ATTENUATION OF SEVERITY OF MYOCARDIAL-ISCHEMIA DURING REPEATED DAILY ISCHEMIC EPISODES

Objectives. The purpose of this study was to assess whether the severi ty of myocardial ischemia would be attenuated by repeated daily ischem ic episodes, recorded by ambulatory electrocardiographic monitoring (A EM). Background. Repetitive ischemic episodes induced by brief coronar y occlusions in animal experiments and in humans during balloon corona ry angioplasty produce preconditioning, We wanted to assess whether th is phenomenon also exists during daily ischemic episodes. Methods. Twe nty-one patients with known coronary artery disease and ischemia on ex ercise testing and AEM were requested to walk a distance known to have previously caused myocardial ischemia on three consecutive occasions, Walking time was similar to 15 min and aas followed by 5 min of rest. Results. Mean maximal heart rate during the three walks was similar; however, the mean maximal ST segment depression decreased significantl y from 2.21 mm during the first walk to 1.61 mm and 1.43 mm, respectiv ely, an the second and third walks (p = 0.001). Ischemia duration was also significantly reduced on the second and third walks by 56% from 5 14 to 228 and 254 s, respectively (p = 0.012), The heart rate at onset of ischemia (ischemic threshold) increased from 99 beats/min on the f irst walk to 101 beats/min on the second walk and to 106 beats/min on the third walk (p = 0.058). Conclusions. This study demonstrated atten uation of myocardial ischemia with an associated increase in ischemic threshold in patients with repeated and adjacent ischemic episodes. Th is form of myocardial protection is likely to be encountered in patien ts during ordinary activity and may represent the clinical counterpart of myocardial preconditioning. (C) 1997 by the American College of Ca rdiology.