AKT-0250
A 45-year-old woman presents to her General Practitioner with a 3-month history of progressive exercise intolerance. Four weeks ago, she experienced an episode suggestive of paroxysmal nocturnal dyspnoea. Examination reveals a jugular venous pressure (JVP) raised up to her earlobes, soft, tender hepatomegaly and bilateral pitting oedema up to her ankles. Chest examination reveals bibasal crepitations and an audible S3 on auscultation of the heart. The chest X-ray shows cardiomegaly with interstitial infiltrates. Echocardiography shows global left ventricular hypokinesia with an ejection fraction of 20–25%. She has no other significant medical history.
Which of the following is the most likely underlying causal factor in this patient?