An 89 yeаr оld mаn with HTN аnd DM2 presents tо the ED after suffering a syncоpal episode at home. He reports that he has had progressively worsening dyspnea, particularly marked with exertion, as well as intermittent chest pressure over the past several months. He stood to walk to his bathroom today and had a brief episode of light-headedness prior to losing consciousness and falling to the ground. His wife was home and called EMS who brought him to the ED. On auscultation you note that the patient has a systolic ejection murmur and ECG is notable for increased amplitude of the R wave in V5 and absent Q-waves. Which diagnosis most likely to make given this patient's presentation?