ADAPTATION TO MYOCARDIAL-ISCHEMIA DURING REPEATED DYNAMIC EXERCISE INRELATION TO FINDINGS AT CARDIAC-CATHETERIZATION

It has been suggested that the myocardium is able to recruit endogenou s protective mechanisms in response to repeated ischemia and reperfusi on. We set out to study whether this is manifested in patients with co ronary artery disease in the form of fewer signs of myocardial ischemi a during the second of two successive exercise tests and whether any r elations exist between ischemia adaptation and findings at cardiac cat heterization. Twenty-one patients with typical angina pectoris symptom s underwent two repeated bicycle exercise tests with identical protoco ls, followed by cardiac catheterization and coronary angiography the n ext day. The first exercise test was discontinued whenever a 2 mm ST d epression in the electrocardiogram (EGG) was achieved or further exerc ise was limited by symptoms. The second exercise test was performed af ter disappearance of the symptoms or ST depression or both. Kaplan-Mei er survival analysis for the appearance of a 1 mm ST depression demons trated improved ischemia tolerance during the second test, when the re quired time for its appearance was significantly longer (6.5 +/- 0.8 m in vs 4.5 +/- 0.5 min; p = 0.005), The maximal intensity of anginal pa in was lower during the second exercise (2.2 +/- 1.0 min vs 0.7 +/- 0. 3 min in Borg's scale; p < 0.001), and the time required for disappear ance of the ST depression was shorter after this exercise (3.0 +/- 0.8 min vs 6.2 +/- 0.9 min; p = 0.003), with a similar tendency in the di sappearance of angina, The rate-pressure product on the appearance of a 1 mm ST depression was significantly higher during the second test ( 17,990 +/- 1210 mm Hg x min(-1) vs 15,960 +/- 869 mm Hg x min(-1); p = 0.009). Eighteen of the patients had three-vessel disease, as evidenc ed by coronary angiography, and the change in the time required for th e appearance of a 1 mm ST depression in the repeated exercise tests wa s inversely correlated with the severity of the left anterior descendi ng (LAD) coronary artery obstruction (r = -0.61; p = 0.006) and left v entricular end-diastolic pressure (r = -0.50; p = 0.03). No significan t correlation with the degree of collateral vessels was found, We conc lude that most patients with extensive coronary artery disease are abl e to increase their tolerance of ischemia during repeated dynamic exer cise and that increased vasodilation and oxygen delivery are the major mechanisms for this warm-up phenomenon, On the other hand, collateral s visible in routine resting angiography do not predict the degree of adaptation to ischemia during repeated dynamic exercise.