13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

S-8

RR variability as a tool in implanted ICDs to predict tachyarrhythmias

Gerhard Hoh.
Klinikum Dessau, Abt. Kardiologie, Klinik für Innere Medizin, Dessau, Germany

Background

Experimental and clinical observations point out that an imbalance of the autonomic nervous system, especially reduced parasympathetic (vagal) activity, may be a potential risk factor for precipitating ventricular tachycardia and ventricular fibrillation (VT/VF)^1,2. The suggested underlying pathophysiologic mechanism is that high sympathetic activity, and concurrant lack of the protective effect of parasympathetic tone, decreases the fibrillation threshold and therefore predisposes to ventricular fibrillation^3,4. Variations in autonomic balance are reflected in the heart rate. Determination of cyclic changes in heart rate (heart rate variability or HRV) is thus a suitable instrument for indirect measurement of autonomic activity as well as other related factors predisposing to ventricular tachyarrhythmia and sudden cardiac death. It has been well established in recent years by several studies that decreases in heart rate variability correlate with the occurrence of ventricular tachyarrhythmias of different etiology^5-8. It has also been shown that certain measures of heart rate variability constitute independent statistical predictors of sudden death in specific patient groups, for example in post myocardial infarction patients^9-12, and more recently in patients with idiopathic dilated cardiomyopathy^13,14. It has not however been possible to identify individual patients who will suffer an episode of ventricular arrhythmia or sudden death from currently established heart rate variability measures.

Recently more attention is being focused on the time period immediately preceding episodes of ventricular tachycardia and ventricular fibrillation for analysis of the mechanisms initiating these tachyarrhythmias. It is of special interest to identify specific changes in heart rate variability and possibly specific critical sequences of RR intervals in order to predict future episodes of tachyarrhythmia before their occurrence. Up-to now systematic investigation concerning this aspect of heart rate variability has been limited by the small number of episodes available for analysis; these usually being coincidentally recorded by Holter electrocardiography (Holter-ECG)^15,16.

This strong limitation in systematically assessing larger patient groups on a routine basis can be circumvented by utilizing the storage function for RR intervals preceding episodes of ventricular tachyarrhythmia which is available in some of the newer implantable cardioverter defibrillators (ICDs).