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Acta Scientiae Veterinariae, 2014. 42: 1196.
RESEARCH ARTICLE
ISSN 1679-9216
Pub. 1196
Twenty-four Hour Ambulatory Electrocardiography (Holter Monitoring)
in Normal Unsedated Cats
Fernanda Lie Yamaki1, Elaine Cristina Soares1, Guilherme Gonçalves Pereira1, Ronaldo Jun Yamato1,
Luciana Gallatti1, Fabio Sandoli de Brito2, Moacir Leomil Neto1 & Maria Helena Matiko Akao Larsson1
ABSTRACT
Background: Standard electrocardiogram (ECG) performed during a clinical examination has a limited ability to detect
many arrhythmias. Holter or 24-h ambulatory electrocardiography (AECG) is the most sensitive non-invasive test for
demonstrating transient arrhythmias, that allows continuous recording of cardiac electrical activity while the patient is
engaged in normal daily activities. This study was undertaken to define 24-h AECG parameters, including variations in
heart rate, and the types and incidence of arrhythmias in clinically normal adult cats to provide a baseline for comparison
for cats suspected of having cardiac diseases.
Materials, Methods & Results: Twenty clinically normal adult cats, with an equal number of males and females, weighting
from 2.8 to 7.6 kg (mean 4.10 ± 1.22), were used. All animals had no historical or clinical evidence of systemic diseases,
with unremarkable physical examination, and with no alterations on either thoracic radiography, electrocardiographic,
and echocardiographic evaluations, as well as on clinical pathology or blood pressure measurement. Ambulatory electrocardiographic recording was performed for 24-h, with a 3-lead, modified bipolar, transthoracic system. The owner was
requested to keep a diary to record the time of exercising, feeding, and other behaviours. The records were analysed using
a microprocessor. In the current study, regular sinus rhythm was predominant, there was no evidence of atrioventricular
conduction block, or ST segment alterations and the minimum heart rate was 102 ± 23 bpm, while the maximum heart
rate was 242 ± 17 bpm and the mean heart rate was 151 ± 26 bpm.
Discussion: The main disadvantage of routine clinical ECG is that it records only a short period of heart rhythm. Continuous 24-h AECG monitoring is an obvious way of circumventing this problem. The normal heart rhythm in felines is usually
regular, varying from sinus rhythm to sinus tachycardia. Sinus arrhythmia is considered uncommon or abnormal, and when
present, it is usually associated with respiratory disorders. Nonetheless, sinus arrhythmia occasionally occurs in cats when
they are relatively relaxed. Consistently, it was noted that 95% (19/20) of the cats presented an apparent respiratory sinus
arrhythmia with alternating periods of heart rate increase and decrease. Sinus arrhythmia has been previously observed in
normal cats when they were calm and quiet in their home environment with either telemetry or Holter monitoring. In cats,
sinus arrhythmia is commonly associated with bradycardia (sinus bradyarrhythmia). This finding may be an indication that
the vagal tone is an important factor in the genesis of this rhythm. The heart rate variability parameters obtained through
telemetry suggest that parasympathetic tone was higher (and sympathetic tone lower) when the cats were in their home
environment. In the current study, the minimum heart rate was lower than that of hospitalized normal cats (102 ± 23 bpm
versus 117 ± 15 bpm), while the maximum heart rate was higher (241 ± 17 bpm versus 241 ± 21 bmp) and the mean heart
rate was lower (151 ± 26 bpm versus 151 ± 16 bpm), but without statistical significance. There were no gender differences
in the mean values for minimum, mean and maximum heart rate, a finding that is in contrast to a previous study in which
females presented with higher mean values for minimum and mean heart rates than males did. This study suggests that
occasional ventricular (and supraventricular) ectopic activity may occur in healthy young cats. However, it is still unclear
how many premature beats can be considered “normal” in cats.
Keywords: holter monitoring, feline, sinus arrhythmia, heart rate, unsedated cats.
Received: 28 December 2013
Accepted: 18 June 2014
1
Published: 23 June 2014
Departamento de Clínica Médica (VCM), Faculdade de Medicina Veterinária e Zootecnia (FMVZ), Universidade de São Paulo (USP), São Paulo, SP,
Brazil. 2Centro de Cardiologia do Hospital Sirio-Libanês, São Paulo, SP, Brazil. CORRESPONDENCE : M.H.M.A. Larsson [[email protected] - Fax:
+55 (11) 30911283]. Departamento de Clínica Médica, Faculdade de Medicina Veterinária e Zootecnia (FMVZ) - USP. Av. Prof. Dr. Orlando Marques
de Paiva n. 87. CEP 05508-270 São Paulo, SP, Brazil.
