Exercise-induced QTc-interval changes for predicting improvement in regional blood flow in ischemic myocardium and cardiac output after coronary angioplasty in patients with right bundle-branch block

Background: We have previously shown that QT-interval changes are more usef ul than ST-T changes in evaluating the severity of exercise-induced myocard ial ischemia in patients with right bundle-branch block (RBBB). Hypothesis: The purpose of this study was to evaluate whether the improveme nt in regional myocardial blood flow (RMBF) in ischemic areas and cardiac o utput after percutaneous transluminal coronary angioplasty (PTCA) can be pr edicted by exercise-induced QT-interval changes prior to PTCA. Methods: The RMBF and cardiac output were quantified with nitrogen-13 ammon ia positron emission tomography at rest and during exercise in 20 patients with RBBB and ischemic heart disease before and 6 months after PTCA, and in 9 healthy volunteers. Results: Before PTCA, exercise-induced prolongation by < 20 ms or shortenin g of the Bazett-corrected QT (QTc) interval (454 +/- 38 to 451 +/- 41 ms, p = NS) was observed in 13 patients (Group 1) and prolongation by greater th an or equal to 20 ms (429 +/- 44 to 466 +/- 50 ms, p < 0.002) was observed in 7 (Group 2). The number of regions of exercise-induced ischemia was sign ificantly greater in Group 2 than in Group 1 (4.0 +/- 1.2 vs. 2.1 +/- 1.2, p < 0.01). The RMBF in regions of exercise-induced ischemia and cardiac out put at rest was not significantly different between Groups 1 and 2, whereas during exercise both the parameters were significantly lower in Group 2 th an in Group 1 (both p < 0.05). After successful PTCA, RMBF both at rest and during exercise improved significantly in Group 1 (0.67 +/- 0.04 to 0.71 /- 0.06 ml/min/g, 0.74 +/- 0.05 to 0.84 +/- 0.08 ml/mim/g; both p < 0.0001) , but did not improve significantly in Group 2 (0.63 +/- 0.05 to 0.65 +/- 0 .07 ml/min/g, 0.65 +/- 0.04 to 0.69 +/- 0.11 mi! min/g; both p = NS). Cardi ac output during exercise improved significantly in Group 1 (6.4 +/- 0.7 to 7.4 +/- 0.9 l/min, p < 0.002) but not in Group 2 (5.7 +/- 0.6 to 5.9 +/- 0 .6 l/min; p =NS). Conclusions: Our results suggest that the marked prolongation of the QTc in terval induced by pre-PTCA exercise may predict a lack of improvement in RM BF in ischemic areas and cardiac output after PTCA in patients with RBBB an d ischemic heart disease.