Differential Diagnosis

The patient's presentation of a sudden syncopal attack and an ejection systolic murmur that becomes louder with Valsalva and standing, but decreases with squatting and hand grip, suggests a condition affecting the heart's outflow tract. The family history of sudden death further narrows the differential diagnosis.

• Single Most Likely Diagnosis

  • HOCM (Hypertrophic Obstructive Cardiomyopathy): This condition is characterized by an asymmetrically hypertrophied left ventricle, which can cause obstruction of the left ventricular outflow tract (LVOT). The murmur of HOCM is typically an ejection systolic murmur that increases with maneuvers that decrease ventricular volume (such as Valsalva or standing) and decreases with maneuvers that increase ventricular volume (such as squatting or hand grip). The family history of sudden death is also consistent with HOCM, as it is a leading cause of sudden cardiac death in young athletes.

• Other Likely Diagnoses

  • Aortic Stenosis: While aortic stenosis can present with an ejection systolic murmur, it typically does not vary with Valsalva or changes in posture to the same extent as HOCM. However, it remains a consideration, especially in the context of a systolic murmur.
  • Other forms of cardiomyopathy: Though less likely, other cardiomyopathies could potentially present with similar symptoms, especially if there is significant outflow tract obstruction.

• Do Not Miss Diagnoses

  • Aortic Dissection: Although less likely given the chronic nature of the symptoms and the specific murmur characteristics, aortic dissection can present with a sudden onset of symptoms, including syncope, and must be considered due to its high mortality rate if missed.
  • Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): This condition can lead to sudden cardiac death, often precipitated by exercise or stress, and should be considered in the differential, especially with a family history of sudden death.

• Rare Diagnoses

  • Congenital Heart Diseases with Left Ventricular Outflow Tract Obstruction: Conditions like subaortic stenosis or supravalvular aortic stenosis are rare but could present with similar symptoms.
  • Other rare cardiomyopathies: Such as restrictive cardiomyopathy or arrhythmogenic left ventricular cardiomyopathy, which might present with less typical features but could be considered in the differential diagnosis based on the clinical presentation and further diagnostic workup.