Biventricular pacing in heart failure: back to basics in the pathophysiology of left bundle branch block to reduce the number of nonresponders

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Abstract

Cardiac resynchronization therapy is a novel nonpharmacologic approach to treating patients who have advanced heart failure with left bundle branch block (LBBB). Such a therapy is based on the original theory that synchronous biventricular pacing is able to reduce the interventricular delay caused by LBBB in patients with heart failure. Although there is convincing evidence that biventricular pacing increases the left ventricular ejection fraction, decreases mitral regurgitation, and improves symptoms caused by heart failure, the percentage of nonresponders to such therapy has been described as high as about one third of patients with heart failure having LBBB. Factors responsible for this relatively high prevalence are reviewed, the most important of them probably being left intraventricular dyssynchrony, which can persist after biventricular pacing, notwithstanding right and left interventricular resynchronization. Such a dyssynchrony, as evaluated by tissue Doppler imaging, may be because of the discordance between the site of the left ventricular pacing and the site of the left ventricular delay. Therefore, to characterize the pathophysiologic pattern of LBBB, the investigators suggest an assessment of the electromechanical dysfunction with a noninvasive reliable technique, such as tissue Doppler imaging, which can be repeated after biventricular pacing.

Section snippets

Pathophysiologic factors in patients who are nonresponders

Several factors could be responsible for this relatively high prevalence of patients with an unchanged or worsened condition. One reason could be the lack of simultaneous activation of each wall of the left ventricle together with its own specular segment (intraventricular dyssynchrony). Such unfavorable mechanical activation of the left ventricle may persist after biventricular pacing, notwithstanding the simultaneous activation of left and right ventricles (interventricular

Imaging and diagnostic testing to evaluate nonresponder patients

In such a clinical condition, the accuracy of M-mode echocardiography in detecting the most delayed wall could be reduced by the lack of a substantial gradient between the left ventricular walls because of the uniformity in the activation delay throughout the entire left ventricular mass. For this reason, we have proposed tissue Doppler imaging as a more accurate technique than the traditional M-mode or 2-dimensional echocardiography in determining the optimum pacing site before the

Conclusions

In conclusion, we believe the following: (1) Although there is compelling evidence that biventricular pacing may be beneficial in nonpharmacologic treatment of advanced heart failure, patients with LBBB may have several differences in electromechanical activation patterns, and thus an individual assessment, as well as a pathophysiologic characterization of the LBBB type, should be undertaken before any decision about the pacing is made. (2) In theory, the site of the left ventricular delay

Acknowledgements

The authors thank Mary Monique Rendall, BA, for reviewing the manuscript, and Rossano Salidu for reviewing the iconography.

References (18)

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