Right Bundle Branch Block in Patients With Cardiogenic Shock: Further Evidence Supporting the Critical Nature of the “Forgotten” Ventricle*

Abstract

T he right ventricle is sometimes referred to in the literature as the "forgotten" ventricle, primarily due to the historic importance when compared with the left ventricle as well as the key role of the left ventricle with regards to systemic circulation physiology (1-4). Although the informed readers of Critical Care Medicine will already have an appreciation for the importance of the right ventricle, the concept of clarifying and exploring the important role of the right ventricle and right ventricular dysfunction in systemic issues such as cardiogenic shock (CS) continues to be a critical area of research. Along those lines, in this issue of Critical Care Medicine, Rusnak et al ( 5) present a study looking at the prognostic impact of right (RBBB) and left bundle branch block (LBBB) in patients with CS.Using their Cardiogenic Shock Registry Mannheim registry, a prospective single-center registry including consecutive CS patients admitted to their ICU, the authors found 248 patients from June 2019 to May 2021 with either RBBB or LBBB. In terms of results, they found that patients with RBBB had the highest 30-day all-cause mortality (72.5%) when compared with patients with LBBB (52.9%) and no bundle branch block (BBB) (50%), with the findings persisting even looking at patients with CS and cardiac arrest. After a detailed multivariate logistic regression analysis was performed, RBBB still demonstrated a negative impact on 30-day all-cause mortality (hazard ratio, 1.81; 95% CI, 1.1-2.9; p = 0.018). Other factors associated with mortality were lactate, acute physiology score, and troponin I.What might be some of the mechanisms behind this worsening of outcomes with RBBB in patients with CS. There are a few major areas that can connect the presence of RBBB with worse outcomes in CS. The first would be "impact on cardiac function" (6). RBBB can disrupt the coordinated contraction of the right ventricle, impairing right ventricular dysfunction. Another contributory mechanism would be "ventricular dyssynchrony" (7), with RBBB causing delays in right ventricular contraction. In the setting of CS, this dyssynchrony can exacerbate the worsening of the cardiac output. Of great concern is the potential for "progression to complete heart block" (8). Notable in patients with underlying structural heart disease, this complication can compound the effects of CS.Other potential connections between the presence of RBBB and worsened outcomes in CS include "increased myocardial oxygen demand" and "compromised electrical stability" (9-11