Resolution of Left Bundle Branch Block–Induced Cardiomyopathy by Cardiac Resynchronization Therapy
What is the response of cardiac resynchronization therapy (CRT) in patients with a left bundle branch block (LBBB) and subsequent decline in left ventricular ejection fraction (LVEF)?
This was a retrospective single-center case study of candidates for CRT who: 1) had a history of LBBB, 2) LVEF >50%, 3) subsequent drop in LVEF to <40% with heart failure (HF) symptoms, 4) evidence of mechanical dyssynchrony, and 5) a super response to CRT with LVEF increasing to >45% and improvement in New York Heart Association (NYHA) class to class I.
Of the 375 patients undergoing CRT implant, six met the above inclusion criteria. Mean patient age was 50.5 years, QRS duration was 137 ± 21 ms, and time to HF onset was 11.6 years after LBBB diagnosis. Two patients meeting criteria 1-5 above were excluded due to lack of super response to CRT. In the six patients evaluated, CRT led to an improvement in LVEF (nadir mean 31 ± 7% improving to 56 ± 8%), LV end-diastolic volume (62 ± 14 mm improving to 52 ± 12 mm), and measures of strain (p < 0.05 for all comparisons).
The authors concluded that they have identified the presence of a cardiomyopathy induced by an LBBB (mechanical dyssynchrony) that resolves following CRT.
In this very small case series, patients with an LBBB who progress to HF demonstrated improvements in LVEF and NYHA class. It is not surprising, however, that LVEF, LV dimensions, and NYHA class improved from baseline because these factors were the inclusion criteria. The authors’ main aim was to show that this HF etiology exists, as many of us have also seen in clinical practice. However, we cannot confidently conclude from this study that an LBBB itself induces cardiomyopathy. While it is feasible that LBBB-induced dyssynchrony could directly cause HF, this small study demonstrates an association only. Other factors (e.g., neurohormones, cellular level metabolic dysfunction) may exist to induce the preceding LBBB and then HF.
Keywords: Cardiac Pacing, Artificial, Ventricular Function, Left, Cardiomyopathies, Heart Failure, Bundle-Branch Block, Stroke Volume, New York, Neurotransmitter Agents, Cardiac Resynchronization Therapy
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