How much tachycardia is too much on a Holter monitor?
I recently reviewed a Holter, done for palpitations, on a clinic patient - and while he didn't have any concerning arrhythmias, he was tachycardic almost 10% of the time, which struck me as a little high.
Although we know that a normal resting heart rate for adults is between 60 and 100 bpm, there is surprisingly little normative data to categorize this 10% number as within normal limits or high. Honestly, the best data I found was from a Google study that tracked 400+ "healthy" adults, average age 35yo, which showed typical diurnal variation:
Figure 2. The distribution of mean RHR estimates for both daytime and night-time
While I couldn't find the answer I wanted in PubMed, I did end up going down the road of inappropriate sinus tachycardia, and I read a good review article, which I'm attaching for you here. It's a decent summary for when we encounter this possible diagnosis in clinic. I learned that there can be some overlap between the presentation of inappropriate sinus tachycardia (IST) and postural orthostatic tachycardia syndrome (POTS) which is important to differentiate, that young women are most often affected, and that nadolol and ivabradine are better options than metoprolol for medical therapy.
We're going to monitor our patient, not start any therapy for now, but this article is practice changing for me in that I'll reach for nadolol first now when I'm looking for a medication to help with the symptoms of inappropriate sinus tachycardia.
Olshansky B, Sullivan RM. Inappropriate sinus tachycardia. EP Europace2018;21(2):194-207. doi:10.1093/europace/euy128
Speed CA, Arneil T, Harle RK, et al. Measure by Measure: Resting Heart Rate Across the 24 Hour Cycle. Published online November 24, 2021. doi:10.1101/2021.11.24.21266320
