Serial exercise testing in patients with effort angina: variable tolerance, fixed threshold.

To investigate the frequency and mechanism of variable threshold angina, seven treadmill exercise tests were performed in each of 28 patients with stable effort angina and exercise-induced ST segment depression. Each patient had tests at 8 AM on 4 days within a 2 week period and on 1 of these days had three additional tests at 9 AM, 11 AM and 4 PM. Time to 1 mm ST depression increased from 277 +/- 172 seconds on day 1 to 319 +/- 186 seconds on day 2, 352 +/- 213 seconds on day 3 and 356 +/- 207 seconds on day 4 (p less than 0.05). Rate-pressure product at 1 mm ST depression remained constant. Similarly, time to 1 mm ST depression increased from 333 +/- 197 seconds at 8 AM to 371 +/- 201 seconds at 9 AM and to 401 +/- 207 seconds at 11 AM and decreased to 371 +/- 189 seconds at 4 PM (p less than 0.01). Again, rate-pressure product at 1 mm ST depression remained constant. The standard deviation for time to 1 mm ST depression, calculated as a percent of the mean for each patient's seven tests and then averaged for the entire group, was 22 +/- 11%. The standard deviation for rate-pressure product at 1 mm ST depression, calculated in the same way, was significantly less at 8.4 +/- 2.8% (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)