September 22, 2020
2 min read
Although typically a benign finding, right bundle branch block may be associated with increased risk for low exercise tolerance, CVD and death, even in patients with no prior CVD, researchers reported.
A review of the Mayo Clinic integrated stress center database for exercise stress tests of 22,806 patients from Minnesota found that individuals with right bundle branch block experienced heightened risk for all-cause mortality, CV death, hypertension, low aerobic capacity, slow heart rate recovery and dyspnea, irrespective of CVD status.
“One possible pathophysiological mechanism by which right bundle branch block may contribute to mortality, specifically cardiovascular mortality, may include ventricular dyssynchrony. This phenomenon may occur in patients with right bundle branch block caused by delayed right ventricular systole,” Prakriti Gaba, MD, fellow in cardiovascular medicine at Brigham and Women’s Hospital, and colleagues wrote. “In turn, right bundle branch block may also be caused by myocardial disease secondarily involving the right bundle, suggesting some subclinical myopathic process. Thus, right bundle branch block may signal the development of early myocardial disease, including idiopathic fibrosis, amyloidosis, sarcoidosis and systemic sclerosis, which, as they progress, could lead to complete heart block, ventricular arrhythmias, HF or death.”
For the prospective analysis, the cohort included patients with no history of CVD (36% women; mean age, 52 years) who had full mortality and outcomes data. Among the cohort, 0.96% were diagnosed with right bundle branch block. Patients were followed for a mean of 12.4 years.
During the study period, 8.05% of the cohort died, with 2.83% dying of CVD.
After adjustment for age, sex, diabetes, hypertension, obesity, smoking and use of a heart rate-lowering drug, investigators found that right bundle branch block was predictive of all-cause mortality (HR = 1.5; 95% CI, 1.1-2) and CV mortality (HR = 1.7; 95% CI, 1.1-2.8).
Analyses of exercise tests showed that patients with right bundle branch block had more hypertension (34.1% vs. 23.7%; P < .0003), decreased functional aerobic capacity (82% vs. 90%; P < .0001), slower heart rate recovery (13.5 beats per minute vs. 17.1 beats per minute; P < .0001) and a higher rate of dyspnea (28.2% vs. 22.4%; P < .0399) compared with those without right bundle branch block.
“Heart rate recovery after exercise and functional exercise capacity as measured by metabolic equivalent tasks was significantly slower and lower, respectively, in patients with right bundle branch block compared with those without the rhythm abnormality,” the researchers wrote. “This may be because of the hemodynamic effects of having a right bundle branch block, that is greater dyssynchrony in ventricular relaxation (because of depolarization dyssynchrony), ventricular remodeling and resultant development of HF or arrhythmias. Alternatively, it is possible that the right bundle branch block suggests some element of premature conduction disease that may lead to subtle or subclinical chronotropic abnormalities prior to stress testing.”