Disguised Dip: An Unusual Atrial Signature on ECG

A 27-year-old man presented with dyspnea (New York Heart Association class III), occasional palpitations, and progressive ankle swelling.On examination, his heart rate was 106 bpm.and blood pressure was 106/70 mm Hg.He exhibited elevated jugular venous pressure with prominent C and V waves, bilateral pitting pedal edema, and a parasternal heave.Auscultation revealed a pansystolic murmur at the left parasternal area and an early diastolic murmur at the left third intercostal space.A 12-lead ECG (Figure 1) was obtained.What is the most probable diagnosis based on the ECG, and what is the underlying mechanism?Please turn the page to read the diagnosis.