IMPROVEMENT IN ISCHEMIC PARAMETERS DURING REPEATED EXERCISE TESTING -A POSSIBLE MODEL FOR MYOCARDIAL PRECONDITIONING

Repeated short episodes of coronary occlusion in experimental animals, and in humans during balloon angioplasty, cause myocardial preconditi oning. This study examines whether myocardial ischemia induced by repe ated exercise testing can reduce the extent of ischemia induced by sub sequent exercise tests. Twenty-six patients with positive stress tests underwent 3 treadmill exercise tests at 30-minute intervals. Two addi tional tests were performed on each of the previous 2 days in order to eliminate and/or reduce the training effect. All 3 exercise tests wer e of similar work load. in spite of that, total ischemic time was mark edly shortened from 633 to 399 seconds (p<0.0001) as well as the recov ery time from 259 to 126 seconds (p<0.0001) between the first and the second tests. There was no further improvement on the third test. Time to I-mm ST depression was prolonged from 487 to 593 seconds (p=0.004) and double product at I-mm ST depression was increased in the second test from 20,322 to 22,325 mm Hg/second (p=0.008), implying a higher i schemic threshold. An improvement of greater than or equal to 10% in l ess than or equal to 1 ischemic parameter was observed in 25 of the 26 patients and in greater than or equal to 2 of the ischemic parameters in 76% of the patients. Improvement in ischemic parameters develops d uring repeated exercise induced ischemia in most patients. We suggest that this phenomenon, which was previously known as ''warm up,'' is th e clinical counterpart of myocardial preconditioning which develops no t only during ischemia caused by reduction in coronary flow, but also during demand-induced ischemia. (C) 1996 by Excerpta Medica, Inc.