TOXICOLOGICAL SCIENCES 112(2), 532–542 (2009)
doi:10.1093/toxsci/kfp214
Advance Access publication September 11, 2009
A Single Exposure to Particulate or Gaseous Air Pollution Increases the
Risk of Aconitine-Induced Cardiac Arrhythmia in Hypertensive Rats
Mehdi S. Hazari,*,1 Najwa Haykal-Coates,* Darrell W. Winsett,* Daniel L. Costa,† and Aimen K. Farraj*
*Environmental Public Health Division; and †Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North
Carolina 27711
Received July 27, 2009; accepted August 28, 2009
Epidemiological studies demonstrate an association between
arrhythmias and air pollution. Aconitine-induced cardiac arrhythmia is widely used experimentally to examine factors that
alter the risk of arrhythmogenesis. In this study, Wistar-Kyoto
(WKY) and spontaneously hypertensive (SH) rats acutely exposed
to synthetic residual oil fly ash (s-ROFA) particles (450 mg/m3)
were ‘‘challenged’’ with aconitine to examine whether a single
exposure could predispose to arrhythmogenesis. Separately, SH
rats were exposed to varied particulate matter (PM) concentrations (0.45, 1.0, or 3.5 mg/m3 s-ROFA), or the irritant gas
acrolein (3 ppm), to better assess the generalization of this
challenge response. Rather than directly cause arrhythmias, we
hypothesized that inhaled air pollutants sensitize the heart to
subsequent dysrhythmic stimuli. Twenty-four hour postexposure,
urethane-anesthetized rats were monitored for heart rate (HR),
electrocardiogram, and blood pressure (BP). SH rats had higher
baseline HR and BP and significantly longer PR intervals, QRS
duration, QTc, and JTc than WKY rats. PM exposure caused
a significant increase in the PR interval, QRS duration, and QTc
in WKY rats but not in SH rats. Heart rate variability was
significantly decreased in WKY rats after PM exposure but
increased in SH rats. Cumulative dose of aconitine that triggered
arrhythmias in air-exposed SH rats was lower than WKY rats and
even lower for each strain postexposure. SH rats exposed to varied
concentrations of PM or acrolein developed arrhythmia at
significantly lower doses of aconitine than controls; however,
there was no PM concentration–dependent response. In conclusion, a single exposure to air pollution may increase the sensitivity
of cardiac electrical conduction to disruption. Moreover, there
seem to be host factors (e.g., cardiovascular disease) that increase
vulnerability to triggered arrhythmias regardless of the pollutant
or its concentration.
Disclaimer: The research described in this article has been reviewed by the
National Health and Environmental Effects Research Laboratory, U.S.
Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and the policies
of the agency nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
1
To whom correspondence should be addressed at Environmental Public
Health Division, U.S. Environmental Protection Agency, 109 Alexander Drive,
B143-01, Research Triangle Park, NC 27711. Fax: (919) 541-0034. E-mail:
[email protected].
Key Words: aconitine; air pollution; cardiac arrhythmia;
inhalation.
Epidemiological, experimental, and clinical studies point to
a significant association between arrhythmias and air pollutant
exposures. For example, hospital admissions for arrhythmias
increased by 49% during a 1985 smog episode in West
Germany (Wichmann et al., 1989). Peters et al. (2000) showed
a significant correlation between the frequency of cardioverter
defibrillator discharge and the levels of certain gaseous and
particulate matter (PM) air pollutants, also indicating a relationship between air pollution and cardiac arrhythmia. While the
relative risk of death due to PM air pollution is higher for
exacerbation of respiratory conditions, the greater proportion of
the population with underlying cardiovascular disease yields
substantially more deaths related to cardiovascular-associated
mortality (Dockery, 2001). Hospitalization due to cardiovascular complications were found to be significantly associated
with PM10, CO, and NO2 (Linn et al., 2000) between 1992 and
1995 in Los Angeles, CA, USA, and when related to air
pollution appear to be quite dependent on underlying heart
disease (Pope et al., 2008). In rats with severe cardiac disease,
exposures of increasing doses of a model PM raised the
incidence of cardiac arrhythmia as well as other cardiographic
abnormalities, a response not observed in normal rats
(Watkinson et al., 1998; Wellenius et al., 2002). These similar
findings between the humans and rats linked by underlying
cardiac disease suggest commonalities that might be exploited
in studies with the rat which could shed light on the conditions
or circumstances which promote these events in humans.
A novel approach has been employed to explore the
tendency or sensitivity to arrhythmogenic episodes associated
with air pollutant exposure. This approach takes advantage of
the potential for pollutants to ‘‘sensitize’’ individuals to
subsequent cardiac stimuli rather than examine direct exposurerelated cardiac events per se. Aconitine, a cardiotoxic alkaloid
derived from the plant Aconitum (wolfsbane), is widely used to
produce ventricular arrhythmias in laboratory animals. Aconitine targets voltage-dependent sodium channels in various
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AIR POLLUTION INCREASES RISK OF TRIGGERED CARDIAC ARRHYTHMIA
excitable tissues, including the myocardium, suppressing their
inactivation and thereby interfering with repolarization of the
cardiomycyte membrane in preparation for the next beat.
Therefore, this drug has come to be used to produce
experimental arrhythmia, often as a positive control in drugtesting paradigms, which assess potential arrhythmogenic
properties (e.g., doxorubicin; Dragojevic-Simic et al., 2004)
and test the efficacy of antiarrhythmic drugs (Bartosova et al.,
2007; Lu and De Clerck, 1993). Recently, aconitine was used
to compare arrhythmia susceptibility of healthy animals and
those with cardiovascular disease (Li et al., 2007). The present
study takes advantage of the arrhythmogenic properties of
aconitine to, for the first time, test arrhythmia sensitivity
following exposure to air pollutants. Here, we sought to
determine whether inhalation exposure to particulate or
gaseous air pollutants increases the risk of arrhythmogenesis
in a rat model of hypertension.
We adapted a simple cardiac challenge test using the wellestablished arrhythmogenic properties of aconitine to (1)
determine if hypertensive rats are more at risk of developing
cardiac arrhythmia when compared to normotensive rats; (2)
compare the impact of a single inhalation exposure to
a synthetic PM that is similar in transition metal content to
residual oil fly ash (ROFA), an emission source pollutant
particle found in fossil fuel emissions, on arrhythmogenicity in
normotensive and hypertensive rats; and (3) determine if
increasing concentrations of PM or acrolein, a potent gaseous
pulmonary irritant found in cigarette smoke, increase the risk of
developing cardiac arrhythmia in hypertensive rats. We
hypothesized that inhaled air pollutants sensitize the heart to
dysrhythmic stimuli rather than directly cause arrhythmias.
MATERIALS AND METHODS
Animals
Eleven-week-old male Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats (Charles River, Wilmington, MA) weighing 300–400 g were
studied. Upon arrival, animals were housed two per cage with food and water
available ad libitum in a facility approved by the Association for Assessment
and Accreditation of Laboratory Animal Care. All experimental protocols were
approved by and in accordance with the guidelines of the Institutional Animal
Care and Use Committee of the U.S. Environmental Protection Agency,
Research Triangle Park, NC.
Implantation of Radiotelemeters
Radiotelemeters were implanted in all animals as previously described
(Campen et al., 2000; Watkinson et al., 1995). Briefly, animals were weighed
and anesthetized with ketamine hydrochloride/xylazine hydrochloride solution
(1 ml/kg, ip; Sigma-Aldrich, St Louis, MO). Using aseptic technique, each
animal was implanted with a radiotelemetry transmitter (Model TA11CTAF40; Data Sciences International, Inc., St Paul, MN) in the abdominal cavity
through a small incision. The electrode leads were guided through the
abdominal musculature via separate stab wounds and tunneled sc across the
lateral ventral thorax; the distal portions of the leads were secured in positions
that approximated those of the lead II of a standard electrocardiogram (ECG).
