Clinically significant arrhythmias were frequently detected in patients with CA, with differences observed between transthyretin amyloid cardiomyopathy (ATTR-CM) and light-chain cardiac amyloidosis (AL-CA), according to prospective ILR monitoring data.

This single-center study published in Journal of the American College of Cardiology enrolled 110 treatment-naïve patients with newly diagnosed CA, including ATTR wild-type cardiomyopathy (ATTRwt-CM; n=43), variant ATTR cardiomyopathy (ATTRv-CM; n=20), and AL-CA (n=47). All participants underwent comprehensive phenotyping, including cardiac magnetic resonance imaging, followed by ILR implantation to prospectively assess arrhythmic events.
Bradyarrhythmias requiring Class I pacemaker implantation occurred in 17.3% of patients overall and were more common in ATTR-CM compared with AL-CA (23.8% vs 8.5%; P=0.036).

Baseline conduction abnormalities, including prolonged QRS duration, were associated with subsequent bradyarrhythmic events (sub-distribution hazard ratio [sHR] 1.03, 95% CI 1.01-1.04; P<0.001). Greater myocardial amyloid burden, measured by extracellular volume (ECV), was also associated with increased bradyarrhythmia risk (sHR 1.06, 95% CI 1.02-1.10; P=0.002).
Among patients without prior atrial fibrillation (AF), new AF developed in 28.2% and occurred more frequently in ATTR-CM than AL-CA (50.0% vs 12.2%; P<0.001). Higher ECV values were associated with increased AF risk (sHR 1.04, 95% CI 1.00-1.09; P=0.038).

During follow-up, 21 patients (19.1%) died, including 10 patients with ATTR-CM and 11 with AL-CA. Terminal cardiac rhythm was uniformly pulseless electrical activity (PEA) in ATTR-CM, while 81.8% of deaths in AL-CA were associated with PEA and 18.2% with sustained ventricular arrhythmias.

The findings demonstrated a high burden of often asymptomatic arrhythmias in CA. Arrhythmic patterns differed according to amyloid subtype and were associated with myocardial amyloid burden and disease phenotype.