Download qt interval variability and qt/rr relationship in patients

QT INTERVAL VARIABILITY AND QT/RR
RELATIONSHIP IN PATIENTS WITH
POSTMYOCARDIAL INFARCTION IMPAIRMENT OF
THE LEFT VENTRICLE FUNCTION AND DIFFERENT
TYPES OF VENTRICULAR ARRHYTHMIAS.
Krzysztof Szydło, MD, PhD, Maria Trusz-Gluza MD, PhD, Artur Filipecki MD, PhD,
Witold Orszulak MD, PhD, Dagmara Urbańczyk MD, Krystian Wita MD, PhD,
Jolanta Krauze MD, PhD
I Dept. of Cardiology, Silesian Medical University, Ziolowa 47, 40-635 Katowice, Poland
e-mail: [email protected]
Abstract:
Circadian variability of QT interval and QT/RR
relationship are still under intensive investigation.
The purpose of the study was to analyze if the
variability of QT interval and QT dynamicity
differentiate post myocardial infarction (MI)
patients (pts) with impaired left ventricular
function and different types of ventricular
arrhythmias. One hundred pts with previous MI
(>30 days) were included: 50 pts with benign
(NoVT/VF) and 50 pts with malignant ventricular
arrhythmias (all of them underwent ICD
implantation). QT was calculated beat-to-beat
from the Holter recordings from two periods - day:
6 a.m.- 9 a.m. and 2 p.m.- 10 p.m.; night: 10 p.m.6 a.m. The QT interval, QT corrected to the heart
rate, QT variability and QT/RR regression slope
were measured. Comparison of these parameters
revealed
remarkable
differences
between
NoVT/VF and VT/VF groups both in day and
night periods. All indices were higher in VT/VF
pts despite on the analyzed period, but no
differences between themselves at day and night
periods were found. In conclusion, increased
variability of QT and especially QT/RR slope may
be useful tool in stratification of post MI patients
with left ventricular dysfunction and selection
those who are at higher risk of malignant
arrhythmic events.
interval and its adaptation to the heart rate (HR).
Moreover, new methods, which may be helpful in
stratification of patients (pts) being at higher risk
of sudden cardiac death, are still investigated.
Many papers showed that prolonged QT interval
duration (QT), QT corrected to the heart rate
(QTc) and higher QT dispersion can be found in
pts with post myocardial infarction (MI) left
ventricle dysfunction (given as left ventricle
ejection fraction - LVEF), especially in those with
the history of malignant ventricular arrhythmias
(ventricular tachycardia- VT or ventricular
fibrillation- VF) 1,2.
Nowadays, the special attention is paid on the
variability of QT, QTc and QT/RR, which can be
analyzed from the 24-hours Holter recordings.
Long-term analysis of QT/RR relationship was
found to be very promising. Its slope indicates
heart rate dependency of the QT interval. It seems
that residual ischemia, impairment of the left
ventricle function and autonomic imbalance with
adrenergic predominance may influence on QT
parameters and QT/RR relationship 3,4.
The aim of the study was to analyze if the
variability of QT interval parameters and QT/RR
relationship may be helpful in differentiation of
post MI patients with impaired function of the left
ventricle and different types of ventricular
arrhythmias.
INTRODUCTION:
Recent years have shown a new interest in the QT
interval analyzes due to the more sophisticated
techniques of beat-to-beat measurement of QT
METHOD:
The study population consisted of 100 post MI pts
(>30
days)
with
premature
ventricular
contractions, episodes of non-sustained ventricular
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tachycardia, sustained VT (sVT) or documented
VF. Patients were divided into two groups: 50 pts
without sVT or VF (NoVT/VF) (36 males, age 63±10 yrs, EF - 41±9%, 28 pts with anterior MI)
and 50 pts with sVT or VF (VT/VF) who
underwent ICD implantation (37 males, age 61±10 yrs, EF - 37±11%, 34 pts with anterior MI).
Coronary artery lesion score (1, 2 or 3-vessel
disease) was taken from the coronary angiograms
(lesion >70% was regarded as significant). Holter
recordings were performed using Reynolds
Pathfinder 700 system with sampling rate of 256
Hz. Two periods were analyzed - day: 6 a.m.- 9
a.m and 2 p.m.- 10 p.m. and night: 10 p.m.- 6 a.m.
