Variability of results during repeat exercise stress testing in patients with stable angina pectoris: Role of dynamic coronary flow reserve

In some patients with stable angina, the variability of results during repeated exercise tests is higher than in others with similar symptoms. The aim of the study was to assess whether this difference can be explained by a different susceptibility of the coronary arteries to vasoconstrictor stimuli. Ten patients (group A) with stable angina, who developed myocardial ischemia (angina and ST segment depression >0.1 mV) following ergonovine-induced coronary constriction, and 10 other patients (group B) with stable angina, but a negative ergonovine test result, were subjected to two treadmill exercise tests. The variability of heart rate and heart rate-blood pressure product at 0.1 mV ST segment depression was significantly higher in group A than in group B (12 ± 4 vs 4 ± 4 bpm, respectively, p <0.001 and 3366 ± 1900 vs 930 ± 960 bpm × mm Hg, respectively, p <0.005), such as the variability of heart rate-blood pressure product at the onset of angina (3887 ± 2400 vs 1428 ± 1800 bpm × mm Hg, respectively, p <0.04). The remaining exercise parameters were always more variable in group A than in group B, but these differences did not achieve statistical significance. Thus patients with stable angina who develop myocardial ischemia in response to ergonovine have a larger variability of results during repeat exercise testing. Such findings could be explained by an enhanced susceptibility to the coronary constrictor effects of exercise resulting in dynamic changes in coronary flow reserve.