Body heat was maintained both during and immediately following the surgery.
533
Animals were given food and water and were housed individually. All animals
were allowed 7–10 days to recover from the surgery and reestablish circadian
rhythms.
Radiotelemetry Data Acquisition and Analysis
Radiotelemetry methodology (Data Sciences International, Inc.) was used to
track changes in cardiovascular function by monitoring ECG and heart rate
(HR). This methodology provided continuous monitoring and collection of
physiologic data from individual rats to a remote receiver (DataART2.1; Data
Sciences International, Inc.). ECG waveforms were continuously acquired and
saved during the 5-min baseline period and aconitine challenge, which did not
last longer than 40 min. HR was obtained from the ECG.
ECG Analysis
ECGAuto software (EMKA Technologies USA, Falls Church, VA) was
used to visualize individual ECG signals, analyze and quantify ECG segment
durations, and identify cardiac arrhythmias. Using ECGAuto, P-wave, QRS
complex, and T-wave were identified for individual ECG waveforms and
compiled into a library. Analysis of all experimental ECG traces was then based
on established libraries. The following parameters were determined for each
ECG waveform: PR interval; QRS duration, which was measured as the
beginning of the R-wave (nadir of Q-wave) until the S-wave reached the
isoelectric line because Q-waves were not clearly discernable in many traces;
QT interval; QT corrected for HR (QTc) using Bazett’s formula; corrected JT
interval (JTc ¼ QTc QRS); and ST interval, which was measured from the
nadir of the S-wave until the end of the T-wave or when it reached the
isoelectric line. The Lambeth Conventions (Walker et al., 1988) were used as
guidelines for the identification of cardiac arrhythmic events in rats.
Arrhythmias were identified as occurring sequentially during aconitine
challenge as ventricular premature beats (VPBs), ventricular tachycardia
(VT), and ventricular fibrillation (VF). Figure 1 shows examples of arrhythmias
typically found in the animals in this study.
Heart rate variability (HRV) was calculated as the mean of the differences
between sequential HRs for the complete set of ECG signals using ECGAuto.
For each 1-min stream of ECG waveforms, mean time between successive QRS
complex peaks (RR interval), mean HR, and mean HRV-analysis–generated
time-domain measures were acquired. The time-domain measures included
standard deviation of the time between normal-to-normal beats (SDNN) and
root mean squared successive differences (RMSSD). HRV analysis was
also conducted in the frequency domain using a fast Fourier transform. The
spectral power obtained from this transformation represents the total harmonic
variability for the frequency range being analyzed. In this study, the spectrum
was divided into low-frequency (Lf ) and high-frequency (Hf ) regions. The
ratio of these two frequency domains (Lf/Hf ) was calculated as an estimate of
the relative balance between sympathetic (Lf ) and vagal (Hf ) activity.
Groups
Table 1 shows the exposure groups. SH rats (n ¼ 6 per group) were assigned
to one of the following exposure groups: (1) filtered air, (2) 450 lg/m3 (low),
(3) 1 mg/m3 (medium), (4) 3.5 mg/m3 (high) synthetic residual oil fly
ash (s-ROFA), or (5) 3 ppm acrolein, exposed and then challenged with
aconitine 24 h later to measure sensitivity to arrhythmias associated
with increasing concentrations of s-ROFA and to assess the transferability of
this approach to a known gaseous irritant, acrolein. Concurrently, WKY rats
(n ¼ 6 per group) were exposed to either filtered air or 450 lg/m3 (low)
s-ROFA and then challenged with aconitine 24 h later to assess the effect of
strain on arrhythmogenicity following exposure.
Exposure
s-ROFA-Like PM. The PM used in this study was synthetically generated
by combining metal compounds in molar ratios reflecting those observed in
a model historic PM ROFA (Southern Research Institute, Birmingham, AL; an
emission air pollution particle that was collected as a fugitive stack emission
postemission control at a Florida Power & Light plant that burned #6 grade
residual oil containing 1% sulfur [Hatch et al., 1985]). After a 2-day
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HAZARI ET AL.
FIG. 1. Typical ECG traces showing normal sinus rhythm, VPB, VT, and VF.
acclimatization routine in the nose-only exposure system, the rats were exposed
one time for 3 h to 450 lg/m3, 1 mg/m3, or 3.5 mg/m3 of the PM2.5 fraction
(mass median aerodynamic diameter was 2.09 lm and the geometric standard
deviation was 3.37) of the PM or filtered air in two separate 24-port nose-only
flow-by inhalation chambers (Lab Products, Seaford, DE) as previously
described. Particle concentration was determined gravimetrically on Teflon
filters (45-mm diameter with 1-lm pore size; VWR Scientific, West Chester,
PA) using a Mercer cascade impactor (Intox Products, Albuquerque, NM), and
real-time PM concentration was estimated with an aerosol monitor (Dust Track;
TSI Inc., St Paul, MN) on the chamber exhaust. Extracts from the Teflon filters
were analyzed quantitatively for 28 metals and sulfur (expressed as sulfate) on
a PerkinElmer 4300DV ICP-OES elemental analyzer (PerkinsElmer, Waltham,
MA). Samples were extracted with either deionized H2O or 1M HCl. Mean
(± SD) of H2O-soluble content of metals and SO4 in microgram per gram were
as follows: Fe ¼ 1118 ± 210, Ni ¼ 10,144 ± 947, V ¼ 21,849 ± 2342, and SO4 ¼
335,077 ± 28,529. Mean (± SD) 1M HCl-soluble content of metals and SO4 in
microgram per gram were as follows: Fe ¼ 135,586 ± 7904, Ni ¼ 12,398 ±
713, V ¼ 89,852 ± 5432, and SO4 ¼ 421,845 ± 22,923.
TABLE 1
Exposure Groups
Strain
WKY (air)
WKY (s-ROFA)
SH rat (air)
SH rat (s-ROFA)
SH rat (s-ROFA medium)
SH rat (s-ROFA high)
SH rat (acrolein)
Exposure (n ¼ 6)
Filtered air
450 lg/m3 s-ROFA
Filtered air
450 lg/m3 s-ROFA
1.0 mg/m3 s-ROFA
3.5 mg/m3 s-ROFA
3 ppm acrolein
Acrolein. Animals were exposed to 3 ppm acrolein for 3 h, while
a separate control group was simultaneously exposed to filtered air. Gas was
metered from a 1000-ppm cylinder into a glass mixing chamber where the gas
was mixed with dry filtered dilution air to achieve a final concentration of 3
ppm of acrolein with a total flow of 6 l/min. All animals were monitored for
a 15-min baseline period prior to being exposed in a whole-body plethysmograph (Model PLY3213; Buxco Electronics, Inc., Wilmington, NC), which
continuously and noninvasively monitored respiratory function in the conscious
animals. The actual chamber concentration was measured using an HP5890 gas
chromatograph (Hewlett Packard, Palo Alto, CA) equipped with manual
injection, a flame ionization detector, and a DB-VRX capillary column (Agilent
Technologies, Foster City, CA). The plethysmograph pressure was monitored
using Biosystems XA software (Buxco Electronics, Inc.).
