Approach Considerations
In neonates within 24 hours after birth, pulse oximetry is routinely performed as a predischarge screening to rule out congenital heart disease and measured preductally (right arm) and postductally (lower extremity). Oxygen saturation may be lower in the legs (postductal circulation) because of right-to-left shunting at the level of the ductus arteriosus if patent.
The evaluation for sepsis in infants presenting with shock includes blood, urine, and cerebrospinal fluid (CSF) cultures.
Echocardiography is the diagnostic procedure of choice in all ages. In certain circumstances, exercise stress testing, cardiac catheterization, or both may be indicated.
Chest radiography may reveal cardiomegaly with pulmonary venous congestion, primarily in neonates who present with critical stenosis and symptoms of heart failure. Otherwise, this test is not helpful in asymptomatic patients although aortic root dilation may be identified.
Electrocardiography (ECG) is not especially useful in neonates or young children with significant aortic valve disease. In older patients, it may reveal left ventricular hypertrophy with or without a strain pattern.
Go to Imaging in Aortic Stenosis for more complete information on this topic.
Echocardiography
In the neonate, transthoracic echocardiography usually provides complete diagnostic and hemodynamic information. Essential considerations are the details of valve anatomy, anulus size, distribution of valve tissue, degree of left ventricular hypertrophy, and left ventricular systolic function. The presence or absence of associated lesions, such as mitral valve disease, coarctation of the aorta or subaortic stenosis, can also be well delineated.
Patients presenting with critical aortic valve obstruction and poor left ventricular systolic function may have echodense endocardium typical of endocardial fibroelastosis. Variable degrees of left ventricular hypoplasia or dilation may also be noted. These findings usually indicate that the severe obstruction was present for a significant amount of time prenatally.
In older patients, transthoracic echocardiography is usually diagnostic; in rare cases, however, a large adolescent patient may require transesophageal echocardiography to clearly delineate the left ventricular outflow tract and to detail the valve anatomy. Three-dimensional echocardiography may better delineate the aortic valve anatomy in hopes of determining whether balloon valvuloplasty versus surgical intervention would be more effective.
Doppler echocardiography is used to estimate the severity of aortic valve stenosis noninvasively. The peak instantaneous systolic gradient often overestimates the transvalvular peak-to-peak gradient obtained during cardiac catheterization. This appears to be related to the pressure recovery phenomenon. Mean Doppler gradients correlate better with peak to peak gradients measured during cardiac catheterization.
In neonatal critical aortic valve stenosis with poor left ventricular systolic function and low cardiac output, the Doppler-derived peak instantaneous gradient may be low and is therefore not indicative of the severity of obstruction.
In a retrospective study (1984-2012) comprising 360 pediatric patients with congenital valvar aortic stenosis reviewing the longitudinal assessment of the Doppler-estimated maximum gradient (DEMG) in this group pre- and post-balloon valvuloplasty, investigators found a statistically significant increase in DEMG over time. [4] Post-balloon valvuloplasty, the rate of DEMG change was lower compared with the preprocedure values. The investigators indicated more frequent evaluations of DEMG progression should be made in these patients during periods of rapid somatic growth. [4]
Exercise stress testing and echocardiography
Exercise stress testing can usually be performed in children aged 6 years or older with aortic stenosis and may elicit symptoms that may not be evident by routine history. Resting Doppler gradients can be helpful in determining whether exercise restrictions are necessary [3] .
Exercise stress testing may also provide risk stratification if intervention is being contemplated. Factors such as heart rate, blood pressure response to exercise (blunted), exercise duration (reduced), provocable arrhythmias (ventricular ectopy of left ventricular origin) or electrocardiographic (ECG) ischemic changes, and measured oxygen consumption provide useful data on which to base decisions whether intervention is necessary.
Stress echocardiography is useful in delineating the response of the left ventricle to increasing afterload during exercise. The exercise stress test findings establish a baseline against which to compare subsequent study results, especially if the patient's symptoms change, the Doppler-derived gradient worsens or in the evaluation of the effectiveness following an intervention.
Cardiac Catheterization
Cardiac catheterization is usually performed in infants, children, and older adolescents with aortic stenosis in anticipation of balloon aortic valvuloplasty. Occasionally, the peak systolic gradient measured in the catheterization laboratory with the patient under conscious sedation is significantly less than that estimated by Doppler echocardiography, and this should be taken into consideration regarding whether intervention is indicated. It is an even greater problem when the procedure is performed under general anesthesia, used in some institutions
Other indications for catheterization may include the need to evaluate left ventricular filling pressures (impaired diastolic function secondary to left ventricular hypertrophy) and for accurate hemodynamic assessment in patients with multiple levels of obstruction, such as mitral stenosis or subaortic stenosis in combination with aortic valve stenosis. In the latter instance, high-fidelity catheters capable of discriminating between multiple levels of obstruction in close proximity are probably preferable but are significantly more difficult to use, especially in young patients.
Magnetic Resonance Imaging
Compared with echocardiography, magnetic resonance imaging (MRI) is rarely used to assess the details of aortic valve anatomy and is much more difficult to use in neonates, who have faster heart rates and more motion artifacts. Obtaining an MRI of infants and young children may require sedation, which carries risk of sudden death and, therefore, should be undertaken with close supervision and administered by an experienced anesthesiologist. New developments in gated MRI for assessing ventricular function may make MRI increasingly useful in adult patients.
Histologic Findings
In the presence of significant obstruction from aortic stenosis, the left ventricular myocardium hypertrophies concentrically. Critically ill neonates may have extensive endocardial fibroelastosis, especially in the presence of a dilated nonhypertrophied left ventricle. Patients with chronic aortic stenosis and significantly elevated left ventricular systolic pressure may exhibit fibrotic changes in the myocardium.
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Valvular calcification of aortic stenosis is seen with cardiac fluoroscopy during catheterization.
