RELATION BETWEEN EXERCISE-INDUCED MYOCARDIAL-ISCHEMIA AS ASSESSED BY N-13 AMMONIA POSITRON-EMISSION-TOMOGRAPHY AND QT INTERVAL BEHAVIOR IN PATIENTS WITH RIGHT BUNDLE-BRANCH BLOCK

Exercise-induced myocardial ischemia is difficult to detect with ST-T changes in patients with right bundle branch block (RBBB). We sought t o predict exercise-induced myocardial ischemia with QT interval behavi or during exercise in patients with RBBB. Twenty-two patients with ang iographically proven coronary artery disease and RBBB and 9 healthy vo lunteers underwent nitrogen-13 ammonia positron emission tomography wi th bicycle ergometer exercise at a fixed workload of 25 W. Regional my ocardial blood flow (RMBF) and electrocardiographic changes were measu red both at rest and after 5 minutes of exercise. The QT interval was measured from the onset of the QRS complex to the offset of the T wave in lead V-5. The Delta QT and Delta RMBF, which indicated values afte r 5 minutes of exercise minus values at rest, were negatively correlat ed (r = -0.74, p <0.001). Exercise-induced shortening of the QT interv al (422 +/- 27 to 381 +/- 38 ms, p = 0.0020) was observed in 15 patien ts (group 1) and no change or prolongation (411 +/- 45 to 420 +/- 37 m s, p = NS) was observed in 7 patients (group 2). Multivessel disease w as significantly more frequent but collateral circulation was signific antly less in group 2 than in group 1 (p <0.01, p <0.05, respectively) . Cardiac output at rest was significantly lower in groups 1 and 2 tha n in healthy volunteers (4.52 +/- 0.83 and 4.51 +/- 0.84 vs 6.20 +/- 0 .83 L/min; p = 0.0014, p = 0.0003). Although RMBF at rest did not diff er significantly among groups 1 and 2 and healthy volunteers (0.63 +/- 0.20 vs 0.69 +/- 0.13 and vs 0.77 +/- 0.14 ml/min/g), RMBF after 5 mi nutes of exercise was significantly lower in group 2 than in group 1 a nd healthy volunteers (0.78 +/- 0.11 vs 0.96 +/- 0.20 and vs 1.20 +/- 0.18 ml/min/g; p = 0.0289, p <0.0001). The number of regions of critic al coronary artery disease was significantly greater in group 2 than i n group 1 (4.0 +/- 1.2 vs 2.1 +/- 1.3, p = 0.0039). Our results sugges t that the absence of QT interval shortening during exercise may indic ate severe myocardial ischemia induced by exercise in patients with RB BB and coronary artery disease. (C) 1998 by Excerpta Medica, Inc.