ABSTRACT
Introduction Aortic valve stenosis (AS) occurs in 3-6% of patients with congenital heart disease.1 The aortic valve may be of adequate size for the body surface area but morphologically stenotic and dysplastic, anatomically small and dysplastic, or morphologically normal but small. The anatomic types of aortic valvular stenosis include unicuspid, bicuspid, tricuspid, quadricuspid, and undifferentiated aortic valves. The most common malformation of the aortic valve seen in patients with AS is the bicuspid valve. In these patients, thickening and partial fusion of the leaflets can cause clinically severe valve stenosis, even in infancy. Unicuspid aortic valve is present when there is fusion of all three leaflets of the valve. Most newborns with severe or critical AS requiring intervention in the first month of life have either a unicuspid or a severely stenotic bicuspid aortic valve. The unicommissural valves have either no true commissure and a tiny central opening or a small eccentric slit-like opening extending to the annulus. Males are affected three to five times as often as females. In the neonate, critical AS is a complex disorder, frequently associated with varying degrees of left ventricular and annular hypoplasia, mitral valve anomalies, endomyocardial fibroelastosis, and myocardial ischemia. Other cardiovascular anomalies such as aortic coarctation, patent ductus arteriosus, and ventricular septal defect occur in 20% of the patients and should be evaluated before an invasive procedure is undertaken. Numerous studies have attempted to demonstrate a correlation between left-sided heart structure sizes or hemodynamic relations and survival of biventricular versus single ventricle repair in critical AS.2-7 Neonates with critical AS suffer from low cardiac output and shock secondary to poor left ventricular function and/or mitral insufficiency. Outcome is usually fatal in most of these patients within the first weeks of life with medical treatment alone. Intervention in the first days of life is therefore required in these patients. Open or closed surgical valvotomy was the only technique available until the mid-1980s. The use of percutaneous balloon aortic valvuloplasty was first introduced in 1984 and
has become the first-line treatment for critical aortic valve stenosis in neonates.6,8-12
Precatheterization assessment and management Newborns with critical AS present with some degree of heart failure and not infrequently in cardiogenic shock. When the diagnosis is made prenatally, arrangements should be made so the baby is born in a surgical center in order to avoid treatment delays due to the transfer. These newborns should be mechanically ventilated and sedated soon after birth to decrease the oxygen demands. Patients who present in shock should be hemodynamically stabilized as much as possible, but intervention should not be postponed for this reason. Acid-base status, blood count, coagulation times, and electrolytes should be evaluated and corrected if necessary.13 Prostaglandin (PGE1) is started to augment cardiac output in the setting of a failing and obstructed left ventricle. We recommend inserting both venous and arterial umbilical catheters since these catheters can later be used as vascular access during the catheterization. Inotropic support is commonly initiated to increase cardiac output. Agents with the least chronotropic effect, such as dopamine or dobutamine, are the most commonly used. Their effect on the heart rate should be carefully monitored because a decrease in the filling time of the left ventricle can further compromise cardiac output. Transthoracic echocardiography is the imaging method of choice to establish the morphology and function of the aortic valve, assess left ventricular function, and rule out other congenital cardiac anomalies in newborns. The number and morphology of the aortic valve cusps are best determined from the parasternal short-axis view at the base of the heart. The movement of the aortic valve leaflets should be carefully examined in a slow-motion playback mode to determine the number of valve cusps. In many cases, the leaflets are immobile and a systolic opening cannot be
visualized. Although defining the details of the aortic valve anatomy is important, it does not modify the management plan for these patients. The annulus and proximal ascending aorta are better visualized from the parasternal longaxis view. The annulus is usually 5 to 8 mm in diameter and post-stenotic dilatation of the ascending aorta is commonly seen. Several studies have shown a correlation between various left-sided heart structure sizes or hemodynamic relations and survival of biventricular repair in critical AS. A multi-variate equation and a risk factor analysis to predict suitability of biventricular repair in critical AS have been described by Rhodes et al.6 In this study, outcome was estimated by scoring the presence of three components measured by echocardiography: indexed aortic root diameter (3.5 cm/m2 or less), indexed mitral valve area (4.74 cm2/m2
or less), and a left ventricular long axis to heart long axis ratio of 0.8 or less. Different studies have described other predictors of biventricular suitability in critical AS.3,4,12
Medical centers taking care of these patients should develop and become familiar with their own decision algorithms.
