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Hypertrophic Obstructive Cardiomyopathy

-genetic dz characterized by marked left ventricular hypertrophy in the absence of chronic pressure overload (HTN or aortic stenosis). The hypertrophy specifically involves the interventricular septum and left ventricular outflow tract.

Epidemiology
– most common cause of sudden cardiac death in young athletes in the US
-occurrence rate of 1 in 500
– most common (Mendelian) genetic heart disease
-Presents after puberty (average age in mid-20s)

Pathogenesis
-genetic abnl in muscle cell proteins
-autosomal dominance with variable penetrance. Most genes for sarcomere proteins (B-myosin heavy chain and myosin binding protein C most common)
-mutations cause myofibril disarray and heart muscles do not contract properly. This results in compensation and the left ventricle to hypertrophy with the interventricular septum becoming asymmetrically enlarged
-hypertrophy of the inventricular septum leads to two major problems
1. decreased ability for the heart to fill during diastole causing diastolic heart failure
2. Intermittent outflow obstruction.  Hypertrophy of the interventricular septum causes narrowing of the left ventricle outflow tract. Ejection of blood through a narrowed outlet causes a Venturi effect, where Venturi forces pull the anterior mitral leaflet towards the septum during systole causing obstruction. This is called systolic anterior movement of the mitral valve (SAM). The amount of obstruction depends on the amount of left ventricular filling. During periods of increased exercise, the heart rate is faster leading to a shorter diastolic period. Since there is less time to fill the left ventricle, the outflow tract becomes narrower, causing more obstruction. However, if the heart is slower, this allows more time for the left ventricle to fill in diastole, which widens the outflow tract and causes less obstruction.

Signs and symptoms
-Most patients have few or no symptoms
-Symptoms include:
-dyspnea – due to diastolic dysftn and fluid backing up into the lungs.
-angina – due to increased myocardial oxygen demand from thickened wall, than supply of oxygen
-orthopnea/paroxysmal nocturnal dyspnea – impaired diastolic function
-dizziness – due to  outflow tract obstruction and decreased blood flow to the brain
-palpitations – due to fibrosis and myofibrillar disarray – causing ventricular arrhythmias: premature atrial contractions, premature ventricular contractions, a-fib, a-flutter, SVTs, and v-tach.
-syncope/sudden death – ventricular arrhythmias that are caused by fibrosis and myofibrillar disarray

Physical Exam
-systolic crescendo-decrescendo ejection murmur along lower left sternal border or apex that increases with decreased preload (valsalva or standing up), and decreases with an increased preload (squatting) or increased afterload (clenched fist)

Routine tests
– labs: elevated BNP
-CXR – cardiac silhouette ranges from normal to markedly increased. Left atrial enlargement can be observed when significant mitral regurgitation is present.
-EKG – LVH, left atrial abnormality, and left axis deviation. You may also see WPW with certain mutations, deep and broad Q waves in inferior and precordial lateral leads (likely related to gross septal hypertrophy rather than MI) and TY wave changes

Special tests
-Echocardiogram will show an increased septum: LV wall thickness ratio ( >1.5:1)
-Cardiac MRI: especially useful when echo is questionable
-Cardiac cath: most accurate test to  determine precise gradients of pressure acrossoutflow tract

Confirmatory tests
-Genetic testing
-Cardiac muscle biopsy: will show myofibril disarray

Treatment:

Asymptomatic patients

o    A significant number of patients will not have any symptoms and will have a normal life expectancy. However, these patients should still be counseled to avoid particularly strenuous activities and medications that decrease preload such as nitrates or diuretic blood pressure medications.

2) Medications
-Medications are used to relieve symptoms: palpitations, dyspnea, angina, syncope

·         Beta blockers are considered first-line agents, as they can slow down the heart rate and allow for increased diastolic filling and decreased myocardial oxygen consumption. This reduces obstruction in outflow tract and ischemia respectively.

·         Non-dihydropyridine calcium channel blockers such as verapamil and diltiazam can also be used.

·         Disopyramide: decreases contractility and SVT arrhythmias.

·         Amiodarone: the only agent proven to reduce the incidence and risk of cardiac sudden death. Very effective at converting atrial fibrillation and atrial flutter to sinus rhythm.

3) Surgical myomectomy

·         For patients who remain severely symptomatic despite medical therapy and/or with an outflow gradient of more than 50 mm Hg.

·         Involves removing a portion of the inter ventricular septum to widen the outflow tract.

·         Complications include possible death, arrhythmias, infection, incessant bleeding, septal perforation/defect, and stroke.

4) Alcohol septal ablation

·         Involves injection of alcohol into one or more septal branches of LAD.

·         The ablation is a “controlled heart attack” in which the part of the septum involved with the outflow tract is infarcted and subsequently contracts into a scar.

·         Less invasive but produces similar results to septal myomectomy.

5) Ventricular pacing

·         Pacemaker activates the inter ventricular septum before the ventricular free wall. This decreases the gradient across outflow tract.

·         Will also help treat arrhythmias.

·         Indications: 1) family history of sudden death 2) wall thickness > 30 mm. 3) unexplained syncope 4) history of ventricular arrhythmias

6) Cardiac transplant

·         For cases refractory to all treatments.

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