QUANTIFICATION OF ISCHEMIA-INDUCED VULNERABILITY BY PRECORDIAL T-WAVEALTERNANS ANALYSIS IN DOG AND HUMAN

Objective: The aim was to examine the regional specificity of T wave a lternans and the value of precordial ECG monitoring for non-invasive t racking of cardiac vulnerability during acute coronary artery occlusio n and reperfusion in animals and humans. Methods: The left ventricular ECC was monitored during two acute occlusions of the left anterior de scending coronary artery and subsequent reperfusion in each of 61 chlo ralose anaesthetised dogs, and over 150 000 beats were analysed. In su bgroups of these animals, lead II and precordial lead V-5 were monitor ed or epicardial electrograms were recorded. In seven patients, lead I I and precordial leads V-1-6 were monitored during angioplasty. T wave alternans magnitude was quantified by complex demodulation. The same recording equipment and analytical methods were used in the clinical a nd experimental studies. Results: A close temporal correspondence and linear correlation was found between T wave alternans magnitude - but not ST segment depression or ventricular premature beat incidence - an d the incidence of spontaneous ventricular tachycardia and fibrillatio n during acute coronary artery occlusion and reperfusion. Epicardial e lectrograms showed alternans to be regionally specific, occurring in t he ischaemic but not in the normal zones, and to predict spontaneous v entricular fibrillation and ventricular tachycardia (sensitivity = 79% , specificity = 86%). A significant linear relationship (r(2) = 0.86, p < 0.01) between alternans magnitude detected in V-5 and the left ven tricular intracavitary lead indicates that the precordial leads could be used to assess cardiac vulnerability from the body surface. Lead V- 5 showed greater resolution than lead II. In humans, the precordial le ads overlying the ischaemic zone were superior to lead II or Frank lea ds for alternans detection during both the occlusion and the reperfusi on phases. In both animals and humans, alternation invariably occurred during the first half of the T wave, coinciding with the vulnerable p eriod of the cardiac cycle and suggesting an important electrophysiolo gical link to cardiac vulnerability. Conclusions: Alternans is regiona lly specific and is linearly projected to the precordium. Quantificati on of its magnitude in the precordial ECG may provide a non-invasive m eans for tracking cardiac vulnerability during acute myocardial ischae mia and reperfusion in both animals and humans.