Impaired Low-Frequency Oscillations of Heart Rate in Patients With Prior Acute Myocardial Infarction and Life-Threatening Arrhythmias

Myocardial infarction results in abnormal cardiac autonomic function, which carries an increased risk of cardiac mortality, but it is not well known whether autonomic dysfunction itself predisposes patients to life-threatening arrhythmias or whether it merely reflects the severity of underlying ischemic heart disease. To determine the significance of abnormalities of cardiovascular neural regulation on the risk for ventricular tachycardia (VT), heart rate (HR) variability in the time and frequency domain were compared in a case-control study between 30 patients with a prior myocardial infarction and a history of sustained VT (n = 18) or cardiac arrest (n = 12) (VT group) and 30 patients with a prior myocardial infarction but no arrhythmic events (control group). The patient groups were carefully matched with respect to age, sex, location, ejection fraction, number of prior infarctions, number of diseased coronary arteries, and β-blocking medication. In all patients in the VT group, inducibility into sustained VT was achieved, but none of the control patients had inducible nonsustained or sustained VT during programmed electrical stimulation. Patients in the VT group had a significantly tower SD of the RR intervals (p < 0.01), and reduced ultra low-, very low-, and low-frequency power spectral components of HR variability (p < 0.001 for all) than controls, but the high-frequency component of HR variability did nor differ significantly between groups. In multiple regression analysis, reduced very low-frequency power or HR variability was the strongest independent predictor of VT susceptibility. These data indicate that the factors that modulate the low-frequency oscillations of HR are related to susceptibility for VT independent of the severity of underlying heart disease in patients with prior myocardial infarction.