DEAR DR. ROACH: What is the difference between NSVT and AVNRT? I am a 69-year-old female taking metoprolol once a day.—T.A.

ANSWER: Medical abbreviations are confusing. Even when I spell them out — nonsustained ventricular tachycardia, and atrioventricular nodal re-entrant tachycardia — the names hardly make sense unless you know the vocabulary. A medical-school anatomy course has more unfamiliar words for most students than a first-year college language course.

NSVT is the more straightforward. A “tachycardia” is simply a fast heartbeat, defined as greater than 100 beats per minute. “Nonsustained” simply means it doesn’t last a long time (less than 30 seconds). And “ventricular” means that the electrical impulse making the heart go abnormally fast is coming from the ventricle. On the EKG, these are “wide complex,” which makes it easily identifiable for the clinician. Metoprolol sometimes is used to prevent NSVT due to its multiple beneficial heart effects.

In AVNRT, the electrical impulse making the heart go fast is coming from the AV node, an electrical structure in the heart that is supposed to coordinate the electrical and mechanical functions of the heart. The electrical impulse reaches the node before the blood from the atria has finished filling the ventricles, so the AV node slows the electrical impulse to the ventricle until the optimum time for the ventricle to contract. It’s called “re-entrant” because, in addition to the normal, slow electrical path, there is a fast pathway in some people. The impulse can go down the slow pathway, then back up the fast pathway (or vice versa), over and over again. These normally are “narrow complex” on the EKG, and there often is a finding called a “delta wave” that can help make the diagnosis. Metoprolol sometimes is used to prevent tachycardia in people with AVNRT, since it slows down the slow pathway. It isn’t usually the primary treatment unless symptoms are very mild.

DEAR DR. ROACH: I developed blood clots in both legs while in the hospital for 10 days. The doctor put me on warfarin. I have been on it for the past three months, but a scan shows no improvement at all. How long will I need to stay on warfarin, and can I fly while on this drug? Also, I had to stop taking testosterone for my bone loss because I was told that I cannot take both warfarin and testosterone replacement together. — D.M.

ANSWER: For most people who have had a blood clot for a defined, transient risk factor, such as surgery, anticoagulation with warfarin or one of the newer agents is prescribed for three months. People without a known risk factor, or those with a risk factor that can’t be treated, may need longer or even indefinite treatment.
One study from 2009 used ultrasound to decide whether to continue warfarin treatment for an extra three months. This is not a standard recommendation, but it might be reasonable, especially in people with continued symptoms. The risk of the blood clot going to the lung (the major risk in a deep vein thrombosis) is small after three months of anticoagulation.

Flying is usually considered safe if the dose of warfarin is correct, according to the INR level, usually 2-3. Although testosterone can make warfarin levels go up, most people can continue taking testosterone, but the dose of warfarin will need to be adjusted. One type of synthetic testosterone, oxandrolone, has a dramatic effect on INR levels and should be used with extreme caution with warfarin, if at all.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Health newsletters may be ordered from www.rbmamall.com.