A 28-year-old male presents with palpitations and shortness of breath for 3 months. Physical exam reveals cardiomegaly, ventricular gallop rhythm, grade III/VI systolic blowing murmur at the apex, few crackles in both lungs, hepatomegaly, and lower limb edema. Echocardiography shows significant left atrial and left ventricular enlargement. The diagnosis is dilated cardiomyopathy. The most common cause of death in this condition is: