Usefulness of Apple Watch Electrocardiograms for Identifying the Origin of Premature Ventricular Contractions

Abstract

Background: The Apple Watch (AW) can record single-lead electrocardiograms (ECGs) and has been investigated for arrhythmia detection. In this study we evaluated its accuracy in identifying the origin of premature ventricular contractions (PVCs) vs. standard 12-lead ECGs.

Methods and Results: A total of 7 patients with PVCs were assessed using both 12-lead and AW ECG recordings. The QRS polarity observed in the AW recordings was consistent with that of the standard ECGs in most cases, demonstrating its utility in estimating three distinct PVC origins.

Conclusions: The AW holds potential as an auxiliary tool for PVC origin assessment, contributing to arrhythmia management in clinical practice.

In recent years, the Apple Watch (AW), a widely used consumer wearable device, has attracted attention for its ability to record single-lead electrocardiograms (ECGs). Studies have demonstrated its effectiveness in detecting atrial fibrillation (AF). In the Apple Heart Study of 419,297 participants, 2,161 (0.52%) received irregular pulse notifications via their AW.¹ Similarly, the AW Series 6 demonstrated a sensitivity of 85% and specificity of 75% when detecting AF based on automatic algorithm interpretation.² Recent studies have also compared the AW single-lead ECG and standard 12-lead ECG. Saghir et al. reported moderate to strong agreement between the AW and 12-lead ECGs for basic ECG intervals in healthy adults.³ Samol et al. investigated the feasibility of using the AW to record not only the traditional Einthoven leads (I, II, III), but also the Wilson-like precordial leads (Wr, Wm, Wl), which correspond to the standard V₁, V₄, and V₆ leads of a 12-lead ECG.⁴ Premature ventricular contractions (PVCs) are a common arrhythmia in clinical practice, and traditionally their origin is determined by 12-lead ECG, which provides comprehensive information about the electrical activity of the heart. In this study we aimed to assess whether the AW can accurately estimate the origin of PVCs by comparing its single-lead ECG recordings with those obtained from standard 12-lead ECGs.

Methods

Study Participants

We prospectively enrolled patients before catheter ablation therapy who had had PVCs recorded on 12-lead ECG during hospitalization. A total of 7 patients were enrolled, 4 men and 3 women, with a mean age of 58.5±19.1 years.

12-Lead ECG

Standard 12-lead ECGs were recorded using a conventional ECG machine (EFS-8800 system, Fukuda Denshi, Co., Tokyo, Japan) with a paper speed of 25 mm/s. All ECG recordings were made while the patient was in the supine position after a resting period of 1 min. These recordings served as the reference standard for comparison with the AW ECG recordings.

AW ECG Recordings

An AW Series 8® (Apple Inc., Cupertino, CA, USA) was used for single-lead ECG recordings immediately after the 12-lead ECG recordings. The recording procedure followed established protocols and was adapted for PVC detection. ECG recordings were performed with the patient in the supine position with the AW back electrode placed on the body surface and the patient touching the digital crown with a finger. Recordings lasted 30 s. The following lead configurations were used (Figure A).

Figure.

(A) Illustrations of the lead configurations. Lead I: Apple Watch (AW) placed on the left wrist, with the right index finger touching the digital crown, Lead II: AW placed on the left lower abdomen, with the right index finger touching the digital crown, Lead III: AW placed on the left lower abdomen, with the left index finger touching the digital crown. Wilson-like V₁ (W-V₁): AW placed at the fourth intercostal space, right parasternal, corresponding to lead V₁. Wilson-like V₂ (W-V₂): AW placed at the fourth intercostal space, left parasternal, corresponding to lead V₂. Wilson-like V₃ (W-V₃): AW installed between the V₂ and V₄ leads. Wilson-like V₄ (W-V₄): AW placed at the fifth intercostal space on the midclavicular line, corresponding to lead V₄. Wilson-like V₆ (W-V₆): AW placed at the fifth intercostal space in the left midaxillary line, corresponding to lead V₆. (B) Case 1: Comparison of PVC waveforms recorded by AW and 12-lead ECG in a 78-year-old male patient. The AW (Right) and 12-lead ECG (Left) both display similar polarity patterns, indicating a RVOT origin. The AW shows negative polarity in leads W-V_1–3 and positive polarity in leads II, III, W-V₆, aligning with the 12-lead ECG findings. Case 2: Waveform comparison for an 81-year-old male with left ventricular basal inferior wall PVCs. The AW shows negative polarity in leads II, III and positive polarity in leads W-V_1–4, consistent with the 12-lead ECG findings. Case 3: 19-year-old male patient’s PVCs with discordant polarities in leads II and III, consistent with a septal inferior origin. The AW shows this discordance, displaying negative polarity in leads W-V_1–4, and positive polarity in leads W-V₆, aligning with the 12-lead ECG findings. PVC, premature ventricular contraction; RVOT, right ventricular outflow tract.

