Mortality in insureds with complete right or left bundle branch block.

Area of Science:

• Cardiology
• Epidemiology
• Preventive Medicine

Background:

• Prospective mortality study initiated May 1, 1954, at New England Mutual Life Insurance Company.
• Included individuals with electrocardiograms (ECG); data coded on punch cards for interpretation, clinical findings, and demographics.

Purpose of the Study:

• To assess mortality risk associated with electrocardiogram abnormalities, specifically right bundle branch block (RBBB) and left bundle branch block (LBBB).
• To determine if cardiovascular impairment influences mortality in patients with RBBB and LBBB.

Main Methods:

• Analysis of mortality data from 28,687 ECG interpretation records (1954-1966) with follow-up through 1975.
• Comparison of observed deaths versus expected deaths in policyholders with complete RBBB and LBBB.
• Stratification of analysis based on the presence or absence of associated rated cardiovascular (CV) impairment.

Main Results:

• Complete RBBB cases: 22 observed vs. 7.72 expected deaths with CV impairment; 11 observed vs. 8.11 expected deaths without CV impairment.
• Complete LBBB cases: 6 observed vs. 2.72 expected deaths with CV impairment; 3 observed vs. 1.78 expected deaths without CV impairment.
• Follow-up exposure data available for 231 RBBB and 45 LBBB policyholders.

Conclusions:

• Excess mortality in complete RBBB was statistically significant (95% confidence level) when associated with CV impairment.
• Excess mortality in complete RBBB was minimal and not significant when RBBB was an isolated finding.
• Mortality data for LBBB were insufficient to establish statistical significance, even with associated CV impairment.