Cardiac resynchronization therapy in patients with heart failure and narrow QRS complexes (≤ 130 ms): role of speckle tracking echocardiography and different interventricular (VV) pacing intervals.

Purpose: Response to cardiac resynchronization therapy (CRT) in patients with heart failure with reduced ejection fraction (HFrEF) depends on the degree of correction of interventricular (VV) electromechanical dyssynchrony between the left and right ventricles (LV, RV). Wide (> 130 ms [ms]) QRS interval is used as a qualifying ECG parameter for CRT device implantation. In this study, we aimed to evaluate myocardial strain (S) and myocardial strain patterns (SP) and strain rate (SR) by speckle tracking echocardiography (STE) and mechanical characteristics at different VV intervals in acute settings and long-term outcome from "sequential LV-RV" pacing programming in patients with narrow (< 130 ms) and wide (> 130 ms) QRS complexes as a basis for extending CRT in select patients with narrow QRS.

Methods: From a previously established cohort of patients who had undergone CRT device implantation, we identified patients with narrow (< 130 ms) and wide (> 130 ms) QRS complexes, groups A and B respectively. In all patients, we assessed myocardial SP and SR by STE, and mechanical characteristics at VV intervals: "LV Off," "VV0," "VV60," and "RV Off" to provide "RV-only," "simultaneous BiV," "sequential LV-RV," and "LV-only" pacing in the acute settings, and subsequently long-term clinical outcomes with CRT devices programmed to VV60. We compared acute STE characteristics and long-term clinical outcomes between the groups.

Results: The study cohort comprised 271 patients (age 69.2 ± 10.3 years [mean ± SD], male-60%). Group A (n = 69) and group B (n = 202) were well matched for the clinical variables, including distribution of patients with ischemic versus non-ischemic cardiomyopathies. QRS width and left ventricular ejection fraction (LVEF) in groups A and B were 120.1 ± 12.3 ms and 152.1 ± 12.9 ms (p < 0.05), and 22.3 ± 9.4%, and 23.3 ± 10.2% (p = not significant [NS]). With VV0, VV60, and LV-only timings, corresponding LVEF rates in the acute settings were 31.45 ± 10.9%, 40.08 ± 8.3%, and 44.32 ± 7.98% (p < 0.01) in group A, and 38.94 ± 8.5%, 46.91 ± 7.33%, and 49.9 ± 8.94% (p < 0.01) in group B, and accounted for similar incremental percentage increase in LVEF compared to baseline in group A (43.2 ± 51.7%, 80.9 ± 61.4%, and 93.4 ± 65.6% respectively) and group B (67.3 ± 82.0%, 100.6 ± 94.3%, and 112.9 ± 95.7% respectively) (p = NS). Abnormal SP and SR were consistently observed with RV pacing that improved with VV60 and LV-only pacing in both groups. Strain scores at different VV timings were similar between the groups (p = NS). At 1-year follow-up, LVEF improved from 22.4 ± 8.0% to 39.8 ± 11.5% (p ≤ 0.001) for the total cohort with similar increments observed in both groups (p = NS). There were fewer NYHA III-IV class patients at 1 year in both groups.

Conclusions: Comparable myocardial SP and SR characteristics and LVEF improvement with VV60 and LV-only pacing in the acute setting and long-term outcome of CRT by "sequential LV-RV" pacing seen in patients with both narrow and wide QRS duration suggest that CRT device implantation may be justified in select patients with HFrEF and narrow QRS duration (< 130 ms) who have demonstrable dyssynchrony and abnormal myocardial SP and SR characteristics.