Laboratory Studies
Laboratory evaluation is usually not helpful in pulmonary valve stenosis.
Hemoglobin and hematocrit measurements in patients with cyanosis may be helpful in that they are increased in patients with right-to-left shunt. The degree of polycythemia is proportional to the degree and duration of right to left shunt. Microcytosis and hypochromia suggest iron deficiency and warrant treatment with iron supplement.
Oximetry provides information of potential right-to-left shunting in borderline cyanotic lesions but does not help in identifying the cause of the shunt (pulmonary, interatrial, interventricular, great arterial).
Although arterial blood gas (ABG) analysis is usually not needed, one notable exception is the hyperoxia test in the newborn with cyanosis of undetermined origin. [28, 29]
The fraction of inspired oxygen (FIO2) of 1 (100% oxygen) generally does not increase the partial pressure of oxygen to more than 100 mm Hg in patients with a cyanotic congenital heart defect (right-to-left intracardiac shunt).
Electrocardiography
Electrocardiographic (ECG) findings are usually normal in mild pulmonary stenosis. Right-axis deviation and right ventricular hypertrophy occur in moderate and severe valvar pulmonary stenosis. The degree of right ventricular hypertrophy is well correlated with the severity of pulmonary stenosis.
Some studies demonstrated good correlation between the height of the R wave in lead V1 and right ventricular peak systolic pressure; the height of the R wave in V1 in mm multiplied by 5 is predictive of right ventricular peak systolic pressure. While the electrocardiogram is a useful noninvasive tool in the evaluation of severity of pulmonary stenosis, Doppler echocardiography provides a more direct indication of the severity of obstruction.
Right atrial hypertrophy and right ventricular hypertrophy with strain pattern are observed when pulmonary stenosis is severe.
A superior QRS axis (left-axis deviation) is seen with dysplastic pulmonary valves and Noonan syndrome.
Staging
The severity of pulmonary valve obstruction may be categorized (staged) as follows, based on peak-to-peak catheter-measured pulmonary valvar gradient [30] :
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Trivial – Gradient of less than 25 mm Hg
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Mild – Gradient of 25-49 mm Hg
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Moderate – Gradient of 50-79 mm Hg
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Severe – Gradient of more than 80 mm Hg
This severity classification is useful in categorizing patients as per the natural history studies and in formulating treatment algorithms.
Chest Radiography
Chest radiographs reveal a prominent main pulmonary artery segment, but the size of the heart is usually normal (see the image below).
Valvar Pulmonary Stenosis. Posteroanterior chest roentgenogram in a patient with valvar pulmonic stenosis showing a normal-sized heart with normal pulmonary vascular markings. Note prominent main pulmonary artery. Reproduced with permission from Rao PS: Diagnosis and management of acyanotic heart disease: Part I – Obstructive lesions. Indian J Pediatr. 2005; 72: 495-502.
Pulmonary vascular markings are usually normal, but they may be decreased in severe pulmonary stenosis with associated right-to-left shunt.
Cardiomegaly with right ventricular and right atrial enlargement may be seen in severe valvar pulmonary stenosis, with or without tricuspid insufficiency.
Echocardiography
The sine qua non of diagnosis is 2-dimensional and Doppler echocardiography. A thickened pulmonary valve with restricted systolic motion (doming) in the parasternal short axis and subcostal views is demonstrated. [31]
Multiple views are used to confirm the absence of coexistent congenital cardiac disease. Dilatation of the main pulmonary artery distal to the stenotic orifice commonly occurs. Markedly thickened, nodular, and immobile pulmonary valve leaflets may be recognized easily and suggest dysplastic pulmonary valves.
The pulmonary valve annulus can also be visualized and measured. Measurements can be compared with normal values to determine if the annulus is hypoplastic. Such measurements are also useful in selecting the diameter of the balloon to be used during balloon valvuloplasty.
Pulsed, continuous-wave (or high-frequency pulsed), and color Doppler evaluation, in conjunction with 2-dimensional echocardiography, is most useful in confirming the clinical diagnosis and in quantitating the degree of obstruction. [32, 33, 34, 35]
Pulsed Doppler interrogation of the right ventricular outflow tract with sample volume moved across the pulmonary valve demonstrates an abrupt increase in peak Doppler flow velocity, which suggests pulmonary valve obstruction. In addition, the flow pattern in the main pulmonary artery is turbulent instead of laminar. Color Doppler imaging also shows smooth, laminar subpulmonary flow (blue) and some flow acceleration (red) immediately beneath the pulmonary valve, with turbulent (mosaic) flow beginning immediately distal to the pulmonary valve leaflets.
