Changes in heart rate and heart rate variability before ambulatory ischemic events

OBJECTIVES The aim of this study was to determine the time course of autono mic nervous system activity preceding ambulatory ischemic events. BACKGROUND Vagal withdrawal can produce myocardial ischemia and may be invo lved in the genesis of ambulatory ischemic events. We analyzed trajectories of heart rate variability (HRV) 1 h before and after ischemic events, and we examined the role of exercise and mental stress in preischemic autonomic changes. METHODS Male patients with stable coronary artery disease (n = 19; 62.1 +/- 9.3 years) underwent 48-h ambulatory electrocardiographic monitoring. Freq uency domain HRV measures were assessed for 60 min before and after each of 68 ischemic events and during nonischemic heart rate-matched control perio ds. RESULTS High-frequency HRV decreased from -60, -20 to -10 min before ischem ic events (4.8 +/- 1.3; 4.6 +/- 1.3; 4.4 +/- 1.2 ln [ms(2)], respectively; p = 0.04) and further from -4, -2 min, until ischemia (4.4 +/- 1.3; 4.1 +/- 1.3; 3.7 +/- 1.2 ln [ms(2)]; p's < 0.01). Low frequency HRV decreases star ted at -4 min (p < 0.05). Ischemic events occurring at high mental activiti es were preceded by depressed high frequency HRV levels compared with event s at low mental activity (p = 0.038 at -4 min, p = 0.045 at -2 min), wherea s the effects of mental activities were not observed during nonischemic con trol periods. Heart rate variability measures remained significantly decrea sed for 20 min after recovery of ST-segment depression when events were tri ggered by high activity levels. CONCLUSIONS Autonomic changes consistent with vagal withdrawal can act as a precipitating factor for daily life ischemia, particularly in episodes tri ggered by mental activities. (C) 2001 by the American College of Cardiology .