1
F.L. Yamaki, E.C. Soares, G.G. Pereira, et al. 2014. Twenty-four Hour Ambulatory Electrocardiography (Holter Monitoring)
in Normal Unsedated Cats.
Acta Scientiae Veterinariae. 42: 1196.
INTRODUCTION
Radiography and Echocardiographic evaluation
The thoracic radiography were evaluated
qualitatively, and quantitatively (using the “Vertebral
Scale System”) [2]. Echocardiographic evaluation
indicated no chamber enlargement, and diastolic left
ventricular wall and interventricular septal thickness
were  5 mm [7].
In animals with normal results (no historical
or clinical evidence of systemic diseases, with unremarkable physical examination, and with no alterations
on either thoracic radiography, electrocardiographic,
and echocardiographic evaluations, as well as on
clinical pathology or blood pressure measurement),
the ambulatory electrocardiographic recording was
performed for 24-h, with a 3-lead, modified bipolar,
transthoracic system, using an analogic1 or a digital2
recorder, respectively recorded on cassette tape, or on
fleshcard. For this, hair was shaved from an area of approximately 6.0 cm wide and 8.0 cm height on either
side of the precordium, just behind the front legs. The
electrodes were placed fairly close together because
of small size of the thorax. Self adhesive disposable
electrodes3 were applied to the prepared areas of skin
and the adhesion reinforced by adhesive tape strips.
The leads were attached to the electrodes patches. An
adhesive tape was wrapped around the chest, over the
electrodes and leads wires. An auto-adhesive elastic
bandage4 was wrapped around the chest, to cover the
lead wires and recorder.
Given the short duration, standard electrocardiogram (ECG) is unreliable for consistently detecting even frequent arrhythmias, and they are likely to
result in over- or underestimation of the severity of any
identified rhythm disturbance [20]. A typical resting
electrocardiogram of 5 min duration only samples 0.3%
of a 24-h period [14]; consequently, Holter recording
(a type of ambulatory electrocardiography, or AECG)
was developed to overcome some of the limitations of
the short period recorded by standard ECG [6].
Long-term ECG recording is the most sensitive non-invasive test for demonstrating transient
arrhythmias [17]. In human medicine, it is the most
useful non-invasive test for evaluating patients with
arrhythmias [15] and establishing possible correlations
with clinical signs [6,14,15,19].
Holter monitoring is a form of AECG that allows continuous recording of cardiac electrical activity
while the patient is engaged in normal daily activities.
The indications for Holter monitoring are as follows:
the evaluation of symptoms that may be related to
rhythm disturbances (the classic indication) [3,13,19],
the detection of myocardial ischemia [14], the assessment of risk and prognosis in patients with or without
symptoms [3], the assessment of rhythm in patients
with or without symptoms [18,21], and the determination of antiarrhythmic therapy efficacy [6,11,19].
There are few reports of AECG in cats [5,8,20].
The present study was undertaken to define
24-h AECG parameters, including variations in heart
rate, and the types and incidence of arrhythmias in
clinically normal adult cats to provide a baseline
for comparison for cats suspected of having cardiac
diseases.
Record data
The record starting time was noted and then
the cat was taken home or to the cattery where a
normal daily routine was encouraged. The owner was
requested to keep a diary to record the time of exercising, feeding, and other behaviours.
The records were analysed using a cassette
tape recorder microprocessor5 or a Fleshcard recorder
microprocessor6.
Full-disclosure printouts and standard report
parameters were obtained. The authors examined all
the full-disclosure reports to ensure that the reported
heart rhythm and hourly counts of ectopic complexes
were as accurate as possible.
Data evaluated included hourly and 24-h summaries of minimum, mean and maximum heart rate;
heart rhythm, and hourly counts of ectopic complexes.
Any abnormalities of sinus node function or atrioventricular conduction was also noted.
MATERIALS AND METHODS
Animals
Twenty clinically normal adult cats, with an
equal number of males and females, weighting from 2.8
to 7.6 kg (mean 4.10 ± 1.22), were used. The animals
were either from the cattery of Department of Internal
Medicine of School of Veterinary Medicine and Animal
Science of University of São Paulo or were selected at
the Cardiology Service at the Veterinary Hospital of
University of São Paulo. In the latter case, they were
housed in their home environment.
2
F.L. Yamaki, E.C. Soares, G.G. Pereira, et al. 2014. Twenty-four Hour Ambulatory Electrocardiography (Holter Monitoring)
in Normal Unsedated Cats.
