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Controversies in Imaging

Is echocardiographic assessment of dyssynchrony useful to select candidates for cardiac resynchronization therapy?

Echocardiography Is Useful Before Cardiac Resynchronization Therapy if QRS Duration Is Available

Jacob Abraham, MD and Theodore P. Abraham, MD

From the Translational Cardiovascular Ultrasound Laboratory, Division of Cardiology, Johns Hopkins University, Baltimore, Md.

Correspondence to Theodore P. Abraham, MD, Johns Hopkins University, 600 N Wolfe St, Carnegie 568, Baltimore, MD 21287. E-mail tabraha3@jhmi.edu

An extract of the first 250 words of the full text is provided, because this article has no abstract.

	Introduction

 
Cardiac resynchronization therapy (CRT) has emerged as one of the few therapies available for patients with advanced heart failure (HF) that favorably affects symptoms, functional status, hospitalization rates, and mortality rate.^1,2 It is thought that CRT achieves these benefits by coordinating contraction between ventricular segments that at baseline are dyssynchronous.³ Synchronized electrical excitation of the ventricles leads to near-simultaneous mechanical activation of the normal and delayed segments, resulting in greater stroke volume and reduction of mitral regurgitation with improved neurohormonal profile and reversal of adverse ventricular remodeling. The early large-scale clinical trials that established these benefits of CRT were limited to patients with prolonged QRS duration, a simple and convenient marker of delayed electrical activation. On the basis of these data, current guidelines recommend CRT for patients with ejection fraction <35%, moderate to severe symptoms (New York Heart Association class III to IV), and QRS >120 ms.

Response by Prinzen and Auricchio p 79

A consistent finding from all trials of CRT, however, is a lack of clinical or echocardiographic benefit in approximately one third of patients ("nonresponders").⁴ Unlike pharmacological therapy, CRT is complex, invasive, and costly; therefore, improved identification of patients likely to benefit is a clinical imperative. One factor among many underlying this high rate of nonresponse is that QRS duration is an imperfect surrogate for the disorder actually targeted by CRT: mechanical dyssynchrony. Mechanical dyssynchrony may involve delay in mechanical activation of the left ventricle (LV) relative to the right ventricle (RV) (interventricular dyssynchrony) or of one . . . [Full Text of this Article]

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