How Dangerous Is Heart Block?

Q: I am a fit 49-year-old woman in good health with good cholesterol levels. I had an echo cardio stress test due to chest pain, and the cardiologist discovered that I have left bundle branch block. He did not seem too concerned about this, but after I researched this on the internet, I am. Should I worry? Are there any preventative measures I can take? How will this affect me as I age?

A: First, a few words about left bundle branch block, or LBBB. A left bundle branch block is a pattern that is seen on an electrocardiogram (ECG).

In addition to showing the heart rate and rhythm of the heart, ECGs also pick up abnormalities in the way electrical impulses move throughout the heart. Normally, the wave of electrical activity moves smoothly down both sides of your heart. This produces a particular pattern on the ECG.

If a person has an abnormal slowing though any part of the heart, doctors call this heart block. Left bundle branch block reflects slower movement of electrical activity through the left side of your heart than the right.

It sounds as though the left bundle branch block was discovered during a stress test when your heart rate went up. Doctors call this rate related bundle branch block.

The question raised by your ECG tracing is: Why is electrical activity moving through your heart’s left side more slowly than in most people? One reason can be scarring of your heart muscle (and the electrical fibers that lie within it) by a heart attack or other disease affecting the heart. More common is mild damage to the electrical system resulting from high blood pressure or some other process.

The key issue is not whether LBBB is bad for you—the question is why do you have it? If it results from a heart attack or other major heart disorder, that can be pretty serious. If it is from high blood pressure or some undetectable other process, that’s not so bad (assuming you get your high blood pressure under control).

If your echocardiogram showed that your heart function was normal, then you are almost surely in the second group. And if your echocardiogram remained normal while you exercised, that paints an even better picture.

What if your stress echo was fine, and you don’t have high blood pressure; and we are left with the conclusion that your LBBB is due to some other process that has damaged your electrical system? In this case, I would tell you not to worry about your LBBB—unless you developed other symptoms suggesting electrical conduction problems. Such symptoms might be fainting or near-fainting spells, or inability of your heart to accelerate with activity or spells of very rapid heart beats. Any of these should prompt immediate contact with your doctor.

But in the absence of such symptoms, additional testing is not usually needed.

See All Harvard Articles on Cardiovascular Health     

More on MSN Health & Fitness:

• Listening to the Female Heart
• Congenital Heart Block
• Matters of the Heart

Thomas H. Lee, M.D., is Professor of Medicine at Harvard Medical School and the Harvard School of Public Health, and Chair of the Editorial Boards of the Harvard Heart Letter, a publication that he helped to found. He is CEO of the Partners Community HealthCare, Inc., the integrated healthcare delivery system established by Brigham and Women's Hospital, Massachusetts General Hospital, and their parent company, Partners HealthCare System, Inc. Dr. Lee is a practicing internist and cardiologist.

Do you have a health question you'd like to ask Harvard Medical School's experts? Send an e-mail to experts@microsoft.com. Please include Ask Harvard in the subject line.

Our experts respond to one question each week and the responses are posted on Mondays on MSN Health. We regret that we cannot provide a personalized response to every submission.