Right bundle branch block: are we looking in the right direction?

The right bundle branch is a long, thin, and discrete structure composed of high-velocity conduction Purkinje fibres. It is located in the right side of the interventricular septum and occupies a subendocardial position in its superior and inferior thirds and deeper in the middle third. There are no ramifications in most of its course, but it starts to branch as it reaches the base of the anterior papillary muscle. The appearance of a right bundle branch block (RBBB) alters the ventricular activation sequence, produces a QRS prolongation, and changes the orientation for Rand S-wave vectors, thus generating a typical electrocardiogram (ECG) pattern (Figure 1). The prevalence of RBBB in the general population is estimated at between 0.2% and 0.8%, and it clearly increases with age. It may be associated with different cardiac structural diseases such as ischaemic heart disease, myocarditis, hypertension, congenital heart disease, cor pulmonale, and pulmonary embolism. Its prognosis depends on the type and severity of the associated heart condition; for example, in patients with ischaemic heart disease the presence of RBBB is a well-established mortality predictor. 4 The same is true for patients with heart failure where at least two different studies showed a worse prognosis for patients with RBBB hospitalized with this condition. Nevertheless, all previously published data suggest an excellent prognosis in patients free of heart disease. Previous studies of athletes and aeroplane pilots with long follow-up show a favourable prognosis with a very low rate of cardiovascular events or indication for pacemaker implantation. 9 Several epidemiological studies analysed the prognosis of RBBB in individuals without heart disease. The Reykjavik Study found 126 cases of RBBB in 9135 males and 67 cases in 9627 females, with a greater incidence with increasing age. A higher mortality from heart disease (P , 0.01) was found in men with RBBB compared with the control population, but this difference was not significant when risk factors of heart disease were taken into account by multivariate Cox analysis. In 1996 Fahy et al. published a 9.5-year follow-up study of 310 healthy individuals with RBBB that were identified from 110 000 participants in a cardiovascular screening programme. Isolated RBBB was more prevalent than isolated left bundle branch block (LBBB) (0.18% vs. 0.1%, P , 0.001), and the prevalence of both abnormalities increased with age (P , 0.001). Survival was no different for those with LBBB or RBBB. However, the prevalence of cardiovascular disease and cardiac mortality was greater in the LBBB group (P 1⁄4 0.01). A Swedish study monitored 855 patients who were 50 years old in 1963 for 30 years. The prevalence of BBB increased from 1% at 50 years of age to 17% at 80 years, resulting in a cumulative incidence of 18%. There was no significant relationship between BBB and the development of ischaemic heart disease, and no significant increase in mortality during follow-up. In a community-based study (Olmsted County), 706 RBBB patients were identified from a population of 123 700 individuals. Of those, 12% had LBBB with left axis deviation (LAD); 20% had LBBB without LAD; 26% had left anterior hemiblock; and 42% had RBBB. At 9-year follow-up, the presence of RBBB did not alter the prognosis. The most recent study is a Finnish study that evaluated the 12-lead ECGs of 10 899 Finnish middle-aged subjects from the general population (52% were men; mean age 44+ 8.5 years) and followed them for 30+ 11 years. A prolonged QRS duration was defined as QRS ≥ 110 ms and an intraventricular conduction delay as QRS ≥ 110 ms, without the criteria of complete or incomplete BBB. Prolonged QRS duration predicted all-cause mortality [relative risk (RR) 1.48; 95% confidence interval (CI) 1.22–1.81; P , 0.001], cardiac mortality (RR 1.94; 95% CI 1.44–2.63; P , 0.001), and sudden arrhythmic death (RR 2.14; 95% CI 1.38–3.33; P 1⁄4 0.002). LBBB also predicted arrhythmic death (P 1⁄4 0.04), but RBBB was not associated with increased cardiovascular or all-cause mortality. Based on these data, the position generally accepted is that individuals with isolated, chronic RBBB that are asymptomatic do not