Infundibular Pulmonary Stenosis Workup

Blood work investigations are helpful in acute-stage management when an infant presents with cyanosis or heart failure.

Chest radiography

Findings on chest radiography may include the following:

• Heart size is usually within reference ranges but, at times, may be slightly enlarged. Pulmonary vasculature is reduced in patients with cyanosis or in those with cardiac failure (see image below).

  Infundibular Pulmonary Stenosis. Chest radiograph of a 2-year-old boy with severe pulmonary stenosis (infundibular). Note the mild cardiomegaly, reduced pulmonary vascularity, and absence of poststenotic dilatation of pulmonary artery.

• Cardiomegaly or dilatation of the right ventricle may be evident in severe cases and becomes more marked with tricuspid regurgitation or cardiac failure.

• Pulmonary vascularity is usually normal, except in severe cases with right-to-left shunt across the atrial or ventricular septa.

• In infants with severe or critical pulmonary stenosis, cardiomegaly with a huge cardiac silhouette is the rule. Pulmonary vascular markings are also reduced.

• Poststenotic dilation of the main pulmonary artery seen in PVS is not a feature.

Doppler echocardiography

Noninvasive Doppler studies play a major role in demonstrating the presence, magnitude, and site of the obstruction. They also help find associated cardiac anomalies.

Doppler studies can be very useful in evaluating right ventricle size and function and pulmonary valve anatomy. ^[6] Note the following:

• The projections used to obtain these views are the standard and high-parasternal short axis and the subcostal sagittal views. The ventricular cavity and tricuspid valve can also be easily assessed.

• A subcostal oblique view is especially helpful to visualize hypertrophy of the right ventricle outflow tract (RVOT).

• Contrast echocardiography may detect the presence of right-to-left shunting at the atrial or ventricular level.

In mild obstruction, cardiac chambers are normal. Their only abnormality may be the hypertrophied infundibulum with a turbulent flow across it. High flow velocity is confirmed with pulsed wave and continuous wave Doppler studies.

In moderate-to-severe obstruction, the right ventricle is dilated and hypertrophied, and the right atrium may also be dilated, with the atrial septum bulging toward the left atrium. In cases of dynamic obstruction that characterize the infundibular hypertrophy, a late-peaking Doppler signal is recorded across the RVOT.

Doppler studies can be used to quantify the pressure drop across the stenosed infundibulum. The peak velocity measured across the RVOT is used to calculate the pressure gradient, using the modified Bernoulli equation, p = 4V² (p is the peak instantaneous pressure gradient in mm Hg across the obstructed infundibulum, whereas V is peak flow velocity in m/sec distal to the obstructive orifice). Note the following:

• The technique is as accurate as cardiac catheter data in prediction of pressure gradients across the RVOT.

• Doppler studies measure the actual instantaneous pressure gradient, which is about 10% more than the peak-to-peak gradient measured using cardiac catheterization. ^[7]

Do not allow for possible energy losses caused by the elongated obstruction or the presence of narrowing at more than a single level in patients with infundibular obstruction.

Transesophageal echocardiography

Transesophageal echocardiography is more widely used for the diagnosis and more important during interventions, including surgical correction.

Electrocardiographic findings may include the following:

• With mild stenosis, ECG findings are usually within reference ranges. Occasionally, a rightward shift of the main QRS frontal axis may be present.

• Moderate-to-severe cases show right-axis deviation and right ventricle hypertrophy, proportional to severity.

• Except in the newborn period, the height of the R wave in right chest leads provides an assessment of the right ventricle pressure.

• Upright T waves and QRS in right chest leads and incomplete right bundle-branch block may be present but do not necessarily indicate severity of obstruction. Tall p waves suggest right atrial enlargement (p pulmonale).

• In infants with maximal obstruction bordering on pulmonary atresia, the evidence for right ventricle hypertrophy may be less convincing, and left ventricle dominance is rarely observed.

• The abrupt transition in the pattern of the QRS complex in the mid-precordial leads, a pattern often found with tetralogy of Fallot, is not seen.

Cardiac catheterization

Cardiac catheterization is not essential for diagnosis or to assess severity. The procedure is sometimes undertaken before surgical intervention and in infants for whom other associated lesions must be evaluated. Occasional reports of balloon dilatation of RVOT are available, but results are not encouraging. The procedure is not recommended in patients with infundibular pulmonary stenosis (IPS).

Resting peak systolic pressures in the right ventricle of more than 30-35 mm Hg, as well as pressure gradients across the stenotic infundibulum of more than 10-15 mm Hg, are considered abnormal.

In mild IPS, pulmonary artery pressure is normal. In severe IPS, a marked reduction of mean pulmonary artery pressure and obliteration of the usual pulsatile configuration of the pressure tracing are present.

The presence of IPS may be suggested by the withdrawal pressure tracing. In some cases of combined valvar and discrete infundibular stenosis, two pressure gradients may be encountered; the first at the valve and the second at the infundibular level. Note the following:

• Pressure gradients may be encountered at more than one level, making it difficult to assess the severity of all but the most proximal stenoses.

• In severe valvar stenosis with diffuse infundibular narrowing, a characteristic infundibular pressure pulse pattern is frequently observed.

• End-diastolic pressure in the right ventricle may be normal or elevated with severe obstruction or right ventricle failure.

The degree of right ventricle hypertension is the main indicator of severity. Mild stenosis is present when the proximal systolic pressure is less than 60 mm Hg. With moderate stenosis, this pressure may be as high as 100 mm Hg; above this level, the stenosis is considered severe. Other hemodynamic findings in severe stenosis include the following:

• Right ventricle end-diastolic and right atrial a wave pressures are elevated.

• A high v wave in the right atrium indicates tricuspid regurgitation.

• A right-to-left shunt at the atrial or ventricular level should be sought in all patients with cyanosis.

• A left heart catheterization is indicated in all patients with subvalvular stenosis that may be a component of a hypertrophic cardiomyopathy.

Angiocardiography

The following features may be noted on angiography:

• Right ventriculography in right anterior oblique projection demonstrates obstruction at the infundibular level.

• The best all-purpose projection for evaluation of the pulmonary outflow tract and pulmonary arteries is an anteroposterior projection with a 45° head-up tilt.

• When taken along with the lateral projection, a good view is obtained of all the important structures.

• This projection makes distinguishing the hourglass variant from bottle-shaped sinuses possible.

• A 4-chamber axial oblique projection may occasionally be preferred to visualize the pulmonary artery bifurcation.

Left-sided angiocardiography is indicated when a ventricular septal defect or a left-sided obstruction is present. The long-axis oblique projection is the most useful and is the best tool to accurately diagnose this lesion. Note the following:

• Always perform biplane angiocardiography when evidence of a significant intraventricular pressure gradient has been found during cardiac catheterization.

• Anterior projections reveal filling defects within the right ventricle between the outflow and inflow areas.

Isolated infundibular stenosis of the pulmonary artery is a mass of muscle-fibrous tissue that creates an obstacle to blood flow in the right ventricle.

Morphogenetic regularities of compensatory and adaptive reactions in isolated infundibular stenosis are similar to those in hypertrophic cardiomyopathy.

Some investigators have suggested that abnormalities in the structure of the hypertrophied myocardium in isolated stenosis of the right ventricle infundibulum are caused by a fundamental error in the cardiac morphogenesis and do not reflect an increased degree of cardiac hypertrophy.