Exploration of Arrhythmia Burden in Cardiac Amyloidosis Using Implantable Loop Recorders

BACKGROUND: Cardiac amyloidosis (CA) is a progressive infiltrative cardiomyopathy associated with conduction disease and arrhythmias, although their true burden and relationship with disease phenotype remain incompletely defined. OBJECTIVES: The purpose of this study was to prospectively characterize arrhythmic burden using implantable loop recorders and explore associations with amyloid subtype and disease characteristics. METHODS: In this prospective single-center observational study, 110 treatment-naïve patients with a new diagnosis of transthyretin amyloid cardiomyopathy (ATTR-CM) or light-chain cardiac amyloidosis (AL-CA) underwent comprehensive phenotyping, including cardiac magnetic resonance, followed by implantable loop recorder implantation. RESULTS: Among 110 patients (ATTRwt-CM: 43, ATTRv-CM: 20, AL-CA: 47) bradyarrhythmias with a Class I indication for pacemaker implantation occurred in 17.3% and were more frequent in ATTR-CM than AL-CA (15 [23.8%] vs 4 [8.5%]; P = 0.036). Baseline conduction abnormalities (QRS duration: sHR: 1.03; [95% CI: 1.01-1.04]; P < 0.001) and higher myocardial amyloid burden were associated with subsequent bradyarrhythmic events (ECV: sHR: 1.06 [95% CI: 1.02-1.10]; P = 0.002). New atrial fibrillation occurred in 28.2% of patients without prior atrial fibrillation and was more frequent in ATTR-CM than AL-CA (15 [50.0%] vs 5 [12.2%]; P < 0.001) with higher amyloid burden associated with increased risk (ECV: sHR: 1.04; 95% CI: 1.00-1.08; P = 0.038). During follow-up 21 (19.1%) patients died (ATTR-CM: 10 [15.9%]; AL-CA: 11[23.4%]). In patients with ATTR-CM, the terminal cardiac rhythm was uniformly pulseless electrical activity; in patients with AL-CA, PEA was the terminal rhythm in 9 (81.8%) patients and 2 (18.2%) had sustained ventricular arrhythmias. CONCLUSIONS: In CA, clinically significant arrhythmias are common and frequently asymptomatic. Arrhythmic burden and patterns differ between amyloid subtypes and are closely associated with disease phenotype and myocardial amyloid burden. These findings provide prospective insights into arrhythmogenesis in CA and support the need for further studies to refine risk stratification and inform management strategies. (Exploration of Arrhythmia Burden in Cardiac Amyloidosis Using Implantable Loop Recorders [EXCALIBUR]; NCT04856267).