Post Hoc Analysis of the LOOP Trial

A groundbreaking post hoc analysis of the Implantable Loop Recorder Detection of Atrial Fibrillation (AF) to Prevent Stroke (LOOP) trial has unearthed a previously underestimated prevalence of bradyarrhythmias in individuals aged 70 and above with cardiovascular risk factors. The study concluded that one in five individuals over 70 years old with cardiovascular risk factors may have bradyarrhythmias when subjected to long-term continuous monitoring for AF.

The study results were published in the journal JAMA Cardiology.

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Growing attention is directed towards heart rhythm monitoring and technologies aimed at identifying subclinical atrial fibrillation (AF), potentially resulting in the inadvertent discovery of bradyarrhythmias. Hence, researchers conducted a Post Hoc analysis of the LOOP randomized trial to investigate the impact of long-term continuous monitoring for atrial fibrillation (AF) using an implantable loop recorder (ILR) compared to standard care across four sites in Denmark.

Between January 2014 and May 2016, the trial enrolled 6004 participants, all aged 70 or older, with conditions such as hypertension, diabetes, heart failure, or prior stroke. The focus was on evaluating bradyarrhythmia diagnoses, pacemaker implantations, syncope events, and sudden cardiovascular deaths over a median follow-up period of 65 months.

Findings:

• Intriguingly, the ILR screening group, comprising 1501 participants, exhibited a staggering 6.21-fold increase in bradyarrhythmia diagnoses compared to the control group (4503 participants), where only 3.8% received such a diagnosis.
• Significantly, a large proportion of bradyarrhythmia cases in the ILR group (79.8%) were asymptomatic, highlighting the potential value of continuous monitoring in capturing silent cardiac irregularities.
• The most prevalent types of bradyarrhythmias identified were sinus node dysfunction and high-grade atrioventricular block. Age, male gender, and a history of prior syncope were identified as risk factors associated with bradyarrhythmias.
• Notably, the ILR screening group experienced a noteworthy increase in pacemaker implantations (4.5%) compared to the control group (2.9%).
• However, there was no discernible difference in the occurrence of syncope or sudden cardiovascular death between the two groups.
• Bradyarrhythmias, identified through continuous monitoring, were found to be correlated with subsequent syncope, cardiovascular death, and all-cause mortality.
• Crucially, the impact of bradyarrhythmia on these outcomes remained consistent across both the ILR and control groups.

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In conclusion, this study suggests that more than one in five individuals over 70 years old with cardiovascular risk factors may have bradyarrhythmias when subjected to long-term continuous monitoring for AF. The utilization of ILR screening significantly heightened the detection of bradyarrhythmias and led to more pacemaker implantations compared to standard care. While shedding light on this hidden aspect of cardiac health, the study underscores the need for comprehensive heart rhythm monitoring, offering invaluable insights for diagnostic and therapeutic considerations in managing cardiovascular health in the elderly.

Further reading: Diederichsen SZ, Xing LY, Frodi DM, et al. Prevalence and Prognostic Significance of Bradyarrhythmias in Patients Screened for Atrial Fibrillation vs Usual Care: Post Hoc Analysis of the LOOP Randomized Clinical Trial. JAMA Cardiol. 2023;8(4):326–334. doi:10.1001/jamacardio.2022.5526