Cardiomyopathies

Cardiomyopathies are diseases of the heart muscle. They may be genetic or acquired. Following types are seen as below:

I) Dilated cardiomyopathy: It is characterized by dilation of all four chambers of the heart. It is seen in viral infections such as Coxsackie B virus, viral hepatitis, HIV, alcohol, thiamine deficiency, drugs like cocaine, amphetamines, doxorubicin and daunorubicin, cobalt (high in beer), organic solvents “glue sniffers”, pregnancy, ischemic heart disease, post MI, hypertension, diabetes, thyroid disease, genetic or inherited factors. Inherited mutations in sarcomere proteins such as cardiac troponin T and I, beta myosin, alpha myosin, actin, dystrophin etc may be seen. Most cases are idiopathic. Decreased contractility from cardiomyopathy causes cardiac failure. On gross examination, the heart appears globular with dilation of all four chambers and microscopy shows hypertrophy of some fibres with atrophy of others. It presents with fatigue, dyspnea, orthopnea, tachypnea, tachycardia and heart failure. Examination shows displaced point of maximal impulse, murmurs from mitral and tricuspid regurgitation, S3 and S4, arrhythmias and narrow pulse pressure. Echo shows reduced ejection fraction.

II) Hypertrophic cardiomyopathy: It is a relatively common condition with an incidence of 1 in 500 individuals. It may be inherited as an autosomal dominant condition, resulting from mutations in genes coding for sarcomere proteins such as beta myosin (MYH7), myosin binding protein C (MYBPC3), troponin I and T. Most mutations are missense mutations or rarely, frameshift mutations. Acquired causes are long standing hypertension, aging, diabetes or thyroid disorders. There is asymmetric hypertrophy of the myocardium with septal hypertrophy more than ventricular wall. Septal hypertrophy may be limited to the apical septum in non-obstructive type or it may extend up to the mitral valve causing an obstructive hypertrophy with subaortic stenosis or HOCM. Increased stiffness of the left ventricle wall causes diastolic dysfunction. Intramural branches of coronary arteries may be mechanically obstructed causing relative ischemia.

Many patients will be asymptomatic; others will present with exertional dyspnea, exercise intolerance, orthopnea, edema, syncope, chest pain, palpitations and unfortunately, sudden cardiac death . Symptoms of heart failure with a high ejection fraction is the clue for diagnosis. Atrial fibrillation, ventricular tachycardia, ectopic beats and ventricular fibrillation can occur.

Examination will show displaced apical impulse, brisk pulses, S4, prominent “a” wave in JVP, harsh, midsystolic murmur. Mitral regurgitation may be present.

Factors affecting intensity of murmur in HOCM

Increase murmur intensity (increase LVOT)*

• Valsalva maneuver**
• Erect position
• Immediately after exercise
• Isoproterenol
• Amyl nitrite inhalation
• Sublingual nitroglycerine
• Digitalis

Decrease murmur intensity (decrease LVOT)

• Squatting
• Handgrip
• Reclining
• Beta blockers
• Increased preload

*LVOT is left ventricle outflow obstruction

**Valsalva maneuver consists of expiration against a close nose and mouth. It causes an increase in intrathoracic pressure, reduces venous return to the heart, increases afterload, increases total peripheral resistance and reduces cardiac output.

Echo shows asymmetric septal hypertrophy and systolic anterior motion of the mitral valve causing dynamic obstruction to (LV) left ventricular outflow (in obstructive type). Obstruction is dependent on the blood volume contained in the LV. Any factor that reduces the LV volume will increase LV outflow obstruction and vice versa. Elongation of the anterior or both leaflets of the mitral valve may be present. The left ventricle shows a normal end-diastolic volume, a high normal or elevated (more than 70%) ejection fraction and a reduced end-systolic volume. ECG will show nonspecific ST-T wave changes, left atrial hypertrophy, LVH, deep Q waves and arrhythmias. Endomyocardial biopsy is the gold standard for diagnosis. Microscopically, bundles of hypertrophied myocardial fibres are arranged in irregular bundles in a haphazard fashion with interstitial fibrosis.

Asymptomatic patients do not need treatment. Symptomatic patients are treated with beta blockers, disopyramide, verapamil/diltiazem, symptomatic treatment for heart failure and arrhythmias. ICD (implantable cardioverter defibrillator) should be inserted in those at high risk of sudden cardiac death. Surgical septal myectomy or alcohol induced septal ablation is recommended in patients with refractory heart failure with LV outlet obstruction.

III) Restrictive cardiomyopathy: The ventricle walls become stiff and rigid causing restriction to ventricular filling. It is seen in cardiac amyloidosis, endocardial fibroelastosis, endomyocardial fibrosis, after radiation exposure, sarcoidosis, Pompe’s disease, hemochromatosis, systemic sclerosis and open-heart surgery. The ventricular compliance is decreased resulting in diastolic dysfunction. Systolic function remains normal. Typically, the ventricular volume and wall thickness remain normal as there is no muscle hypertrophy, but infiltration as seen in Pompe’s disease or amyloidosis etc., can cause increased wall thickness. It presents with shortness of breath, fatigue, orthopnea, chest pain, palpitations and other signs of heart failure. Examination shows decreased pulse volume, raised JVP, edema, hepatomegaly, S3 (gallop rhythm), murmurs from MR and/or TR etc. S4 may or may not be present. Kussmaul’s sign is absent. ECG shows non-specific ST-T changes and is low voltage. Ejection fraction is normal as contractility is not affected.

Endocardial fibroelastosis is seen in infants and adults as a result of intrauterine endocardial anoxia or metabolic/ischemic/valvular disorders respectively. It is characterized by pearly-white thickening of the endocardium resulting from collagen and elastic tissue deposition. Endomyocardial fibrosis is characterized by fibrous scarring of the endocardium and adjacent myocardium. It is seen in Southeast Asia, South America and Africa.

IV) Takotsubo cardiomyopathy or broken heart syndrome: It is characterized by transient left ventricular dysfunction in the absence of coronary disease, myocarditis or other known factors like valvular diseases. It is classically seen in post-menopausal women after sudden, unexpected emotional or physical stress. Echo shows transient hypokinesis or dyskinesis of the left ventricle with regional wall motion abnormalities and ballooning of the left ventricle; ECG shows ST elevation and T wave inversion in many cases; CK-MB and Troponin T are slightly elevated . Angiography is normal. Serum catecholamines and BNP are elevated. It clinically presents similar to acute coronary syndrome. Histopathology shows contraction bands. Coronary microcirculation is compromised in most patients.