QT duration analyzed beat after beat, was firstly
determined automatically and next corrected
manually in at least 10-15 points of each period.
The following data were used: QT interval, QTc
corrected to the heart rate with the Bazzet's
formula, QT variability - standard deviation of all
successive intervals (QTSD) and QT/RR linear
regression slope (QT/RR). Minimal, average and
maximal heart rates (HR) were also obtained.
Statistical analyses were performed using the
following tests: chi-square, U Mann-Whitney,
Friedmann’s ANOVA and t-Students.
RESULTS.
Groups were not differentiated by age, gender, EF,
and size of MI. The extent of coronary artery
lesions was also very similar in NoVT/VF and
VT/VF groups: 2.5±0.8 vs. 2.5±0.7. Furthermore,
minimal, average and maximal HR were similar in
both observed periods in each group, average HR:
at day - 72±11 vs. 68±10 bpm and at night - 66±12
vs. 64±10 bpm for No VT/VF vs. VT/VF,
respectively. Note, that VT/VF pts had no
differences in average HR. In contrast, comparison
of parameters describing repolarization revealed
differences both in QT and QTc (table 1) as well
in the QT variability and QT/RR slope (table 2). In
VT/VF pts both during day and night period
values of QT, QTc and QT/RR slope were higher
than in NoVT/VF group. There was also a trend to
higher variability of QT. All analyzed parameters
did not differ significantly between themselves at
day and night periods when were calculated
separately in study groups.
Table 1. QT and QTc in study groups at day and
night periods (abbreviations are given in text).
Day period
QT (ms)
QTc (ms)
No VT/VF
386±39
414±22
VT/VF
421±36
446±31
significance (p)
<0.01
<0.001
Night period
No VT/VF
401±44
412±24
VT/VF
430±35
442±30
significance (p)
<0.05
<0.001
Table 2. QTSD and QT/RR slope in study groups
at day and night periods (abbreviations are given
in text).
Day period
QTSD (ms) QT/RR slope
No VT/VF
18±4
0.14±0.05
VT/VF
22±4
0.21±0.05
significance (p)
=0.05
<0.05
Night period
No VT/VF
15±5
0.15±0.04
VT/VF
18±8
0.19±0.05
significance (p)
ns
<0.05
DISCUSSION.
New sophisticated methods of the QT duration
analysis and its relation to the heart rate give us
additional information about dynamicity of the
myocardial
repolarization,
which
reflects
myocardial vulnerability to generation of
malignant arrhythmias 3,4,5. However, many other
factors may influence on the results of the QT
variability or QT dynamicity analyses. Therefore,
we cross-matched groups with benign and
malignant ventricular arrhythmias to obtain more
objective findings. Our groups did not differ in
age, gender, infarct size and the coronary artery
lesions score. A commercial Holter system was
used to measure RR and QT intervals. The waking
and sleeping period were considered separately.
Our study showed a trend in increase of QT, not
QTc, at nighttime in both groups, which might be
related to longer RR intervals. Previous reports on
the circadian pattern of the QTc interval were
inconsistent, even in normal subjects 1. However,
QT and QTc were significantly higher in our
VT/VF group, both at day and nighttime. Higher
values of QT and QTc intervals in post MI pts
were previously described by many authors and
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Molnar et al. found significant differences
between day and night QTc in survivors of sudden
cardiac death but not in the control group 6.
QTSD and QT/RR refer to the flexibility of the
QT interval and provide important information
about abnormalities in the dynamics of the
repolarization. Dynamicity of the QT interval is a
surrogate of action potential physiology at the
cellular level. The study on healthy subjects
published by Jensen et al. showed satisfying
reproducibility of this measurement and the
presence of day/night variations. There was a
significant difference between the day and night
slopes, the latter being less steep than the former (0.08±0.008 vs. 0.054±0.003) 7. Our results,
which were obtained in post MI pts with left
ventricular dysfunction were higher, with no
significant differences between day and night
values. This phenomenon can be related to
concomitant dysfunction of autonomic nervous
system, which is observed in these patients. In
VT/VF pts both during waking and sleeping
period, QT/RR slope was higher than in NoVT/VF
group. There was also a trend to higher variability
of QT.
