Precardioversion Heart Rhythm Monitoring Using Smartphone Photoplethysmography: The SMARTBEATS Randomized Clinical Trial

Background

Atrial fibrillation and atrial flutter are common heart rhythm disorders in which the upper chambers of the heart beat in an irregular or overly fast pattern. A standard treatment for many patients is electrical cardioversion, a planned procedure that delivers a controlled shock to restore normal sinus rhythm. Although cardioversion is effective, it is also resource-intensive and requires hospital time, staff coordination, and procedural preparation.

One practical problem is that some patients convert back to normal rhythm on their own before the scheduled procedure. When this happens, the cardioversion may no longer be needed and the appointment is often canceled on the same day. These cancellations waste healthcare resources and can be frustrating for patients, who may have fasted, arranged transportation, or taken time off work.

This trial examined whether simple heart rhythm monitoring with smartphone photoplethysmography, combined with reminders to support anticoagulation adherence, could identify spontaneous rhythm conversion before the day of cardioversion and reduce unnecessary cancellations.

What is smartphone photoplethysmography?

Photoplethysmography, often abbreviated PPG, is a technique that uses a smartphone camera and flash to detect small changes in light reflection from the skin, usually from a fingertip. These changes correspond to tiny pulsations in blood flow with each heartbeat. By analyzing the pulse pattern, the device can help detect whether the rhythm is regular or irregular.

This approach is attractive because it is inexpensive, widely available, and easy for patients to use at home. Unlike traditional monitoring systems, it does not require a separate wearable device or repeated hospital visits. In this study, every PPG recording was paired with a single-lead electrocardiogram for validation, helping confirm the accuracy of the rhythm interpretation.

Study design

The SMARTBEATS trial was a randomized, single-blinded clinical study conducted at a tertiary hospital in Sweden from September 2022 to February 2025. Adults aged 18 years and older with persistent atrial fibrillation or atrial flutter who were scheduled for cardioversion were eligible.

Patients were excluded if they had a cardiac implantable electronic device or if they were unable to provide consent or follow the study procedures. In total, 206 patients were randomized. After randomization, 3 participants were excluded because they had a cardiac implantable device, leaving 104 patients in the intervention group and 99 in the control group for the final analysis.

The intervention group used smartphone-based heart rhythm monitoring before cardioversion and also received reminders intended to support adherence to anticoagulation therapy. The control group received standard care only, without additional monitoring or reminders.

How the intervention worked

Participants in the intervention arm performed ambulatory heart rhythm recordings using their smartphones before the scheduled cardioversion. Recordings were automatically transferred after completion and reviewed daily by the study team. A single-lead electrocardiogram was recorded at the same time as each PPG measurement to verify the rhythm data.

If a participant in the intervention group spontaneously returned to sinus rhythm before the planned procedure, the study team contacted the patient and the cardioversion was canceled in advance. This proactive approach meant that unnecessary hospital visits could be avoided.

In the control group, no additional monitoring was done. If a patient happened to convert to sinus rhythm before the procedure, the change was only discovered on the day of cardioversion, and no special action was taken beforehand.

Main findings

The participants completed 5,226 heart rhythm recordings before cardioversion. The median number of daily recordings per participant was 2.1, showing that patients were generally able to use the smartphone method reliably and repeatedly.

The main outcome was the proportion of same-day cancellations of scheduled cardioversions. In the intervention group, 4.8% of cardioversions were canceled on the same day, compared with 23.2% in the control group. This difference was statistically significant.

When looking specifically at cancellations caused by spontaneous return to sinus rhythm, the benefit was even more pronounced. Only 1.0% of patients in the intervention group had same-day cancellations for this reason, compared with 18.2% in the control group.

These results suggest that monitoring with smartphone PPG allowed the care team to detect rhythm changes early and avoid many unnecessary cardioversion appointments.

Clinical significance

The findings are important because they address a common workflow problem in rhythm management of atrial fibrillation. Even though cardioversion remains an important treatment, many patients do not need it once they have already returned to normal rhythm. Identifying those patients before the procedure can reduce wasted resources and improve the patient experience.

This study also shows that smartphone-based monitoring can be a highly scalable digital health intervention. Because the method uses technology that many patients already own or can easily access, it could potentially be expanded to larger populations and different care settings without major infrastructure changes.

Another practical advantage is improved communication around anticoagulation. Patients scheduled for cardioversion are often treated with blood thinners to reduce stroke risk. Reminders may help patients stay on track with this important medication, although the main reported outcome in this trial was reduced same-day cancellation.

Why this matters for patients and hospitals

For patients, avoiding a canceled procedure means less inconvenience, fewer missed workdays, and less emotional stress. For hospitals, it means better use of operating rooms, staff time, and pre-procedure planning.

In busy cardiology services, even a modest reduction in cancellations can improve scheduling efficiency. The trial suggests that a simple digital tool may help align care more closely with each patient’s actual rhythm status at the time of the planned procedure.

Limitations and considerations

Although the results are promising, there are several considerations. The study was conducted in a single tertiary center in Sweden, so the findings may not automatically apply to all healthcare systems or patient populations. In addition, the intervention required patients to perform regular smartphone recordings and comply with the study process, so real-world adherence may vary.

The monitoring strategy also depends on reliable access to a smartphone and basic comfort using digital tools. This may be a barrier for some older adults or patients with limited technology access. Still, the high number of successful recordings in this trial suggests that many patients can use the method effectively with appropriate support.

It is also important to note that smartphone photoplethysmography is a screening and monitoring tool, not a replacement for full clinical assessment. Decisions about cardioversion should continue to consider symptoms, stroke prevention, underlying heart disease, and the physician’s overall judgment.

Conclusion

The SMARTBEATS randomized clinical trial found that precardioversion heart rhythm monitoring using smartphone photoplethysmography significantly reduced same-day cancellations of scheduled cardioversion in patients with atrial fibrillation or atrial flutter. The intervention was practical, scalable, and effective at identifying spontaneous return to sinus rhythm before the procedure.

These results support the use of digital rhythm monitoring as a useful addition to standard care, especially when the goal is to improve efficiency and avoid unnecessary procedures. As smartphone-based health tools continue to evolve, they may play an increasingly important role in routine cardiovascular care.