Although these concentrations are relatively high compared to ambient air,
such challenges can be reached occupationally as in the case of ROFA and
cigarette smoke exposures (10 ppm mainstream smoke) in the case of acrolein
(Reinhardt and Ottmar, 2004; Song et al., 2004). For instance, Cavallari
et al. (2008a) found that boilermaker welders were exposed to mean
PM2.5 concentrations of 1.12 mg/m3; however, the concentrations actually ranged
from 0.12 to 3.99 mg/m3. Other studies in similar cohorts have documented
occupational concentrations of 0.47 mg/m3 of PM10 (Liu et al., 2005) and 0.44 mg/
m3 (Kim et al., 2004) and 0.65 mg/m3 (Cavallari et al., 2008b) of PM2.5.
Nevertheless, the specific aim of the study was to ascertain the feasibility of
a postexposure challenge approach for assessing enhanced cardio-sensitivity to
dysrrhythmias.
Aconitine Challenge
We have previously demonstrated that the number of arrhythmias are
dramatically increased in SH rats in the 24-h period following a single ROFA
exposure (Farraj et al., 2009). Similarly, Dockery et al. (2005) have suggested,
in the reverse situation, that assessment of pollutant concentrations 24 h prior to
the arrhythmia would provide a good estimate of a subject’s exposure.
Therefore, 24 h after particle or gaseous irritant exposure, animals were
AIR POLLUTION INCREASES RISK OF TRIGGERED CARDIAC ARRHYTHMIA
535
anesthetized with urethane (1.5 g/kg, ip) for the aconitine challenge;
supplemental doses of the anesthetic were administered iv when necessary to
abolish pain reflex. Animal body temperature was maintained at ~36C with
a heating pad. The left jugular vein and right carotid artery were cannulated
with P.E. 50 polyethylene tubing (Becton-Dickinson, Sparks, MD) for the
administration of aconitine and measurement of blood pressure (BP),
respectively. Ten microgram per milliliter aconitine was continuously infused
at a speed of 0.2 ml/min, while ECG was continuously monitored and timed.
Sensitivity to arrhythmia was measured as the threshold dose of aconitine
required to produce VPBs, VT, and VF and was calculated using the following
formula:
Threshold dose ðlg=kgÞ for arrhythmia ¼ 10 lg=ml 3 0:2ml=min 3
time required for inducing arrhythmiaðminÞ=body weightðkgÞ:
Statistics
The statistical analyses for all the data in this study were performed using
SAS version 9.1.3 software (SAS Institute Inc., Cary, NC). PROC MIXED and
PROC GLIMMIX procedures were used to analyze all ECG- and HRVgenerated data. Tests of normality were performed for all continuous variables,
and parametric methods of analysis were used. A linear mixed model with
restricted maximum-likelihood estimation analysis (SAS) and least squares
means post hoc test were used to determine statistical differences for all data.
All aconitine dose-response data were analyzed using an ANOVA. A p value
of < 0.05 was considered as statistically significant. A significant interaction
resulted in pairwise comparisons performed as a subtest of the ANOVA model
adjusting the significance level for multiple comparisons using Tukey’s post
hoc test. Reported values represent means ± SE.
FIG. 2. Postexposure body weight and HR of WKY and SH rats. (A)
WKY rats exposed to s-ROFA had significantly lower body weight when
compared to air-exposed WKY rats and s-ROFA-exposed SH rats. (B) One day
following exposure, WKY rats had lower HR when compared to SH rats. Black
bars ¼ air; gray bars ¼ s-ROFA. *Significantly different from WKY (air);
§significantly different from WKY (s-ROFA), p < 0.05, n ¼ 6.
caused a significant decrease in MAP in WKY rats but had only
a minor, not significant, decrease in the SH rats (Fig. 3C).
Electrocardiogram
SH rats had significantly longer PR intervals, QRS duration,
QTc, and JTc when compared to WKY rats. Exposure to
s-ROFA caused a significant increase in PR interval, QRS
duration, and QTc in WKY rats but had no effect on SH rats.
There was no difference in ST interval duration between any of
the groups (Fig. 4).
RESULTS
Postexposure Comparison of WKY and SH Rat Strains
There were some basic differences among WKY and SH
rats; they were largely consistent with what were expected to
be observed for these two strains.
Body Weight and Heart Rate
There were no significant differences in the preexposure
body weights of any group, although SH rats were slightly
heavier. There was also no significant change in body weight
within a group between preexposure and postexposure (data
not shown). However, 24 h after exposure, WKY rats exposed
to s-ROFA had significantly lower body weights than airexposed WKY rats (Fig. 2A). There was no change in SH body
weights due to exposure to s-ROFA. However, 1 day following
exposure, urethane-anesthetized SH rats exposed to air only
had higher HR when compared to WKY rats. SH rats exposed
to s-ROFA had a significant decrease in HR relative to the air
controls (Fig. 2B).
Blood Pressure
There was no significant difference in the systolic and
diastolic BPs, as well as mean arterial pressure (MAP), of SH
rats when compared to WKY rats. However, a single exposure to
s-ROFA caused a small decrease in both systolic and diastolic
BP in both strains (Figs. 3A and 3B). Exposure to s-ROFA
Heart Rate Variability
SH rats had shorter RR interval than WKY rats as might be
expected with higher HRs. When adjusted for HR, air-exposed
SH rats had lower baseline overall and short-term HRV when
compared to air-exposed WKY rats. Lf, Hf, and Lf/Hf ratio was
lower in air-exposed SH rats when compared to air-exposed
WKY rats.
s-ROFA-exposed WKY rats exhibited lower mean RR
interval, significantly decreased overall and short-term HRV,
and significantly decreased power in the low and high-frequency
range when compared to air-exposed WKY rats. In contrast,
s-ROFA-exposed SH rats had higher RR interval, significantly
increased overall and short-term HRV, and increased power
in the low and high-frequency range when compared to
air-exposed SH rats. Exposure to s-ROFA caused an increase
in Lf/Hf in WKY rats and decrease in SH rats (Fig. 5).
Aconitine Challenge
During aconitine infusion, the first arrhythmia to be
manifested was the VPB, a form of irregular heartbeat in
which the lower chambers of the heart contract prematurely.
These anomalies, which are the most common form of
arrhythmia, are often perceived and described as skipped beats
or palpitations. Continued infusion of aconitine then elicited
three or more successive VPBs or VT, which is fast abnormal
heart rhythm that is potentially life threatening. VTs are
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HAZARI ET AL.
FIG. 3. Prechallenge arterial BP in WKY and SH rats. One day following exposure, systolic pressure (A), diastolic pressure (B), and mean BP (C) were not
significantly different in anesthetized SH rats when compared to WKY rats. Black bars ¼ air; gray bars ¼ s-ROFA. n ¼ 6.
dangerous, because if persistent, they can lead to VF or fatal,
uncoordinated, discordant contraction of the ventricles (Fig. 1).
Significant drops in BP occurred as VT became sustained and
transitioned to VF, which occurred at lower cumulative doses
of aconitine in SH rats when compared to WKY rats.
Figure 6 shows the dose of constantly infused aconitine that
elicited arrhythmia in WKY and SH rats. The cumulative dose
of aconitine necessary to trigger VPB, VT, and VF in SH rats
was significantly lower than WKY rats. Exposure to s-ROFA
further decreased the dose of aconitine that elicited arrhythmia
when compared to the respective air-exposed animals for each
strain (Fig. 6).
Figure 7 shows that exposure to varying concentrations of
s-ROFA or acrolein increases the risk of developing cardiac
arrhythmias in hypertensive rats. The cumulative dose of
aconitine necessary to trigger VPB, VT, and VF in SH rats
exposed to 0.45, 1.0, or 3.5 mg/m3 s-ROFA was significantly
lower than air-exposed controls. Interestingly, there was no effect
of increasing s-ROFA concentration on the dose of aconitine that
elicited arrhythmia. Exposure to acrolein also significantly
decreased the dose of aconitine that triggered arrhythmia when
compared to air-exposed controls; the doses were comparable to
those observed in the s-ROFA-exposed rats (Fig. 7).
