Don't ignore exertional heart irregularities. (The clinic).

? I am a 73-year-old, 150-lb. male runner. I've been racing for 25 years. After taking three months off to recover from a heel injury, I notice my heart now starts skipping every three beats when I exceed approximately 135 bpm. This usually starts at around 2:00 into a run at 10:00/mile pace. I run about 25 miles per week. A 12-minute medical stress test took me up to 160 bpm, but the test was stopped before my heart became erratic. I don't feel the skipping, but it shows on my heart monitor and when I take my pulse. My pulse usually recovers after 30 or 60 seconds. Am I damaging my heart, or is it safe to race?

Robert Moffitt, Jacksonville, FL

Cardiac symptoms with exertion should be thoroughly evaluated, especially given the stress placed on your heart during races. It is encouraging that a stress test to 12 minutes to a heart rate of 160 was normal. However, it may take longer for you to develop symptoms. Older people can develop abnormalities in the heart's conduction system. Results can be mild, annoying symptoms like yours, or may progress to dangerous fainting spells. Coronary artery blockage can also present this way.

I recommend a more thorough cardiac evaluation with a 24-hour heart monitor. You should wear the monitor during a run in an effort to diagnose the problem. Consider a nuclear medicine stress test, which is more sensitive than a regular treadmill test. An echocardiogram will help evaluate the structure of your heart. Make sure lab tests are done to exclude problems, such as hyperthyroidism. Bring these persistent symptoms to your physician or seek the advice of a cardiologist. Avoid caffeine, as well as stimulant medications (especially some over-the-counter cold and allergy meds). Some prescription medications may also affect your heart.

Jeffery M. Hubbard, MD, Clovis, CA

You may have developed a medical condition called a heart block, which is a type of arrhythmia. Some types of heart blocks are due to aerobic fitness and are of no concern. These benign heart blocks are believed to be caused by fluctuations in the nerve signals that control your heart rate. Other than the skipped beats, you are not complaining of any chest pain, fainting or difficulty breathing. So that's a possibility. However, there are other types of blocks that are associated with heart disorders. The only way to know is by observing the block pattern in a resting EKG, during a stress EKG, or during a 24-hour ambulatory electrocardiogram (Holter test).

Carlos Jimenez, MD, San Juan, Puerto Rico 

Given that there was no effect with the stress test, which I assume used a sophisticated EKG recording, another possibility is a defect in the heart rate monitor. You could check it out by having a friend use it to see if the skipped beats are recorded.

Melvin Williams, PhD, Norfolk, VA

Abnormal heart beat may be associated with clot formation. In some cases anticoagulants or beta blockers may be indicated to control the rate.

Marvin Bloom, MD, Burlingame, CA