A 44-year-old woman has been complaining of a 4-year history of increasing dyspnea and fatigue. Physical examination reveals increased JVP and a reduced carotid pulse. Precordial examination reveals a left parasternal lift, loud P2, and right-sided S3 and S4. There are no audible murmurs. CXR reveals clear lung fields and an ECG shows evidence of right ventricular hypertrophy. Pulmonary function tests show a slight restrictive pattern. A diagnosis of primary pulmonary hypertension (PPH) is made. Which of the following is the most likely cause of death in this condition?