Electrical and mechanical dyssynchrony in patients with right bundle branch block

Abstract

The prevalence of Right Bundle Branch Block (RBBB) as seen in a routine electrocardiogram is about 3 to 5 % of the general population. Patients with RBBB have specific signs of conduction delay seen on ECG with wide QRS (electrical dyssynchrony). RBBB may be associated with some anatomical heart disease and some with arrhythmias. Although the majority of patients with RBBB on ECG have fairly benign reputation, in some reports, RBBB is an independent predictor of cardiovascular mortality as well as all-cause mortality. 1-3 Moreover, the new onset of RBBB predicts a higher rate of coronary artery disease, congestive heart failure, and cardiovascular mortality. When cardiac disease is present, the coexistence of RBBB suggests an advanced disease. 1 One of the mechanisms for heart failure is that RBBB can cause left ventricular mechanical dyssynchrony (LVMD). The LVMD might be interventricular, intraventricular, or both. Several articles showed some correlation with electrical activation. 4-7 Still, the relationship between electrical disturbance and LVMD is partly unclear among these patients with RBBB.However, patients with RBBB may have as well LVMD with or without LV dysfunction. The relevance of LVMD in patients with RBBB and LV dysfunction is in applying those patients for cardiac resynchronization therapy (CRT).The major indication for CRT is in patients with LBBB with QRS width above 120 msec and LV dysfunction and heart failure. [8][9][10] The importance of LVMD in those patients with LBBB has been vastly studied by several imaging modalities especially by echo-Doppler, and also by MRI and phase analysis by GATED SPECT MPI. 8-12 LVMD in LBBB is part of the guidelines in selection of patients for CRT.Several studies compared the efficiency of LVMD in LBBB compared to RBBB. The first study on dogs by MJ Byrne et al found that less LVMD is induced by RBBB than in LBBB in failing hearts as such the impact of CRT on these dogs is reduced. 8 RBBB was studied in patients with impaired LV function. It was found that patients with increased time difference (TD) of septal-lateral activation by echo-Doppler, improved clinically after CRT. 4 However in a large study on 561 consecutive patients who received CRT, 89 (16%) patients had RBBB. LV dyssynchrony was assessed by tissue echo-Doppler, before and 6 months after CRT. The authors found that at long-term follow-up, LVMD and mitral regurgitation were identified as independent predictors of all-cause mortality and heart failure hospitalization among RBBB patients. 12 As such assessment of LVMD may have a crucial decision in the treatment of CHF patients with RBBB by selecting CRT as a preferable treatment in addition to medical therapy.Most of those studies assessing the LVMD in patients with RBBB were done by echo-Doppler. Although there are many publications on LVMD including different clinical subsets by phase analysis and SPECT MPI, 10-17 the issue on patients with RBBB specifically has not been evaluated.In this issue of the Journal of Nuclear Cardiology, Sillanm...

Cardiac resynchronization therapy in a patient with Ebstein’s anomaly and left ventricular noncompaction: Rethink the resync?

“…6 Although there is limited data, it is possible that in patients with non-LBBB restoration of AV synchrony itself can contribute to the clinical response to CRT such as improving mechanical dyssynchrony or reducing diastolic mitral regurgitation. 7 This suggests a need to more carefully scrutinise these patients with non-LBBB QRS morphologies (particularly since up to 18% of patients with Ebsteins anomaly may have some degree of LV impairment). 1 In a retrospective review of ICD recipients by Gleva et al 8 , EA was associated with an increase in device implantation complication rates in ACHD patients.…”