Effects of nitrates on R-wave variations after exercise in coronary heart disease: differences in patients with and without angina pectoris.
With the purpose of investigating the pathophysiology of changes in the R wave after exercise and its relationship with left ventricular function, we studied 44 patients with coronary heart disease. They were classified into the following three groups: group A, 11 patients with angina pectoris and no prior myocardial infarction; group B, 18 patients with angina pectoris and prior myocardial infarction; and group C, 15 patients with prior myocardial infarction but no angina. All patients performed two exercise tests; one was a control test, and the other was performed after the sublingual administration of 5 mg of isosorbide dinitrate. In group A, variations in the R-wave voltage in control test and in the test after isosorbide dinitrate were 1.5 +/- 0.8 mm and -1.2 +/- 0.9 mm (P less than 0.05), respectively. In group B, results were 1.2 +/- 0.7 mm on the control test and -0.7 +/- 0.6 mm after isosorbide dinitrate (P less than 0.002), and in group C were -1.6 +/- 1.2 mm on the control test and -0.7 +/- 0.7 mm after isosorbide dinitrate (not significant). Thus, the two groups of patients with angina showed an increase of the R-wave after exercise in the control test but a decrease after the administration of nitrates, whereas the patients without angina showed a reduced R-wave after exercise both before and after the administration of nitrates (like normal subjects). This study suggests that ischemic ventricular dysfunction with exercise results in an increase in the R-wave, while exercise after nitrates results in a decrease in the R-wave consistent with less or no ventricular dysfunction due to nitrate therapy.