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CLINICAL RESEARCH: HEART FAILURE

Limitation of exercise tolerance in chronic heart failure: distinct effects of left Bundle-Branch block and coronary artery disease

^* Department of Echocardiography, The Royal Brompton Hospital, London, United Kingdom

Manuscript received September 19, 2003; accepted October 15, 2003.

^* Reprint requests and correspondence: Dr. Alison M. Duncan, The Echocardiography Department, The Royal Brompton Hospital, Sydney Street, London SW3 6NP, United Kingdom.
a.duncan{at}ic.ac.uk

OBJECTIVES: 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 VO₂) and percentage of the normal predicted peak VO₂ (%predicted peak VO₂) were obtained from exercise testing.

RESULTS: Left bundle branch block reduced peak VO₂ (by 10.5 ml·kg^–1min^–1) and %predicted peak VO₂ (by 33%, both p < 0.001) compared with patients without LBBB. Coronary artery disease reduced peak VO₂ (by 5.5 ml·kg^–1min^–1, p < 0.001) and %predicted peak VO₂ (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 VO₂ (r = –0.68) and %predicted peak VO₂ (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 VO₂. Prediction of maximum exercise capacity in DCM is therefore possible from time-domain analysis of LV function at rest.

Abbreviations and Acronyms   CAD = coronary artery disease   CV = coefficient of variation   DCM = dilated cardiomyopathy   E/A ratio = ratio of early transmitral flow velocity to atrial flow velocity   EF = ejection fraction   F = variance ratio   LBBB = left bundle branch block   LV = left ventricular   LVEF = left ventricular ejection fraction   peak VO2 = peak exercise capacity   %predicted peak VO2 = percentage of the normal predicted peak VO2   RMS = root mean square   t-IVT = total isovolumic time   Vcf = mean velocity of circumferential fiber shortening rate   VCO2 = carbon dioxide production   VE = minute ventilation

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