This is not the most likely diagnosis because the patient's symptoms and echocardiogram findings have been present for a long period, indicating a chronic process rather than acute events such as a myocardial infarction.

Although this condition can also lead to heart failure, it is typically due to systolic dysfunction rather than diastolic dysfunction and is not typically associated with increased left ventricular thickness.

This condition is characterized by rigid ventricular walls, causing diastolic dysfunction. However, it doesn't cause increased left ventricular thickness seen in this patient.

This patient's symptoms, physical exam findings, and echocardiogram are indicative of heart failure due to left ventricular hypertrophy, likely secondary to longstanding hypertension (also known as hypertensive heart disease). This is due to long-term volume overload caused by increased afterload, resulting in thickening of the heart muscle and decreasing compliance, leading to diastolic dysfunction and eventually heart failure.