DISCUSSION
Routinely, toxicological assessments of air pollutants focus
on the direct impacts of one or more pollutants on the targeted
tissue of organ systems. With air pollution, notably PM, there
FIG. 4. Postexposure differences in ECG parameters between WKY and SH rats. Both air-exposed and s-ROFA-exposed SH rats had significantly longer PR
intervals (A), QRS duration (B), QTc (C), and JTc (D) 1 day after exposure when compared to WKY rats. Exposure to s-ROFA caused a significant increase in PR
interval (A), QRS duration (B), and QTc (C) in WKY rats. There was no difference in ST interval duration between any of the groups (E). *Significantly different
from WKY (air); §significantly different from WKY (s-ROFA), p < 0.05, n ¼ 6.
AIR POLLUTION INCREASES RISK OF TRIGGERED CARDIAC ARRHYTHMIA
537
FIG. 5. Group data of HRV in WKY and SH rats exposed to s-ROFA. One day after exposure, s-ROFA-exposed WKY rats had lower RR interval (A),
significantly decreased SDNN (B) and RMSSD (C), and significantly decreased Lf (D) and Hf (E) when compared to air-exposed WKY rats (black bars). s-ROFAexposed SH rats had higher RR interval (A), significantly increased SDNN (B) and RMSSD (C), and increased Lf (D) and Hf (E) when compared to air-exposed
SH rats (gray bars). Exposure to s-ROFA caused an increase in Lf/Hf in WKY rats and decrease in SH rats (F). *p < 0.05, n ¼ 6.
are extensive reports of cardiac impacts, including arrhythmias,
which require hospitalization or potentially lead to other
morbidities or death. The findings presented here suggest that
perhaps the impact of pollutant exposure is less direct in
eliciting effects but more in the prestaging of a response to
FIG. 6. Increased risk of arrhythmia in hypertensive rats is exacerbated by
exposure to air pollution. Constant infusion of aconitine (2 lg/min) triggers
VPB, followed by VT, VF, and progression to cardiac arrest (CA) in airexposed WKY (black bars) and SH rats (dark gray bars). The cumulative dose
of aconitine necessary to trigger VPB, VT, VF, and CA in SH rats was lower
than WKY rats and lower following exposure to s-ROFA for each strain of rat
(light gray bars). *Significantly different from WKY (Air); §Significantly
different from WKY (s-ROFA); p < 0.05, n ¼ 6.
other cardiostimulatory challenges, i.e., a ‘‘sensitization.’’ A
single inhalation exposure to toxic air pollutants (either PM or
gaseous irritant), as used in this study, appeared to increase the
‘‘sensitivity’’ of the cardiac electrical conduction system, much
as the lungs become hyperresponsive to nonspecific stimuli
(e.g., methacholine, saline, dryness) following exposure to
respiratory toxicants (Bateson and Schwartz, 2008). It is also
apparent that part of this sensitivity results from underlying
cardiovascular disease. The stress to the body from exposure to
PM and acrolein suggests that they may not only enhance
sensitivity but also impart a temporal longevity beyond the
initial period of insult, 24 h in this case. Although air pollution
is often seen as a factor that sets off adverse cardiac events,
here we demonstrate that a single exposure increases the
vulnerability of the heart to developing arrhythmia by a subsequent trigger. This cardiac ‘‘hypersensitivity’’ may be a more
serious risk than direct toxic injury because it is insidious and
may occur at substantially lower doses.
The SH rat is widely used as a model for the study of
hypertension and progressive cardiovascular disease. Intrinsic
differences in the BP, myocardial substrate, or autonomic
nervous system function of the WKY and SH rat strains likely
contribute significantly to arrhythmogenic vulnerability. Although measured under anesthesia in this study, baseline HR
and BP were still higher in SH rats when compared to WKY
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HAZARI ET AL.
FIG. 7. Exposure to varying concentrations of PM or an irritant gas
increases the risk of developing cardiac arrhythmias. Constant infusion of
aconitine (2 lg/min) triggers VPB, followed by VT, VF, and progression to
cardiac arrest (CA) in air-exposed SH rats. The cumulative dose of aconitine
necessary to trigger VPB, VT, VF, and CA in rats exposed to increased
concentrations of s-ROFA or acrolein was significantly lower than air-exposed
controls. *Significantly different from air-exposed control; p < 0.05.
rats, regardless of exposure group. Anesthesia has depressive
effects on centrally mediated physiological function, e.g., one
study showed that sodium pentobarbital anesthesia lowered the
dose of aconitine at which ventricular arrhythmias occurred,
possibly due to decreased arterial baroreceptor function (Shu
et al., 2004). The authors demonstrated that conscious rats with
sinoaortic denervation, or depressed baroreflex sensitivity
(BRS), responded to a lower threshold dose of aconitine than
control rats. However, under pentobarbital anesthesia, control
rats and sinoaortic denervated rats had comparable responses,
suggesting depression of BRS by pentobarbital increased
sensitivity to aconitine. In the current study, the effects of
anesthesia were assumed to be minimal since urethane, which
is considered to have minor effects on the cardiovascular
system and its reflexes (Koblin, 2001; Maggi and Meli, 1986),
was used instead of pentobarbital. Thus, it may be likely that
SH rats are more sensitive to the arrhythmogenic effects of
aconitine than WKY rats because of inherent depressed BRS,
which is known to be impaired in hypertensive states (Gerritsen
et al., 2001; Mortara et al., 1997; Struyker-Boudier et al.,
1982).
It is important to note that at 11 weeks of age, despite some
elevation in BP, the SH rats probably had not fully developed
the hypertensive phenotype; older animals may have been
a better representation of this group. Regardless, the finding
that SH rats had greater baseline arrhythmia susceptibility
when compared to the normal WKY rats was in agreement with
the results of Li et al., who showed that 20-week-old Lyon
Hypertensive (LH) rats were more prone to ventricular
arrhythmias when compared to normotensive Lyon rats.
However, Li et al. (2007) found that BP level was not an
independent determinant of arrhythmia sensitivity to aconitine
in LH rats, which when considered with the results from the
younger less hypertensive SH rats in our study indicates that
BP by itself probably does not affect the dose at which
aconitine induces arrhythmia. Instead, it may be a combination
of hemodynamic abnormalities, cardiac electrical disturbance,
and other factors that contribute to the heightened sensitivity of
hypertensive rats.
Although we were cautious about making any definitive
conclusions about ECG in our urethane-anesthetized rats and
the role anesthesia plays in arrhythmogenesis, these findings
were consistent with our previous results showing that there
were baseline differences in the ECG of conscious WKY and
SH rats and the results of others who used anesthetized rats
(Hazari et al., 2009; Kelishomi et al., 2008; Xin et al., 2007).
SH rats had longer PR intervals than WKY rats. PR interval
prolongation might be due to slowing of intra-atrial propagation or more likely slowing of conduction in the atrioventricular (AV) node since no change in P-wave duration
was detected. This baseline difference between the normotensive and hypertensive rat strains may contribute to the
sensitivity of the animals to cardiotoxic insults, particularly
electrical dysfunction, and therefore arrhythmogenesis. However, since changes in PR intervals are associated with
supraventricular factors (i.e., nonconducted P-waves and AV
block in humans) (Scheidt, 1986), it is unclear whether they
represent a predisposition to the types of ventricular arrhythmia
observed during aconitine challenge. Nonetheless, given the
PM exposure–related increase, PR interval may be a sensitive
indicator of developing cardiotoxicity or cardiac stress in the
normotensive strain, particularly since naive SH rats have
comparatively elevated baseline PR intervals, which ostensibly
are unaffected by exposure.
