Stress-induced QTc-interval shortening as an ancillary marker of ischemia in patients with complete left bundle branch block

BACKGROUND: 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. METHODS: 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'. RESULTS: 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). CONCLUSION: 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.