The GUARD-AF trial, presented at the European Society of Cardiology (ESC) Congress 2024, demonstrated that screening for undiagnosed atrial fibrillation (AF) in primary care settings using iRhythm Technologies' Zio XT patch significantly increased the detection of new AF cases. However, the study did not show a significant reduction in stroke hospitalization rates. The trial, sponsored by Bristol-Myers Squibb-Pfizer Alliance, randomized 11,905 patients aged 70 years and older from 149 primary care sites in the US to either screening with the Zio XT long-term continuous monitoring (LTCM) patch or usual care.
Increased AF Detection with Zio XT Patch
The study found that the Zio XT LTCM led to a notable increase in new AF diagnoses, with 5.0% in the screening group compared to 3.3% in the usual care group over a median follow-up of 15 months. This increase in detection also correlated with a higher rate of oral anticoagulation initiation in the screening group (4.2% vs 2.8%), a crucial step in preventing stroke in AF patients. The results highlight the potential of long-term continuous monitoring to identify AF in individuals who may not be diagnosed through traditional methods.
Stroke Hospitalization Rates and Trial Limitations
Despite the increased AF detection, the trial did not observe a significant difference in the primary endpoint of stroke hospitalization between the two groups. This lack of significant difference is attributed to the trial being stopped early due to the COVID-19 pandemic, which resulted in truncated enrollment and reduced statistical power. The study was initially planned to enroll 52,000 patients, but only 11,905 were included before the trial was halted.
Feasibility of Home-Based Monitoring
One of the key findings of the GUARD-AF trial was the feasibility of primary care-initiated, home-based monitoring in an older population. The study demonstrated that virtual enrollment and self-application of the Zio XT patch were effective, with 20% of participants enrolling virtually and receiving the device by mail. Wear time and analyzable time were similar and high in both self-applied and clinic-applied groups, confirming the practicality of this approach.
Characteristics of Detected AF Episodes
In the 252 participants with AF detected on 14-day LTCM, the majority (88%) had low-burden paroxysmal AF. Most of those detected with AF had the condition present less than 1.0% of the time, suggesting that many patients with diagnosed AF may miss detection with shorter monitoring periods such as a 12-lead ECG (10 seconds), smartwatch ECG (30 seconds), or ambulatory monitoring of shorter duration such as 48 hours. Only 32 of 252 had AF at the start of the ECG recording.
Expert Commentary
According to Dr. Renato Lopes, Professor of Medicine at the Duke Clinical Research Institute and Duke University, the study confirms that AFib is common in older patients and can be identified with cardiac monitoring in primary care. He noted that most participants with AFib had short, infrequent episodes that would be missed with traditional methods. Dr. Lopes suggested that identifying these short episodes could prompt physicians to more aggressively treat heart disease risk factors and potentially reduce the downstream risk of heart failure.
Future Directions
iRhythm's Chief Medical and Scientific Officer, Mintu Turakhia MD, stated that the findings support the evidence that undiagnosed AFib is common and can be found with Zio’s 14-day long-term monitoring. He added that iRhythm’s undiagnosed arrhythmia pilot programs leverage many features seen in GUARD-AF, such as virtual enrollment and self-applied patches at home. Ongoing clinical trials, such as AMALFI, and those in development will have longer follow-up or assess a wider range of outcomes, including heart failure, cardiovascular hospitalization, health care utilization, and costs.
