Evaluation of left bundle branch block as a reversible cause of non-ischaemic dilated cardiomyopathy with severe heart failure. A new concept of left ventricular dyssynchrony-induced cardiomyopathy.

OBJECTIVES: We sought to determine if amelioration of left bundle branch block (LBBB)-induced contraction disturbances achieved by left ventricular (LV)-based pacing could result in sustained reversal of severe LV dysfunction in certain patients with chronic heart failure due to non-ischaemic cardiomyopathy.
BACKGROUND: It has been shown that LBBB induces asynchronous contraction of LV. However, whether such a functional contraction disturbance, if present for an extended period of time, could account for a dilated cardiomyopathy remains unknown.
METHODS: The study population comprised 29 patients with dilated cardiomyopathy, sinus rhythm, LBBB and severe heart failure (14 patients in New York Heart Association (NYHA) class III and 15 in class IV). Patients were followed prospectively after resynchronization therapy. LV function was considered to be normalized when ejection fraction (EF) was >50% at 1 year.
RESULTS: Five among the 29 patients (17%: group 1) demonstrated both complete normalization of LV function following resynchronization therapy (EF: from 19+/-6 to 55+/-3%, P = 0.001) and clinical improvement (mean NYHA class: 3.4+/-0.5 to 1.8+/-0.4, P = 0.02; 6-min walk distance: 300+/-136 to 444+/-75 m, P = 0.12; peak VO2: 11.9+/-4 to 15.8+/-2 ml/min/kg, p = 0.03). Among the remaining 24 patients (83%: group 2) EF improved but did not normalize (from 21+/-8 to 23+/-11%, ns). Baseline clinical features could not predict which patients would exhibit the reversal of LV dysfunction.
CONCLUSIONS: Normalization of LV function 1 year after resynchronization therapy in a small but important number of patients suggests that long-standing LBBB may be a newly identified reversible cause of cardiomyopathy.