Several groups using different systems reported
that after MI QT dynamicity was impaired in pts
with spontaneous ventricular arrythmias 4,8,9,10.
Huikuri et al. found that pts with VT/VF at
outcome differed from control pts by a steeper
QT/RR slope and a reduced difference between
daytime and nighttime slopes 11. The largest study
on MI pts was performed by Chevalier et al.8.
QT/RR relationship was found to be independent
predictor of the sudden cardiac death in pts after
MI. They analyzed prospectively 265 pts with
recent MI, 9-14 days after its onset. They found
out the remarkable steeper QT/RR slope at day
period in pts in whom malignant ventricular
arrhythmia occurred during the follow-up.
According to this study QT/RR slope >0.18 had
the highest predictive value. Our study confirms
this observation, but retrospectively. Patients with
VT/VF had higher values of QT/RR slope at
daytime and also at nighttime- 0.21±0.05 and
0.19±0.05,
respectively.
Sympathetic
predominance in pts with VT/VF may also be
explained by the tendency to higher values of
QTSD observed in our study. We think that higher
values of QTSD are related to the lack of
flexibility of QT to changes in RR intervals.
Similar results were obtained by Oikarinen et al. 2,
but the standard deviation of QT was calculated in
this study from standard 12-lead surface ECG.
CONCLUSIONS.
Simple evaluations available in commercial Holter
systems such as variability of QT and especially of
QT/RR slope may be useful tool in stratification of
post MI patients with left ventricular dysfunction
and selection those who are at higher risk of
malignant arrhythmic events.
References:
1. Smetana P, Pueyo E, Hnatkova K, Malik M.
Circadian pattern of QTc interval. In Malik M, Camm J,
eds: Dynamic Electrocardiography. NY, Blackwell
Futura Publishing Co, 2004, 315-325
2. Oikarinen L, Vitasalo M, Toivonen L. Dispersion of
the QT interval in postmyocardial infarction patients
presenting with ventricular tachycardia or with
ventricular fibrillation. Am J Cardiol 1998;81:694-697
3. Extramiana F, Maison-Blanche P, Badilini F, et al.
Circadian modulation of QT rate dependence in healthy
volunteers: Gender and age differences. J Electrocardiol
1999;32:33-43
4. Coumel P, Maison-Blanche P. QT dynamicity as a
predictor for arrhythmia development. In Oto A,
Breithardt G, eds: Myocardial Repolarization: From
Gene to Bedside. Armonk, NY: Futura Publishing Co,
2001, 173-186
5. Zareba W. QT-RR slope: dynamics of repolarization
in the risk stratification. J Cardiovasc Electrophysiol
2003;14:234-235
6. Molnar J, Rosenthal JE, Weiss J, et al. QT interval
dispersion in healthy subjects and survivors of sudden
cardiac death: circadian variation in a twenty-four-hour
assessment. Am J Cardiol 1997;79:1190-1193
7. Jensen B, Larroude C, Rasmessen L, et al. Beat-tobeat QT dynamics in healthy subjects. ANE 2004;9:311
8. Chevalier P, Burri H, Adeleine P, et al. QT
dynamicity and sudden cardiac death after myocardial
infarction: results of a long-term follow-up study. J
Cardiovasc Electrophysiol 2003;14:227-233
9. Extramiana F, Neyroud N, Huikuri HV, et al. QT
interval and arrhythmic risk assessment after
myocardial infarction. Am J Cardiol 1999;83:266-269
10. Atiga WL, Calkins H, Lawrence JH, et al. Beat-tobeat repolarization lability identifies patients at risk for
sudden cardiac death. J Cardiovasc Electrophysiol
1998;9:899-908
11. Huikuri HV, Koistinen MJ, Yu-Mayry S, et al.
Impaired low frequency oscillations of heart rate in
patients with prior acute myocardial infarction and lifethreatening arrhythmias. Am J Cardiol 1995;76:56-60
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