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CLINICAL STUDY: HEART FAILURE

Limitation of cardiac output by total isovolumic time during pharmacologic stress in patients with dilated cardiomyopathy: Activation-mediated effects of leftbundle branch block and coronary artery disease

^* Department of Echocardiography, The Royal Brompton Hospital and Imperial College of Science, Medicine and Technology, London, United Kingdom

Manuscript received July 12, 2002; revised manuscript received August 27, 2002, accepted September 20, 2002.

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

OBJECTIVES: We sought to separate the effects of associated left bundle branch block (LBBB) and coronary artery disease (CAD) on peak cardiac output (CO) during dobutamine stress in patients with dilated cardiomyopathy (DCM).

BACKGROUND: The mechanisms limiting CO during stress in patients with DCM are unclear. Both LBBB and CAD may do so by prolonging the total isovolumic time (t-IVT).

METHODS: A total of 59 patients with DCM—34 with CAD (20 normal activation [NA], 14 LBBB) and 25 without CAD (15 NA, 10 LBBB)—were studied. The total IVT (s/min; calculated as: ) and CO were measured by Doppler echocardiography.

RESULTS: At rest, t-IVT was 8 s/min longer with LBBB (p < 0.001), was unaffected by CAD, and did not correlate with rest CO. During stress, CO correlated with t-IVT (r = –0.73, p < 0.001) in all four patient groups. In the absence of CAD, t-IVT became shortened (NA by 7 ± 3 s/min; LBBB by 9 ± 4 s/min) and correlated with a fall in the QRS duration (NA: r = 0.87; LBBB: r = 0.91), and CO increased with stress (NA by 4.7 ± 2.7 l/min; LBBB by 4.0 ± 2.3 l/min; all p < 0.001). With CAD, t-IVT did not shorten normally with stress. Instead, t-IVT was 5.6 s/min longer and CO was 3.3 l/min lower than in those without CAD (both p < 0.001), and t-IVT did not correlate with the QRS duration.

CONCLUSIONS: In patients with DCM, t-IVT during pharmacologic stress depends on changes in ventricular activation induced by LBBB or CAD and is, by itself, a major determinant of peak CO during stress.

Abbreviations and Acronyms   CAD   coronary artery disease   CO   cardiac output   DCM   dilated cardiomyopathy   ECG   electrocardiogram or electrocardiographic   LBBB   left bundle branch block   LV   left ventricular   MR   mitral regurgitation   NA   normal activation   SV   stroke volume   t-IVT   total isovolumic time

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