than normal in patients with mild stenosis and increased pulmonary flow The right ventricular systolic pressure rises with systemic hypertension or on administration of pressor agents such as phenylephrine, but it falls in the presence of a vasodilator agent The right ventricular pressure may also fall, along with aortic pressure, during or particularly after exercise when the systemic vascular resistance is decreased As already indicated, a fall in systemic resistance with no change in resistance to right ventricular emptying will result in an increased right-to-left shunt Therapeutic Options In many centers, primary complete correction is now the treatment of choice, almost no matter what the age or size of the patient Precise timing may depend on the experience of the particular unit, although there is a role for interventional catheterization in some Otherwise the medical management of a symptomatic child focuses principally on preparation for surgery Medical Management Management of Hypercyanotic Crises or Spells When treating a child undergoing a hypercyanotic crisis, the first actions should be to place the child in the knee-chest position and administer oxygen by face mask If the child is extremely restless, an intravenous line should be inserted and a small dose of morphine sulphate, 0.1 mg/kg, may be all that is required to abort the crisis If this fails, treatment with a β-blocking agent such as propranolol will reduce tachycardia and increase systemic resistance It may also reduce hypercontractility in response to the endogenous release of catecholamine, but there is no evidence for a specific effect to reduce infundibular muscular spasm The drug should also be administered intravenously Half of this should be given rapidly and the remaining half more slowly over the next few minutes If this fails to lead to prompt improvement, arterial blood gases should be assessed Accompanying metabolic acidosis should be corrected Intubation and ventilation may be required in extreme cases, and at this stage an intravenous vasoconstrictor, such as phenylephrine, is often effective Rarely it will be necessary to construct an emergency systemicto-pulmonary arterial shunt In any case, the patient should immediately be referred for definitive intervention and treated orally with propranolol during the interim Surgical Management The symptomatic infant or child requires surgery, and there is little controversy regarding those over a few months of age For neonates and young infants, some centers continue to offer surgical palliation, temporizing by constructing a systemic-to-pulmonary arterial shunt In recent years there has been a resurgence in transcatheter palliation, including balloon dilation and stenting of the right ventricular outflow tract18–20 and stenting of the arterial duct The role of these interventions, usually reserved for the smaller patient or those with additional anomalies, remains uncertain Palliative Procedures Systemic-to-Pulmonary Arterial Shunt Helen Taussig noted that, in patients with tetralogy, persistent patency of the arterial duct often prevented the onset of cyanosis From this, she and Alfred Blalock concluded that it would be beneficial to use the subclavian artery to create an artificial duct The procedure is traditionally performed on the side opposite to that of the aortic arch On this side, the subclavian artery arises from the brachiocephalic artery rather than directly from the aorta Because of this, kinking is less likely to occur at its origin when it is turned down to become a shunt When the arch is right-sided, a left-sided shunt is normally performed Although several alternatives were used in the 1950s and 1960s, they were never as popular or consistently effective as the Blalock-Taussig shunt Today, modification of the classic shunt by the placement of interposition grafts has achieved such excellent results, with low mortality and adequate patency, that the modified shunt has become the procedure of choice The modified version is now frequently performed through a median sternotomy rather than the classic thoracotomy approach Following the creation of such interposition shunts in small infants, most units choose to treat their patients with heparin in the initial postoperative period followed by aspirin until the time of corrective surgery Nonetheless acute thrombosis of the shunt, although rare, remains an important comorbid feature, in addition to concerns regarding stenosis of the pulmonary artery, potential damage to the recurrent laryngeal or phrenic nerves, and adverse physiologic effects such as increased flow of blood to the lungs, systemic steal syndrome, and so on For these reasons, use of the modified Blalock-Taussig shunt is becoming less frequent Definitive Repair Technical Considerations Intracardiac repair involves reconstituting the ventricular septum and relieving subpulmonary obstruction (Video 35.16) The operation is now rarely performed via a large ventriculotomy, with transatrial closure of the septal defect now almost universal Any ventriculotomy, even when it involves a transjunctional incision to relieve obstruction in the subpulmonary outlet, is minimized given the late results now being observed in survivors of correction as they reach adulthood The hypertrophied outlet septum together with its parietal and septal extensions are excised as indicated In the past, whether a transjunctional patch —usually described as a “transannular” patch (although of course the arterial valvar leaflets are not supported in annular fashion)—would be necessary was often decided on the basis of measurements made on preoperative angiograms to determine the sizes of the pulmonary arteries relative to the aorta The need for a transannular patch can also be determined during the operation by using Hegar dilators to measure the narrowest part of the pulmonary outflow tract “Free” pulmonary incompetence is inevitable when a patch is placed across the ventriculopulmonary junction A unicusp aortic homograft (“monocusp”) has been used by some in an attempt to avoid this complication, but no evidence has accrued to show that the late results of this strategy are superior to the use of a nonvalved patch The ventricular septal defect is closed using a patch of knitted Dacron, Teflon, or pericardium secured with either continuous or interrupted sutures Surgery should ideally result in normal right ventricular pressures, absence of any gradient in pressures between the right ventricle and the pulmonary arteries, and a competent pulmonary valve Unfortunately the nature of the subpulmonary obstruction rarely allows this ideal result The last decade has seen a shift away from the obsession with complete relief of obstruction and toward attempts to preserve the pulmonary valve, even at the expense of a modest degree of residual stenosis The belief is that this will minimize the adverse late effects of