The original EchoCRT (Echocardiography Guided Cardiac Resynchronization Therapy) trial evaluated cardiac resynchronization therapy (CRT) in patients with New York Heart Association Class III-IV heart failure (HF), left ventricular (LV) ejection fraction ≤35%, QRS duration <130 ms, and echocardiographic LV dyssynchrony.¹ All subjects underwent CRT defibrillator implantation and were then randomly assigned to CRT-ON (set to maximize CRT therapy) versus CRT-OFF (set to minimize right ventricular pacing). The study was stopped due to futility because no difference was demonstrated in the primary composite outcome of all-cause mortality or HF hospitalization (28.7% CRT-ON vs. 25.2% CRT-OFF; hazard ratio [HR] 1.2; p = 0.15). Mortality was actually higher in the CRT-ON group (11.1 vs. 6.4%; HR 1.8; p = 0.02).

A sub-analysis of EchoCRT, which was presented at European Society of Cardiology Congress 2016 and then published in The European Heart Journal, focused on the prognostic implications of LV global longitudinal strain (GLS).² LV GLS by speckle tracking was feasible in 755 subjects (of the 809 from the original study). Each 1% absolute unit decrease in LV GLS was associated with 11% increase in the primary outcome (HR 1.1; p < 0.001).

Subjects were divided between those with LV GLS <6.2% (i.e., lowest quartile for GLS) and ≥6.2%. Among patients with GLS <6.2%, the primary outcome was significantly higher in patients with CRT-ON compared with CRT-OFF (45.7 vs. 28.7%; HR 2.0; p = 0.009). In contrast, among patients with LV GLS ≥6.2%, there was no significant difference in event rate (24.5 vs. 23.7%; HR 1.09; p = 0.62). Therefore, low LV GLS is associated with worse outcomes in patients with HF with narrow QRS; outcomes in this low GLS group are further worsened by CRT.

Of note, per the authors, the interaction between treatment group (CRT-ON vs. CRT-OFF) and LV GLS was not statistically significant and was underpowered (likely due to limited number of patients with GLS <6.2%). Thus, the sub-analysis is considered exploratory/hypothesis-generating.

References

1. Ruschitzka F, Abraham WT, Singh JP, et al. Cardiac-resynchronization therapy in heart failure with a narrow QRS complex. N Engl J Med 2013;369:1395-405.
2. Bax JJ, Delgado V, Sogaard P, et al. Prognostic implications of left ventricular global longitudinal strain in heart failure patients with narrow QRS complex treated with cardiac resynchronization therapy: a subanalysis of the randomized EchoCRT trial. Eur Heart J 2017;38:720-26.

Keywords: Cardiac Resynchronization Therapy, Defibrillators, Diagnostic Imaging, Echocardiography, Heart, Heart Failure, Heart Ventricles, Medical Futility, Ventricular Function, Left

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