Angina of effort with a variable threshold: a unique entity due to different mechanisms?

Variable threshold during exertion is a common feature in patients with chronic exertional angina. Changes in coronary vasomotor tone, when occurring at sites of critical narrowings, are a plausible explanation for variability of symptoms in these patients. However, the evidence supporting this hypothesis is still uncertain. Accordingly, we performed four computer assisted, multistage bicycle ergometer tests, without drugs, in 30 patients with chronic exertional angina, exercise induced ST depression, and a history of variable anginal threshold during exertion. Significant coronary artery disease was documented in each case by coronary arteriography. Patients were tested at the same time of day within a two week period. Comparison was made between each single test and the average of the remaining three. Time to 0.1 mV ST depression showed significant (+/- 20%) changes in 27 (90%) patients. Variability was shown in two out of four tests in 25 patients (83%), in three tests in 10 (33%), and in four tests in 2 (7%). Rate pressure product at 0.1 mV ST depression was concurrently changed (+/- 20%) in 20 patients (67%). Variability in two, three and four tests was observed in 7 (22%), 2 (7%) and 2 (7%) patients, respectively. Changes in time to 0.1 mV ST depression paralleled those in rate-pressure product at the onset of ischemia in 6 patients (22%) (dynamic ischemic threshold). Rate pressure product at 0.1 mV ST depression was unchanged despite variations in time to 0.1 mV ST depression in 10 patients (37%) (fixed ischemic threshold). The remaining 11 patients (41%) showed variable exercise tolerance associated with fixed (13 tests) and dynamic (13 tests) ischemic threshold.(ABSTRACT TRUNCATED AT 250 WORDS)