ECG, Holter or long-term monitoring: which test answers which question?

An ECG is a test that records the electrical activity of the heart: electrodes are placed on the skin, and the rhythm appears on a paper strip or on a screen. According to AFib Matters, a resting ECG can detect palpitations that are constant. If a symptom comes and goes, what matters most is a recording made exactly during the symptom.

According to AFib Matters, in atrial fibrillation the rhythm is completely irregular. According to the review of the 2024 ESC/EACTS guideline (Rienstra and colleagues, Europace), it is detected by a 12-lead ECG or a single-lead recording lasting at least 30 seconds, if the P waves do not repeat and the R–R intervals are irregular. Counting your pulse by hand may make you suspect an irregular rhythm, but it cannot reliably confirm it, especially when the heart is beating fast.

A Holter is a portable device that records your rhythm for 24–48 hours during your everyday life. According to the guideline on ambulatory ECG monitoring of the health system of British Columbia, Canada (BC Guidelines), a 24–48-hour Holter is suitable for people whose symptoms occur almost every day.

If symptoms are infrequent, nothing may happen during the 24–48 hours the Holter is worn. According to the same guideline, if a Holter does not give a clear answer, simply repeating it may not help when symptoms are infrequent; the doctor chooses the next step.

BC Guidelines links the choice to how often symptoms occur:

• for infrequent, unpredictable symptoms, an external recorder (an event or loop recorder) is used and worn for up to about one month; according to AFib Matters, an event recorder is switched on during a symptom, while an external loop recorder records continuously and saves the part around the symptom;
• for symptoms that occur less than once a month, an implantable loop recorder is used: this is a small monitor placed under the skin that works for up to about 3 years and is considered an invasive method.

The guideline stresses one more point: if event monitoring is limited to one month without good reason, an arrhythmia may be missed. The doctor sets how long monitoring lasts based on how often your symptoms occur.

Sometimes a rhythm recording alone is not enough. When a slow heartbeat (bradycardia) is suspected, the 2021 ESC/EHRA guideline (as summarized by the ACC) provides for the following: a detailed history and examination; in patients with symptoms, cardiac imaging (to assess the heart's structure and pumping function); an exercise test if symptoms occur during or after physical exertion; and testing for sleep apnea if there are signs of it or if the rhythm slows markedly during sleep.

This list applies to a slow rhythm. The doctor will tell you which additional tests you need based on your symptoms and examination.

If the doctor orders monitoring, the preparation is simple but useful:

• Start a symptom diary. AFib Matters recommends writing down the duration, triggers and accompanying symptoms before the appointment: the time of each episode, what you were doing and what you felt.
• On the days you wear the device, write the time of each symptom in your diary: this way the doctor can find exactly that minute in the recording.
• Unless the doctor tells you otherwise, go about your usual day: the recording should cover the conditions in which your symptoms appear.

Tell the specialist who fits the device, or your doctor: what symptoms you have and how often, what medicines you take, and whether your skin is sensitive to adhesive electrodes. And ask: how long the device is worn, whether it has a button and when to press it, whether you can wash, what to do if an electrode comes off, and when and by whom the result will be explained.