1. Lead I: AW placed on the left wrist, with the right index finger touching the digital crown.

2. Lead II: AW placed on the left lower abdomen, with the right index finger touching the digital crown.

3. Lead III: AW placed on the left lower abdomen, with the left index finger touching the digital crown.

4. Chest leads: AW positioned at locations corresponding to standard 12-lead ECG chest leads (e.g., V_1–6), with the right index finger touching the digital crown.

The chest lead recordings (pseudo-unipolar Wilson-like leads) were positioned as follows:

1. Wilson-like V₁ (W-V₁): AW placed at the fourth intercostal space, right parasternal, corresponding to lead V₁.

2. Wilson-like V₂ (W-V₂): AW placed at the fourth intercostal space, left parasternal, corresponding to lead V₂.

3. Wilson-like V₃ (W-V₃): AW installed between the V₂ and V₄ leads.

4. Wilson-like V₄ (W-V₄): AW placed at the fifth intercostal space on the midclavicular line, corresponding to lead V₄.

5. Wilson-like V₆ (W-V₆): AW placed at the fifth intercostal space in the left midaxillary line, corresponding to lead V₆.

For all chest lead recordings, the patient maintained contact between both hands and the chest, ensuring consistent signal quality. The recorded data were digitally stored using the Health Application on an iPhone SE (Apple Inc.).

Data Conversion and Analysis

All single-lead AW ECG recordings were automatically converted to PDF documents using the “send pdf to your doctor” function and printed for further analysis. The ECGs were classified based on signal quality. Recordings were classified as having moderate signal quality if ≥3 consecutive QRS complexes including PVC exhibited noise-free signal quality without artifacts in the iso-electric lines between QRS complexes. Two experienced cardiologists independently assigned the AW ECG recordings to corresponding leads from the standard 12-lead ECG for each patient. The cardiologists visually compared the AW ECGs to the standard 12-lead ECG leads I–III and V_1–6. Subsequently, 4 medical students, not involved in the comparison, used a solution table to verify the correctness of the assignments.

Results

On 12-lead ECG, PVCs of right ventricular outflow tract (RVOT) origin were recorded in 5 patients, those of left ventricular (LV) basal inferior wall origin in one, and those of RV septal inferior origin in one. In comparison with the ECGs recorded by the AW, the polarity of QRS amplitude of the limb leads were consistent in all cases, and the polarity in both W-V₁ and W-V₂ leads was also consistent (Table). The 3 patients with different origins of PVCs are shown in the Figure. The first case, a 78-year-old male, showed consistency in PVC origin (i.e., RVOT) between the AW and 12-lead ECGs. In this case, the AW displayed a negative polarity in leads W-V_1–3 and a positive polarity in leads II, III, W-V₆, aligning with the 12-lead ECG findings (Figure B, Case 1). The second case, an 81-year-old male, exhibited LV basal inferior wall PVCs. The AW showed negative polarity in leads II, III and positive polarity in leads W-V_1–4, consistent with the 12-lead ECG findings (Figure B, Case 2). The third case, a 19-year-old male, had discordant polarities in leads II and III, consistent with a RV septal inferior origin. The AW showed this discordance, displayed a negative polarity in leads W-V_1–4, and a positive polarity in leads W-V₆, aligning with the 12-lead ECG findings (Figure B, Case 3).

Table.

Patients’ Characteristics, Lead Polarities of QRS Amplitude and the Origin of PVC

Case no.	Age (years)	Sex	I/I-AW	II/II-AW	III/III-AW	V1/W-V1	V2/W-V2	V3/W-V3	V4/W-V4	V6/W-V6	PVC type
1	78	M	−/−	+/+	+/+	−/−	−/−	−/−	+/+	+/+	RVOT
2	81	M	+/+	−/−	−/−	+/+	+/+	+/+	+/+	−/+	LV
3	19	M	+/+	+/+	−/−	−/−	−/−	−/−	−/−	+/+	RV septum
4	50	F	−/−	+/+	+/+	−/−	−/−	−/NA	+/+	+/+	RVOT
5	64	M	−/−	+/+	+/+	−/−	−/−	−/+	+/+	+/+	RVOT
6	61	F	+/+	+/+	+/+	−/−	−/−	−/NA	+/+	+/+	RVOT
7	57	F	+/+	+/+	+/+	−/−	−/−	+/NA	+/+	+/+	RVOT

+ positive polarity of QRS amplitude in the corresponding lead; − negative polarity of QRS amplitude in the corresponding lead. AW, Apple Watch; F, female; LV, left ventricular; M, male; PVC, premature ventricular contractions; RVOT, right ventricular outflow tract.