QTc was also prolonged in control SH rats when compared
to control WKY rats. Prolonged QRS complex duration
accounted for the relatively increased QTc in SH rats
since there was no difference in ST interval between the
strains. Lengthening of QRS complex duration is thought to
facilitate ventricular arrhythmogenesis (Kashani and Barold,
2005; Madias, 2008; Scheidt, 1986). Prolonged QTc, which
is classically used to measure repolarization time, is also well
recognized as a risk factor of arrhythmogenesis and adverse
cardiac events in healthy individuals (De Bruyne et al., 1999)
and is predictive of mortality in patients with advanced heart
failure (Vrtovec et al., 2003). However, it has been suggested
in humans that because the QT interval includes ventricular
depolarization, its prognostic value is limited when QRS
complex contributes to QT prolongation. Alternatively, JTc
(QTc QRS) may be a more appropriate and independent
measure of ventricular repolarization (Crow et al., 2003; Das,
1990; Spodick, 1992). Our findings demonstrate that SH rats
had longer action potential durations at baseline than WKY
rats, which suggests that the presence of QRS complex
lengthening may point to a predisposition to ventricular
arrhythmia. SH rats also had prolonged time of repolarization,
as demonstrated by the increased JTc, which may have
increased the likelihood of arrhythmic events (Fossa, 2008).
It may also have enhanced the heterogeneity of repolarization,
which is considered a significant prerequisite for ventricular
AIR POLLUTION INCREASES RISK OF TRIGGERED CARDIAC ARRHYTHMIA
arrhythmia in humans and animals (Akar and Rosenbaum, 2003;
Kuo et al., 1983). Moreover, the occurrence of arrhythmia,
which is more frequent in naı̈ve SH rats when compared to
WKY rats (Hazari et al., 2009), could induce further electrical
remodeling of cardiac tissues leading to alterations in activation
sequence (Rosen, 2001).
Exposure to PM also increased QTc in WKY rats reflecting
in part the increase in QRS complex duration as was seen in the
SH strain. It is uncertain whether these changes represent the
mechanism underlying the increased sensitivity of the PMexposed WKY rats to aconitine when compared to the airexposed controls since the response was not statistically
significant, although it is not entirely unlikely that increases
in the same ECG parameters that were prolonged in SH rats at
baseline indicate a tendency to develop electrical dysfunction
and cardiotoxicity in the background normotensive strain.
There was no significant effect of PM on the ECG parameters
of SH rats, suggesting the exposure caused arrhythmia
sensitivity through mechanisms that may not include an effect
on ECG or that the strain already had changes, which did not
become further altered. This is in agreement with a study in
conscious SH rats, which showed that a single inhalation
exposure to ROFA had no effect on ECG parameters (Farraj
et al., 2009). Instead, it may be a combination of hypertension,
underlying cardiac electrical dysfunction, autonomic imbalance, and/or other hemodynamic mechanisms that contribute to
the heightened sensitivity of the SH strain to aconitine
postexposure. Oxidative stress, which has been shown to
mediate PM-related effects on cardiovascular function and
ECG (Brook et al., 2004; Gurgueira et al., 2002), and which is
known to be elevated in hypertensive rats (Bartha et al., 2009),
may also play a role in the strain’s response to aconitine.
Subchronic exposure and ECG monitoring studies are
necessary to clarify this issue and further determine the
persistence of arrhythmia sensitivity in these strains of rat.
Decreased HRV has been associated with cardiovascular
disorders such as congestive heart failure, hypertension,
arrhythmia, and sudden cardiac death (Task Force of the
European Society of Cardiology and the North American
Society of Pacing and Electrophysiology, 1996). In the current
study, changes in HRV cannot be definitively assessed as
a biomarker of effect because ECG, and therefore HRV, was
not measured prenose-only restraint but rather was compared
across the air and pollutant cohorts. Nevertheless, prior to
aconitine challenge, air-exposed control SH rats had decreased
HRV when compared to air-exposed WKY rats, particularly in
the RMSSD (short-term component). Since SDNN only reflects
long-term global components, the value of its decrease in the
context of this study is probably limited. Nonetheless, these
data and lower Hf values in air-exposed SH rats indicate
a diminished parasympathetic component regulating HR
(European Society of Cardiology, 1997; Rowan et al.,
2007). Decreases in HRV, which reflect imbalance in the
parasympathetic and sympathetic components of cardiovascu-
539
lar control, are associated with increased cardiac risk especially
in those with preexisting disease or cardiac events
(Devlin et al., 2003; Pope et al., 2004; Tsuji et al., 1996). In
particular, reduced parasympathetic tone has been found to
play an important role in ventricular arrhythmogenesis
(Kjellgren and Gomes, 1993; Zareba et al., 2001); this
propensity may partially explain the observed sensitivity in
the SH strain.
Exposure to PM caused a decrease in HRV in WKY rats
when compared to air-exposed controls. Similar decreases in
HRV have been observed in a cardiac-infarcted SpragueDawley rat model exposed to ROFA that also exhibited an
increased incidence of arrhythmia (Wellenius et al., 2002). As
was suggested previously, oxidative stress due to exposure may
mediate the decreased HRV and when combined with electrical
changes lead to heightened arrhythmia sensitivity. In contrast,
SH rats had an increase in HRV following PM exposure.
Similar increases in HRV, particularly the parasympathetic
component, have also been reported in young human subjects
exposed to ultrafine particles (UFP) (Zareba et al., 2009)
and concentrated ambient particles (CAPs) (Gong et al.,
2003). The mechanisms governing this increase in HRV
postexposure are not yet fully understood. In our experiments,
the 24-h postexposure delay in ECG measurement, use of
anesthesia, age, and degree of hypertension may have impacted
the response. Studies of HRV and air pollution seem to indicate
that older people, particularly those with underlying cardiovascular disease, experience decreases in HRV upon exposure.
It is plausible that the HRV may have decreased if the SH rats
used in this study were older and had further developed their
hypertensive phenotype.
According to these findings, postexposure aconitine-induced
arrhythmia sensitivity seemed to be independent of the type of
air pollutant, particle, or gaseous. Interestingly, increasing
concentrations of the same PM did not dose-dependently affect
the amount of aconitine necessary to elicit arrhythmia. Thus,
the air pollutants used, gaseous or particulate, may have been
sufficiently potent to trigger a common cascade of events that
led to arrhythmogenesis, keeping in mind the vulnerable nature
of the subjects. This result is both confounding and intriguing
since it suggests that it may not be the specific components of
the pollutant, but rather the generalized insult that causes
toxicity, perhaps again when laid upon the vulnerable host. It
has been postulated that the broad mechanisms governing
responses to air pollution include neural reflexes, which alter
autonomic function and control, inflammation, particularly in
the upper airways of obligate nose-breathing animals, such as
rats, and chemical effects on ion channel function in the heart,
whether from the pollutant molecule or innate mediators
(Zareba et al., 2001). Increased production of reactive oxygen
species (ROS) has also been proposed as a common contributor
to air pollution–related cardiotoxicity. UFP, fine, and coarse
particles, diverse bulk sources of urban ambient particles, and
inhalation of CAPs and diesel exhaust have been found to
540
HAZARI ET AL.
cause cardiovascular effects via ROS-mediated mechanisms
(see review by Simkhovich et al., 2008). ROFA-induced lung
oxidative stress has been demonstrated by electron spin
resonance (Kadiiska et al., 1997). In fact, in a comparison of
WKY and SH rats, the latter were found to have more oxidative
burden and decreased antioxidant capacity following ROFA
exposure (Kodavanti et al., 2000). Although many of
these studies use intratracheal instillation as the mode of
exposure, a study by Costa et al. (2006) showed that
either inhalation or instillation of ROFA causes similar levels
of pulmonary injury and inflammation, which is another
plausible cause of compromised cardiopulmonary function.
