TOPIC16: hypertrophic cardiomyopathy

Question 1

what is Hypertrophic cardiomyopathy? How does it manifest?

Answer 1

• myocardial hypertrophy
• abnormal DIASTOLIC filling (myocardium doesn’t relax)
• ventricular outflow OBSTRUCTION
• characterised by maladaptive LVH inappropriate for the degree of afterload (hallmark of HCM is LVH)
• prevalance is 1-2:500

-the hypertrophy is classically localised to the proximal interventricular spetum, resulting in a dynamic obstruction.

• manifestation as:
  1. hyperdynamic systolic function
  2. LVOT obstruction due to systolic anterior motion (SAM) of anterior mitral valve leaflet

3. impaired myocardial relax.
4. raised filling pressure
5. myocardial ischemia
6. propensity to SVT & VT/VF

Question 2

etiology of HCM

Answer 2

• genetic defect of the myocardial sacromere proteins ( beta-myosin in heavy chain, cardiac troponin T & I , myosin light chain, myosin binding protein etc) causing myofibril disarray, myocardial fibrosis & myocardial hypertrophy)
• most common form is a AD inherited cardiac condition

Question 3

Diagnosis

Answer 3

1. Medical history
   - pts often asymptomatic so can be identified through family screening
2. Physical examination:
   - forceful apical impulse due to LVH
   - S4 heart sound due to pressure overload

• double apical pulse due to outflow tract obstruction
• possible mid-systolic ejection murmur
• pansystolic murmur due to mitral regurg resulting from the SAM of the mitral valve
• fatigue, breathlessness (diastolic filling impaired)
• angina (due to increased work after LVH)
• palpitations.

–> APPROX 5% of pts may develop progressive left ventricular dilation and failure due to ongoing myocardial fibrosis and chronic small vessel ischemia.

3.ECG:
-LVH
-deep Q waves in the inferior and lateral leads due to septal hypertrophy
-ventricular ectopic beats
ARRYTHMIAS CAN CAUSE SUDDEN DEATH!
hypertrophic cmp is a common cause of sudden death in young atheletes.

4. Echo:
   - confirms diagnosis
   - estimates chamber size and wall thickness
   - demonstrates outflow tract and intracavitary gradients
   - shows valvular impairment with regurgitation

CO: decreased since the left ventricular hypertrophy leads to diastolic dysfunction, so if the ventricle cannot fill, it cannot pass the needed amount of blood.

5. Cardiac MRI
6. perform exercise test because syncope during exercise can occur- the subaortic hypertrophy of the ventricular septum (proximal septum hypertrophy) can lead to functional aortic stenosis.
7. Biopsy can show myofiber hypertrophy with disarray (disoriented and tangles myofibers)
8. Holter monitoring
9. genetic testing- screening for family members

Question 4

treatment of HCM

Answer 4

1. Medical:
   - beta blockers (Sotalol)
   - calcium channel antagonists (if beta blockers not tolerated)
   - other antiarrythmics (amiodarone)
2. non pharmacological:
   - surgical septal myotomy-myectomy (Morrow procedure)
   - alcohol septal ablation- chemical infarction of the proximal portion of the IV septum by injection of alcohol into the 1st or 2nd septal perforator arteries
   - ICD
   - dual chamber pacing

Question 5

LVOT obstruction mechanism

Answer 5

Occurs as a consequence of forward motion of the anterior mitral leaflet towards the hypertrophied proximal interventricular septum in systole.

• two mechanisms:
  1. anterior displacement of papillary muscles
  2. ‘venturi effect’ caused by rapid ejection of blood across a narrow LVOT which sucks the anterior mitral valve leaflet against the septum