Outcomes with Isolated Right Bundle Branch Block
Abstract & Commentary
By Michael H. Crawford, MD, Editor
Source: Bussink BE, et al. Right bundle branch block: Prevalence, risk factors, and outcome in the general population: Results from the Copenhagen City Heart Study. Eur Heart J 2013;34:138-146.
The appearance of right bundle branch block (RBBB) and incomplete RBBB (IRBBB) in otherwise healthy individuals is believed to be benign, but several cardiac and pulmonary diseases are known to be associated with RBBB and IRBBB. Thus, the prognosis of subjects with incidentally discovered RBBB is unclear. Investigators from Denmark have explored this issue in the Copenhagen City Heart Study prospective database of almost 19,000 subjects entered from 1976-2003. Patients with prior myocardial infarction (MI), heart failure, or left BBB were excluded, leaving 18,441 individuals followed until 2009. The primary endpoints were all-cause mortality, major cardiovascular (CV) events, and admission for chronic obstructive pulmonary disease (COPD). Complete RBBB and IRBBB were defined as QRS complexes on the ECG with terminal slowing with a cut point of 120 msec QRS duration defining the two types. History, physical examination, and pulmonary spirometry data were collected on each subject. Follow-up was complete in 99.5% of the subjects over a median time of 20 years. Men had a higher incidence of IRBBB (4.7% vs 2.3%, P < 0.001) and RBBB (1.4% vs 0.5%, P < 0.001). IRBBB was more common in men and women < 40 years old and in men > 80 years old. RBBB increased in frequency with age in both sexes. RBBB was associated with higher blood pressure in men and higher cholesterol in women. IRBBB was associated with lower BMI in both sexes. Among the 10,327 subjects free of BBB at the first examination who returned for the second evaluation 5 years later, 133 men and 116 women developed IRBBB. Multivariate analysis in them showed an association with male sex, increasing age, and low BMI. Similarly, in the 33 men and 18 women who developed RBBB, multivariate predictors were male sex, increasing age, high blood pressure, and initial IRBBB. The risk of CV events and death were similar for both sexes with the exception of MI (more common in men). RBBB was associated with a higher risk of all-cause and CV mortality (hazard ratio [HR] 1.31; 95% confidence interval [CI], 1.11-1.54) and (HR 1.87; 95% CI, 1.48-2.36), respectively. RBBB was also associated with a higher risk of myocardial infarction (HR 1.67; 95% CI, 1.16-2.42) and pacemaker insertion (HR 2.17; 95% CI, 1.22-3.86), but not heart failure, atrial fibrillation, or COPD. IRBBB was not associated with adverse outcomes. The authors concluded that RBBB on ECG is twice as common in men and is associated with increased all-cause mortality and major CV events in both sexes, whereas IRBBB was not.
Occasionally, I am asked to see someone because of a new RBBB on a routine ECG. Usually if the person has no symptoms or signs of heart disease, I assume this is a benign finding based on the results of the U.S. Air Force (USAF) study. However, the USAF study almost exclusively involved young men who were arguably very healthy. We know that RBBB can be a sign of cardiac disease, especially conduction system disease, and more recent studies in older hospital-based populations have suggested that RBBB is associated with CV disease and adverse outcomes. Thus, this population-based study from Denmark is of interest.
The strengths of this study are that it includes all adults of both sexes who are free of overt CV disease, it is large, and long-term follow-up for 20 years was almost 100%. They had two groups of RBBB subjects: those with RBBB on intake and those who developed it during the study. RBBB on intake was uncommon, ranging from 0.6% in women < 40 years old to 14% in men > age 80, and it was more common (2-3 fold) in men. Initial RBBB was associated with systemic hypertension and older age, but not other CV risk factors in men, suggesting a degenerative process. Those who developed RBBB had a higher risk of death and major CV events, including pacemaker insertion, but not heart failure or atrial fibrillation. Since most of the events occurred in older men, it is difficult to tease out the pathophysiologic relationship between RBBB and the CV events, as CV events are more common in older men. Although RBBB has been associated with the development of right ventricular hypertrophy, in this study it was not predictive of hospitalization for COPD.
IRBBB did tend to progress to RBBB, but was not predictive of CV events. This is consistent with the USAF study where recruits with IRBBB who underwent right and left heart catheterization had no increase in cardiac disease compared to a control group. I was somewhat surprised by this since IRBBB can be a sign of right ventricular volume overload, e.g., atrial septal defect. However, the majority of ASD patients with IRBBB also have right axis deviation. Details about the ECG frontal plane axis are not given in the paper. A lack of detailed clinical information is the main limitation of this study.
Given that in apparently healthy subjects there was a 30% increase in CV disease events if RBBB developed, some sort of evaluation of these patients seems to be in order. What would be reasonable beyond the history, physical examination, and the ECG? A chest X-ray seems reasonable and perhaps an echocardiogram to assess cardiac structure and function. The association with coronary disease was weak in this study, so stress testing would seem optional, only if there was high suspicion of this disease and coronary angiography would probably be overkill in most subjects. A more detailed evaluation of a random sample of this study might provide better guidance for how to manage a new RBBB on ECG.