Coronary heart disease. Differential hemodynamic, metabolic, and electrocardiographic effects in subjects with and without angina pectoris during atrial pacing.

Right atrial pacing was performed in 41 subjects with coronary heart disease. Twenty developed angina pectoris during pacing, while 21 did not. The extent of coronary artery disease, as judged by selective cinearteriography, was similar in the two groups. Both had significant increases in heart rate and pressure-time per minute, but there was no significant difference in either of these parameters between groups. Among the hemodynamic parameters measured, the only statistically significant change was in the cardiac index which fell slightly but significantly in the angina group. There were no differences in myocardial oxygen extraction either within each group or between groups. In the angina group, however, 14 of 20 subjects exhibited abnormal myocardial lactate metabolism during pacing. The mean change was highly significant (P < 0.01). In the nonangina group, eight of 21 subjects had abnormal lactate metabolism during pacing and the mean change was significant (P < 0.05). There was no correlation between abnormal lactate metabolism and electrocardiographic evidence of myocardial ischemia in either group. Sublingual nitroglycerin, given to five subjects with angina while pacing was continued, resulted in prompt relief of symptoms, but abnormal lactate metabolism and ST-segment depression were unaffected after 10 min. By contrast, when anginal symptoms were relieved in five subjects by cessation of pacing, symptomatic improvement was accompanied by marked improvement in lactate metabolism after 10 min. Although angina pectoris appears to be related statistically to subnormal left ventricular function and abnormal lactate metabolism, there is significant individual variation.