AF and Holter monitor testing

A Holter monitor is a wearable, continuous ECG recording system that is usually worn for 24-72 hours at home. It's lightweight and portable- see the picture below (six-pack not included 😉). Whereas a 12-lead ECG gives your medical team a 10-second snapshot of your heart rhythm whilst you're in the hospital, a Holter monitor allows them to see what your heart rhythm is doing at home, whilst you're sleeping and *hopefully* during any palpitations you experience.

So in theory, it's a fantastic test if your symptoms occur intermittently- however, it is frequently misused; ordered as a reflex when the likelihood of it providing useful information is low- especially if you're already known to have AF!

We'll discuss two circumstances where I think it can add value:

To give a more comprehensive profile of your AF heart rate control to help decide if you need a higher/lower dose of heart rate controlling medications.
If you've had treatment for your AF and subsequently want to check that you aren't having any brief episodes of AF- especially if you're having some non-specific symptoms.

Persistent (continuous AF) can often be asymptomatic and very well rate controlled for the 15-minutes you're sat peacefully in the doctor's clinic. However, some patients only experience symptoms overnight/when you first wake up or perhaps when you're doing exercise. It's hard to guess what's happening during these brief moments of symptom and so your doctor may order a Holter monitor to record your heart rhythm profile over a 24-48 hours to see what is happening during these times. Perhaps your heart rate goes too slowly at night-time or perhaps it inappropriately accelerates during exercise (or perhaps it doesn't accelerate at all!). These issues may be modified by tweaking the dose of your heart rate medications but the data needs to be captured first. It is crucial that you keep a detailed 'symptom diary' during the period of Holter monitoring so that your medical team can match your symptoms to the exact time on the ECG trace- these records are invaluable to say what the problem is or potentially what it isn't (because if your heart rate at the time of symptoms isn't abnormal, it may mean we need to look for another cause).

2. Some electrophysiologists routinely do Holter monitoring at 3-, 6-, 12 months after AF treatments (like catheter ablation) and this can be useful to detect asymptomatic AF episodes. The amount of AF that is found after ablation depends on the frequency and duration of heart rhythm monitoring.

adapted from the results of the Circa-Dose study. The figure shows the sensitivity of intermittent rhythm monitoring to detect atrial arrhythmia recurrence as a function of monitoring frequency (number of random monitoring events, 1–10) and monitoring duration (24 hours, 48 hours, 7 days, and 14 day ECG monitors)

Alternatively, some doctors may only order the test if you report symptoms suggestive of recurrence e.g. palpitations, dizziness, shortness of breath and again a symptom diary is invaluable. Different arrhythmias can occur after ablation or symptoms may be due to 'ectopics' which are often harmless and need no treatment at all. So keeping a precise symptom diary can help match your symptom to the exact period of heart rhythm monitoring. Misuse can arise if your doctor requests the wrong test duration if you are getting symptoms after your ablation. If you get palpitations once in a month- a 24-hour monitor has a low (~3% chance) of being put on on the day you have symptoms. In this case, a longer monitoring duration could be more appropriate as it's more likely to capture your symptoms.

The reality is we haven't got a consensus on the best way to monitor heart rhythms after AF ablation- the pragmatic view is to 'follow the symptoms' andtry to characterise these...because what would we do with asymptomatic AF anyway?

Smart-device ECG monitors have revolutionised the follow-up strategy for some patients after AF treatments, giving them 24/7 access to ECG recordings that can be made whenever they have symptoms. The AFFU-AW study is evaluating the clinical value of this type of 'patient-led' monitoring strategy.

Ahmad K, Dorian P. Rate control in atrial fibrillation: looking beyond the average heart rate. Curr Opin Cardiol. 2006 Mar;21(2):88-93. doi: 10.1097/01.hco.0000210303.33866.c7. PMID: 16470141.

Aguilar M, Macle L, Deyell MW, Yao R, Hawkins NM, Khairy P, Andrade JG. Influence of Monitoring Strategy on Assessment of Ablation Success and Postablation Atrial Fibrillation Burden Assessment: Implications for Practice and Clinical Trial Design. Circulation. 2022 Jan 4;145(1):21-30. doi: 10.1161/CIRCULATIONAHA.121.056109. Epub 2021 Nov 24. PMID: 34816727.