Question: I take 50 mg of metoprolol twice a day. If this controls the heart rate at approximately 80, how does this work if the heart would normally speed up during exercise? Does the heart work harder at the lower rate than it would if the heart rate would speed up to get the required blood flow? Can this over work the heart & cause damage during physical activity?
Dr. Hibberd's Answer:
Metoprolol belongs to a family of drugs called beta blockers. Beta blockers have been used for many years for treating hypertension, cardiac disorders, and migraines. Beta blockers block the "beta" adrenergic receptors in heart muscle preventing the heart from accelerating its rate into high ranges. Beta blockers have been shown to significantly reduce mortality in patients who are victimized by coronary ischemia (heart attack). They are very versatile (available intravenously and orally), inexpensive, and "cardio-protective."
Our heart muscle works best and most efficiently in neutral rate ranges of 60-100. As the rate slows toward 60, compensatory mechanisms actually allow the heart chambers to empty more completely, often actually increasing efficiency with less strain on the heart itself (and more efficient use of the blood supplied by the coronary arteries). Some patients with severe asthma, brittle diabetes, cardiomyopathy, and conduction system problems are not able to tolerate beta blockers without problems, and are often not prescribed these agents.
Demands for cardiac blood from coronary arteries are at a maximum during accelerated heart rates, so mild blocking of the heart rate is protective for many of us. Overwork occurs at the higher heart rates, and beta blockers protect our heart muscle from these high rates. True, there is a slight tradeoff in efficiency when we look at the raw figures, but this tradeoff often yields far greater benefits in many patients.
In the past, beta blockers weren’t given in cases of heart failure, but when carefully calibrated, beta blockers can now be used in congestive heart failure with significant improvement (to the surprise of the older cardiologists) in mortality figures. This represents an about-face in teaching as we often see in medicine as evidence-based information becomes more available. This is a good example of an older drug with new indications thanks to continued research. Beta blockers are true heart-protecting agents for those who need them, but they are not approved for "prevention," as in anti-aging and supplement regimens, in healthy patients.
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