Hype and Hope in the Use of Echocardiography for Selection for Cardiac Resynchronization Therapy

Behold, the people is one, and they have all one language, and now nothing will be restrained from them, which they have imagined to do. Let us go down, and there confound their language, that they may not understand one another’s speech. — —The story of the Tower of Babel, from Genesis 11. Initially, the rationale behind the use of echocardiography to assess mechanical synchrony seemed straightforward. Not all patients with left bundle-branch block (LBBB) have mechanical dyssynchrony, and this entity could be identified by measuring the contraction delay between different cardiac walls. It was hoped that better selection with echocardiography would minimize the nonresponder rate of cardiac resynchronization therapy (CRT).Articles p 2608 and p 2617 Then matters started to get complicated. In addition to a variety of measurements of the onset, peak, and offset of contraction, many individual centers have reported a dozen or more permutations of these measurements with different imaging modalities that could be used to predict responsiveness to CRT.1 This Tower of Babel of markers of mechanical dyssynchrony was compounded by the use of a variety of definitions of procedural success, including clinical evaluation (composite scores, New York Heart Association class, and quality-of-life scores), exercise capacity (10% improvement), and indices of left ventricular (LV) function (>15% reduction of LV volumes, >5% increase in LV ejection fraction, decrease in Tei index, and reduction of mitral regurgitation). To the astute observer, the fecundity of this field should ring alarm bells: A truly effective modality is unlikely to beget so many variants.With the publication of the Predictors of Response to CRT (PROSPECT) trial in this issue of Circulation ,2 the use of echocardiography for clinical decision making in CRT has progressed from ambiguity to negativity. This landmark multicenter study of nearly 500 patients at 53 …