Repeated Exercise Induced Ischemi Causes Myocardial Preconditioning

Repeated short episodes of coronary occlusion in experimental animals cause myocardial preconditioning which reduces the extent of further ischemia. The purpose of the present study was to assess whether preconditioning also occurs during repeated exercise induced ischemia. Twenty-six coronary patients with positive exercise tests had 3 treadmill exercise tests at 30 minutes intervals. Two additional stress tests were performed on each of the previous 2 days, in order to eliminate/reduce the training effect. The 1st exercise test was regarded as baseline, while the 2nd (ex-2) and 3rd (ex-3) were compared to the 1st. Time to 1 mm ST depression (STD), recovery time (from maximal ischemi to 1 mm STD), total ischemic time (from 1 mm STD during exercise to regression of ischemi to 1 mm), double product at 1 mm STD and exercise duration were assessed. Preconditioning (defined as an improvement of 10% or more) was seen in 2 or more parameters in 76% of the patients. These dat indicate that total ischemic time and recovery time were markedly reduced and that time to 1 mm STD was prolonged and the double product at 1 mm of STD (ischemic threshold) was higher in the second exercise. This is the first evidence that myocardial preconditioning occurs during repeated exercise induced ischemia