Abstract Body (Do not enter title and authors here): Background:
Arrhythmia-induced cardiomyopathy (AIC) is a potentially reversible cause of heart failure triggered by sustained arrhythmias. Its true real-world prevalence and clinical recognition remain limited. This study aimed to assess the frequency, predictors, and outcomes of AIC in patients with newly diagnosed left ventricular systolic dysfunction (LVSD) and concurrent arrhythmia, undergoing rhythm control while protected by a wearable cardioverter-defibrillator (WCD).

Methods:
We analyzed 780 patients treated with a WCD between 2017 and 2023. Among them, patients with newly diagnosed idiopathic LVSD (LVEF <35%) and arrhythmias (atrial fibrillation, flutter, or ventricular ectopy >20%) were identified. Diagnostic workup included echocardiography, cardiac MRI, and ischemia testing or coronary angiography. Patients underwent rhythm control (cardioversion, antiarrhythmic drugs, and/or catheter ablation) and were followed up to 6 months. AIC was defined as LVEF improvement >15% in patients with restored sinus rhythm.

Results:
Among 780 patients treated with a WCD, 142 (18.2%) had first diagnosis of LVSD in the presence of arrhythmia (Figure 1). Of these, 68 (47.9%) had an identifiable etiology (Figure 2). The remaining 74 (52.1%) with idiopathic LVSD were analyzed. At mean follow-up of 133 days (4.5 months), 20 (27%) of 74 patients remained in arrhythmia (non-responders). Among 54 responders with restored sinus rhythm, 32 (59.3%) fulfilled AIC criteria; 22 (40.7%) were non-AIC. LVEF improved from 28% to 43% in AIC vs. 24% to 32% in non-AIC. Full recovery (LVEF >50%) was achieved in 56.3% of AIC patients during follow-up. Atrial fibrillation was most common (81.3% AIC vs. 95.5% non-AIC), followed by flutter; ventricular ectopy occurred in 9.4% of AIC cases. Heart failure therapy was comparable. Non-AIC patients showed larger LVEDD/LVESD, lower heart rates, more mitral regurgitation, and more frequent late gadolinium enhancement on MRI. No appropriate WCD shocks occurred. ICDs were implanted in 36.4% of non-AIC vs. 3.1% of AIC patients (p=0.001). No deaths were reported. LVEF <25% predicted lack of full recovery (p=0.04).

Conclusions:
AIC is a common and reversible form of LVSD in patients with arrhythmia and newly diagnosed idiopathic cardiomyopathy. Early rhythm control supported by WCD, combined with detailed diagnostics including cardiac MRI and ischemia testing, enables identification of reversible dysfunction and may reduce unnecessary ICD implantation.