title: Initial and Secondary ST-T Alternans During Acute Myocardial Ischemia in the In-Situ Pig Heart.
abstract: The factors responsible for the ST-T wave alternans (STTA) and associated arrhythmias during acute ischemia have not been clarified.In acutely ischemic porcine myocardium, we recorded transmural unipolar and bipolar electrocardiograms and mid-myocardial extracellular K(+) ([K(+)]e) from the center of the ischemic zone during 8-minute episodes of ischemia. Two different STTAs occurred. The initial STTA, which occurred at 4 minutes 15 seconds ± 12 seconds of ischemia during sinus rhythm, was most prominent in the subendocardium, independent of [K(+)]e and activation block, and heart rate dependent. It occurred in 13/19 (68%) occlusions at heart rates ≤ 100 bpm and in 22/23 (96%) at > 100 bpm. The second STTA was more obvious and greatest in the subepicardium. It began in the later phase of ischemia and was also heart rate dependent (5/19 [26%] occlusions at heart rates ≤ 100 bpm and 10/23 [44%] at > 100 bpm). This STTA was consistently associated with 2:1 change in the bipolar electrogram morphology, possibly due to 2:1 conduction block. Ventricular fibrillation (VF) occurred only at > 100 bpm.The initial STTA may be independent of conduction abnormalities and represent primary repolarization alternans. The second STTA may be secondary to and indicative of 2:1 activation block or marked alternans of the action potential amplitude/duration. The associated VF most likely reflects the underlying conduction abnormality.
authors.affiliation: Division of Cardiology, Department of Medicine, Nihon University School of Medicine.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Watanabe
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Gettes
mesh_terms: D000200:Action Potentials; D000208:Acute Disease; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D004562:Electrocardiography / Q000379:methods; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods; D006329:Heart Conduction System / Q000378:metabolism / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology*; D008955:Models, Cardiovascular; D017202:Myocardial Ischemia / Q000150:complications / Q000378:metabolism / Q000503:physiopathology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D011188:Potassium / Q000378:metabolism; D013552:Swine; D013997:Time Factors
chemical_list: D011188:Potassium