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Blunted diurnal variation of ventricular rate in patients with permanent atrial fibrillation and ventricular tachycardia

A. Incze, A. Frigy, E. Carasca, D. Dobreanu, S. Cotoi.

3rd Medical Clinic, University of Medicine and Pharmacy Targu-Mures, Romania

Abstract
Introduction
Patients and Methods
Results
Conclusions and Discussion
References

Abstract
Background. Diurnal variation of ventricular rate in atrial fibrillation (AF) is a well known phenomenon and it is mainly related to the autonomic modulation of atrioventricular conduction.
Methods. The diurnal variation of ventricular rate and its variability were studied in 24 AF patients (6 female, 18 male, mean age 62.7 years) without (nonVT) and 12 patients (4 female, 8 male, mean age 64 years) with (VT) episodes of sustained or nonsustained ventricular tachycardia. In both groups the etiology of permanent AF was ischaemic heart disease, including former myocardial infarction (more than 6 months old), NYHA II and III functional class. All the patients received digoxin and/or verapamil for rate control. In every patient a 24-hours Holter (Del Mar Avionics) recording was performed. Only RR intervals between baseline QRS complexes were considered. The mean of RR intervals (MNN), the SDNN and rMSSD were calculated for daytime (07:30-21:30) and nighttime (00:00-07:00). The day and night parameters were compared (table below) using paired t-test and Wilcoxon`s Signed Rank test (significant p<0.05).
Results.
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In contrast with the nVT group, in the VT group the significant nighttime increase of the parameters was absent.
Conclusions. The blunted diurnal behavior of ventricular rate in VT patients reveals the failure of parasympathetic control, with potential role in the genesis of arrhythmias. Ventricular rate analysis may serve as basis for risk stratification in the setting of permanent AF.

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Introduction:

Permanent atrial fibrillation (PAF) is the most frequent arrhythmia in the clinical practice. The relevance of PAF is represented by troublesome symptoms, hemodynamic (hypodiastolic heart failure and hypoperfusion of vital organs) and thromboembolic complications (stroke). Ventricular rate plays a major role in determining the hemodynamic condition of the PAF patients, both the mean frequency and the irregularity of the rhythm affecting the cardiac output.
It is largely recognized that the mean ventricular rate and its irregularity are modulated in a great amount by fluctuations in the cardiac autonomic tone. The sympathetic and parasympathetic drive affect the refractority of the atrial myocardium and the atrioventricular node, influencing the number and amplitude of atrial impulses and - finally - the concealed conduction in the AV node. Thus, short-term and long-term (circadian) variations in the ventricular rate and its irregularity (variability) reflect the autonomic control of the heart
[ 1,2,3, 4] . This is very similar with the well known variations of the sinus rate (heart rate variability, HRV).
The circadian pattern of HRV is altered in patients with heart failure, ischaemic heart disease (after myocardial infarction), severe hypertension and ventricular arrhythmias. These patients present the lack of decrease in heart rate and increase in HRV parameters during nighttime, due to defectous parasympathetic control and/or sympathetic hyperactivity
[ 5, 6,7,8] .
In our study we tested the relevance of circadian variations of ventricular rate in patients with PAF and episodes of ventricular tachycardia.

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Patients and Methods:

24-hours Holter (Del Mar Avionics) recordings were performed in 24 PAF patients (6 female, 18 male, mean age 62.7 years) without (nonVT) and 12 patients (4 female, 8 male, mean age 64 years) with (VT) episodes of sustained (>30s) or nonsustained ventricular tachycardia. In both groups the etiology of PAF was ischaemic heart disease, including former myocardial infarction (more than 6 months old), of NYHA II or III functional class. All the patients received digoxin and/or verapamil for the control of ventricular rate.
Well known parameters of HRV were calculated for quantifying the ventricular rate and its variability: the mean of RR intervals (MNN), the standard deviation of RR intervals (SDNN) and the root mean square of successive RR intervals differences (rMSSD) were obtained for daytime (07:30-21:30) and nighttime (00:00-07:00). Only RR intervals between baseline QRS complexes were considered for analysis. The day and night parameters in the two groups were compared using paired t-test and Wilcoxon`s Signed Rank test, when normality test failed (significant p<0.05) using the SigmaStat for Windows statistical package.

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Results:

Mean values of day and night parameters in the two groups (nVT and VT) and p values resulted from comparing them are presented in table 1. In contrast with the nVT group, in the VT group the significant nighttime increase of the parameters was absent.

Table 1

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Values of day and nighttime mean heart rate and variabilty parameters in the two groups. Lack of significant (p<0.05) increase during night in the VT group.

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Conclusions and Discussion

The blunted diurnal behavior of ventricular rate and its variability in VT patients reveals the failure of parasympathetic control during nighttime.
Autonomic influences are playing a well defined role (as modulating factors) in the genesis of ventricular arrhythmias, a fact demonstrated by experimental and clinical studies [ 9, 10] .
Hypersimpathycotonia and impaired vagal control could be demonstrated by using HRV analysis in the setting of sinus rate. Lack of circadian variation of heart rate and HRV are indicators of altered autonomic control. We demonstrated this pattern in PAF patients presenting ventricular arrhythmias, the autonomic dysfunction having a potential role in arrhythmogenesis.
Our results indicate that ventricular rate analysis may serve as basis for risk stratification in the setting of PAF, fact which has to be confirmed by further studies.

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References

1. Nagayoshi H, Janota T, Hnatkova K, Camm AJ, Malik M. Autonomic modulation of ventricular rate in atrial fibrillation. Am J Physiol, 1997 (Heart Circ Physiol); 272: H1643-H1649
2. Raeder EA. Circadian fluctuations in ventricular response to atrial fibrillation. Am J Cardiol, 1990; 66:1013-1016
3. van den Berg MP, Haaksma J, Brouwer J, Tieleman RG, Mulder G, Crijns HJGM. Heart rate variability in patients with atrial fibrillation is related to vagal tone. Circulation, 1997; 96: 1209-1216.
4. Toivonen L, Kadish A, Kou W, Morady F. Determinants of the ventricular rate during atrial fibrillation. J Am Coll Cardiol, 1990; 16: 1194-1200
5. Makik M. Heart rate variability. Curr Opinion Cardiol, 1998; 13:36-44
6. Itou T, Obata S, Tateishi O. Characteristics of circadian rhythm of heart rate variability in patients with sudden cardiac death after myocardial infarction. Ann Noninvasive Cardiol, 1998; 3: 183-193
7. Kautzner J, Camm A.J. Clinical relevance of heart rate variability. Clin Cardiol, 1997; 20:162-168
8. Huikuri HV. Heart rate variability in coronary artery disease. J Intern med, 1995; 237:349-357
9. Zipes DP, Miyazaki T. The autonomic nervous system and the heart: basis for understanding interactions and effects on arrhythmia development. In DP Zipes, J Jalife (eds.): Cardiac electrophysiology: from cell to bedside. Philadelphia, WB Saunders, 1990
10. Schwartz PJ. The autonomic nervous system and sudden death. Eur Heart J, 1998; 19(suppl F): F72-80

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Questions, contributions and commentaries to the Authors: send an e-mail message (up to 15 lines, without attachments) to arritmias@listserv.rediris.es , written either in English, Spanish, or Portuguese.

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© CETIFAC
Bioengineering
UNER
Update
Dic/02/1999