A 62-year-old woman is reviewed three months after a large anterior myocardial infarction. She has mild exertional breathlessness but no recurrent chest pain; the ECG continues to show ST-segment elevation in the anterior leads. Echocardiography demonstrates a thin, scarred apical region that bulges outwards during systole, with no flow through the wall and no intracardiac mass. Which one of the following is the most likely diagnosis?