The retrospective analyses drew on data from more than 1.1 million patients using Zio long-term continuous monitoring ECG devices. Investigators presented findings at the American College of Cardiology (ACC) 2025 Scientific Sessions in Chicago.
Results demonstrated that short-term (24-48-hour) monitoring, like with Holter devices, fails to detect a significant proportion of actionable arrhythmias, even in patients reporting “daily symptoms.” Investigators also found that symptom-rhythm correlation (SRC) comes in notably low for most arrhythmias. This underscores that the selection of monitoring duration based on the frequency of symptoms alone can lead to undetected arrhythmias.
Altogether, iRhythm says the findings highlight the benefits of Zio and the limitations of shorter-term Holter monitoring. The company says the data builds on its comprehensive clinical evidence program and emphasizes its ongoing commitment to expanding evidence that supports improved patient outcomes.
“These findings challenge the long-held assumption that frequent symptoms justify short-duration monitoring,” said Dr. Mintu Turakhia, iRhythm chief medical and scientific officer and EVP of product innovation. “They reinforce the limitations of Holter-duration monitoring and highlight the value of Zio long-term continuous monitoring up to 14 days. Once again, iRhythm’s real-world data are contributing evidence that can help guide both clinical practice and payer policy.”
A look at the gaps in short-term Holter monitoring reported by iRhthym
iRhythm says that, among daily symptom patients diagnosed with actionable arrhythmias, 64% went undetected through two days of monitoring. That indicates that 24-48-hour monitoring, like with Holter, would have failed to detect them, the company says.
Additionally, non-daily symptom patients had had an 80.9% arrhythmia yield, compared to 69.1% in daily symptom patients. This indicates that greater symptom frequency does not necessarily reflect increased arrhythmia burden. Across all arrhythmia types, the mean time to the first detected episode came in at greater than 48 hours, regardless of symptom frequency. iRhythm again noted that this points to the limitations of short-term monitoring.
In another study, iRhythm determined that symptoms alone proved unreliable. With most arrhythmia types, fewer than one in five patients in the analysis documented a symptom coinciding with an arrhythmic episode. Symptom-rhythm correlation came in higher for patients reporting daily vs. non-daily symptoms.
Even for AFib (the most commonly symptomatic arrhythmia), iRhythm says more than half of all cases registered as asymptomatic. Meanwhile, Zio frequently detected ventricular tachycardia, AV block and significant pauses without patient-reported symptoms. This suggested that selection of monitor duration should not be based on symptom frequency alone, and that long-term continuous monitoring may offer advantages over other monitoring types with shorter duration or those which rely on patient triggered events to initiate recording.
