Hypertrophic Cardiomyopathy: Asymmetric Septal Hypertrophy

History: 45 year-old female with an abnormal EKG and echocardiography was referred for evaluation of cardiac structure and function. She gave no history of palpitations, dizziness or syncope. Her father died suddenly due to a cardiac cause.

Technique: Short and long axis FIESTA images were obtained for evaluation of cardiac morphology and function. Myocardial delayed enhancement images were acquired to look for any myocardial fibrosis.

Findings: The maximum end-diastolic wall thickness measured at the anteroseptum is 27 mm consitent with severe left ventricular hypertrophy (Figure 1). The phase contrast images obtained perpendicular to left ventricle outflow tract did not reveal outflow tract obstruction (not shown here). The myocardial delayed enhancement images demonstrated a focal fibrosis anteroseptally at the point of right ventricular insertion site (Figure 2). This pattern of fibrosis has been described in the literature previously and is most likely consistent with fibrosis secondary to shear-stress effect.

Comment: Hypertrophic cardiomyopathy (HCM) refers to abnormal thickening of the left ventricle that is not secondary to a known condition (such as AS or HTN).  The myocardial hypertrophy can be focal or diffuse.  Patients with HCM can be subdivided based on the appearance of the left ventricle. There are a number of subtypes including: 1) asymmetric septal hypertrophy, 2) concentric hypertrophy, 3) apical hypertrophy (oriental variant), and 4) mid-cavity obstruction. In some cases, hypertrophy of the septum causes obstruction in the left ventricular outflow tract.

HCM is a common endpoint for a diverse group of mutations in genes that encode for structural proteins in the heart.  Patients with HCM can be asymptomatic, can present with arrhythmias, dizziness, syncope, heart failure or sudden death.

Patients with obstructive physiology can be treated medically with beta blockers or calcium channel blockers to relieve the obstruction. If the medical therapy proves insufficient to control symptoms, these patients are candidates for surgical myectomy for relief of the obstruction. An alternative to surgery is the alcohol septal ablation technique. Patients with high risk factors for sudden cardiac death are considered for prophylactic defibrillator placement.

Major risk factors for sudden death include:

  1. Cardiac arrest (ventricular fibrillation)
  2. Spontaneous sustained ventricular tachycardia
  3. Family history of sudden death
  4. Unexplained syncope
  5. Left ventricular wall thickness >30mm
  6. Abnormal blood pressure on exercise
  7. Nonsustained ventricular tachycardia

Minor risk factors for sudden death:

  1. Atrial fibrillation
  2. Myocardial ischemia
  3. LV outflow obstruction
  4. High-risk mutation
  5. Intense (competetive) physical exertion

 

References:

  1. ACC/ESC Expert Consensus Document on Hypertrophic Cardiomyopathy. JACC Vol.42, No 9, 2003
  2. Nishimura RA, Holmes DR. Hypertrophic obstructive cardiomyopathy. N Engl J Med. 2004;350:1320-7