Porth's Essentials of Pathophysiology, 4e

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Circulatory Function

U N I T 5

In coarctation, the pressure in the legs is lower and may be difficult to obtain. Patients with coarctation are often identified during a diagnostic workup for hypertension. Most patients with moderate coarctation remain other- wise asymptomatic owing to collateral vessels that form around the area of narrowing. Left untreated, however, coarctation will result in left ventricular hypertension and hypertrophy and significant systemic hypertension (see Chapter 18). Infants with severe coarctation dem- onstrate early symptoms of heart failure and may pres- ent in critical condition upon ductal closure. Reopening of the duct with prostaglandin E 1 , if possible, and emer- gent surgery are needed in this subgroup. 88 Children with coarctation causing a blood pressure gradient between the arms and legs of 20 mm Hg or greater should ideally be treated by 2 years of age to reduce the likelihood of persistent hypertension. 88 A sur- gical approach typically involves resection of the nar- rowed segment of the aorta and end-to-end anastomosis of healthy tissue. This can usually be accomplished without cardiopulmonary bypass, with a mortality rate near zero. Balloon angioplasty with or without stent placement has also been used, although the presence of residual gradients and the reliability of the surgical approach have limited this technique. 88 Functional Single-Ventricle Anatomy. Several forms of complex congenital heart disease result in only one functional ventricle. Functional single-ventricle anat- omy is the most common form of congenital heart dis- ease diagnosed on routine prenatal ultrasonography. There may be a single right or a single left ventricle, or a ventricle of indeterminate morphology. 89–92 Hypoplastic left heart syndrome, a term used to describe a group of closely related cardiac anomalies characterized by under- development of the left cardiac chambers, is the most common form of this disorder. 92 Several other forms of double-inlet ventricle have been described; however, all forms of this disease result in similar pathologic effects and follow a common pathway of intervention. 89–93 All forms of single-ventricle anatomy result in a common mixing chamber of pulmonary and systemic venous return and cause varying degrees of cyanosis (Fig. 19-23). The single ventricle must pump blood to both the pulmonary and systemic circulations, and thus the flow to each circulation is determined by the resistance in each system. 89–92 As pulmonary vascular resistance falls, flow to the pulmonary circulation will be preferential and systemic circulation will be compro- mised. In some defects, such as hypoplastic left heart syndrome, systemic flow depends on a patent ductus arteriosus. Neonates with this lesion typically present with extreme cyanosis and symptoms of heart failure as the ductus begins to close. 92 Although functional single-ventricle anatomy cannot be completely repaired, the surgical palliation of these defects has been one of the most innovative interven- tions for congenital heart disease. The goal of surgical palliation is to redirect systemic venous return directly to the pulmonary arteries and allow the single ventricle to deliver oxygenated blood to the systemic circulation.

Ductus arteriosus

Very small ascending aorta

Pulmonary artery

Atrial septal opening

Left atrium

Underdeveloped left ventricle

Right atrium

Right ventricle

This is accomplished in a series of two to three staged surgical palliation interventions during the child’s first years of life. Stage one palliation is designed to ensure unobstructed systemic blood flow and adequate flow to the pulmonary circulation. Stage two, a bidirectional cavopulmonary shunt, redirects systemic venous return from the superior vena cava directly to the pulmonary arteries. Stage three connects flow from the inferior vena cava directly into the pulmonary arteries so that the pulmonary and systemic circulations are effectively separated. 93 Cardiac transplantation is also used as an intervention for the most complex forms of single-ventricle congenital heart disease. Survival rates for children with complex forms of single-ventricle heart disease have improved markedly, but long-term outcomes remain uncertain. Ventricular dysfunction, arrhythmias, and thromboses plague this population of patients. Defining the optimal medical and surgical management strategies for these patients remains an active area of research in pediatric cardiol- ogy and cardiac surgery. 89–93 Kawasaki Disease Kawasaki disease is an acute vasculitis (i.e., inflamma- tion of the blood vessels) with potential for involvement of the coronary arteries. The disease occurs predomi- nantly in young children; about 80% of patients are younger than 5 years of age. 94,95 First described in Japan in 1967 by Dr. Tomisaku Kawasaki, the disease is the leading cause of acquired heart disease in North America and Japan. 35,36,67,68 Although most common in FIGURE 19-23. Functional single-ventricle anatomy with an underdeveloped left ventricle and small ascending aorta. Because of the markedly decreased left ventricular compliance, most of the pulmonary venous blood returning to the left atrium shunts left to right at the atrial level. Pulmonary arterial blood flows into the pulmonary arteries as well as right to left across a patent ductus arteriosus into the aorta.