Heart rate variability and sudden death secondary to coronary artery disease during ambulatory electrocardiographic monitoring

Data are analyzed from 5 patients who died suddenly during ambulatory electrocardiographic monitoring. Three of the patients were also assessed in terms of 2 recently developed indexes of heart rate (HR) variability. One of these, the standard deviation of RR intervals during successive 5-minute segments averaged over 24 hours, has been reported to be a putative index of vagal tone. Comparisons were made with HR variability findings in 20 normal volunteers. Sudden death was due to ventricular tachycardia degenerating into ventricular fibrillation in all cases. Both early (3 patients) and late cycle (2 patients) ventricular premature complexes initiated the terminal dysrhythmia. An increased density of ventricular ectopic activity was noted in the hour before onset of ventricular fibrillation. HR variability as measured by the standard deviation was significantly (p <0.01) lower in the patients who died suddenly (30 ± 10 ms) than in the normal subjects (76 ± 14 ms). These findings support suggestions that HR variability analysis may be useful in identifying patients at a higher risk of sudden death.