Is the shortening of the QTc interval in Q-wave leads showing ST segment shift during exercise testing a new ECG marker of myocardial ischemia and viability in patients with previous anterior myocardial infarction?

PURPOSE: To evaluate whether the shortening of the QTc-interval, measured in Q-wave leads showing ST segment elevation during exercise testing may be a marker of stress-induced transmural ischemia (and indirectly of myocardial viability) in the infarct zone in patients with prior Q-wave anterior myocardial infarction. METHODS: We evaluated 15 consecutive patients (Group A) with previous anterior myocardial infarction presenting these peculiarities: 1) ST segment elevation over Q waves during exercise testing; 2) critical (> 75%) stenosis of LAD; 3) evidence by echocardiography and stress-redistribution-reinjection 201thallium myocardial scintigraphy (SRR201TIMS) of viable myocardium in the infarct zone (akinetic segments with normal echo-reflectivity plus > 7 mm end-diastolic wall thickness and significant 201thallium redistribution after reinjection). The study control group (Group B) consisted of 15 patients with previous myocardial infarction, critical stenosis of LAD and evidence of scarring by imaging techniques (increased echo-reflectivity associated with an end-diastolic wall thickness < 6 mm and no 201thallium redistribution in infarcted areas). The QTc interval was measured at rest and at peak stress in all leads, and particularly in infarct-related leads showing ST-T changes, and the lead-by-lead fractional difference percentage between the QTc intervals (delta QTc) was calculated. The delta QTc was measured again during exercise testing in 11 patients from Group A (Group A1) who showed significant contractility recovery three months after complete myocardial revascularization. A delta QTc shortening < -10% was considered "significant". RESULTS: In 14/15 patients from Group A, a significant delta QTc shortening was measured, while in 14/15 patients from Group B no significant delta QTc shortening was detected (sensitivity = 93.3%; specificity = 93.3%) (p < 0.0001). The mean delta QTc in Group A was -18.1 +/- 8.5%; the mean delta QTc in Group B was -4.2 +/- 7.8% (p < 0.0001). No patient from Group A1 showed a significant delta QTc shortening in Q-wave leads (mean delta QTc group A1 = +6.9 +/- 14.8%). CONCLUSIONS: delta QTc shortening in infarct-related leads during exercise testing is a simple ECG marker of transmural ischemia and, indirectly, of myocardial-viability. This sign is no more evident after myocardial revascularization and may be useful in identifying "hibernating-myocardium".