From the Guidelines
Premature atrial contractions (PACs) on an Apple Watch ECG typically appear as early beats with an abnormal P wave followed by a normal QRS complex, often with a compensatory pause afterward. The early P wave may look different from normal P waves and can sometimes be hidden in the preceding T wave, as described in the context of premature atrial beats 1. The rhythm is irregular specifically around the PAC, with the premature beat occurring earlier than expected in the normal cardiac cycle.
The QRS complex of a PAC usually looks similar to normal beats because the electrical impulse still travels through the normal conduction pathway after originating from an ectopic atrial focus. Apple Watch's single-lead ECG has limitations in detecting PACs compared to standard 12-lead ECGs, so some PACs might be missed or appear subtle, highlighting the need for advancements in signal processing algorithms to improve detection capabilities 1.
Some key points to consider when interpreting PACs on an Apple Watch ECG include:
- The device's ability to detect arrhythmias such as atrial fibrillation with clinical-level accuracy 1
- The importance of sharing recordings with a healthcare provider for proper interpretation, especially if symptoms like palpitations, skipped beats, or lightheadedness are experienced
- The potential for unclassifiable tracings, which may improve with technological advances in wearable ECG devices 1
- The limitations of current wearable devices in providing continuous monitoring and measuring arrhythmia burden, although daily and nightly use can ultimately provide near-continuous recordings 1.
From the Research
PACs on an ECG
- Premature atrial contractions (PACs) are a type of arrhythmia that can be detected on an electrocardiogram (ECG) 2.
- The Apple Watch has a built-in ECG feature that can detect heart rhythms and is approved by the FDA for screening and detecting atrial fibrillation 3, 4.
- However, there is limited information on what PACs look like on an ECG on an Apple Watch.
ECG Readings on Apple Watch
- Studies have shown that the Apple Watch ECG is reliable and accurate in detecting atrial fibrillation and other arrhythmias 4, 5.
- The Apple Watch ECG can detect various ECG characteristics, including heart rate, PR intervals, QT intervals, QRS complex, and RR intervals 5.
- However, the specific appearance of PACs on an Apple Watch ECG is not well-documented.
Limitations of Current Evidence
- There are no studies that specifically investigate the appearance of PACs on an Apple Watch ECG.
- While the Apple Watch ECG has been shown to be accurate in detecting atrial fibrillation and other arrhythmias, its ability to detect PACs is not well-established 3, 4, 5.
- Further research is needed to determine the reliability and accuracy of the Apple Watch ECG in detecting PACs.