Ejection fraction lbbb

The short version: LBBB is a marker of underlying heart disease, not an independent cause of death, but it reliably predicts a low ejection fraction and who will benefit from resynchronization therapy.

Left bundle branch block is an electrical wiring problem in the heart. The signal that should spread evenly across the left ventricle instead takes a detour, making the left side contract late and out of sync. This mechanical dyssynchrony is what drags down the ejection fraction, the percentage of blood the heart pumps out with each beat. In a large Swedish registry of over 21,000 heart failure patients, those with LBBB had a 5-year mortality of 69% compared to 61% without it [15]. But once the researchers adjusted for how sick the patients actually were, LBBB itself was no longer an independent predictor of death [15]. The block is a sign of the damage, not the cause of it.

The real question is whether the ejection fraction is low enough to justify cardiac resynchronization therapy, a pacemaker that re-coordinates the contraction. The evidence here is unusually solid. Multiple randomized trials show that CRT improves ejection fraction, symptoms, and survival in patients with LBBB, a wide QRS (over 120-130 ms), and an ejection fraction under 35% [16, 40]. The COMPANION trial (1,520 patients) found CRT reduced the combined risk of death or hospitalization [16]. The CARE-HF trial (813 patients) showed CRT lowered all-cause mortality [16]. The improvements are not small: one study of end-stage patients reported 1-, 2-, and 3-year survival of 93%, 88%, and 85% after CRT [22]. Another study of 325 patients found ejection fraction rose from 33% to 44% after left bundle branch area pacing [29].

The evidence for CRT in LBBB with low ejection fraction is about as good as it gets in cardiology: multiple large randomized trials with hard clinical endpoints, funded by device manufacturers but replicated independently. The mechanism is well understood: the dyssynchrony wastes energy, and resynchronization restores efficiency [8]. The risk of the procedure itself is low but real: lead dislodgement in about 2% of cases, perforation in about 3% [29]. The alternative, no intervention, carries a 5-year mortality of roughly 70% in this population [15].

My call: for a patient with LBBB and an ejection fraction below 35%, CRT is a net-beneficial intervention supported by high-quality evidence. Confidence: high.