From Wrist to Precision: Enhanced Atrial Flutter Detection with Modified Smartwatch Single-Lead Electrocardiogram Placement

Background Smartwatches, such as the Apple Watch (AW), are well-established tools for detecting atrial fibrillation (AF). We hypothesize that atrial flutter (AFL) is frequently misdiagnosed using traditional single-lead ECG configurations and that modified device positioning could substantially improve diagnostic accuracy. Methods Standard smartwatch lead I (AW-I) recordings were obtained from 75 patients, including 25 with AFL, 25 with AF, and 25 with sinus rhythm (SR). Additionally, modified lead II (AW-II) recordings were collected for all AFL cases, resulting in a total of 100 tracings. Twenty blinded physicians from four different specialties independently analyzed all recordings. Results Physicians' ability to detect AFL using the AW-I lead was poor, with only 11.6% correctly identified (p=0.362). AFL was most often misdiagnosed as AF (55.6%), undetermined (21%), or SR (11.8%). Diagnostic accuracy improved significantly with the AW-II lead, exceeding 80% among electrophysiologists, cardiologists, and primary care physicians (p=0.001). Variable AV conduction was strongly associated with correct diagnosis exclusively through the AW-II lead (OR 1.85, 95% CI 1.14–3.0, p=0.012). Conclusion The standard lead I configuration used by smartwatches is prone to misclassifying AF as AFL, particularly in the setting of variable conduction. A simple modification to lead II positioning significantly enhances diagnostic accuracy. This adjustment may be especially valuable during post–PVI surveillance and in broader clinical scenarios where precise rhythm identification can influence therapeutic decision-making.