Autonomic balance in patients with angina and a normal coronary angiogram

The pathophysiology of angina pectoris in patients with a normal coronary angiogram is not clear. Furthermore, the pathophysiological impact of ST changes in syndrome X is controversial. The purpose of this study was to investigate cardiac autonomic function, by measuring 24 h heart rate variability, in patients with and without electrocardiographic evidence of ischaemia during exercise. Thirty-two patients with angina pectoris, a normal coronary angiogram, echocardiogram, hyperventilation test and gastro-oesophageal investigation were studied. Fourteen healthy subjects served as controls. Fifteen patients had significant ST segment depression during stress testing, whereas 17 had no electrocardiographic signs of ischaemia. Heart rate variability was calculated as (1) mean RR = mean of all normal RR intervals, (2) the difference in mean RR level between when awake and when asleep (mean RR wake-sleep)-a tentative index of sympathetic activation, (3) the standard deviation (SD)-a broad band measure of autonomic balance, and (4) a percentage of successive RR interval differences > or = 6% (pNN6%)-an index of vagal modulation. The coronary vascular resistance was measured at rest and during pacing. Mean RR and autonomic indexes did not differ between patients with a positive exercise test and controls (831/884 ms; 24 h SD 125/134 ms; pNN6% 6.715.4%, respectively). Patients with a normal exercise test had shorter mean RR (758 ms vs 844 ms; P < 0.05) and significantly reduced 24-h SD (103 ms vs 134 ms; P < 0.05) than controls, whereas values for vagal index (6.5% vs 5.4%) did not differ from healthy controls. Mean RR wake-sleep also tended to be lower in patients with a normal exercise test (-125 ms vs -173 ms) compared to controls (P < 0.1). Patients with a positive exercise test had a significantly attenuated reduction in coronary vascular resistance during pacing in comparison to patients with a normal exercise test (-0.131 -0.26 mmHg x min. ml-1; P < 0.05). The findings suggest the occurrence of general elevated sympathetic activation in angina patients with a normal exercise test. Patients with a positive exercise test exhibited no signs of autonomic dysfunction although these patients had altered coronary vascular resistance indicating microvascular angina. This supports the suggestion that patients with a normal exercise test constitute an independent pathophysiological entity.