Review Question - QID 108253

A 3-year-old boy is taken to the ER by his parents due to his elevated temperature. He has had a fever (>101.1 deg F) for a little over a week, and over that time, his parents noticed his eyes had gotten a little pink, and his palms and soles were red and swollen. His lips and tongue are also peeling. His parents note he has not taken any new medications, and they did not notice any runny nose, sore throat, cough, or changes in his bowel or bladder habits. In the ER, his vitals are as follows: temperature is 101.3 deg F (38.5 deg C), blood pressure is 90/60 mmHg, pulse is 125/min, and respirations are 20/min. His exam is notable for bilateral injected conjunctivae, right-sided cervical lymphadenopathy, erythematous and edematous palms and soles, and erythema multiforme-like rash over his trunk. Appropriate lab tests and imaging were performed. Which of the following is the most worrisome complication of this boy's disease process?