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SPA Newsletter.
Williams Syndrome, Supravalvar Aortic Stenosis and Cardiac Arrest During AnesthesiaSudden death is a well-recognized complication of Williams syndrome and non-syndromic supravalvar aortic stenosis (SVAS), with a number of the deaths occurring during or following the administration of anesthesia or sedation. This review summarizes the pathophysiology of congenital SVAS, providing insight into the mechanisms and thereby possible prevention of cardiac arrest during anesthesia. Williams syndrome is the association of SVAS with mental retardation, growth retardation and characteristic facies (full face, broad forehead, heavy cheeks, wide mouth, pouting lips).1 Multiple peripheral pulmonary artery stenosis, a friendly nature, and hypoplasia of the mandible with dental abnormalities was added to the symptom complex today known as Williams-Beuren syndrome.2,3 Non-syndromic SVAS is a dominantly inherited single gene disorder that shares with Williams syndrome similar cardiovascular abnormalities, but lacks the cognitive, behavioral and phenotypic abnormalities.4 The defining feature of congenital SVAS is aortic narrowing at the level of the sinotubular junction caused by a loss-of function mutation of the elastin gene on chromosome 7q11.23.5,6 In approximately 30% of cases there may be narrowing of the entire ascending aorta and sometimes the arch branches, or localized stenoses of mesenteric and renal arteries. The main histologic feature is a media with increased number of hypertrophied smooth muscle cells, increased collagen content and reduced elastic tissue in the form of broken and disorganized elastin fibers (elastin arteriopathy). The most likely mechanism of cardiac arrest and sudden death is myocardial ischemia from coronary insufficiency leading to myocardial infarction and/or arrhythmia. 4 The impairment in coronary blood flow (CBF) may be due to: 1) coronary orifice obstruction by the thickened aortic or sinus wall, 2) adhesion of an aortic valve leaflet to the sinotubular ridge causing obstruction of a coronary orifice, 3) exposure of the coronary arteries to elevated prestenotic systolic pressure, resulting in dilatation and tortuosity and promoting premature arteriosclerosis, 4) elastin arteriopathy of the coronary arteries themselves, 5) systemic hypotension and 6) severe ventricular hypertrophy with increased myocardial mass and increased intramyocardial pressure resulting in a critical perfusion mismatch and subendocardial ischemia. Obstructions of the pulmonary vasculature have been reported in up to 83% of cases.7,8 Multiple peripheral pulmonary artery stenoses are usually present, and central pulmonary arteries can have localized stenoses or generalized hypoplasia. Multi-level right ventricular outflow tract obstruction leads to right ventricular pressure load and hypertrophy, which can also result in critical perfusion mismatch and subendocardial ischemia. The combination of coronary artery obstruction and biventricular outflow tract obstruction may carry the greatest risk of sudden death.4 Congenital SVAS is thus not a 'simple lesion' and every patient should be considered at risk for myocardial ischemia. Numerous cases of cardiac and non-cardiac procedure-related cardiac arrest and death have been reported.4,9 Although some fatalities have been associated with catheter manipulation at the coronary orifices or balloon angioplasty, others occurred before the procedure had begun or after apparently successful completion. Acute decompensation in the setting of hemodynamic stress probably involves a drop in cardiac output and a consequent decrease in coronary blood flow, made worse by ventricular hypertrophy and/or coronary artery obstruction. Presenting signs in patients who have been monitored at the time of arrest are hypotension, bradycardia and ventricular fibrillation. In the preoperative evaluation, significant factors on history include syncope, angina, fatigue or dyspnea (during feeds in infants or with play or exercise in older children and adults), hemodynamic instability during previous anesthesia or sedation, and symptoms of renal dysfunction or calcium homeostasis abnormalities (association of Williams syndrome with infantile hypercalcemia). On physical examination, evidence of cardiac failure, hypertension, differing limb blood pressures and abdominal bruits should be sought. The electrocardiogram should be examined for evidence of acute or chronic ischemia (infarction), left and right ventricular strain, and chamber hypertrophy. There is, however, a poor relationship between the degree of left ventricular hypertrophy in the electrocardiogram and the systolic pressure gradient as the elevation in left ventricular pressure precedes the development of hypertrophy 1-3. Echocardiography, cardiac catheterization, and/or cardiac magnetic resonance imaging may be used to determine the SVAS gradient, aortic arch integrity, aortic valve anatomy, coronary circulation, wall motion abnormalities, degree of right ventricular outflow tract obstruction and pressure, and ventricular function. Of note, the degree of SVAS appears to be a poor predictor of coronary stenosis.4 A feature common to many of the reported deaths is sudden deterioration, a rapid downhill course, and lack of response to resuscitation.4,9 Although there is insufficient data in the anesthetic literature to support a specific anesthetic technique for congenital SVAS, a prudent approach would be to use a similar anesthetic regimen as for adults with ischemic heart disease. The goal of anesthetic management is meticulous attention to myocardial oxygen supply and demand. It is also important to keep in mind right ventricular oxygen balance in those patients with pulmonary artery stenosis. Decreased myocardial oxygen supply may be caused by decreased coronary blood flow or decreased arterial oxygen content or availability.10 Decreased CBF may be due to the coronary artery obstruction, tachycardia (decreased diastolic perfusion time), systemic hypotension (especially diastolic), increased preload (decreased coronary perfusion pressure) and hypocapnia (coronary vasoconstriction). Decreased oxygen delivery may be caused by anemia, hypoxemia and reduced oxygen release from hemoglobin (alkalosis, hypothermia, decreased 2,3-DPG). Myocardial oxygen demand is increased by tachycardia, increased myocardial muscle mass and contractility, and increased wall tension (increased preload, increased afterload). Arrhythmias which increase heart rate or decrease ventricular filling by loss of coordinated atrial contraction will have a deleterious effect on oxygen balance and cardiac output, thereby increasing the risk of ischemia. The hemodynamic goals for SVAS are to 1) maintain normal heart rate (particularly avoiding tachycardia), 2) maintain sinus rhythm (to preserve filling of the stiff ventricle), 3) maintain adequate preload - because of the decreased ventricular compliance, excessive preload may lead to significant elevations in left ventricular end-diastolic pressure and left atrial pressure with consequent pulmonary edema, whereas inadequate preload may lead to a marked decrease in stroke volume, 4) maintain ventricular contractility - ventricular function can vary from excellent (hyperdynamic) to severely depressed, and 5) maintain left ventricular afterload, as diastolic hypotension will result in a decreased coronary perfusion pressure. In contrast to valvar aortic stenosis, the presence of an obstructive lesion above the coronary ostia aggravates the adverse effect of hypotension on CBF by presenting a gradient between the ascending aorta and the coronary ostia. For the pulmonary artery stenosis, the hemodynamic goals are the same except that a decrease in pulmonary vascular resistance (afterload) is desirable in maintaining right ventricular output. Control of ventilation to avoid hypoxia, hypercarbia and acidosis, and to maintain adequate lung volume may be advantageous in the more fragile patient with pulmonary artery stenoses. In conclusion, patients with Williams syndrome and non-syndromic SVAS should be regarded as at high risk during anesthesia, especially if there is bilateral outflow tract obstruction or evidence of myocardial ischemia. References
Barry Kussman, MD
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