Acta Scientiae Veterinariae. 42: 1196.
Regarding the rhythm, the presence of sinus
arrhythmia was defined as more than 10% difference
between RR intervals or more than 0.10 s difference
between consecutive PP intervals. Measurements of
the total time duration of sinus arrhythmia was not attempted. Calculation of the degree of sinus arrhythmia
was done by the formula (RR-rr)/rr whilst the arrhythmia was most marked. The largest difference between
consecutives RR intervals was also calculated.
sinus rhythm or sinus tachycardia with no ectopic
complexes.
The results about AECG are presented on
Figure 1 and Table 1.
Regular sinus rhythm was predominant, there
was no evidence of atrioventricular conduction block,
or ST segment alterations and the minimum heart rate
was 102 ± 23 bpm, while the maximum heart rate
was 242 ± 17 bpm and the mean heart rate was 151
± 26 bpm.
Regular sinus rhythm was predominant; however, periods of sinus arrhythmia were evident in almost
all of the animals [95% (19 of 20)], especially when
the heart rate was lower, resulting in sinus bradyarrhythmia at times.
There was no evidence of atrioventricular conduction block, or ST segment alterations.
Six cats (30%; 3 females and 3 males) had
single ventricular ectopic complexes (Table 2). Single
supraventricular premature complexes occurred only in
2 animals (1 female with 3 supraventricular extrasystoles and 1 male with 4 supraventricular extrasystoles).
The female presented with 3 events/h and the male
with 1 event/h.
Data and Statistical analysis
All data analysis was performed using the
Minitab statistical analysis program7.
Results are presented as mean ± standard error
of the individual groups means. A statistically significant difference was defined as P < 0.05.
The parametric data were analysed by Student
t-test, with the gaussian distribution confirmed by
Kolmogorov-Smirnov method. The non-parametric
data were analysed by Friedman method.
RESULTS
Auscultation revealed no murmur, gallop
sound, or arrhythmia. The resting ECG showed
Figure 1. Hourly mean values for minimum, mean, and maximum heart rates from 20 healthy cats are depicted
over a 24-h period. HOVET/FMVZ/USP. São Paulo, 2013. (1)Beats per minute.
3
F.L. Yamaki, E.C. Soares, G.G. Pereira, et al. 2014. Twenty-four Hour Ambulatory Electrocardiography (Holter Monitoring)
in Normal Unsedated Cats.
Acta Scientiae Veterinariae. 42: 1196.
Table1. Results of ambulatory ECG recording in 20 healthy cats. HOVET/FMVZ/USP. São Paulo, 2013.
Number of
QRS(1)
Exam
Duration(2)
HR min.(3)
Min
bpm(6)
bpm
bpm
HR mean(4)
HR max.(5)
Minimum
128,187
1,235
75
100
208
Maximum
288,970
1,438
174
203
279
Mean
210,178
1,385
102
151
242
Median
210,979
1,413
95
153
250
40,180
61
23
26
17
SD
(7)
(1)
Total number of QRS complexes in 24 h; (2)Duration of exam in minutes; (3)Minimum heart rate; (4)Mean heart rate; (5)Maximum heart rate; (6)Beats per minute; (7)Standard deviation.
Table 2. Presence of ventricular extrasystoles in healthy cats. HOVET/FMVZ/USP. São Paulo, 2013.
Animal
Gender
VE(1)
Morphology of QRS
complex
Maximum frequency of occurrence(2)
2
female
18
monomorphic
4 VE/min at 2:34 AM
4
female
3
polymorphic
1 VEIh at 7:00 AM, 8:00 AM, 3:00 PM
5
female
6
polymorphic
2 VEImin at 4:36 PM
12
male
7
polymorphic
2 VE/h at 08:00 AM
14
male
1
monomorphic
1 VEIh at 9: 00 PM
19
male
5
polymorphic
2 VE/h at 7:00 PM
(1)
Total ventricular extrasystoles; (2)Maximum frequency of occurrence (per minute or per hour) .
DISCUSSION
[13,17] or abnormal [10], and when present is usually
associated with respiratory disorders. Even though,
occasionally sinus arrhythmia occurs in cats that are
more relaxed [9].
Sinus arrhythmia is defined as an irregular
rhythm originating in the sinoatrial node. It presents as
a variation in heart rate in a cyclic mode with respiratory movements (respiratory sinus arrhythmia) or irregularly with no relation with respiratory movements.
