Transient sympathovagal imbalance triggers ''ischemic'' sudden death in patients undergoing electrocardiographic holter monitoring

Objectives. The aim of this study was to investigate the relation between ''ischemic'' sudden death (arrhythmic death preceded by ST segment shift) and autonomic nervous system activity. Background. Mechanisms precipitating sudden death are poorly known despite the importance of detecting functional factors that may contribute to such a fatal event. Methods. We analyzed the tapes of eight patients (seven men and one woman with a mean age of 66 +/- 8 years) who had ischemic sudden death during ambulatory electrocardiographic (Holter) monitoring. Four patients had unstable and four had stable angina; none was taking antiarrhythmic drugs. Twenty patients with angina and transient myocardial ischemia during Holter monitoring served as control subjects. Arrhythmias, ST segment changes and heart rate variability were analyzed by a computerized interactive Holter system. Results. Five patients had ventricular tachyarrhythmias (ventricular fibrillation in three, ventricular tachycardia in two), and three had bradyarrhythmias (atrioventricular block in two, sinus arrest in one) as the terminal event; all eight patients showed ST segment shift (maximal change 0.46 +/- 0.16 mV; with ST elevation in two) that occurred 41 +/- 34 min (mean +/- SD) before sudden death. The standard deviation of normal RR intervals (SDNN) was 89 +/- 33 ms during the 10 +/- 6 h of Holter monitoring; 5 min before the onset of the fatal ST shift, SDNN measurements were significantly lower than during the initial 5-min period (48 +/- 10 vs. 29 +/- 9 ms; p = 0.002). In control patients, the SDNN was 102 +/- 39 ms during Holter monitoring, whereas it measured 56 +/- 30 ms 5 min before the most significant episode of ST shift (p < 0.01 vs. 129 +/- 9 ms in the group with sudden death). Conclusions. Autonomic dysfunction, as detected by a marked decrease in heart rate variability, is present in the period (5 min) immediately preceding the onset of the ST shift precipitating ischemic sudden death. These data suggest that sympathovagal imbalance may trigger fatal arrhythmias during acute myocardial ischemia, thus resulting in sudden death.