Baroreflex sensitivity, but not heart rate variability, is reduced in patients with life-threatening ventricular arrhythmias long after myocardial infarction

Low values of heart rate variability (HRV, a marker of vagal tone) and baroreflex sensitivity (BRS, a marker of vagal reflexes) identify patients at higher risk soon after myocardial infarction (MI). However, it is still unknown whether HRV and BRS correlate with malignant arrhythmias after the recovery from the transient post-MI autonomic disturbance. This study assessed whether HRV and BRS would differ in patients with malignant ventricular arrhythmias occurring long after MI compared with those in a control population. Twenty-eight patients entered the study: 14 patients with episodes of sustained ventricular tachycardia or ventricular fibrillation occurring more than 1 year after MI, age (mean +/- SEM) 64 +/- 2 years, and left ventricular ejection fraction 34% +/- 3% (VT/VF group) were compared with 14 similar patients with no ventricular tachycardia (control group). Mean RR interval was not different in the two groups (844 +/- 37 msec in VT/VF and 892 +/- 24 msec in control group). Also, no difference was found in any time- or frequency-domain measure of heart rate variability. However, patients in the VT/VF group had a significantly lower baroreflex sensitivity compared with patients in the control group (4.2 +/- 0.5 vs 8.0 +/- 1.1 msec/mm Hg, p = 0.008). Thus BRS but not HRV was reduced in patients with life-threatening ventricular arrhythmias occurring long after MI. A persistent depression of vagal reflexes may play a role in the occurrence of malignant arrhythmias, and analysis of BRS may potentially be helpful in the identification of patients at high risk long after myocardial infarction.