In 2005,Blanc et al (2)described five patients with dilated cardiomyopathy whose cardiac function was "normalized" by cardiac resynchronization therapy (CRT) suggesting that longstanding LBBB could cause a cardiomyopathy that was potentially reversible by CRT.Prior to Blanc's paper animal studies had demonstrated that LBBB could cause progressive cardiac structural and functional loss that could be to some degree reversible with CRT.Blanc suggested that his paper introduced "a new concept of left ventricular dyssynchrony-induced cardiomyopathy"
In 2013 Vaillant (4) et al published data that tended to confirm Blanc's thesis.
The topic of concern here is so called isolated LBBB as a cause of cardiomyopathy. i.e LBBB not associated with ischemic heart disease or other recognized causes of a cardiomyopathy , LBBB as a cause of a dyssynchronopathy.
HV Barot et al (3) from Lahey clinic identified patients with LBBB ,without evidence of coronary artery disease or other recognized cause of cardiomyopathy and an LVEF greater than 45% and followed them for 40 +/- 24 months. Of a total of 94 patients meeting the entry criteria, 13 developed a significant decrease in EF to 31+/-7 % .
All lone LBBB instances are not created equal.The degree of dyssynchrony and the patterns of altered depolarizations vary as does the resultant degree of loss of LV function and the likelihood and rate of progression of a cardiomyopathy.
From a clinical point of view several questions are important. What factors indicate that a aymptomatic patient with LBBB will develop heart failure? What should the clinical managment be when a patient with LBBB develops a significant decrease in ejection fraction?
The experience reported by Wang et al (5) strongly suggests that the usual heart failure package of medications is not very effective in LBBB induced heart failure.At what point should CRT ( either BI-V or His Bundle pacing) be considered ?
1) Grines,CL et al Functional abnormalities in isolated left bundle branch block.The effect of interventricular asynchrony.Circulation 1989:79, 845
2) Blanc,JJ et al Evaluation of left bundle branch block as a reversible cause of non-ischemic dilated cardiomyopathy with serve heart failure. A new concept of left ventricular dyssynchroncy-induced cardiomyopathy. Europace. 2005,7 604-610
3)Barot, HV Incidence of Left bundle branch block-associated cardiomyopathy. Journal of Cardiac Failure August 2017, vol 23, issue 8, supplement, p S55
4) Vaillant, C. et al Resolution of left bndle branch block-induced cardiomyopathy by cardiac resynchronization therapy. J Am Coll. Cardiol. 2013:61, 1089
5)Wang,NC et al New onset left bundle branch block-associated idiopathic nonischemic cardiomyopathy and time from diagnosis to cardiac resynchronization therapy. The NEOLITH II study PACE 2018 Jan 4