Dr Niraj Sharma: Hello and welcome, I am Doctor. Sharma, a cardiologist and cardiac electrophysiologist. As we move through the holiday season, I truly hope you are finding a little time to breathe, reset and spend moments with the people who matter. Whether you are listening during a commute between cases or just taking a break, I am really glad you are here. Thank you for joining me today.
Let's dive into this special December smartwatch episode. Why this issue? There are now roughly four fifty five million smartwatch users worldwide in 2024. That number is projected to exceed five sixty million in 2025. In The United States, about 28% of the overall population wears a smartwatch.
More than half of adults aged 18 to 34 have one on their wrist. 90% of smartwatch users rely on them for health and fitness tracking, including heart rhythm alerts and irregular pulse notifications. Bottom line: Patients are now screening themselves for atrial fibrillation, or AF, twenty four hours a day. This issue provides a clinically grounded framework for how to interpret smartwatch data in real world practice. Question one: How accurate are smartwatches for detecting AF?
Key evidence: First, the Apple Watch ECG meta analysis by Shahid et al. The single lead tracing demonstrated both a sensitivity and specificity of ninety five percent for detecting AF. Second, the multi device meta analysis by Barrera and colleagues, including more than 17,000 patients. Across Apple, Samsung, and Withings, sensitivity was 95% and specificity ninety six percent Third, photoplethysmography based devices versus adhesive ECG patches from Sibomana et al. Mid-ninety percent accuracy.
Clinical take: A clean smartwatch strip is usually trustworthy, especially from major vendors. Accuracy is high but most data come from high prevalence cohorts, so general screening accuracy is not the same as device accuracy. Question two: What happens in real world arrhythmia environment? Key evidence: In multicenter comparisons, the Apple Watch had 69% sensitivity when every inconclusive strip was treated as incorrect. About 20% of recordings were unclassified.
The cart ring using PPG performed better with 85% sensitivity, 90% specificity, and only 2% inconclusive. In the Eisenhager JAK EP study, nineteen percent of smartwatch tracings were inconclusive across five devices. Pacing, left bundle branch block, low voltage, and ectopy were the most common causes. Clinical take. When smartwatches make a firm call, they are typically accurate, but in many EP patients inconclusive strips are extremely common.
Move early to patch or implantable monitoring when clarity is needed. Question three: Can smartwatches replace Holters or implantable monitors after AFib ablation? Key evidence: In the circa dose cohort of three forty six post ablation patients with implantable monitors, the Apple Watch atrial fibrillation burden algorithm had eighty two percent sensitivity. The irregular rhythm notification was seventy one percent. Fitbit's algorithm was sixty four percent.
Smartwatches outperformed typical intermittent Holter strategies. Correlation with implantable monitor burden exceeded 0.97. Most missed episodes were ultra low burden events, clinical take. For many post ablation patients, smartwatch monitoring is better than episodic halters, but when anticoagulation hinges on detecting very low burden an implantable monitor remains superior. Question four: Why are so many smartwatch alerts false positives?
Even with 95 sensitivity and specificity, in a population with one percent AF prevalence, the positive predictive value is only about sixteen percent, meaning most alerts are false positives. In the Fitbit Heart Study, only thirty two percent of irregular pulse notifications were confirmed as AF on subsequent patch monitoring. Clinical take: Device accuracy does not equal screening accuracy. Pretest probability must be considered, especially in young, low risk patients. Practical pathways for electrophysiology: Scenario one: The watch shows AF with a good quality strip.
Confirm once, then manage based on CHADS VASc, not the device. Scenario two: No alerts but high stroke risk. Do not de escalate anticoagulation solely because a watch is quiet. Scenario three: Post ablation follow-up. Smartwatches are useful for moderate risk patients.
Use implantable monitors for high risk, low burden decision making. Scenario four: Paced or left bundle branch patients. Expect many inconclusive recordings. Scenario five: Young, low risk, anxious individuals explain false positives turn off alerts when they cause more harm than help. Clinical bottom line: Smartwatches are powerful tools for detecting AF, but they are not definitive diagnostic devices.
They outperform sporadic holters but remain inferior to implantables when anticoagulation decisions depend on detecting very low burden Algorithms fail in predictable situations such as pacing, bundle branch block, and low voltage signals, and positive predictive value collapses in populations with low AF prevalence. I hope you found this issue interesting. Thank you for listening to this special holiday season episode of EPH Journal Watch. I appreciate you taking the time to learn, think, and stay engaged with the latest in electrophysiology. If you found this episode helpful, please subscribe to EP Edge Journal Watch on LinkedIn and get all references and graphics.
Also, out the EP Edge Newsletter podcast for more deep dive issues in electrophysiology. Wishing you a warm, safe and peaceful holiday season. This is Doctor. Sharma. Thank you again for joining me and bye for now.