“First-degree AV block—a benign entity?” Insertable cardiac monitor in patients with 1st-degree AV block reveals presence or progression to higher grade block or bradycardia requiring pacemaker implant

Background: First-degree AV block has in the past generally been considered a benign condition. A few recent studies have shown that 1st-degree AV block is associated with an increased risk for heart failure, pacemaker (IPG) implantation, and death. We investigated the outcomes of patients who received an insertable cardiac monitor (ICM) (Medtronic Reveal XT®) within the scope of the INSIGHT XT study and had 1st-degree AV block at baseline. Methods: The observational, international, multi-center INSIGHT (R)XT study prospectively enrolled 1003 patients implanted with an ICM for arrhythmia diagnosis, irrespective of the clinical indication. This analysis includes 37 patients who had documented 1st-degree AV block at enrolment. Patients with known concurrent higher grade block at enrolment were excluded. Results: The indications for rhythm monitoring and ICM implantation were syncope/pre-syncope in 54.1%, cryptogenic stroke in 18.9%, AF with rhythm control intervention in 21.6%, and unexplained palpitations in 5.4%. Mean age was 68 ± 14 years, 75.7% were male, and concurrent bundle branch block was present in 8.1%. The median follow-up time was 12.2 months (IQR3.9–15.9). Fifteen patients (40.5%) received an IPG during the follow-up, and in 93.3% of the cases, the implant was needed to treat a now detected more severe bradycardia or progression of the conduction disease. Conclusions: ICM either revealed progression of 1st-degree AV block to a higher grade block (53%) or detected an already existing more severe bradycardia warranting an IPG in 40.5% patients. This finding supports the conclusion that 1st-degree AV block might be a risk marker for more severe intermittent conduction disease and is not benign in all patients. Further studies may reveal patient subgroups which are at risk for demonstrating or developing higher grade AV block and may warrant a future IPG implantation.