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In patients with left bundle branch block (LBBB), ischemia-induced repolarization changes associated with QTc-interval shortening may be recorded during coronary angioplasty.We aimed to assess whether these repolarization changes may be predictive of severe coronary artery disease in patients with LBBB.Fifty noninfarcted LBBB patients underwent dipyridamole stress test and coronary angiography for chest pain. To localize the site of ischemia, we considered four groups of conventional ECG leads (V1–V2–V3; V4–V5–V6; aVL–I; III–aVF–II), exploring the anteroseptal, lateral, high-lateral, and inferior left ventricular walls. ST-T changes and QTc intervals were estimated at rest and peak stress, lead by lead, in each group of leads and the fractional percentage difference between rest–stress QTc intervals (ΔQTc) was calculated. A ΔQTc greater than −10% was used to define significant QTc-interval shortening. Coronary stenosis of more than 70% and more than 90% were considered ‘significant’ and ‘severe’.According to dipyridamole stress test response, two groups were identified: group I (35 patients) with dipyridamole-induced ischemia and group II (15 patients) without dipyridamole-induced ischemia. The wall motion score index at peak stress (compared with resting wall motion score index) was significantly higher in group I (1.98 ± 0.13 vs. 1.28 ± 0.08, P < 0.0001) than in group II (1.36 ± 0.18 vs. 1.25 ± 0.08, P = 0.296). The patients of group I showed a significant QTc-interval shortening (ΔQTc = −16.9 ± 3.9%), whereas this did not happen in patients of group II (ΔQTc = +8.8 ± 2.4%, P < 0.0001). The patients of group I also had a more severe stenosis in the vessel related to the stress-induced dyssynergic area (I = 90.5 ± 9.5 vs. II = 34.3 ± 31.1%; P < 0.0001).In patients with LBBB, stress-induced pseudonormalization pattern, associated with QTc-interval shortening, allows the identification of cardiac areas supplied by severely stenosed coronary arteries.