Doppler studies can be used to accurately determine the velocity of flow at single or multiple levels, which then can be converted to reproducible pressure gradients by applying the modified Bernoulli equation, as follows: pressure gradient (in millimeters of mercury) = 4 X (velocity in meters/second)2.
The use of several views and measurements increases the accuracy of the predicted gradient of peak systolic pressure.
Doppler study should be performed when the patient is quiet and in a resting state. Young children and patients who are extremely anxious may have to be mildly sedated.
Severe pulmonary stenosis with gradients of more than 50 mm Hg, as diagnosed using a continuous-wave Doppler recording through the pulmonary valve, should be treated with balloon valvuloplasty or surgery. However, Doppler measurements represent peak instantaneous gradients, whereas catheterization gradients are peak-to-peak gradients; recognition of this concept is more important with aortic-valve gradients than with pulmonary-valve gradients. The peak instantaneous gradient was initially thought to reflect the peak-to-peak systolic gradient measured during cardiac catheterization. However, this peak instantaneous gradient overestimates the peak-to-peak gradient, presumably because of a pressure-recovery phenomenon. [36] In the authors' experience, the catheter peak-to-peak gradient is somewhere in between the Doppler peak instantaneous and mean gradients.
Infundibular gradients secondary to severe right ventricular hypertrophy may be present, but these are not usually observed because severe obstruction of the distal pulmonary valve masks infundibular gradients. [37, 38] However, the infundibular gradients do appear after balloon pulmonary valvuloplasty. A triangular pattern of Doppler signal, similar to that described in subaortic obstruction, is characteristic of infundibular obstruction (see the image below).
Valvar Pulmonary Stenosis. Doppler flow velocity recordings from the main pulmonary artery prior to (left) and 1 day (center) and 10 months (right) after successful balloon pulmonary valvuloplasty. Note that no significant fall in the peak flow velocity is present on the day after the balloon procedure, but a characteristic triangular pattern is present, indicative of infundibular obstruction. At 10-month follow-up, the flow velocity decreased, suggesting resolution of the infundibular obstruction. Reproduced with permission from Thapar MK: Significance of infundibular obstruction following balloon valvuloplasty for valvar pulmonic stenosis. Am Heart J. 1989; Jul; 118(1): 99-103.
Pulmonary insufficiency is easily seen during pulsed, continuous-wave, or color Doppler imaging, but is unlikely to be present without previous surgical or balloon pulmonary valvuloplasty.
Color Doppler and pulsed Doppler interrogation of the atrial septum is useful and may reveal a left-to-right or right-to-left shunt. Because of high sensitivity of color Doppler imaging, contrast echocardiography is not routinely used to document right-to-left shunt.
Most children with pulmonary stenosis do not require evaluation beyond echocardiography.
Computed Tomography Scanning and Magnetic Resonance Imaging
Computed tomography (CT) scanning and magnetic resonance imaging (MRI) may reveal pulmonary valve stenosis, but the state-of-the-art echocardiography and Doppler studies are more useful than CT or MRI in diagnosing and quantitating pulmonary valve obstruction. [1, 39]
Nuclear Studies
Myocardial energy demands and perfusion may be evaluated by performing magnetic resonance spectroscopy and positron emission tomography (PET), respectively. However, the clinical use of these techniques in the management of pulmonic stenosis has not been established. [1, 39]
Cardiac Catheterization and Selective Cineangiography
Catheterization is not indicated in mild pulmonary stenosis but is essential in severe stenosis and is an integral part of balloon pulmonary valvuloplasty. [40] This procedure is used to confirm the diagnosis; to discern the degree of obstruction; to assess the morphology of the right ventricle, pulmonary outflow tract, and pulmonary arteries; and to exclude other associated cardiac abnormalities.
Patients with echocardiographic evidence of clinically significant pulmonary stenosis (50-60 mm Hg) should undergo diagnostic and therapeutic cardiac catheterization with preparation for balloon dilatation of the pulmonary valve. [41]
Oxygen-saturation data usually do not show evidence of left-to-right shunts. A right-to-left shunt across the patent foramen ovale (or an atrial defect) may be present in moderate-to-severe obstruction of the pulmonary valve.
Pressures Measurements
Note the following:
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Right atrial pressure (particularly a wave) may be increased.
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Right-ventricular peak systolic pressure is increased; the magnitude of the pressure is proportional to the degree of obstruction.
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The transpulmonary valve peak-to-peak gradient also indicate the severity of obstruction. A peak-to-peak gradient in excess of 50 mm Hg is usually considered an indication for therapeutic intervention. [41] Some workers use 40 mm Hg as an indication for intervention.
