title: 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.
abstract: BACKGROUND
  We have previously shown that QT-interval changes are more useful than ST-T changes in evaluating the severity of exercise-induced myocardial ischemia in patients with right bundle-branch block (RBBB).
  
  
  OBJECTIVE
  The purpose of this study was to evaluate whether the improvement in regional myocardial blood flow (RMBF) in ischemic areas and cardiac output after percutaneous transluminal coronary angioplasty (PTCA) can be predicted by exercise-induced QT-interval changes prior to PTCA.
  
  
  METHODS
  The RMBF and cardiac output were quantified with nitrogen-13 ammonia 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 shortening 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 > or = 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 significantly 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 output at rest was not significantly different between Groups 1 and 2, whereas during exercise both the parameters were significantly lower in Group 2 than 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/min/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 ml/ min/g; both p = NS). Cardiac 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 interval induced by pre-PTCA exercise may predict a lack of improvement in RMBF in ischemic areas and cardiac output after PTCA in patients with RBBB and ischemic heart 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: T
authors.initials: T
authors.lastname: Michihata
authors.forename: H
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Y
authors.initials: Y
authors.lastname: Akutsu
authors.forename: O
authors.initials: O
authors.lastname: Okazaki
authors.forename: T
authors.initials: T
authors.lastname: Katagiri
authors.forename: K
authors.initials: K
authors.lastname: Harumi
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015906:Angioplasty, Balloon, Coronary; D002037:Bundle-Branch Block / Q000175:diagnosis*; D002302:Cardiac Output / Q000502:physiology; D017023:Coronary Angiography; D003326:Coronary Circulation / Q000502:physiology*; D004562:Electrocardiography; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000628:therapy*; D011237:Predictive Value of Tests; D011379:Prognosis; D012039:Regional Blood Flow; D018709:Statistics, Nonparametric; D014055:Tomography, Emission-Computed