title: Relation between exercise-induced myocardial ischemia as assessed by nitrogen-13 ammonia positron emission tomography and QT interval behavior in patients with right bundle branch block.
abstract: Exercise-induced myocardial ischemia is difficult to detect with ST-T changes in patients with right bundle branch block (RBBB). We sought to predict exercise-induced myocardial ischemia with QT interval behavior during exercise in patients with RBBB. Twenty-two patients with angiographically proven coronary artery disease and RBBB and 9 healthy volunteers underwent nitrogen-13 ammonia positron emission tomography with bicycle ergometer exercise at a fixed workload of 25 W. Regional myocardial blood flow (RMBF) and electrocardiographic changes were measured 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 V5. The deltaQT and deltaRMBF, which indicated values after 5 minutes of exercise minus values at rest, were negatively correlated (r = -0.74, p <0.001). Exercise-induced shortening of the QT interval (422 +/- 27 to 381 +/- 38 ms, p = 0.0020) was observed in 15 patients (group 1) and no change or prolongation (411 +/- 45 to 420 +/- 37 ms, p = NS) was observed in 7 patients (group 2). Multivessel disease was significantly more frequent but collateral circulation was significantly 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 than 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 differ 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 minutes of exercise was significantly lower in group 2 than in group 1 and 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 critical coronary artery disease was significantly greater in group 2 than in group 1 (4.0 +/- 1.2 vs 2.1 +/- 1.3, p = 0.0039). Our results suggest that the absence of QT interval shortening during exercise may indicate severe myocardial ischemia induced by exercise in patients with RBBB and coronary artery disease.
authors.affiliation: Third Department of Internal Medicine, Showa University School of Medicine, Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Watanabe
authors.forename: K
authors.initials: K
authors.lastname: Harumi
authors.forename: Y
authors.initials: Y
authors.lastname: Akutsu
authors.forename: H
authors.initials: H
authors.lastname: Yamanaka
authors.forename: T
authors.initials: T
authors.lastname: Michihata
authors.forename: O
authors.initials: O
authors.lastname: Okazaki
authors.forename: T
authors.initials: T
authors.lastname: Katagiri
mesh_terms: D000641:Ammonia; D002037:Bundle-Branch Block / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002302:Cardiac Output / Q000502:physiology; D003326:Coronary Circulation / Q000502:physiology; D003327:Coronary Disease / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology; D004562:Electrocardiography; D005080:Exercise Test; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000209:etiology; D009590:Nitrogen Radioisotopes; D013997:Time Factors; D014055:Tomography, Emission-Computed
chemical_list: D009590:Nitrogen Radioisotopes; D000641:Ammonia