Sinus arrhythmia tends to disappear with increases of
heart rate. Electrocardiographically, it is characterized
by 0.10 s or greater variability between successive P
waves [13,17] or greater than 10% variability between
RR intervals [4]. Thus, it was noted that 95% (19/20)
of the cats presented an apparently respiratory sinus
arrhythmia, with alternated periods of increase and
decrease of heart rate. Sinus arrhythmia has been
The main disadvantage of the routine clinical ECG is that it records only a short period of heart
rhythm. Continuous 24-h ambulatory ECG monitoring
is an obvious way of circumventing this problem. One
great utility of ambulatory ECG monitoring in cats
is the analysis of heart frequency and rhythm in the
environment.
In very small or debilitated cats, direct attachment of the recorder is not desired. So, the animal
should be placed in a cage with the recorder on the top
of it [5]. Obviously, direct attachment of the recorder
can cause some stress, and should be taken into consideration during interpretation.
The normal heart rhythm in feline is usually
regular [1,9,13,17] varying from sinus rhythm to sinus
tachycardia. Sinus arrhythmia is considered uncommon
4
F.L. Yamaki, E.C. Soares, G.G. Pereira, et al. 2014. Twenty-four Hour Ambulatory Electrocardiography (Holter Monitoring)
in Normal Unsedated Cats.
Acta Scientiae Veterinariae. 42: 1196.
Supraventricular premature complexes are rare,
as in the younger cats from the previous study [8,20].
The incidence of supraventricular extrasystoles might
be related to age; the two animals that showed supraventricular arrhythmia were the oldest of the study, but
no statistically significant conclusions can be drawn
from these two cases.
This study suggests that occasional ventricular
(and supraventricular) ectopic activity may occur in
healthy young cat. However, it is still unclear how
many premature beats can be considered “normal”
in cats.
previously observed in normal cats when they were
calm and quiet in their home environment, by either
telemetry [1] or holter monitoring [20].
As in human beings, sinus arrhythmia was
commonly associated with bradycardia (sinus bradyarrhythmia). This can be an indication that the vagal tone
is an important factor on this rhythm genesis. The heart
rate variability parameters obtained through telemetry
suggested that parasympathetic tone was higher (and
sympathetic tone lower) when the cats were in their
home environment [1].
The mean values for minimum (102 ± 23 bpm),
mean (151 ± 26 bpm versus 157 ± 3.7 bpm) and maximum (242 ± 17 bpm versus 267 ± 5.4 bpm) heart rate
for all animals were very similar, but slightly inferior,
to those determined by Ware [20].
In the current study, minimum heart rate was
lower (102 ± 23 bpm versus 117 ± 15 bpm) and maximum heart rate was higher (279 ± 17 bpm versus 241
± 21 bmp), with mean 24-h mean heart rate similar
(151 ± 26 bpm versus 151 ± 16 bpm) to that found in
hospitalized normal cats [5].
There were no gender differences in mean values for minimum, mean, and maximum heart rate, that
is in contrast to a previous study [20] where females
presented with higher mean values for minimum and
mean heart rate than males.
Single ventricular premature complexes may
occur in normal cats [8,20] normal dogs [12,18] and
human beings [15]. In this study, the animals presented
with fewer ventricular premature complexes than in
Ware’s study [20]; this may be because the animals
in this study were younger and the incidence of ventricular arrhythmias increases with age in cats [8,20]
in dogs [16], and in humans [15].
CONCLUSIONS
It was concluded that 24-h ambulatory electrocardiography can be readily obtained in cats. Sinus
arrhythmia was common, occurring in 95% of cats.
Ventricular extrasystoles were uncommon, whereas
supraventricular extrasystoles were rare.
SOURCES AND MANUFACTURERS
1
Analogic DYNAMIS, Cardios, Sao Paulo, SP, Brazil.
2
Digital 300-6, DMS (Pro Medic), Nevada, CA, USA.
3
Meditrace, Kendall, Mansfield, MA, USA.
4
Coban, 3M, Saint Paul, MN, USA.
5
Software ALT V5.08B, Burdick Inc., Deerfield, WI, USA.
6
Software CardioScan 6, DMS, Sao Paulo, SP, Brazil.
7
Minitab 9.1, Minitab Inc., State College, PA, USA.
Acknowledgements. The authors are grateful for all participant
cat owners and Fumio O. Ito and Wagner Sato Ushikoshi, who
provided statistical analysis. Special thanks to Ana Carolina
Brandão de Campos Fonseca Pinto, who helped with the radiographic examinations.
Declaration of interest. The authors report no conflicts of
interest. The authors alone are responsible for the content and
writing of the paper.
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