Angiography
Right ventricular angiography usually reveals thickened and domed leaflets of the pulmonary valve (see the image below) with a thin jet of contrast material across the pulmonary valve.
Valvar Pulmonary Stenosis. Right ventricular (RV) cineangiogram in the lateral view of a child with valvar pulmonary stenosis demonstrating thickened and domed pulmonary valve leaflets and poststenotic dilatation of the pulmonary artery (PA). Reproduced with permission from Rao PS: Diagnosis and management of acyanotic heart disease: Part I – Obstructive lesions. Indian J Pediatr. 2005; 72: 495-502.
Enlargement and hypertrophy of the right ventricle and a dilated main pulmonary artery are also seen.
In patients with severe or long-standing pulmonary valve obstruction, infundibular constriction may be seen.
Additional cineangiograms at other locations are not necessary unless the echocardiographic and hemodynamic data suggest other abnormalities.
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Valvar Pulmonary Stenosis. In valvar pulmonic stenosis, the severity of obstruction may be judged by auscultatory findings. In mild stenosis, the ejection click (EC) is clearly separated from the first heart sound (S1). The murmur starts with the click, peaks in early systole, and ends far ahead of the aortic component of the second heart sound (A2). The pulmonary component of the second heart sound (P2) is normal to increased in intensity. In moderate pulmonic stenosis, the click is closer to the first heart sound, the ejection murmur peaks later in systole and the murmur reaches the A2, and the second heart sound is widely split with a soft pulmonary component. In severe valvar obstruction, the click is either absent or occurs so close to S1 that it cannot be heard separately, and the murmur peaks late in systole and extends beyond the A2. The second heart sound is widely split with an extremely soft or inaudible P2. Reproduced from Rao PS: Evaluation of cardiac murmur in children. Indian J Pediatr. 1991 Jul-Aug; 58(4): 471-91.
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Valvar Pulmonary Stenosis. Posteroanterior chest roentgenogram in a patient with valvar pulmonic stenosis showing a normal-sized heart with normal pulmonary vascular markings. Note prominent main pulmonary artery. Reproduced with permission from Rao PS: Diagnosis and management of acyanotic heart disease: Part I – Obstructive lesions. Indian J Pediatr. 2005; 72: 495-502.
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Valvar Pulmonary Stenosis. Doppler flow velocity recordings from the main pulmonary artery prior to (left) and 1 day (center) and 10 months (right) after successful balloon pulmonary valvuloplasty. Note that no significant fall in the peak flow velocity is present on the day after the balloon procedure, but a characteristic triangular pattern is present, indicative of infundibular obstruction. At 10-month follow-up, the flow velocity decreased, suggesting resolution of the infundibular obstruction. Reproduced with permission from Thapar MK: Significance of infundibular obstruction following balloon valvuloplasty for valvar pulmonic stenosis. Am Heart J. 1989; Jul; 118(1): 99-103.
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Valvar Pulmonary Stenosis. Right ventricular (RV) cineangiogram in the lateral view of a child with valvar pulmonary stenosis demonstrating thickened and domed pulmonary valve leaflets and poststenotic dilatation of the pulmonary artery (PA). Reproduced with permission from Rao PS: Diagnosis and management of acyanotic heart disease: Part I – Obstructive lesions. Indian J Pediatr. 2005; 72: 495-502.
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Valvar Pulmonary Stenosis. Selected cineradiographic frames of a balloon dilatation catheter placed across a stenotic pulmonary valve. Note "waisting" of the balloon during the initial phases of the balloon inflation (A), which was almost completely abolished during the later phases of balloon inflation (B). Reproduced from Rao PS: Balloon pulmonary valvuloplasty for isolated pulmonic stenosis. In: Rao PS, ed: Transcatheter Therapy in Pediatric Cardiology. New York, NY: Wiley-Liss; 1993: 59-104.
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Valvar Pulmonary Stenosis. Selected frames from the lateral view of the right ventricular (RV) cineangiogram showing severe infundibular stenosis (A) immediately following balloon valvuloplasty (corresponding media file 3, center). At 10 months after balloon valvuloplasty, the right ventricular outflow tract (B) is wide open and corresponds to media file 3, right. Peak-to-peak pulmonary valve gradient was 20 mmHg and no infundibular gradient was present. PA = Pulmonary artery. Reproduced with permission from Thapar MK: Significance of infundibular obstruction following balloon valvuloplasty for valvar pulmonic stenosis. Am Heart J. 1989; Jul; 118(1): 99-103.
