A 51-year-old man has the sudden onset of substernal chest pain which radiates to his left arm and neck. He becomes light-headed and diaphoretic over the next 8 hours. He goes to the emergency room. On examination he is afebrile but has a heart rate of 96/minute with an irregular rhythm. Laboratory studies show an increased serum troponin I. Which of the following features would be most prominent by histopathologic examination of his myocardium at this point in time?