58: Congenital Heart Disease

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CHAPTER 58 Congenital Heart Disease

Robert H. Friesen, MD

1 What is the incidence of congenital heart disease?

Although a variable range can be found in the literature, a reasonable estimate of the incidence is 1 in 250 live births.

2 What causes pulmonary hypertension in association with congenital heart disease?

Pulmonary artery hypertension (PAH) is associated with a variety of disease states and can also be idiopathic. When associated with congenital heart disease, PAH is usually the result of high blood flow and pressure in the pulmonary vasculature caused by left-to-right intracardiac shunting at the ventricular level. This situation is typically present with ventricular or atrioventricular septal defects, in which blood flows along a pressure gradient from the high-pressure left ventricle to the lower-pressure right ventricle.

3 Describe the pulmonary vascular effects of left-to-right shunts

Chronic high flow and pressure in the pulmonary vasculature leads to medial hypertrophy and intimal hyperplasia of the pulmonary arteries, resulting in a progressive increase in pulmonary vascular resistance (PVR). This pulmonary vascular obstructive disease eventually becomes irreversible. This irreversible state is rare in patients younger than 1 year of age, except in special situations (e.g., Down syndrome, high altitude, or concurrent existence of cyanotic heart disease).

Several years of progression of pulmonary vascular obstructive disease can result in PVR being greater than systemic vascular resistance (SVR). When this happens, the intracardiac shunt is reversed and flows right to left. This life-threatening situation is called Eisenmenger’s syndrome.

KEY POINTS: Conditions that Increase Pulmonary Vascular Resistance

4. Stress-inducing noxious stimuli

4 How do left-to-right shunts affect the heart?

Over time both ventricles suffer from such shunting. The right ventricle must pump a higher than normal volume of blood through a progressively resistant pulmonary vasculature. The left ventricle is overworked because it receives a higher volume load from pulmonary venous return and because maintenance of cardiac output is less efficient when some blood exits the left ventricle through a septal defect rather than the aorta. Biventricular dilation, hypertrophy, and eventually ischemia, fibrosis, and failure are the result.

5 What is a pulmonary hypertensive crisis? How is it treated?

In patients with PAH, the pulmonary vasculature is hyperreactive to various stimuli that cause pulmonary vasoconstriction. These stimuli include hypoxia, acidosis, hypercarbia, and stress associated with noxious stimuli such as pain or tracheal suctioning. When PVR suddenly increases as a result of such hyperreactivity to a point at which right ventricular pressure equals or exceeds left ventricular pressure, a pulmonary hypertensive crisis is said to occur. This is a dangerous situation in which death can occur as a result of rapidly progressive right ventricular failure, diminishing pulmonary blood flow and cardiac output, poor coronary artery flow, and hypoxia. Table 58-1 outlines the treatment of pulmonary hypertension.

TABLE 58-1 Treatment of Pulmonary Hypertension

Goal	Method
Increase PO₂	Increase FiO₂ Treat atelectasis Control ventilation

Alkalosis

Hyperventilation

Treat metabolic acidosis

Control stress response Adequate analgesia Pulmonary vasodilation

Inhaled nitric oxide

Intravenous prostacyclin (PGI₂)

FiO₂, Fractional concentration of oxygen in inspired gas; PO₂, partial pressure of oxygen.

6 How does PAH affect perioperative risk?

PAH is an independent predictor of perioperative morbidity and mortality in both adults and children, and the severity of baseline PAH correlates with the incidence of major complications, including cardiac arrest and pulmonary hypertensive crisis. Children with suprasystemic pulmonary artery pressures were eight times more likely to experience a major perioperative complication than were those with subsystemic pulmonary hypertension. Choosing a balanced anesthetic technique that minimizes hemodynamic changes and using perianesthetic pulmonary vasodilators are important in the care of patients with PAH.

7 How are shunts calculated?

Using cardiac catheterization data, relative flows in the pulmonary and systemic circulations can be calculated using the Fick principle (flow is inversely related to oxygen extraction):

where Qp = pulmonary blood flow, Qs = systemic blood flow, SaO₂ = systemic arterial oxygen saturation, SvO₂ = systemic mixed venous oxygen saturation, SpvO₂ = pulmonary venous oxygen saturation, and SpaO₂ = pulmonary arterial oxygen saturation.

8 How are pulmonary vascular resistance and systemic vascular resistance calculated?

Resistance is related to pressure and flow:

where PAP = pulmonary artery pressure, LAP = left atrial pressure, Qp = pulmonary blood flow, MAP = mean arterial pressure, CVP = central venous pressure, and Qs = systemic blood flow. The results of this equation are expressed in Wood units. Multiply by 80 to express in dyne • s • cm⁻⁵.

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