LBBB induced cardiomyopathy

LBBB induced cardiomyopathy

Left bundle branch block (LBBB) induced cardiomyopathy is due to the mechanical dyssynchrony caused by the abnormal activation pattern in LBBB. Response to cardiac resynchronization therapy (CRT) is excellent in this group and may be called super responders. Left bundle branch pacing has shown promise an alternative to biventricular pacing in LBBB induced cardiomyopathy [1].

The relationship between in LBBB and left ventricular dysfunction is complex. LBBB may appear during the course of illness indicating the severity and poor prognosis or it may have a causative role in the development of dyssynchronous contraction leading to worsening of left ventricular function.

Following criteria have been proposed for LBBB induced cardiomyopathy: 1. History of typical LBBB for more than 5 years; 2. Left ventricular ejection fraction (LVEF) more than 50% at the time of diagnosis; 3. Progressive decline in LVEF to less than 40% and development of heart failure with New York Heart Association (NYHA) function class II to IV over several years; 4. Major dyssynchrony; 5. No other identifiable cause for cardiomyopathy; 6. Super response to CRT with LVEF >45% and decrease in NYHA functional class at 1 year [2]. This syndrome was found in 1.6% of the 375 patients screened for CRT between 2007 and 2010 and included in that study.

Others have brought down the criterion for duration of LBBB to more than one year. Major dyssynchrony was identified by interventricular mechanical delay more than 40 ms, aortic pre-ejection delay of more than 140 ms and septal to lateral wall delay more than 65 ms [1].

In another study, patients undergoing CRT between 2018 to 2020 were retrospectively screened for LBBB induced cardiomyopathy. Possible LBBB induced cardiomyopathy was found in 17 of the 159 patients. Left bundle branch pacing was successfully performed in 13 patients. Duration of LBBB before left ventricular dysfunction was 4.2 years on average. Temporary His bundle pacing corrected underlying LBBB in all patients. Significant reduction in QRS duration from a mean of 167.8 ms to 110.4 ms occurred during left bundle branch pacing. Cardiac magnetic resonance imaging done in 8 patients showed no evidence of scar. Left ventricular ejection fraction improved from a mean of 30.4 to 57.4 during follow up and NYHA functional class improved from a mean of 3.1 to 1.2, compared to baseline [1].

CLIMB registry assessed the prevalence and clinical and instrumental features of LBBB induced cardiomyopathy [3]. The criteria used by them was different: 1. Neither family history nor clinically identifiable potential causes for dilated cardiomyopathy (DCM); 2. Negative genetic testing; 3. Echocardiographic features including severe chamber dilation, normal absolute and relative wall thickness, marked dyssynchrony, and normal right ventricular function; 4. Absence of late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (CMR). They analyzed 242 DCM patients from a two-centre registry. Inclusion criteria for the study was age above 18 years, non-ischemic or non-valvular DCM and LBBB on ECG. They identified 30 subjects with the entire dataset required, of which two fulfilled the diagnostic criteria for LBBB induced cardiomyopathy.

NEOLITH II study evaluated new onset LBBB associated idiopathic non-ischemic cardiomyopathy and time from diagnosis to CRT [4]. Among their 123 subjects with LBBB associated idiopathic non-ischemic cardiomyopathy, time from diagnosis to CRT was 9 months or less in 60 subjects and more than 9 months in 63 subjects. Clinical outcomes for adverse events and all-cause mortality were similar in both groups. In subjects who had post CRT echocardiograms, improvement of LVEF to more than 35% was more likely in those implanted within 9 months compared to those had CRT implantation after 9 months. This study apparently did not follow the criteria for LBBB induced cardiomyopathy.

References

1. Ponnusamy SS, Vijayaraman P. Left Bundle Branch Block-Induced Cardiomyopathy: Insights From Left Bundle Branch Pacing. JACC Clin Electrophysiol. 2021 Sep;7(9):1155-1165. doi: 10.1016/j.jacep.2021.02.004. Epub 2021 Mar 31. PMID: 33812829.
2. Vaillant C, Martins RP, Donal E, Leclercq C, Thébault C, Behar N, Mabo P, Daubert JC. Resolution of left bundle branch block-induced cardiomyopathy by cardiac resynchronization therapy. J Am Coll Cardiol. 2013 Mar 12;61(10):1089-95. doi: 10.1016/j.jacc.2012.10.053. Epub 2013 Jan 23. PMID: 23352778.
3. Sanna GD, De Bellis A, Zecchin M, Beccu E, Carta P, Moccia E, Canonico ME, Parodi G, Sinagra G, Merlo M. Prevalence, clinical and instrumental features of left bundle branch block-induced cardiomyopathy: the CLIMB registry. ESC Heart Fail. 2021 Dec;8(6):5589-5593. doi: 10.1002/ehf2.13568. Epub 2021 Sep 12. PMID: 34510787; PMCID: PMC8712772.
4. Wang NC, Li JZ, Adelstein EC, Althouse AD, Sharbaugh MS, Jain SK, Mendenhall GS, Shalaby AA, Voigt AH, Saba S. New-onset left bundle branch block-associated idiopathic nonischemic cardiomyopathy and time from diagnosis to cardiac resynchronization therapy: The NEOLITH II study. Pacing Clin Electrophysiol. 2018 Feb;41(2):143-154. doi: 10.1111/pace.13264. Epub 2018 Jan 24. PMID: 29314085.