ArcaMax

DEAR DR. ROACH: My heart rate variability (HRV) on my heart rate tracker has ranged from 12-14 ms for years now. I read that this means something is going on inside me. Do you have any insight into HRV? I'm a 64-year-old male who is in decent health. My Lipoprotein(a) level is 224 mg/dL, but my other heart tests are OK.

I play pickleball often, walk a lot, and go to the gym once a week. My heart rate is in the 40s when I'm sleeping and in the 50s when I'm resting. I'm 5 feet, 11 inches tall and weigh 170 pounds. -- J.N.J.

ANSWER: HRV is a measurement of how steady the heart rate is. It might be surprising that more variability is better than less variability. The heart should respond to small changes in pressure due to breathing, so a person's HRV provides an assessment of the autonomic nervous system (the vast part of the nervous system that is not under conscious control).

HRV does give information to help guide a person's prognosis for some kinds of heart disease, especially after a heart attack. However, a person's HRV needs to be carefully measured with a clinical instrument under controlled conditions. Home monitors like wearable devices are not as accurate, as they are subject to random error, changes in the nervous system due to caffeine or nicotine, sleep quality, the time of day, emotional stress, and other factors.

The absolute value of HRV from a wearable device is not considered particularly meaningful by experts. However, a trend in HRV over time is potentially significant. I would be more reassured by the unchanging nature of your HRV than the relatively low number that your home device is giving you. (An HRV of 12 ms is low. The most common measurement of HRV is through the standard deviation of NN intervals. A SDNN of less than 50 has a worse prognosis than an SDNN greater than 100 in people who recently had a heart attack.)

Even though HRV does provide some useful information, it is generally not routinely measured. Since your number is on the lower side, however, a more careful look at your other heart-disease risk factors is called for.

It sounds like you are doing well with exercise. Your physician should take a careful look at your diet, as it is also important for heart health. A Lp(a) of 224 mg/dL should be considered a very significant risk factor for heart disease, especially given your family history. Most experts would recommend combined treatment, such as a high-dose statin and a PCSK-9 inhibitor, even if your "regular" cholesterol numbers are in the normal range.

DEAR DR. ROACH: I saw on a TV show that most people with a "penicillin allergy" probably don't have one. Is this true? -- R.C.

ANSWER: Yes, it is. I often ask my patients what they mean by a penicillin allergy. Many don't remember, or they were just told by their parents that they had a reaction. Some recall reactions that are not allergic (such as vomiting or "feeling sick"). Quite a few developed a rash after being on amoxicillin during or after what sounds like a viral infection.

Many diseases, including roseola and infectious mononucleosis, will predispose people to a rash after amoxicillin. But this isn't a true allergy, so a person can be labelled "allergic" when they are not, which may keep them from getting an effective medication. People who are at a low risk for a severe penicillin allergy may get penicillin under medical observation.

Of course, I've had people tell me that they had anaphylaxis, which requires epinephrine. They never receive penicillin again (except in very rare circumstances where penicillin is the only effective treatment).

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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.

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