Idiopathic dilated cardiomyopathy
Idiopathic dilated cardiomyopathy is a form of dilated cardiomyopathy with unknown etiology characterised by progressive left ventricular dilatation and systolic dysfunction. Pathologically, there is increase in the size and weight of the heart. There is ventricular dilatation with near normal wall thickness. The myocardial systolic dysfunction out of portion to the fibrosis.
Incidence and prognosis of idiopathic dilated cardiomyopathy
The incidence of idiopathic dilated cardiomyopathy varies from 3-10 cases per 100,000 population. Death from progressive pump failure occurs at the rate of about 25% in first year, 35-40% in two years and upto 40-80% over five years. Stabilization may occur in about 20% of cases, but complete recovery is rare in idiopathic dilated cardiomyopathy.
Prognosis varies depending on the type of dilated cardiomyopathy with peripartum cardiomyopathy having best prognosis and HIV associated cardiomyopathy the worst. Idiopathic dilated cardiomyopathy, cardiomyopathy due to doxorubicin cardiotoxicity and those due to infiltrative myocardial disease have an intermediate prognosis.
Investigations and management of dilated cardiomyopathy
Chest X-ray PA view will assess the cardiac size in dilated cardiomyopathy and show evidence of pulmonary congestion. Sick persons may present with features of frank pulmonary edema in the form of hilar haze or bat wing pattern of pulmonary edema. Significant left ventricular dysfunction can exist without much of cardiomegaly on chest X-ray as well.
ECG may show sinus tachycardia, left atrial overload and sometimes left ventricular hypertrophy. A wide QRS complex with left bundle branch block pattern may indicate potential benefit from cardiac resynchronization therapy (CRT). ECG is more useful in suggesting diseases which have to be considered in the differential diagnosis like coronary artery disease and severe aortic stenosis. Severe aortic stenosis with heart failure may not have an audible murmur due to the low output state. The murmur may reappear on treatment of heart failure. In aortic stenosis, unlike in aortic regurgitation, severe left ventricular failure need not proscribe surgical options.
Holter monitoring is useful in identifying ventricular arrhythmias which will alter the prognosis, especially sustained ventricular tachycardia. Holter monitoring is indicated in those with history of palpitation, syncope and near syncope.
Echocardiogram is the mainstay for the diagnosis of dilated cardiomyopathy and exclusion of other conditions. Though global hypokinesia of the left ventricle is the hall mark of dilated cardiomyopathy, some regional wall motion abnormalities may not negate the diagnosis of dilated cardiomyopathy.
Coronary angiography is considered in those with age > 40 years and a history suggestive of coronary artery disease or having a high coronary risk profile or an abnormal ECG.
Management of dilated cardiomyopathy
Limitation of activity based on functional status is recommended. Salt and fluid restriction is needed in those with systemic or pulmonary congestion. Medical therapy consists of Angiotensin converting enzyme (ACE) inhibitors, diuretics, digoxin and carvedilol. Hydralazine / nitrate combination can be used as a vasodilator when ACE inhibitors are not tolerated. Another alternative is angiotension receptor blocker (ARB).
Anticoagulation is recommended if the ejection fraction (EF) is <30%, when there is a history of thromboemolism and in the presence of mural thrombi. A thrombus is dilated cardiomyopathy has a higher chance for embolisation than in coronary artery disease. In coronary artery disease, the thrombus is kept away from the blood stream by a segment of myocardium which is poorly contracting while the rest of the myocardium contracts well. In dilated cardiomyopathy since the hypokinesia is global, the thrombus is within the region of the blood flow and has a higher chance for breaking off and embolising. Dopamine, dobutamine and phospho diesterase (PDE) inhibitors like amrinone and milrinone may be used to tide over a crisis in acute decompensated heart failure with dilated cardiomyopathy. Cardiac resynchronization therapy (CRT) is useful in those with dyssynchrony as evidenced by wide QRS complex and left bundle branch block pattern on ECG. Cardiac transplantation is of course the last option for refractory heart failure in dilated cardiomyopathy.
Cardiomegaly on CXR in dilated cardiomyopathy
Cardiomegaly on CXR in dilated cardiomyopathy
Cardiomegaly on chest X-ray (CXR) PA view in dilated cardiomyopathy. The cardiothoracic ratio is increased and there is a bulge along the left border, suggesting aneurysmal dilatation of the left ventricle. This pattern could be due to ischemic variety of dilated cardiomyopathy, sometimes called ischemic cardiomyopathy or ischemic dilated cardiomyopathy. The right border is also shifted to the right, indicating right atrial enlargement. Superior venacaval shadow is seen upwards from the right atrial contour, indicating congested superior vena cava. The shadow has also a superficial semblance to the egg on side appearance, though this is not a case of transposition of great arteries.
Familial dilated cardiomyopathy
Familial dilated cardiomyopathy constitutes about 30% of idiopathic dilated cardiomyopathy. Inheritance patterns vary from autosomal dominant / recessive to X-linked and mitochondrial inheritance patterns. In some families, there may be associated conduction system disease of varying severity.