Study: Researchers ID echo functional metric to predict CRT response
It's difficult to know which patients will respond better than others to cardiac resynchronization therapy (CRT), but researchers in Germany have found that minimizing the longest intraventricular delay before and after device implantation correlates to superior response to CRT, according to a study published in the Sept. 1 edition of Cardiovascular Ultrasound.

"CRT aims at reverse remodeling by biventricular pacing and has been demonstrated to remarkably improve morbidity and mortality in congestive heart failure (CHF) patients," the authors wrote. However, only about 70 percent of patients show a significant response to CRT, which "given its high costs and invasive nature with possible severe side effects—is disappointingly low."

Henryk Dreger, MD, of the Universitätsmedizin Berlin, Germany, and colleagues assessed 37 patients undergoing CRT implantation between April 2008 and December 2009 to determine characteristics that would distinguish "super-responders" from average CRT responders.

Researchers defined "super-responders" as those who achieved a left ventricular ejection fraction (LVEF) increase of over 15 percent six months after to CRT implantation.

They found no significant differences between the groups in LVEF at baseline or at six months, nor were there differences in reductions of QRS duration and LV end-diastolic and end-systolic volumes under CRT.

Similarly, baseline interventricular mechanical delay at baseline and its reduction at CRT showed no significant differences between average and super-responders.

As a marker for intraventricular asynchrony, researchers assessed the longest intraventricular delay, i.e., the delay between the segments with the shortest and longest aortic valve opening and the peak systolic velocity. This parameter at baseline showed no difference between the two groups. CRT significantly reduced the longest intraventricular delay in both groups—with a significant difference between average (66.2 ms) and super-responders (32.5 ms).

Furthermore, super-responders showed a trend for less asynchronous LV segments (1.1) than average responders (2) at follow-up.

Multivariate logistic regression analysis identified the longest intraventricular delay measured one day after device implantation as an independent predictor of superior response to CRT.

Dreger and colleagues noted that all tested echo asynchrony measures in the PROSPECT trial failed to predict response to CRT.

"To some degree, this can be explained by the shortcomings of current indices. In general, however, echocardiography is per se not able to foresee the potential of the left ventricle to undergo reverse remodeling. Accordingly, even near-perfect assessment of asynchrony would not be able to predict response to CRT. In the present study, superior response to CRT did not correlate with the extent of cardiac asynchrony at baseline. This finding might help to understand the disappointing results of the PROSPECT trial," they wrote.

The fact that a greater reduction of the longest intraventricular delay in the present study was associated with superior response to CRT suggests that "cardiac asynchrony is indeed a prerequisite of successful CRT and its correction should remain in our focus."

However, researchers stopped short of recommending asynchrony measurements as predictors of response to CRT.

"Instead, asynchrony quantification should be performed to direct VV [interventricular] delay optimization—aimed at minimization of the intraventricular delay," they concluded.

"Our results confirm once more that LV geometry at baseline is an important factor for positive response to CRT," the authors wrote. "In addition, our data suggest that not the initial extent of cardiac asynchrony but rather a successful reduction of the intraventricular delay correlates with superior response to CRT. Pending confirmation of our results by further studies, we speculate that routine assessment of intraventricular asynchrony before and after device implantation combined with a VV-delay optimization aimed at reduction of the longest intraventricular delay might help to improve response to CRT."