Attenuation of severity of myocardial ischemia during repeated daily ischemic episodes.

OBJECTIVES: The purpose of this study was to assess whether the severity of myocardial ischemia would be attenuated by repeated daily ischemic episodes, recorded by ambulatory electrocardiographic monitoring (AEM).
BACKGROUND: Repetitive ischemic episodes induced by brief coronary occlusions in animal experiments and in humans during balloon coronary angioplasty produce preconditioning. We wanted to assess whether this phenomenon also exists during daily ischemic episodes.
METHODS: Twenty-one patients with known coronary artery disease and ischemia on exercise testing and AEM were requested to walk a distance known to have previously caused myocardial ischemia on three consecutive occasions. Walking time was approximately 15 min and was 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 significantly from 2.21 mm during the first walk to 1.61 mm and 1.43 mm, respectively, on the second and third walks (p = 0.001). Ischemia duration was also significantly reduced on the second and third walks by 56% from 514 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 first 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 attenuation of myocardial ischemia with an associated increase in ischemic threshold in patients with repeated and adjacent ischemic episodes. This form of myocardial protection is likely to be encountered in patients during ordinary activity and may represent the clinical counterpart of myocardial preconditioning.