Accuracy of the Smart Watch iECG for Documentation of Supraventricular Tachycardias in Children

All articles of this category (opens in new window) Background: The documentation of supraventricular tachycardia (SVT) often presents a diagnostic challenge, due to its paroxysmal character. Smart Watches enable patients to record an immediate single-lead ECG (iECG) whenever symptoms occur. We report our data on the accuracy of iECG in comparison to 12-lead ECG during SVT. Methods: All pediatric patients with sustained SVT undergoing electrophysiological study (EPS) were included prospectively between March 2023 and December 2024 ( n = 40). Twelve-lead ECG and iECG were recorded simultaneously as SVT episodes occurred (spontaneously or induced) during EPS. Comparative measurements based on time intervals and amplitudes in lead I (Einthoven) of the 12-lead ECGs (as gold standard) and single-lead iECG were performed. Results: Forty ECGs of SVT during EPS in 39 patients (one repeat EPS) were recorded (5–17 years, 24–95 kg); 21 recordings were with atrioventricular reentrant tachycardia, and 19 recordings with atrioventricular nodal reentrant tachycardia. Comparison of the measurements between lead I of the 12-lead ECGs and the iECGs showed very high correlation (Pearson correlation of intervals: RR [ r = 0.99], QRS [ r = 0.8], QT [ r = 0.86], heart rate [ r = 0.98], and amplitudes: QRS [ r = 0.94], T-wave [ r = 0.92]) and no significant difference of the mean for RR- and QT-intervals as well as heart rate ( p = 0.42, 0.11, and 0.54, respectively). Mean differences of the other values were small (QRS-interval 3.2 ms, QRS amplitude 0.12 mV, and T amplitude 0.03 mV). The HR values of the smart watch algorithm showed a weaker correlation ( r = 0.79) than the measured ones. The smart watch algorithm classified 39 of 40 iECGs correctly as high heart rate (if HR was < 150 bpm) and no signs of atrial fibrillation or heart rate above 150 bpm (no testing of atrial fibrillation by the algorithm). One iECG with an HR of 250 bpm was falsely classified by the algorithm as 126 bpm. Conclusion: Even during SVT episodes with extremely high heart rates, single-lead iECGs, captured by the smart watch, provide comparable results with lead I (Einthoven) ECG recordings. However, the iECG must be measured and evaluated, since the algorithm’s heart rate output is less reliable than the iECG values derived from it, and the algorithm is not capable of detecting SVT. Publication History Article published online: 17 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany