Medical management includes prostaglandin E1 to open the ductus arteriosus, correction of acidosis, and ventilatory and blood pressure support as needed. Surgical repair is stagedwith the first surgery (Norwood procedure) done in the newborn period. Subsequent procedures create a systemic source for the pulmonary circulation (bidirectional Glenn and Fontan procedures), leaving the right ventricle to supply systemic circulation. There have been many modifications to all three stages of the repair. Prognosis for survival has improved significantly over the past two decades.
Extracardiac complications are summarized in Table 144-2.
The force generated by the cardiac muscle fiber depends onits contractile status and basal length, which is equivalent to the preload. As the preload (fiber length, left ventricular filling pressure, or volume) increases, myocardial performance(stroke volume and wall tension) increases up to a point (thenormal Starling curve). The relationship is the ventricular function curve (Fig. 145-1). Alterations in the contractilestate of the muscle lower the relative position of the curve,but retain the relationship of fiber length to muscle work.Heart rate is another important determinant of cardiac work because the cardiac output equals stroke volume times theheart rate. Additional factors also affect cardiac performance(Table 145-1).
Heart failure occurs when the heart is unable to pump blood at a rate commensurate with metabolic needs (oxygen delivery). It may be due to a change in myocardial contractility that results in low cardiac output or to abnormal loading conditions being placed on the myocardium. The abnormal loading conditions may be afterload (pressure overload, such as with aortic stenosis, pulmonary stenosis, or coarctation of the aorta) or preload (volume overload, such as in ventricular septal defect (VSD), patent ductus arteriosus (PDA), or valvular insufficiency. Volume overload is the most common cause of heart failure in children.
The age of presentation is helpful in creating the differential diagnosis (Table 145-2). In the first weeks of life, excessive afterload being placed on the myocardium is most common. Heart failure presenting around 2 months of age is usually due to increasing left-to-right shunts that become apparent as the pulmonary vascular resistance decreases. Acquired heart disease, such as myocarditis and cardiomyopathy, can present at any age.
Total blood volume Venous tone (sympathetic tone) Body position Intrathoracic and intrapericardial pressure Atrial contraction Pumping action of skeletal muscle
Peripheral vascular resistance Left ventricular volume (preload, wall tension) Physical characteristics of the arterial tree (elasticity of vessels or presence of outflow obstruction)
Sympathetic nerve impulses* Circulating catecholamines* Digitalis, calcium, other inotropic agents* Increased heart rate or postextrasystolic augmentation* Anoxia, acidosis† Pharmacologic depression† Loss of myocardium† Intrinsic depression†
Autonomic nervous system Temperature, metabolic rate
From Andreoli TE, Carpenter CCJ, Griggs RC, Loscalzo J: Cecil Essentials of Medicine, ed 5, Philadelphia, 2001, Saunders.
*Increases contractility.
†Decreases contractility.
Severe anemia (hemolysis, fetal-maternal transfusion, hypoplastic anemia) Supraventricular tachycardia Ventricular tachycardia Complete heart block Atrioventricular valve insufficiency High-output cardiac failure (arteriovenous malformation, teratoma)
Asphyxial cardiomyopathy Arteriovenous malformation (vein of Galen, hepatic) Left-sided obstructive lesions (coarctation of aorta, hypoplastic left heart, critical aortic stenosis) Transposition of great arteries Large mixing cardiac defects (single ventricle, truncus arteriosus) Viral myocarditis Anemia Supraventricular tachycardia Complete heart block