Mortality Risk Associated with Electrocardiographic Bundle Branch Blocks in Women

Abstract & Commentary

By Harold L. Karpman, MD, FACC, FACP, Clinical Professor of Medicine, UCLA School of Medicine. Dr. Karpman reports no financial relationships relevant to this field of study.

Synopsis: Prevalent left bundle branch block (LBBB) in cardiovascular disease (CVD)-free women and either LBBB or right bundle branch block (RBBB) in women with CVD were significant predictors of coronary heart disease (CHD) death. In women with LBBB, ST segment J-point depression in lead aVL was also a strong independent predictor of CHD death.

Source: Zhang ZM, et al. Mortality risk associated with bundle branch blocks and related repolarization abnormalities (from the Women’s Health Initiative [WHI]). Am J Cardiol 2012;110: 1489-1495.

The presence of electrocardiographic (ECG) depolarization and repolarization abnormalities has been demonstrated to provide valuable independent information regarding the risk for development of coronary heart disease (CHD) and all-cause death.1-3 Reports from community-based population studies have found none or only marginal CHD risk for subjects with right bundle branch block (RBBB),4-7 but the results for CHD risks in patients with left bundle branch block (LBBB) have been conflicting with some studies reporting a significant increase in mortality.8,9

Zhang and colleagues analyzed and evaluated the risk for CHD and all-cause death associated with LBBB and RBBB during 14 years of follow-up in the 66,450 participants in the Women’s Health Initiative (WHI) study. In CVD-free women, only LBBB was a significant predictor of CHD death and neither block was predictive of all-cause mortality. They also found that ST segment J-point depression in lead aVL in women with LBBB was an independent predictor of CHD death with a more than five-fold increased risk. They concluded that prevalent LBBB in CVD-free women and both LBBB and RBBB in women with CVD were significant predictors of CHD death.

Commentary

ECGs are widely recorded in the offices of family practitioners, cardiologists, emergency departments, and hospitals. LBBB and RBBB are frequent findings in routine ECGs performed on symptomatic and asymptomatic patients. The findings by Zhang et al provide significant statistical information to physicians as well as other members of the medical profession regarding the significance of RBBB and LBBB in women, whether symptomatic or not.10 Also, although it is well known that the ST segments in the left lateral leads in patients with LBBB are always down sloping and often accompanied by negative T waves, if a more pronounced ST J-point depression is found to be present in these subjects, it may be a marker of additional primary repolarization abnormalities with the associated CHD risk being higher than is present in those patients with QRS duration increase and secondary repolarization changes alone. It should be noted that the 10-year mortality follow-up of the Framingham study revealed that the CHD mortality risk ratio in comparison to age- and gender-matched samples of the Framingham population at large was 2.34 for RBBB and 3.6 for LBBB,11 and that the risk for future CHD morbidity and congestive heart failure (CHF) was significantly increased in men and women with RBBB and LBBB compared to the matched reference group. The multivariate risk analysis with adjustment for age, systolic blood pressure, and diabetes for subjects with RBBB or LBBB indicated that the risk for incident CHD morbidity and CHF remained significant in women but not in men.

In summary, clinicians should be aware that detecting a complete LBBB on a screening ECG is a marker of potentially increased CHD risk, at least in women. A complete and thorough cardiac work-up is therefore indicated, and appropriate therapy should be prescribed for any needed lifestyle changes and, of course, for any detected CHD risk abnormalities such as hyperlipidemia, hypertension, or diabetes. All patients should also be advised to avoid starting or to quit cigarette smoking. Since obtaining an ECG is inexpensive and widely available, and since BBBs are usually totally asymptomatic, a case can be made for routine screening ECGs on all adults, especially those in the intermediate-risk group. Finding a BBB in an asymptomatic patient may prove to be quite motivating and beneficial to them when the clinician starts to actively address all of their treatable CHD risk factors.

References

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10. Zhang ZM, et al. Mortality risk associated with bundle branch blocks and related repolarization abnormalities (from the Women’s Health Initiative [WHI]). Am J Cardiol 2012;101:1489-1495.

11. Kreger BE, et al. QRS interval fails to predict coronary disease incidence. The Framingham Study. Arch Intern Med 1991;151:1365-1368.