CLINICAL RESEARCH: HEART FAILURE
Limitation of exercise tolerance in chronic heart failure: distinct effects of left Bundle-Branch block and coronary artery disease
Alison M. Duncan, MB, BS*,*,
Darrel P. Francis, MD*,
Derek G. Gibson, FRCP* and
Michael Y. Henein, MD, PhD, FACC*
* 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.
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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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