Parasympathetic withdrawal antedates dynamic myocardial ischemia in patients with syndrome X

This study was to evaluate the dynamic changes in cardiac autonomic control preceding electrocardiographic (ECG) myocardial ischemia in patients with syndrome X. Twenty-four-hour ambulatory ECG was obtained in 34 consecutive patients in a drug-free state. Fourteen (41%) of them, aged 58.8+/-13.5 yea rs, presented a total of 19 ischemic episodes, mean duration 12.4+/-19.8 mi n (ranged 1 to 90 min). Heart rate variability was measured for 24 h; for 3 min and 30 min before, and during the 15 min (in five 3-min intervals) imm ediately antedating ST segment depression; and for another 3 min after ST s egment back to normal. There were significant progressive shortenings in si nus cycle lengths over the 30 min preceding myocardial ischemia (-30 vs -3 minute, 822+/-32 ms vs 637+/-'23 ins, P<0.05; a decrement of 22.5%). The si nus cycle lengths lengthened after ischemia ceased. High frequency activity , pNNSO and rMSS.D. were significantly reduced from the -30 min baseline to a nidus in the last 3 min before ischemia (P<0.05), whereas low frequency band and low/high frequency ratio did not present significant change. These findings strongly argue that cardiac autonomic control, especially vagal w ithdrawal, is involved in the pathogenesis of dynamic myocardial ischemia i n syndrome X. (C) 1998 Published by Elsevier Science Ireland Ltd. All right s reserved.