1. A 14-year-old boy has just moved with his family from Brazil to the U.S. He starts complaining of shortness of breath and palpitations. Chest x-ray films demonstrate pulmonary congestion, and ECG shows alterations in heart rhythm. Echocardiography reveals biventricular dilatation with massive cardiac enlargement. An endomyocardial biopsy shows diffuse interstitial fibrosis, myocyte necrosis, chronic inflammation, and the presence of intracellular protozoan parasites. The patient may also develop which of the following complications?