Address for correspondence : Bibhuti B Das, MD, Division of Pediatric Cardiology, Suite # 334, University of Louisville, Louisville, KY 40202, USA.E-mail: bdas99@hotmail.com

Pathophysiology :

Heart failure may be defined as that pathophysiological state in which an abnormality of cardiac function is responsible for the failure of the heart to pump blood at a rate commensurate with the metabolic requirements of the body. (12) The heart may fail if it is confronted with: (1) a n excessive preload, i.e. increase in tension in ventricular cardiac muscle fibers leading to excessive expansion of ventricles in diastole as seen in left to right shunt, mitral regurgitation and complete heart block; (2) abnormally high afterload as in hypertension, coarctation of the aorta and aortic stenosis; (3) impaired myocardial contractility as in myopathy, myocarditis; and (4) inadequate diastolic filling as in hypertrophic or restrictive cardiomyopathy, constrictive pericarditis and tachyarrhythmias. Chronic heart failure is a clinical syndrome in which heart disease reduces cardiac output, increases venous pressures, and is accompanied by molecular abnormalities that cause progressive deterioration of the failing heart and premature death of myocardial cells. (13)

At the onset of heart failure various compensatory mechanisms with salutary effects come into play. But the same compensatory mechanisms if pressed into play indefinitely potentiate heart failure , the possible mechanisms of which are described below.

Clinical manifestations :

Heart failure is a clinical syndrome consisting of signs and symptoms that arise from congested organs and hypo-perfused tissues. Impaired myocardial function results in cardiomegaly, tachycardia, gallop rhythm, poor peripheral perfusion and growth retardation. Cardiomegaly occurs in most patients with heart failure except in pulmonary venous obstruction and constrictive pericarditis. A sleeping heart rate above 160 per minute in infants and above 100 per minute in children is usually present in heart failure . A protodiastolic gallop at the time of rapid ventricular filling is a sign of impaired ventricular function. Poor peripheral perfusion manifests itself by cold extremities, weak pulses and low blood pressure associated with skin mottling. Growth retardation is noted in infants with chronic heart failure . Dyspnea and tachypnea are the typical signs of increased pulmonary venous pressure. Respiratory rates may be as high as 80-100 per minute and are associated with retraction, grunting and poor feeding. Wheezing may be the earliest and occasionally the only evidence of pulmonary edema. Rales are relatively uncommon sign of pulmonary edema in the pediatric age group. Cyanosis , in the absence of intracardiac right to left shunt, may be present and is secondary to impaired pulmonary gas exchange as well as due to sluggish peripheral circulation. Signs of systemic venous congestion include hepatomegaly and peripheral edema. Exercise intolerance is an important feature of heart failure in older children and young adults.

Laboratory studies :

It is to be remembered that heart failure is a clinical syndrome and for the most part is not associated with a diagnostic laboratory test. The chest radiograph shows cardiomegaly and increased pulmonary vascular markings. Electrocardiograph is not helpful in the diagnosis of heart failure except when secondary to tachyarrhythmias, heart block or myocardial ischaemia.

Serum brain type natriuretic peptide is a relatively new biochemical marker which has proven to be very useful in the diagnosis of heart failure , especially in patients with acute dyspnea In such a setting, brain type natriuretic peptide levels more than 500 picogram per milliliter have a 90% predictive value for the presence of heart failure and levels less than 100 picogram per milliliter have a 90% predictive value for the absence of heart failure . Brain type natriuretic peptide levels between 100 and 500 picogram per milliliter are somewhat less helpful, and other tests may be needed for diagnosis . (19) Serum brain type natriuretic peptide level in heart failure patients helps to guide and monitor therapy, detects preclinical disease, and possibly reduces the need for cardiac imaging.

Echocardiography is perhaps the most useful test in understanding the mechanism and cause of heart failure in children and young adults. Decreased shortening fraction and ejection fraction, and low velocity of circumferential fibre shortening are direct evidence of left ventricle systolic dysfunction. Doppler-derived indices that are useful in the evaluation of heart failure include change in left ventricular systolic pressure, stress-velocity index and strain rate imaging. Assessment of left ventricle diastolic function include spectral Doppler imaging of the mitral inflow, pulmonary venous Doppler, tissue Doppler imaging and flow propagation velocities by Color M-mode echocardiography. (20) Myocardial performance index (Tei index) is a new echocardiographic parameter in global assessment of left or right ventricular function, although the value of Tei index is age dependent. In children, the normal Tei Index values for left ventricle and right ventricle are reported to be 0.35 plus or minus 0.03 and 0.32 plus or minus 0.03 respectively. (21)

Metabolic exercise testing allows determination of peak oxygen consumption, anaerobic threshold, oxygen pulse, and ventilatory equivalent for carbon dioxide, which are useful to quantitate cardiovascular functional capacity. (22) Cardiac catheterization is sometimes performed in patients with heart failure unresponsiveness to conventional treatment to confirm the diagnosis and to help guide the therapy. Endomyocardial biopsy is useful in establishing the etiology of heart failure in patients with history of systemic diseases such as collagen vascular disease, infiltrative or storage disease, giant cell myocarditis and with rapidly progressive heart failure despite conventional therapy. (23)