Pediatric Mitral Regurgitation (Mitral Valve Insufficiency) Workup

Chest radiography

With mild mitral regurgitation (MR) (mitral valve insufficiency), the heart size is normal.

With increasing mitral regurgitation, cardiomegaly may develop, and left atrial enlargement becomes apparent. Left atrial dilatation caused by chronic rheumatic heart disease often includes radiographically apparent dilatation of the left atrial appendage. Left ventricular (LV) enlargement and pulmonary congestion may also be present.

In cases of acute mitral regurgitation, pulmonary venous vasculature markings may be increased, and pulmonary edema may be seen without signs of left atrial enlargement.

Left lung atelectasis and hyperinflation may be visible due to compression of the left main bronchus by the enlarged left atrium.

Echocardiography

Transthoracic echocardiography (TTE)

Echocardiography is the most valuable technique used to evaluate mitral regurgitation. This imaging modality is usually readily available and portable. Knowledge of the mitral valve apparatus, including the labeling of the scallops of each of the two valve leaflets is essential. An understanding of the anatomy from a surgeon's perspective is needed to explain the findings.

Two-dimensional (2-D) echocardiography allows depiction of the size of the chambers and assessment of the ventricular systolic function, as well as determination of the morphology of the mitral valve leaflets, the annulus, chordal tissue, and papillary muscles. The parasternal long-axis view may provide the best images of mitral valve prolapse, whereas the parasternal short-axis view is better for depicting papillary muscle anatomy and leaflet cleft. The apical four-chamber view is valuable in the evaluation of mitral valve function.

M-mode assessment of cardiac function is extremely important. Cardiac function should be carefully evaluated in mitral regurgitation; different techniques can be used to assess the LV function, including 2-D, three-dimensional (3-D), tissue Doppler, and strain imaging.

The LV function should be hypernormal, indicating a preserved myocardial function with mitral regurgitation. In the presence of normal or mildly depressed function, one should expect myocardial failure postoperatively. In cases of acute rheumatic fever, mitral valve function may return to normal as the inflammation subsides and, indeed, mitral stenosis may develop. Scalloping of the mitral leaflets can occur in mitral valve prolapse and can be seen using M-mode. In addition, the ventricular dimensions should be measured and followed for LV enlargement. LV hypertrophy can also be determined and may be present in hypertrophic cardiomyopathy with mitral regurgitation.

Factors that appear to be associated with early postoperative LV dysfunction after repair of mitral valve regurgitation include lower global circumferential strain magnitude as well as lower global circumferential strain rate magnitude; thus, strain measurements may aid clinicians in determining the timing of pediatric surgical repair. ^[8]

Color-flow Doppler echocardiography demonstrates the width and direction of the regurgitant flow. ^[9] The degree of regurgitation may be underestimated if the jet hugs the walls of the atrium. Furthermore, because the structures are 3-D, multiple views and scans must be performed with optimal transducer frequency to determine the entire regurgitant jet.

Spectral Doppler imaging demonstrates a high-velocity signal across the mitral valve in systole entering retrograde into the left atrium. Mitral regurgitation can be seen and evaluated best in the apical four-chamber and parasternal long views. Concomitant mitral stenosis should also be determined. The peak velocity of mitral regurgitation can be used to calculate several other parameters, including LV contractility (ie, dP/dT).

Visualizing mitral regurgitation is not as difficult as classifying the severity. In adults, many echocardiographic methods are used with varying results. The grading of mitral regurgitation in the pediatric population as mild, moderate, and severe is based on the size and extent of the color-flow Doppler signal (jet area) into the left atrium (left atrial area).

Other factors to consider include left atrium and ventricular size and function. In mild mitral regurgitation, the signal is located in the proximal third of the left atrium near the mitral valve. The left atrium is usually not enlarged, and the ventricular function is normal. In moderate mitral regurgitation, the signal extends to mid cavity, with left atrial dilatation and increased ventricular function. With severe mitral regurgitation, the signal reaches the posterior third of the left atrium and the pulmonary veins, and the left atrium and ventricle are usually enlarged, with increased ventricular shortening fraction. Other techniques useful in quantification include measurement of vena contracta, proximal isovelocity surface area (PISA), pulmonary vein flow reversal, and regurgitant fraction.