This ROFA-induced pulmonary injury, which is characterized
by increased bronchoalveolar lavage protein and albumin
levels and inflammatory cell infiltration, has been found to be
particularly robust in the SH rat (Kodavanti et al., 2000). These
animal studies clearly used higher ROFA concentrations than
the ones used in this study; however, human studies with
comparable ROFA concentrations to ours have indicated that
within 24 h of exposure, subjects experience decrements in
lung function and inflammation (Hauser et al., 1995; Lees,
1980).
Similarly, gaseous pollutants promote oxidative stress and
toxicity (Chuang et al., 2009; Liu et al., 2009). Acrolein has
been found to cause injury and inflammation in the olfactory
and respiratory epithelium of rats (Dorman et al., 2008) and
increased ROS (Roy et al., 2009), and it has resulted in
pulmonary edema and lung hemorrhage in rats at exposure
levels between 2 and 5 ppm (see review by Faroon et al.,
2008). Lastly, studies have even shown that both PM and
gaseous pollutants stimulate airway sensory fibers, which alter
both pulmonary and cardiovascular function by modulating
airway reflexes and autonomic control (Ghelfi et al., 2008;
Hazari et al., 2008; Symanowicz et al., 2004). To clarify these
issues, future studies should examine lower concentrations of
both gaseous and particulate pollutants and variable timing
postexposure to determine if there is a threshold of response.
Here, we demonstrated that there may be a general
vulnerability resulting from exposure to foreign substances in
the airways, particularly since this response was observed with
both pollutant particles and an irritant gas. Using a novel
approach, we were able to demonstrate that although the SH
rats had no overt symptoms of disease, aconitine challenge
following a single exposure to an air pollutant revealed
undetected cardiac sensitivity. Although studies showed that
ROFA particles could increase the incidence and duration of
arrhythmias in rats with severe underlying cardiopulmonary
pathology (Watkinson et al., 1998; Wellenius et al., 2002), we
have demonstrated that there are general factors that render
a host vulnerable to triggered arrhythmias regardless of the
pollutant or its concentration or in the absence of overt direct
adverse health effects. More importantly, the evidence suggests
that it is the host with underlying cardiovascular disease that is
at greatest risk following exposure to a potentially toxic
particulate or gaseous air pollutant. This response after the
inhalation of pollutants likely occurs due to numerous factors;
however, oxidative stress and inflammation, which persist
postexposure, may be critical in the risk of arrhythmogenesis.
In fact, it has been shown that the biological effects of ROFA
exposure occur within 24–48 h (Ghio et al., 2002), rendering
the host temporarily susceptible to triggered adverse events.
More importantly, it is the impact of a single exposure that,
although not considered significant, may be potentially life
threatening in some individuals due to this postexposure period
of sensitivity. Thus, the application of the challenge concept to
studying pollutant impacts opens a new avenue for assessing
imparted health risks to exposure and an alternate mode of
action of pollutants on the host.
ACKNOWLEDGMENTS
We would like to thank Allen D. Ledbetter of the U.S.
Environmental Protection Agency (USEPA) for setting up the
exposure system and preparing and acclimating animals, Dr.
Andrew Ghio for supplying us with the synthetic ROFA
particles, John McGee of the USEPA for the chemical analysis,
and Drs. David Herr and Adriana Lagier for reviewing the
manuscript.
REFERENCES
Akar, F. G., and Rosenbaum, D. (2003). Transmural electrophysiogical
heterogeneity underlying arrhythmogenesis in heart failure. Circ. Res. 93,
638–645.
Bartha, E., Solti, I., Kereskai, L., Lantos, J., Plozer, E., Magyar, K.,
Szabados, E., Kálai, T., Hideg, K., Halmosi, R., et al. (2009). PARP
inhibition delays transition of hypertensive cardiopathy to heart failure in
spontaneously hypertensive rats. Cardiovasc. Res. 83, 501–510.
Bartosova, L., Novak, F., Bebarova, M., Frydrych, M., Brunclik, V.,
Opatrilova, R., Kolevska, J., Mokry, P., Kollar, P., Strnadova, V., et al.
(2007). Antiarrhythmic effect of newly synthesized compound 44Bu on
model of aconitine-induced arrhythmia—compared to lidocaine. Eur. J.
Pharmacol. 575, 127–133.
Bateson, T. F., and Schwartz, J. (2008). Children’s response to air pollutants. J.
Toxicol. Environ. Health 71, 238–243.
Brook, R. D., Franklin, B., Cascio, W., Hong, Y., Howard, G., Lipsett, M.,
Luepker, R., Mittleman, M., Samet, J., Smith, S. C., Jr, et al. (2004). Air
pollution and cardiovascular disease: A statement for healthcare professionals from the Expert Panel on Population and Prevention Science of the
American Heart Association. Circulation 109, 2655–2671.
Campen, M. J., Costa, D. L., and Watkinson, W. P. (2000). Cardiac and
thermoregulatory toxicity of residual oil fly ash in cardiopulmonarycompromised rats. Inhalation Toxicol. 12, 7–22.
Cavallari, J. M., Fang, S. C., Eisen, E. A., Schwartz, J., Hauser, R.,
Herrick, R. F., and Christiani, D. C. (2008a). PM2.5 metal exposures and
nocturnal heart rate variability: a panel study of boilermaker construction
workers. Environ. Health 7, 36–42.
Cavallari, J. M., Fang, S. C., Eisen, E. A., Schwartz, J., Hauser, R.,
Herrick, R. F., and Christiani, D. C. (2008b). Time course of heart rate
variability decline following particulate matter exposures in an occupational
cohort. Inhal. Toxicol. 20, 415–422.
AIR POLLUTION INCREASES RISK OF TRIGGERED CARDIAC ARRHYTHMIA
Chuang, G. C., Yang, Z., Westbrook, D. G., Pompilius, M., Ballinger, C. A.,
White, C. R., Krzywanski, D. M., Postlethwait, E. M., and Ballinger, S. W.
(2009). Pulmonary ozone exposure induces vascular dysfunction, mitochondrial
damage and atherogenesis. Am. J. Physiol. Lung Cell. Mol. Physiol. 297,
L209–L216.
Costa, D. L., Lehmann, J. R., Jaskot, R., Winsett, D. W., Richards, J.,
Ledbetter, A. D., and Dreher, K. L. (2006). Comparative pulmonary
toxicological assessment of oil combustion particles following inhalation or
instillation exposure. Toxicol. Sci. 91, 237–246.
Crow, R. S., Hannan, P. J., and Folsom, A. R. (2003). Prognostic significance
of corrected QT and corrected JT interval for incident coronary heart disease
in a general population sample stratified by presence or absence of wide QRS
complex. Circulation 108, 1985–1989.
541
Gurgueira, S. A., Lawrence, J., Coull, B., Murthy, G. G., and GonzalezFlecha, B. (2002). Rapid increases in the steady-state concentration of
reactive oxygen species in the lungs and heart after particulate air pollution
inhalation. Environ. Health Perspect. 110, 749–755.
Hatch, G. E., Boykin, E., Graham, J. A., Lewtas, J., Pott, F., Loud, K., and
Mumford, J. L. (1985). Inhalable particles and pulmonary host defense:
in vivo and in vitro effects of ambient air and combustion particles. Environ.
Res. 36, 67–80.
