HRV revelation

Heart Rate Variability (HRV) was something I was aware of historically, not as a plotted figure but as a tool to measure adaptation to exercise, specifically with an old Polar cs600x I had for many years. The muppets guide for the likes of me is that it is the regularity (or not) of the R-R interval – the two top spikes on an ECG – the contraction of the two big chambers of the heart. It turns out that if you have an Apple Watch, and an iPhone then the Health Application has likely been recording this for quite some time – with graphs. Graphs to the point of wow… and time writing this article today.

I have always been super sceptical as to the accuracy and reliability of wrist-mounted devices to do anything of worth or credibility. Despite being diagnosed with an arrhythmia – there was a minor eye-roll with the “news” that it would detect these, and the new series-4 doing one lead EKG akin to AliveCor Kardia (although was not licensed for use in the UK when I checked a few weeks ago – interesting). It was all very “oh really”. Then – I saw this:

You do not need to have any kind of specific understanding or training to grasp that something happened in the middle of September. Which sure enough it did.

Reading through the Wikipedia article to see if I can glean a little more information on the causes and trends – the following appeared to be relevant:

β-Adrenergic blockade
The data on the effect of β-blockers on HRV in post-MI patients are surprisingly scant. Despite the observation of statistically significant increases, the actual changes are very modest. In conscious post-MI dogs, β-blockers do not modify HRV. The unexpected observation that before MI, β-blockade increases HRV only in the animals destined to be at low risk for lethal arrhythmias after MI may suggest novel approaches to post-MI risk stratification.

Antiarrhythmic drugs
Data exist for several antiarrhythmic drugs. Flecainide and propafenone but not amiodarone were reported to decrease time domain measures of HRV in patients with chronic ventricular arrhythmia. In another study, propafenone reduced HRV and decreased LF much more than HF. A larger study confirmed that flecainide, also encainide and moricizine, decreased HRV in post-MI patients but found no correlation between the change in HRV and mortality during follow-up. Thus, some antiarrhythmic drugs associated with increased mortality can reduce HRV. However, it is not known whether these changes in HRV have any direct prognostic significance.

Exercise training
Exercise training may decrease cardiovascular mortality and sudden cardiac death. Regular exercise training is also thought to modify cardiac autonomic control. Individuals who exercise regularly have a ‘training bradycardia’ (i.e., low resting heart rate) and generally, have higher HRV than sedentary individuals.

The pattern continues on into October incidentally. Beta-blockers, Flecainide, amongst others continue – no change there. Resting pulse is elevated (initially to 80, now down as far as 60) – and a little chest discomfort from time to time – otherwise I am the same before as afterwards.

The HRV here maps out very clearly good days and bad days – and the Pulmonary Vein Isolation (PVI) ablation of the 17th after (assumedly stress induced) AFib of the 16th.

So yeah – maybe my faith in wrist-mounted monitoring should be re-assessed. Wow.

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