Transesophageal echocardiography (TEE)

TEE may be required if further detailed anatomic information is needed. TEE views correlate better with angiographic grading than transthoracic views. In addition, intraoperative TEE is essential in evaluating mitral valve surgery.

3-D echocardiography

3-D echocardiography provides an excellent anatomic evaluation of the mitral valve and helps clinicians with making decisions regarding therapy and possible surgical intervention.

Cardiac magnetic resonance imaging (MRI)

Cardiac MRI is a relatively newer modality for imaging the heart. Cardiac MRI provides 3-D imaging of the heart and great vessels and does not depend on acoustic windows, as echocardiography does. This modality provides more accurate evaluation of both the left and right ventricular size and function.

The degree of mitral regurgitation determined by cardiac MRI has not been adequately evaluated. However, velocity flow imaging may potentially provide additional information.

Electrocardiography

The 12-lead electrocardiogram (ECG) is likely to show normal results in children with mild mitral regurgitation (MR) (mitral valve insufficiency).

In more chronic mitral regurgitation, ECG findings demonstrate left atrial and left ventricular enlargement.

When pulmonary hypertension is present, ECG may also demonstrate right ventricular hypertrophy.

Rhythm changes, such as atrial fibrillation, are often observed in adults but are rare in children.

Evaluation of mitral regurgitation (MR) (mitral valve insufficiency) in children usually does not require cardiac catheterization. Some pediatric patients undergo catheterization to evaluate other cardiac defects that may be present.

Mitral regurgitation is best evaluated using angiography obtained in the right anterior oblique view. Retrograde flow of injected dye demonstrates the degree of mitral regurgitation, which is quantitatively graded (grades I-IV) depending on the level of left atrial opacification (see below). LV injections obtained via the retrograde approach are preferred to an anterograde approach to prevent the catheter from holding the mitral valve open and creating artifactual mitral regurgitation.

To quantitate mitral regurgitation, a combination of angiography and cardiac output measurements must be used. Either thermodilution or the Fick principle helps measure forward cardiac output, while angiography allows determination of total LV output. Keep in mind that tricuspid regurgitation can invalidate the thermodilution method. ^[10]

Subtracting the forward output from total LV output yields the regurgitant fraction. A regurgitant fraction of 0.5 or greater is generally considered clinically significant.

The LV ejection fraction may be increased initially; however, as the LV decompensates, the ejection fraction decreases to normal or subnormal values, signifying LV failure. As LV failure develops, LV end-diastolic pressure increases, resulting in an increase in left atrial and pulmonary venous pressure. Increased pulmonary venous pressure is manifested as an increase in pulmonary capillary wedge pressure. At catheterization, the wedge pressure a wave amplitude is increased along with a rapid rise of the v wave. The latter occurs when LV compliance decreases.

A study evaluating mitral regurgitation compared cardiac catheterization to echocardiography (transesophageal, transthoracic) and found no advantage to catheterization in clinical decision making. Cardiac catheterization should be used when noninvasive data are discordant, limited, or differ from the clinical status of the patient. Ventriculography may add new information if more complex congenital cardiac problems are present.

Grading of mitral regurgitation using angiography is as follows:

• Regurgitation grade of 1+: Trace amounts of contrast are seen in the left atrium, but the amount is insufficient to outline the left atrium.

• Regurgitation grade of 2+: The contrast opacifies the entire left atrium but less than that of the LV. The contrast clears quickly (within 2-3 beats).

• Regurgitation grade of 3+: The contrast opacifies the left atrium and LV equally.

• Regurgitation grade of 4+: The contrast opacifies the left atrium more than the LV and progresses to the pulmonary veins.