Cardiomyopathies & Myocarditis
Cardiomyopathy is defined as a structural or functional abnormality of the myocardium that is not secondary to structural heart disease, hypertension, or pulmonary vascular disease. Cardiomyopathies are usually classified as follows:
- Dilated cardiomyopathy (DCM) - in which the left ventricle is dilated and has poor systolic function.
- Hypertrophic obstructive cardiomyopathy (HOCM) - also known as idiopathic hypertrophic sub aortic stenosis. HOCM is characterized by ventricular hypertrophy (usually asymmetric) with normal systolic function but abnormal diastolic function.
- Restrictive cardiomyopathy - which is characterized by primary diastolic dysfunction, normal ventricular size and dilated atria.
This is the most common cause of cardiomyopathy in children. It may be secondary to myocarditis, coronary artery disease, and many other conditions. In familial cases, an autosomal dominant transmission is the most frequent pattern of inheritance. Autosomal recessive, X-linked and mitochondrial inheritance have also been described.
The heart in dilated cardiomyopathy is globular and is grossly dilated. The myocardium is pale and mottled and the endocardium is thin. Histologically, there is myocyte hypertrophy and degeneration and interstitial fibrosis as compared to myocarditis, in which there is myocyte necrosis and lymphocytic infiltration.
Systolic dysfunction is manifested by decreased shortening and ejection fractions which leads to increased end-diastolic volume and pressure. The blood flow to kidneys is diminished with resultant salt and water retention and worsening of CHF. Myocardial fibrosis may lead to ventricular arrhythmias secondary to the development of reentry circuits in the ventricles.
CHF signs and symptoms develop as the cardiac output decreases. These include decreased exercise tolerance and dyspnea with exertion. Infants present with poor feeding, diaphoresis during feeding, and failure to thrive. Palpitation and syncope are sometimes the earliest presentation of DCM.
Making the diagnosis
- The condition needs to be differentiated from acute myocarditis (see below).
- The patient usually has tachycardia and tachypnea. The skin may be pale and cold. The peripheral pulses are weak and the blood pressure is in the low normal range with a narrow pulse pressure.
- Breath sounds may be diminished with rales and signs of respiratory distress. Cardiac examination reveals muffled heart sounds, gallop rhythm and possibly mitral regurgitation murmur. Hepatomegaly and other signs of venous congestion may be present.
- Chest radiograph reveals dilatation of the left ventricle and atrium. Pulmonary edema and pleural effusion may be seen.
- There may be atelectasis of the left lower lobe from compression of the left main bronchus by the dilated LA. The EKG shows nonspecific-T change as evidence of ventricular hypertrophy and atrial enlargement.
- Atrial and ventricular arrhythmias are common.
- Echocardiography shows decreased shortening fraction (the percentage of decrease in LV dimensions between diastole and systole. The origin of the coronary arteries should be delineated to rule out coronary anomalies. Pericardial effusion may be present. Cardiac catheterization and myocardial biopsy are useful in confirming the diagnosis and evaluating the patient for potential cardiac transplantation. myocardial biopsy are useful in confirming the diagnosis and evaluating the patient for potential cardiac transplantation.
- Urine examination for organic acids is important to exclude metabolic disorders. Blood studies should also be obtained for abnormalities in lactate, calcium, magnesium, carnitine, pyruvate, BUN and serum electrolytes. Molecular genetic analysis for dystrophin mutations could be diagnostic in some cases.
If cardiac decompensation is present, intravenous inotropic agents such as dobutamine and dopamine (in renal doses) may be useful. Amrinone and milrinone also have positive inotropic effect and also reduce the afterload. When the patient is clinically stable, oral digoxin, ACE inhibitors and B-blockers (carvedilol) may be started. Diuretic therapy is useful for removing excess fluid. Patients with acute and severe decompensation may require ventricular assist devices or extracorporeal membrane oxygenation. Heart transplantation may be considered if all other measures fail.