Noninvasive Assessment of LV Contraction Patterns Using CMR to Identify Responders to CRT
Can cardiac magnetic resonance (CMR) imaging identify patterns of left ventricular (LV) contraction that predict a favorable response to cardiac resynchronization therapy (CRT) in patients with left bundle branch block (LBBB)?
This study prospectively examined 52 patients prior to undergoing clinically indicated CRT (New York Heart Association functional class II-IV, QRS duration >120 ms, and LV ejection fraction ≤35); cine CMR and echocardiography were performed preimplantation, and echocardiography was repeated at 6 months after implantation. Cine CMR was used to determine the pattern of baseline LV contraction. Response to CRT was assessed at 6 months by the presence of reverse remodeling on echocardiography (≥15% reduction in end-systolic LV volume) and symptomatic improvement (New York Heart Association functional class, 6-minute walk distance, and Heart Failure Questionnaire score).
Mean age was 65 ± 13 years, and 88% were male. The cardiomyopathy was ischemic in 48% of cases. Two patterns of baseline LV contraction were observed on cine CMR: homogenous spread of contraction from the septum to the lateral wall (n = 27, type I) and a nonhomogenous U-shaped spread of contraction from the septum to the lateral wall (n = 25, type II). CRT response as measured by reverse remodeling was identified in 26% (7/27) of type I and 80% (20/25) of type II patients (p < 0.001). There was a significant difference in the change of 6-minute walk distance between type I and II patients (55 ± 60 vs. 126 ± 106 m, p = 0.004); no significant differences between groups were observed for New York Heart Association functional class (p = 0.24) or Heart Failure Questionnaire score (p = 0.86).
Cine CMR can identify a pattern of LV contraction in patients with LBBB that predicts an increased likelihood of response to CRT, as measured by symptoms and reverse remodeling.
Although CRT has been demonstrated to be effective in many patients with heart failure and LV dyssynchrony, a significant proportion of patients do not manifest a positive response, and identification of likely responders has been historically challenging. This study demonstrates that routine cine CMR may be able to identify a pattern of LV contraction that predicts a significantly increased rate of reverse remodeling and improvement in hall walk symptoms, although no differences in other measures of heart failure symptoms were observed between groups. While promising, these results need to be validated in a larger multicenter study.
Keywords: Heart Diseases, Nitrofurans, Cardiac Pacing, Artificial, Heart Failure, Ventricular Remodeling, Transcription Factors, Bundle-Branch Block, Stroke Volume, Heart Ventricles, Cardiac Resynchronization Therapy
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