Discussion

The results from the present study suggest that the AW can provide ECG recordings that are sufficient for estimating the origin of PVCs. The ability of the AW to mirror the polarity patterns seen in 12-lead ECGs, as demonstrated in our cases, suggests that the device can be used as a supplementary tool in arrhythmia management.

In Case 1, the 12-lead ECG demonstrated a configuration of left bundle branch block (LBBB) with positive deflections in leads II, III, and aVF, together with positive V₆ deflections. This pattern reflects an arrhythmogenic origin from the RVOT. The relatively consistent waveforms across the chest and limb leads of the AW further support the LBBB localization of this arrhythmia to the RVOT. The significance of differentiating between left and right BBB patterns in the context of arrhythmia origin is profound. LBBB patterns are frequently associated with arrhythmias originating from the right side of the heart, such as the RVOT, and are generally easier to access and ablate due to their superficial localization. Previous studies have suggested that combining V₂ and V₃ lead analysis improves the diagnostic accuracy of differentiating between LVOT and RVOT origins.^5,6 In this study, although the polarity of the V₂ lead was generally consistent with that of standard 12-lead ECGs, the polarity of the V₃ lead was discrepant in Case 5, possibly due to variations in ambulatory ECG and AW electrode placement. As a result, the accuracy of distinguishing between LVOT and RVOT origin might be limited in this study. Conversely, RBBB patterns often point to arrhythmias originating from the LV myocardium where the arrhythmogenic substrate may be more diffuse and deeper within the myocardial tissue, as in Case 2.⁷ In Case 3, a 19-year-old male, the ECG recorded by the AW demonstrated concordance with the 12-lead ECG, specifically showing a positive deflection in lead II and a negative deflection in lead III. This polarity discrepancy between leads II and III suggested an origin of the PVC in the lower septal region. This finding is consistent with previous data reported by Kotake et al., highlighting the importance of limb lead analysis in identifying arrhythmogenic substrates, particularly in complex cases involving the basal septum. Specifically, they highlighted that inferior lead discordance, such as a positive deflection in lead II and a negative deflection in lead III, can be indicative of a para-Hisian or septal origin, further supporting the significance of these measurements.⁸

In particular, the Wr lead, which corresponds to the V₁ position, and leads II and III provide valuable insights into the polarity changes necessary for determining the origin of the PVC. By restricting the recording to these leads, clinicians can potentially obtain more targeted data, thereby improving the utility of the AW in remote arrhythmia monitoring.

Study Limitations

First, this study included only a small number of patients at a single center. Future studies should focus on larger cohorts to further validate our findings and explore the potential for integrating AW-derived ECGs into clinical practice for PVC management. Second, a limitation of utilizing the AW for PVC detection is its brief 30-s recording duration. Because PVCs are often sporadic, this short timeframe may not reliably capture the arrhythmia, potentially resulting in insufficient evaluation.

In conclusion, this study provides evidence supporting the use of the AW for the estimation of PVC origins, demonstrating its potential as a valuable tool in the ongoing monitoring and clinical management of arrhythmias.

Disclosures

Dr. Yamamoto is a member of Circulation Journal’s Editorial Team.

Conflicts of Interest: Dr. Yamamoto has received lecturer fees from Otsuka Pharmaceutical Co., Ltd., Daiichi Sankyo Co., Ltd., and Novartis and research grants from Abbott, Otsuka Pharmaceutical Co., Ltd., Medtronic Japan Co., Ltd., Daiichi Sankyo Co., Ltd., Boston Scientific Co., Ltd., Biotronik Japan Inc., Japan Lifeline Co., Ltd., Mitsubishi Tanabe Pharma Co., Ltd., Fukuda Denshi, Takeda Pharmaceutical Co., Ltd., Ono Pharmaceutical Co., Ltd., and Novartis.

Ethical Considerations

This study was approved by the local ethics committee of Tottori University Hospital (23A049) and was conducted in accordance with the Declaration of Helsinki. All participants were informed of the study’s purpose and procedures, and written informed consent was obtained from all patients.

Data Availability

The deidentified participant data will not be shared.

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