HEART-RATE RESPONSE DURING EXERCISE TESTING AND AMBULATORY ECG MONITORING IN PATIENTS WITH SYNDROME-X

The response of the heart rate during exercise testing and 24-hour ambulatory electrocardiographic (ECG) monitoring performed with patients not receiving antianginal treatment was assessed in 26 patients (9 men and 17 women; mean age 51 +/- 8 years) with syndrome X (angina pectoris with normal coronary arteries), in 27 patients with coronary artery disease (10 men and 17 women; mean age 55 +/- 9 years), and in 21 healthy subjects (8 men and 13 women; mean age 47 +/- 11 years). In patients with syndrome X the slope of the regression line of heart rate versus time (heart rate/time slope) during exercise testing was similar to that of patients with coronary artery disease (3.3 +/- 0.8 versus 3.1 +/- 1.2 beats/min), but significantly lower than that in healthy subjects (4.2 +/- 1.1 beats/min; p < 0.003). In patients with syndrome X the intercept of the heart rate/time slope was significantly higher than that in coronary artery disease patients and healthy subjects (102 +/- 15, 86 +/- 18, and 90 +/- 16 beats/min, respectively; p < 0.015). Resting preexercise heart rate was also significantly higher in syndrome X, compared with coronary artery disease patients and healthy subjects (91 +/- 16, 79 +/- 16, and 80 +/- 14 beats/min, respectively). During ambulatory ECG monitoring, mean diurnal heart rate (from 6 AM to 6 PM) was higher in patients with syndrome X (83 +/- 8 beats/min) than in patients with coronary artery disease (75 +/- 8 beats/min) and healthy subjects (74 +/- 11 beats/min) (p < 0.02). Mean nocturnal heart rate, however, was not significantly different in the three groups (72 +/- 11 versus 70 +/- 8 beats/min versus 69 +/- 10 beats/min, respectively; p = NS). Resting circulating plasma catecholamine levels (measured in 10 of the 26 patients with syndrome X) were within normal limits. Thus the heart rate/time slope during exercise testing in patients with syndrome X is similar to that of patients with coronary artery disease and significantly different from that in healthy subjects. Compared with coronary artery disease patients and healthy subjects, patients with syndrome X exhibit a higher mean diurnal heart rate, which is not associated with increased resting catecholamine levels.