title: Limitation of exercise tolerance in chronic heart failure: distinct effects of left bundle-branch block and coronary artery disease.
abstract: OBJECTIVE
  The aim of this study was to identify resting measurements of left ventricular (LV) function that predict exercise capacity in dilated cardiomyopathy (DCM); in particular, the effects of left bundle branch block (LBBB), coronary artery disease (CAD), and total isovolumic time (t-IVT).
  
  
  BACKGROUND
  The t-IVT is a major determinant of cardiac output during dobutamine stress in DCM, and is itself determined by the presence or absence of LBBB and CAD.
  
  
  METHODS
  A total of 111 patients with DCM, 51 with CAD (29 LBBB), and 60 without CAD (30 LBBB) were studied with echocardiography and cardiopulmonary exercise testing. The t-IVT (in s/min) was measured by Doppler echocardiography, and maximal oxygen consumption (peak Vo(2)) and percentage of the normal predicted peak Vo(2) (%predicted peak Vo(2)) were obtained from exercise testing.
  
  
  RESULTS
  Left bundle branch block reduced peak Vo(2) (by 10.5 ml.kg(-1)min(-1)) and %predicted peak Vo(2) (by 33%, both p < 0.001) compared with patients without LBBB. Coronary artery disease reduced peak Vo(2) (by 5.5 ml.kg(-1)min(-1), p < 0.001) and %predicted peak Vo(2) (by 14%, p < 0.01) compared with those without CAD (p < 0.01). The t-IVT, CAD, LBBB, and QRS duration were univariate predictors of exercise tolerance, but only t-IVT and CAD were independent predictors. The t-IVT at rest correlated with peak Vo(2) (r = -0.68) and %predicted peak Vo(2) (r = -0.74, both p < 0.001). The combination of t-IVT and CAD explained 57% (r = 0.75, p < 0.001) of the total variance in exercise capacity.
  
  
  CONCLUSIONS
  Resting t-IVT and less prominently, CAD, are major determinants of exercise tolerance in DCM. Left bundle branch block significantly determines resting t-IVT and thus peak Vo(2). Prediction of maximum exercise capacity in DCM is therefore possible from time-domain analysis of LV function at rest.
authors.affiliation: Department of Echocardiography, The Royal Brompton Hospital, London, United Kingdom. a.duncan@ic.ac.uk
authors.forename: Alison M
authors.initials: AM
authors.lastname: Duncan
authors.forename: Darrel P
authors.initials: DP
authors.lastname: Francis
authors.forename: Derek G
authors.initials: DG
authors.lastname: Gibson
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Henein
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D000328:Adult; D000368:Aged; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000627:therapeutic use; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D002037:Bundle-Branch Block / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology; D002908:Chronic Disease; D017023:Coronary Angiography; D003324:Coronary Artery Disease / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology; D004452:Echocardiography; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000503:physiopathology; D006801:Humans; D008131:London; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D013223:Statistics as Topic; D013318:Stroke Volume / Q000187:drug effects / Q000502:physiology; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology
chemical_list: D000319:Adrenergic beta-Antagonists; D000806:Angiotensin-Converting Enzyme Inhibitors