Hauser, R., Elreedy, S., Hoppin, J. A., and Christiani, D. C. (1995). Airway
obstruction in boilermakers exposed to fuel oil ash. A prospective
investigation. Am. J. Respir. Crit. Care Med. 152, 1478–1484.
Das, G. (1990). QT interval and repolarization time in patients with
intraventricular conduction delay. J. Electrocardiol. 23, 49–52.
Hazari, M. S., Haykal-Coates, N., Winsett, D. W., Costa, D. L., and
Farraj, A. K. (2009). Continuous electrocardiogram reveals differences in
the short-term cardiotoxic response of Wistar-Kyoto and spontaneously
hypertensive rats to doxorubicin. Toxicol. Sci. 110, 224–234.
De Bruyne, M. C., Hoes, A. W., Kors, J. A., Hofman, A., van Bemmel, J. H.,
and Grobbee, D. E. (1999). Prolonged QT interval predicts cardiac and all
cause mortality in the elderly: the Rotterdam Study. Eur. Heart J. 20,
278–284.
Hazari, M. S., Rowan, W. H., Winsett, D. W., Ledbetter, A. D., HaykalCoates, N., Watkinson, W. P., and Costa, D. L. (2008). Potentiation of
pulmonary reflex response to capsaicin 24h following whole-body acrolein
exposure is mediated by TRPV1. Respir. Physiol. Neurobiol. 160, 160–171.
Devlin, R. B., Ghio, A. J., Kehrk, H., Sanders, G., and Cascio, W. (2003).
Elderly humans exposed to concentrated air pollution particles have
decreased heart rate variability. Eur. J. Respir. 21, 76–80.
Kadiiska, M. B., Mason, R. P., Dreher, K. L., Costa, D. L., and Ghio, A. J.
(1997). In vivo evidence of free radical formation in the rat lung after
exposure to an emission source air pollution particle. Chem. Res. Toxicol. 10,
1104–1108.
Kashani, A., and Barold, S. S. (2005). Significance of QRS complex duration in
patients with heart failure. J. Am. Coll. Cardiol. 46, 2183–2192.
Kelishomi, R. B., Ejtemaeemehr, S., Tavangar, S. M., Rahimian, R.,
Mobarakeh, J. I., and Dehpour, A. R. (2008). Morphine is protective against
doxorubicin-induced cardiotoxicity in rat. Toxicology 243, 96–104.
Dockery, D. W. (2001). Epidemiologic evidence of cardiovascular effects of
particulate air pollution. Environ. Health Perspect. 109, 483.
Dockery, D. W., Luttmann-Gibson, H., Rich, D. Q., Link, M. S.,
Mittleman, M. A., Gold, D. R., Koutrakis, P., Schwartz, J. D., and
Verrier, R. L. (2005). Association of air pollution with increased incidence of
ventricular tachyarrhythmias recorded by implanted cardioverter defibrillators. Environ. Health Perspect. 113, 670–674.
Dorman, D. C., Struve, M. F., Wong, B. A., Marshall, M. W., Gross, E. A., and
Willson, G. A. (2008). Respiratory tract responses in male rats following
subchronic acrolein inhalation. Inhal. Toxicol. 20, 205–216.
Dragojevic-Simic, V. M., Dobric, S. L., Bokonjic, D. R., Vucinic, Z. M.,
Sinovec, S. M., Jacevic, V. M., and Dogovic, N. P. (2004). Amifostine
protection against doxorubicin cardiotoxicity in rats. Anticancer Drugs 15,
169–178.
Faroon, O., Roney, N., Taylor, J., Ashizawa, A., Lumpkin, M. H., and
Plewak, D. J. (2008). Acrolein health effects. Toxicol. Ind. Health 24,
447–490.
Farraj, A. K., Haykal-Coates, N., Winsett, D. W., Hazari, M. S., Carll, A. P.,
Rowan, W. H., Ledbetter, A. D., Cascio, W. E., and Costa, D. L. (2009).
Increased nonconducted P-wave arrhythmias after a single oil fly ash inhalation
exposure in hypertensive rats. Environ. Health Perspect. 117, 709–715.
Fossa, A. A. (2008). The impact of varying autonomic states on the dynamic
beat-to-beat QT-RR and QT-TQ interval relationships. Br. J. Pharmacol.
154, 1508–1515.
Gerritsen, J., Dekker, J. M., TenVoorde, B. J., Kostense, P. J., Heine, R. J.,
Bouter, L. M., Heethaar, R. M., and Stehouwer, C. D. (2001). Impaired
autonomic function is associated with increased mortality, especially in
subjects with diabetes, hypertension, or a history of cardiovascular disease:
the Hoorn Study. Diabetes Care 24, 1793–1798.
Ghelfi, E., Rhoden, C. R., Wellenius, G. A., Lawrence, J., and GonzalezFlecha, B. (2008). Cardiac oxidative stress and electrophysiological changes
in rats exposed to concentrated ambient particles are mediated by TRPdependent pulmonary reflexes. Toxicol. Sci. 102, 328–336.
Kim, J. Y., Mukherjee, S., Ngo, L. C., and Christiani, D. C. (2004). Urinary 8hydroxy-2#-deoxyguanosine as a biomarker of oxidative DNA damage in
workers exposed to fine particulates. Environ. Health Perspect. 112,
666–671.
Kjellgren, O., and Gomes, J. A. (1993). Heart rate variability and baroreflex
sensitivity in myocardial infarction. Am. Heart J. 125, 204–214.
Koblin, D. D. (2001). Urethane: help or hindrance? Anesth. Analg. 94,
241–242.
Kodavanti, U. P., Schladweiler, M. C., Ledbetter, A. D., Watkinson, W. P.,
Campen, M. J., Winsett, D. W., Richards, J. R., Crissman, K. M.,
Hatch, G. E., and Costa, D. L. (2000). The spontaneously hypertensive rat
as a model of human cardiovascular disease: evidence of exacerbated
cardiopulmonary injury and oxidative stress from inhaled emission
particulate matter. Toxicol. Appl. Pharmacol. 14, 250–263.
Kuo, C., Munakata, K., Reddy, C., and Surawicz, B. (1983). Characteristics
and possible mechanism of ventricular arrhythmia dependent on the
dispersion of action potential duration. Circulation 67, 1356–1367.
Lees, R. E. M. (1980). Changes in lung function after exposure to vanadium
compounds in fuel-oil ash. Br. J. Ind. Med. 37, 253–256.
Li, M., Wang, J., Xie, H. H., Shen, F., and Su, D. (2007). The susceptibility of
ventricular arrhythmia to aconitine in conscious Lyon hypertensive rats. Acta
Pharmacol. Sin. 28, 211–215.
Linn, W. S., Szlachcic, Y., Gong, H., Jr., Kinney, P. L., and Berhane, K. T.
(2000). Air pollution and daily hospital admissions in metropolitan Los
Angeles. Environ. Health Perspect. 108, 427–434.
Ghio, A. J., Silbajoris, R., Carson, J. L., and Samet, J. M. (2002). Biologic
effects of oil fly ash. Environ. Health Perspect. 110, 89–94.
Liu, L., Poon, R., Chen, L., Frescura, A. M., Montuschi, P., Ciabattoni, G.,
Wheeler, A., and Dales, R. (2009). Acute effects of air pollution on
pulmonary function, airway inflammation, and oxidative stress in asthmatic
children. Environ. Health Perspect. 117, 668–674.
Gong, H., Jr., Linn, W. S., Sioutas, C., Terrell, S. L., Clark, K. W.,
Anderson, K. R., and Terrell, L. L. (2003). Controlled exposures of healthy
and asthmatic volunteers to concentrated ambient fine particles in Los
Angeles. Inhal. Toxicol. 15, 305–325.
