Clinical Indications for Medical or Surgical Intervention

The interdisciplinary approach that is needed clinically to optimally care for children with congenital heart disease includes accurate assessment of anatomic defects and their physiologic consequences and effective communication of these findings. Management of congenital heart disease revolves around manipulating abnormal pulmonary and systemic blood flows. The consequences of altered blood flow induced by congenital heart disease and the effects of therapeutic interventions invariably influence the pulmonary circulation by increasing pulmonary blood flow (e.g., left-to-right shunting through intracardiac septal defects), decreasing pulmonary blood flow (e.g., right-sided obstructive heart lesions, such as tetralogy of Fallot) (Fig. 50-3), altering the pathway of pulmonary blood flow (e.g., Fontan-Kreutzer repair), or altering the hemodynamics to which pulmonary blood flow (e.g., pulmonary hypertension) is subjected. The clinician must be able to manage such conditions in which there is increased pulmonary blood flow or a paucity of pulmonary blood flow and the associated repercussions as to how they relate to the systemic circulation. Obtaining the optimal balance between these two circulations, which are frequently not in series in the case of congenital heart disease, requires the ability to monitor pulmonary hemodynamics and assess pulmonary vascular impairment successfully. Critically important to an understanding of the physiologic consequences of these defects are the maturational differences that occur in cardiopulmonary function during a child’s development. For example, cardiac function is subject to maturational changes occurring at the cellular level in a variety of processes, including those in the neurocardiac functional unit: changes in neurotransmitter content, the receptor system, innervation, the effector-transducer systems, and the cellular components that are affected by autonomic stimulation (Fig. 50-4). These changes affect the strategies that can be utilized to successfully manage the sequelae of congenital heart disease.

Figure 50-3 Tetralogy of Fallot.

a, artery.

Figure 50-4 Innervation of heart: Schema.

A second approach to children with suspected congenital heart disease is based on risk stratification. Regardless of the anatomic defects, the physiologic consequences necessitating medical intervention, surgical intervention, or both, fall into three broad categories: heart failure, hypoxemia-hypoxia, and risk of pulmonary vascular disease. Stratifying these risks is useful in predicting prognosis and for therapeutic decision making.

Heart failure is defined as the inability of the heart to supply an adequate cardiac output to meet the aerobic metabolic demands of the body, including those incurred by growth. An alteration in one or more physiologic determinants of ventricular function—preload, afterload, contractility, and heart rate or rhythm—can adversely affect cardiac performance beyond the compensatory mechanisms, particularly in fetuses or newborn infants, where cardiac function occurs much higher (and hence less efficiently) on the Frank-Starling curve because of maturational aspects. As a physiologic consequence, fetuses and infants are more dependent on mechanisms that increase heart rate rather than those that increase stroke volume to increase cardiac output in response to increased metabolic demands. Heart failure occurs in patients with significant left-to-right shunts. By increasing pulmonary blood flow, tachypnea ensues. Concomitantly, a decrease in systemic blood flow results, albeit undetectable by conventional physical examination or blood pressure measurements. Nonetheless, this decrease is sufficient to stimulate the sympathetic nervous system, resulting in an increase in heart rate. Infants with congestive heart failure due to congenital heart disease will invariably be tachypneic and tachycardic without a loss in ventricular function. However, these increases in respiratory and heart rates both increase the body’s metabolic needs. An increased amount of energy, and thus a disproportionate proportion of the energy from caloric intake, is required to maintain these basic metabolic needs, and failure to thrive results. The etiology of hypoxemia (abnormal reduction in the arterial oxygen tension) must be established to determine whether therapeutic intervention is necessary immediately. Hypoxia (inadequate tissue perfusion) is always a medical emergency, because high morbidity and mortality are associated with uncorrected metabolic acidosis. Hypoxemia is most often associated with defects characterized by right-to-left intracardiac shunting in which effective pulmonary blood flow is reduced. Pulmonary blood flow may be entirely dependent on the patency of the arterial duct. The arterial duct begins to close shortly after birth, at which time the hypoxemic (and hypoxic) consequences of ductal dependency manifest. Since the 1970s, pharmacologic manipulation of the arterial duct to maintain or reestablish patency by constant intravenous infusion of prostaglandin E₁ has dramatically improved the care of affected children by diminishing hypoxia during transport to a center where diagnostic and therapeutic interventions can more safely take place.

Defining the pathophysiology of pulmonary vascular disease remains an important area of research. The primary approaches used today involve therapeutic interventions to eliminate the risk factors for pulmonary vascular disease in all children identified at high risk. Three principal risk factors must be characterized in the assessment of congenital heart disease: increased pulmonary blood flow from left-to-right intracardiac or extracardiac shunting (e.g., septal defect, patent arterial duct, arteriovenous fistula, transposition of the great arteries) (Fig. 50-5

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