Abnormal autonomic control of the cardiovascular system in syndrome X

Abstract

Anomalies of autonomic control of the coronary circulation may play a role in the development of syndrome X (angina pectoris, ischemia-appearing results on exercise test, and normal coronary arteriograms). Twenty-six patients with syndrome X and 20 healthy sex- and age-matched control subjects were studied by means of analysis of heart rate variability during 24-hour Hotter monitoring. Spectral and nonspectral parameters of heart rate variability were investigated. Mean heart rate was similar in patients with syndrome X and in control subjects. Patients with syndrome X had significantly lower standard deviation of all normal RR intervals, a lower percentage of adjacent normal RR intervals >50 ms in difference (126.4 ± 22 vs 149 ± 43 ms, p <0.05; 6.3 ± 4 vs 11.2 ± 7%, p <0.05; respectively), and a trend toward lower values of time-domain parameters. Lower values of total power and low frequency were also observed in patients with syndrome X (1273 ± 693 vs 1790 ± 989 ms 2, p <0.05; 406 ± 176 vs 729 ± 455 ms 2, p <0.01, respectively). An inverse correlation between heart rate and measures of heart rate variability was found in syndrome X but not in control subjects. High- and low-frequency power showed a similar circadian pattern in syndrome X patients and control subjects. Patients and control subjects were then allocated into 2 groups according to the median RR duration: syndrome X1 and control 1 with high mean heart rate, and syndrome X2 and control 2 with low mean heart rate. The syndrome X1 group had a significantly lower standard deviation of all normal RR intervals, root-mean-square difference of successive RR intervals, percentage of adjacent normal RR intervals >50 ms different, and high and low frequency than did the syndrome X2, control 1, and control 2 groups. In conclusion, patients with syndrome X have a sympathovagal balance shifted toward sympathetic predominance that is more evident in those with an increased mean heart rate. This dysfunction appears to persist throughout the 24 hours and may indicate heterogeneity in autonomic function in syndrome X.