Bundle Branch Block Revisited
ABSTRACT & COMMENTARY
Synopsis: Bundle branch block is a marker of a slowly progressive degenerative disease that affects the myocardium.
Source: Eriksson P, et al. Circulation 1998; 98:2494-2500.
Conflicting data exist concerning the etiology and significance of bundle branch block (BBB) on the electrocardiogram (ECG). Thus, Eriksson and colleagues recorded 12-lead ECGs in a random sample of 855 men who were 50 years old in 1963 when they were recruited in the city of Goteborg, Sweden, and followed them for 30 years with periodic examinations. During the 30 years, 82 subjects with BBB were found (10%). Most acquired BBB after entry; only 1% had BBB at entry. BBB became more prevalent with aging. At age 75 years, right BBB was four times more prevalent than left BBB (39 vs 9%). ECG evidence of left ventricular hypotrophy preceded left BBB in one-quarter of the subjects vs. 6% for right BBB. Risk factors for atherosclerosis, myocardial infarction (MI), and a diagnosis of ischemic heart disease were no different between those who developed BBB and those who did not. However, cardiomegally on chest x-ray (P < 0.05) and congestive heart failure (36% BBB vs 14% of controls; P < 0.01) were more common with BBB. Also, among those who died of cardiovascular causes, more subjects had a history of chronic heart failure with BBB (61%) vs. no BBB (28%; P < 0.01). Eriksson et al conclude that BBB is a marker of a slowly progressive degenerative disease that affects the myocardium.
Comment by Michael H. Crawford, MD
This study is consistent with the old adage that BBB is more commonly associated with cardiomyopathy rather than coronary artery diseases (CAD). In fact, no relation could be established between BBB and risk factors for atherosclerosis or overt CAD. This is consistent with other studies and the observation that BBB is not usually caused by acute MI. Also, the prevalence of BBB is highly correlated with advancing age, being 1% at age 50 and 17% at age 80 in men. Thus, CAD and BBB often coexist and this combination is known to increase mortality in acute MI and chronic CAD patients. Other studies suggest this may be due to a greater propensity to ventricular arrhythmias and sudden death, possibly due to prolonged repolarization. However, acute MI superimposed on a chronic progressive cardiomyopathy may result in a higher than expected mortality due to pump failure.
The major limitation of this study was that the small number of patients with BBB reduced the power for comparing left to right BBB, which many believe are of different significance. Also, ECGs were only recorded every 5-17 years, so details about the onset and potential causes of BBB are hard to decipher. In addition, there are few objective data about other cardiac diseases in this study. Nor are there electrophysiologic data about the site of block or the need for pacing. The implications of this study are that patients who develop or present with BBB should have an echocardiogram done to assess left ventricular function. The need for stress tests or coronary angiography is less clear in the absence of other indications for these procedures.