Apple Watch ECG Captures Pacemaker Activity

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The hysteria surrounding Apple Watch 4’s single lead electrocardiogram (ECG) feature has simmered down over the last few months, but it was brought to my attention that pacemaker activity can also be detected by the application. Unlike 12-lead ECGs which provide significant amounts of data to localize pathologies to certain regions of the heart, 1-lead ECGs provide only basic heart monitoring information (heart rate, arrhythmias like atrial fibrillation, etc.) However, because pacemakers operate at the level of myocardial electrical conduction, it’s no surprise that we can see the characteristic “spikes” on the ECG app!

Now for a real life example – I had full consent from the individual to use their ECG strips, pacemaker information and history.

Let’s say a patient has a dual chamber pacemaker (leads in the right atrium and right ventricle) placed for a slow junctional rhythm in AAI mode at 60 beats per minute (bpm). In this mode, the right atrium is sensed. If an electrical impulse is sensed at least 60 times per minute (ie, from SA node depolarization), then the pacemaker does nothing. If no signal is sensed, then the atrium is paced at 60 bpm. This mode relies on normal conduction through the atrioventricular (AV) node to depolarize the ventricles thereby maintaining AV synchrony.

The top image represents normal sinus rhythm; however, in the same patient, the bottom image shows atrial pacing (at the pre-programmed rate of 60 bpm) with clearly visible atrial spikes.

Now what’s even cooler is this Medtronic pacemaker has a managed ventricular pacing (MVP) feature. This is essentially a ventricular pacing backup if normal AV conduction is lost. The device will switch from an AAI mode to a DDD mode, periodically assess if normal AV conduction returns, and then switch back to AAI pacing at that point. You can even see a short run of atrioventricular pacing (both atrial and ventricular spikes) here on the Apple Watch ECG app! How cool!

Atrial and ventricular pacing


  1. Hi. my husband has a St. Jude dual lead pacer. He concerned about whether or not its ok to wear the Apple Watch 5 because of the magnets. What are your thoughts on it?

    • I’m sorry, but it’s not appropriate for me to give medical recommendations (however benign) over the Internet. This is a good question for your electrophysiologist/cardiologist.

  2. Doug Brown Reply

    My Apple Watch ecg catch’s mode switching as it switches from my setting DDD ( I have rate turned off as well as CLS off) to DDIR. It also shows pacing spikes in ventricular pacing. I have not seen atrial spikes at all thought I am atrial pacing 45% of the time.
    I have a Biotronik Edora duel chamber unit.
    The first time I saw mode switching spikes ( they were confirmed by Biotroniks) they looked like pacing spikes on the ST segment ( bit scary). I have Sick Sinus Syndrome ( Brady Tachy) and previously arrested prior to pacemaker placement.

  3. Jim Scantlen Reply

    Does anyone have information about the Apple Watch being unable to detect paced beats properly? I heard about someone that got a pacemaker after having an Apple Watch and they are now getting alerts for low heart rates on their watch. They had their pacemaker checked and it appears to be functioning normally. It has been difficult to get recordings that overlap to prove what the true rhythm is when the watch is alerting.

  4. Mine does not show pacer spikes. I think it depends on where your leads attach in your heart. Mine are in my septal wall which is more natural than apex. So this isn’t true for all pacemaker people

    • Thanks for sharing! I know a few people who are A-paced and/or AV-paced who this has worked for, but with a single vector EKG, it probably can’t capture everything. The lead location shouldn’t make a difference, but again, the Watch 4 wasn’t even designed for this, so who knows? 😆

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