Session S31.1

Electrocardiographic Response of the Heart to Myocardial Ischemia

KK Aras*, S Shome, DJ Swenson, JG Stinstra, RS MacLeod

University of Utah
Salt Lake City, UT, USA

Introduction: Myocardial Ischemia is a pathological condition initiated by supply and demand imbalance of the blood to the heart. Electrocardiographic (ECG) ST segment shifts are often used as markers for ischemia. Literature suggests that the progression of ischemia, occurs from the endocardium, which has the highest metabolic demand and spreads towards the epicardium, eventually becoming transmural. Our study with animal models has found the progression of ischemia to be more complex and heterogeneous in its distribution.
Methods: We used in situ canine preparation, wherein the animals were subjected to demand ischemia by reducing coronary flow and increasing the heart rate through atrial pacing. Epicardial and transmural electrograms were recorded using a 247 electrode sock and up to 45 transmural needle electrodes.
Results: At reduced coronary flow, increasing heart rates caused pockets of ischemic regions, characterized by ST potential elevations to appear variously distributed in the epicardial, mid-myocardial and endocardial regions. Further reduction in coronary flow and simultaneously increasing the heart rates, increased the extent and the magnitude of the ischemic regions that in certain cases became transmural.
Conclusion: The electrocardiographic response of the heart to myocardial ischemia, contrary to earlier belief, is a much more complex phenomenon characterized by heterogeneous distribution and progression of ischemic regions.

(Abstract Control Number: 19)