Changes in frequency domain measures of heart rate variability in relation to the onset of ventricular tachycardia in acute myocardial infarction

Background. Low heart rate variability (HRV) is associated with an increased risk of arrhythmic death and ventricular tachycardia (VT). The purpose of this study was to examine whether there is a temporal relation between changes in HRV and the onset of spontaneous episodes ofVT in patients at high risk of life-threatening arrhythmias. Methods and Results. Components of HRV in the frequency domain were analyzed before the onset of 28 episodes of nonsustained VT (more than four impulses; duration <30 seconds) and 12 episodes of sustained VT (>30 seconds or requiring defibrillation) in 18 patients with coronary artery disease. Seven patients had survived cardiac arrest not associated with acute myocardial infarction, and 11 had a history of sustained VT. All frequency domain measures of HRV, i.e., total power (p<0.001), high-frequency power (p<0.05), low-frequency power (p<0.01), very-low-frequency power (p<0.01), and ultralow-frequency power (p<0.05), were significantly lower before the onset of sustained VT than before nonsustained VT. Total power of HRV was also lower during the 1-hour period before the onset of sustained VT than the average 24-hour HRV (p <0.05). An indirect correlation existed between the length ofVT and the total power of HRV analyzed during the 15 minutes before the onset ofVT (r=0.54,p<0.01). HRV had a trend toward increasing values before the onset of nonsustained VT (p<0.01) but not befor