3-DIMENSIONAL DISTRIBUTION OF ST-T WAVE ALTERNANS DURING ACUTE-ISCHEMIA

Introduction: A canine model of reversible ischemia was used to measur e the magnitude and transmural distribution of repolarization alternan s, Methods and Results: Twenty-four multielectrode needles were insert ed into a reversibly ischemic region created by 8 minutes of coronary occlusion, One hundred ninety-two unipolar electrograms were simultane ously recorded at 1-minute intervals for 8 minutes of ischemia and 3 m inutes of reflow recovery, Beat-to-beat repolarization alternans was q uantified for all electrograms using the standard deviation of QRST in tegrals, When alternans from animals that fibrillated was compared wit h alternans from animals that did not, the magnitude of alternans in t he fibrillation group was an average standard deviation of 1125 +/- 99 .7 mV-msec at the time of fibrillation and 409 +/- 183 mV-msec at 8 mi nutes of ischemia in the animals that did not fibrillate, The increase in alternans occurred mainly in the mid-myocardial and epicardial reg ions in the animals that fibrillated. QRS morphology of sequential ele ctrograms did not differ in beat-to-beat comparison, suggesting that r epolarization alternans measured was not due to alternating conduction block in the region of reversible ischemia, Conclusion: During acute ischemia, the magnitude and distribution of repolarization alternans a re greater and differ in hearts that experience ventricular fibrillati on, This observation may have clinical utility in arrhythmia predictio n, It also is consistent with the possibility there may be multiple me chanisms for repolarization alternans.