Liu, Y., Woodin, M. A., Smith, T. J., Herrick, R. F., Williams, P. L.,
Hauser, R., and Christiani, D. C. (2005). Exposure to fuel-oil ash and
welding emissions during the overhaul of an oil-fired boiler. J. Occup.
Environ. Hyg. 2, 435–443.
542
HAZARI ET AL.
Lu, H. R., and De Clerck, F. (1993). R 56 865, a Naþ/Ca(2þ)-overload
inhibitor, protects against aconitine-induced cardiac arrhythmias in vivo. J.
Cardiovasc. Pharmacol. 22, 120–125.
Struyker-Boudier, H. A. J., Evenwel, R. T., Smits, J. F., and Van Essen, H.
(1982). Baroreflex sensitivity during the development of spontaneous
hypertension in rats. Clin. Sci. 62, 589–594.
Madias, J. E. (2008). Drug-induced QRS morphology and duration changes.
Cardiol. J. 15, 505–509.
Symanowicz, P. T., Gianutsos, G., and Morris, J. B. (2004). Lack of role for the
vanilloid receptor in response to several inspired irritant air pollutants in the
C57Bl/6J mouse. Neurosci. Lett. 362, 150–153.
Maggi, C. A., and Meli, A. (1986). Suitability of urethane anesthesia for
physiopharmacological investigations in various systems. Part 2: cardiovascular system. Experientia 42, 292–297.
Mortara, A., La Rovere, M. T., Pinna, G. D., Prpa, A., Maestri, R., Febo, O.,
Pozzoli, M., Opasich, C., and Tavazzi, L. (1997). Arterial baroreflex
modulation of heart rate in chronic heart failure: clinical and hemodynamic
correlates and prognostic implications. Circulation 96, 3450–3458.
Peters, A., Liu, E., Verrier, R. L., Schwartz, J., Gold, D. R., Mittleman, M.,
Baliff, J., Oh, J. A., Allen, G., Monahan, K., et al. (2000). Air pollution and
incidence of cardiac arrhythmia. Epidemiology 11, 11–17.
Pope, C. A., III, Hansen, M. L., Long, R. W., Nielsen, K. R., Eatough, N. L.,
Wilson, W. E., and Eatough, D. J. (2004). Ambient particulate air pollution,
heart rate variability, and blood markers of inflammation in a panel of elderly
subjects. Environ. Health Perspect. 112, 339–345.
Pope, C. A., III, Renlund, D. G., Kfoury, A. G., May, H. T., and Horne, B. D.
(2008). Relation of heart failure hospitalization to exposure to fine particulate
air pollution. Am. J. Cardiol. 102, 1230–1234.
Reinhardt, T. E., and Ottmar, R. D. (2004). Baseline measurements of smoke
exposure among wildland firefighters. J. Occup. Environ. Hyg. 1, 593–606.
Rosen, M. (2001). (The Sicilian Gambit). (2001). New approaches to
antiarrhythmia therapy, Part I: emerging therapeutic applications of the cell
biology of cardiac arrhythmia. Circulation 104, 2865–2873.
Rowan, W. R., Campen, M. J., Wichers, L. B., and Watkinson, W. P. (2007).
Heart rate variability in rodents: uses and caveats in toxicological studies.
Cardiovasc. Toxicol. 7, 28–51.
Roy, J., Pallepati, P., Bettaieb, A., Tanel, A., and Averill-Bates, D. A. (2009).
Acrolein induces a cellular stress response and triggers mitochondrial
apoptosis in A549 cells. Chem. Biol. Interact. 181, 154–167.
Scheidt, S. (1986). In Basic Electrocardiography. CIBA-GEIGY Corp, West
Caldwell, NJ.
Shu, H., Yi-Ming, W., Xu, L.-P., Miao, C.-Y., and Su, D.-F. (2004). Increased
susceptibility of ventricular arrhythmias to aconitine in anaesthetized rats is
attributed to the inhibition of baroreflex. Clin. Exp. Pharmacol. Physiol. 31,
249–253.
Simkhovich, B. Z., Kleinman, M. T., and Kloner, R. A. (2008). Air pollution
and cardiovascular injury. J. Am. Coll. Cardiol. 52, 719–726.
Song, Y., Tang, X., Xie, S., Zhang, Y., Wei, Y., Zhang, M., Zeng, L., and
Lu, S. (2004). Source apportionment of PM2.5 in Beijing in 2004. J. Hazard.
Mater. 146, 124–130.
Spodick, D. H. (1992). Reduction of QT-interval imprecision and variance by
measuring the JT interval. Am. J. Cardiol. 70, 628–629.
Task Force of the European Society of Cardiology and the North American
Society of Pacing and Electrophysiology. (1996). Heart rate variability:
Standards of measurement, physiological interpretation, and clinical use.
Eur. Heart J. 17, 354–381.
Tsuji, H., Larson, M. G., Venditti, F. J., Manders, E. S., Evans, J. C.,
Feldman, C. L., and Levy, D. (1996). Impact of reduced heart rate variability
on risk for cardiac events. The Framingham Heart Study. Circulation 94,
2850–2855.
Vrtovec, B., Delgado, R., Zewail, A., Thomas, C. D., Richartz, B. M., and
Radovancevic, B. (2003). Prolonged QTc interval and high B-type
natriuretic peptide levels together predict mortality in patients with advanced
heart failure. Circulation 107, 1764–1769.
Walker, M. J. A., Curtis, M. J., Hearse, D. J., Campbell, R. W. F., Janse, M. J.,
Yellon, D. M., Cobbe, S. M., Coker, S. J., Harness, J. B., Harron, D. W. G.,
et al. (1988). The Lambeth Conventions: guidelines for the study of
arrhythmias in ischaemia, infarction, and reperfusion. Cardiovasc. Res. 22,
447–455.
Watkinson, W. P., Campen, M. J., and Costa, D. L. (1998). Cardiac arrhythmia
induction after exposure to residual oil fly ash particles in a rodent model of
pulmonary hypertension. Toxicol. Sci. 41, 209–216.
Watkinson, W. P., Wiester, M. J., and Highfill, J. W. (1995). Ozone toxicity in
the rat: I. Effect of changes in ambient temperature on extrapulmonary
physiological parameters. J. Appl. Physiol. 78, 1108–1120.
Wellenius, G. A., Saldiva, P. H., Batalha, J. R., Krishna Murthy, G. G.,
Coull, B. A., Verrier, R. L., and Godleski, J. J. (2002). Electrocardiographic
changes during exposure to residual oil fly ash (ROFA) particles in a rat
model of myocardial infarction. Toxicol. Sci. 66, 327–335.
Wichmann, H. E., Mueller, W., Allhoff, P., Beckmann, M., Bocter, N.,
Csicsaky, M. J., Jung, M., Molik, B., and Schoeneberg, G. (1989). Health
effects during a smog episode in West Germany in 1985. Environ. Health
Perspect. 79, 89–99.
Xin, Y. F., Zhou, G. L., Deng, Z. Y., Chen, Y. X., Wu, Y. G., Xu, P. S., and
Xuan, Y. X. (2007). Protective effect of Lycium barbarum on doxorubicininduced cardiotoxicity. Phytother. Res. 24, 1020–1024.
Zareba, W., Couderc, J. P., Oberdörster, G., Chalupa, D., Cox, C.,
Huang, L. S., Peters, A., Utell, M. J., and Frampton, M. W. (2009). ECG
parameters and exposure to carbon ultrafine particles in young healthy
subjects. Inhal. Toxicol. 21, 223–233.
Zareba, W., Nomura, A., and Couderc, J. P. (2001). Cardiovascular effects of
air pollution: what to measure in ECG? Environ. Health Perspect. 109,
533–538.