Introduction and Etiology of Pulmonic Regurgitation
Epidemiology and etiology
A trivial amount of pulmonic regurgitation (PR) is a common finding in the adult population. Minor degrees of PR have been reported in 40% to 78% of patients with morphologically normal pulmonic valves and no other evidence of structural heart disease. , Unlike regurgitation of the tricuspid, mitral, and aortic valves, which can increase significantly with age, PR remains relatively stable over a lifetime in the absence of structural heart disease. However, more severe degrees of PR may be due to underlying pathophysiology and require further evaluation.
There are several pathologic causes of PR. Congenital etiologies include pulmonic valve anomalies with absence or addition of one or more cusps (bicuspid or quadricuspid valves) or pulmonic stenosis with concomitant regurgitation. , Pulmonic regurgitation is a frequent finding after surgical repair of some forms of congenital heart disease such as tetralogy of Fallot, pulmonic stenosis, pulmonary atresia, or absent pulmonic valve syndrome, or following the Ross procedure for treatment of congenital aortic stenosis or regurgitation. , Acquired forms of pulmonic valve disease and resultant regurgitation are rare but include pulmonic valve prolapse from myxomatous valve disease, tumors or masses (e.g., fibroma or papilloma), carcinoid heart disease, and endocarditis. Most commonly, PR occurs secondary to pathology of the right ventricle or pulmonary artery, such as idiopathic dilation of the pulmonary annulus, pulmonary hypertension with pulmonary artery dilation, right ventricular cardiomyopathy, and trauma related to pulmonary artery catheter placement.
Two-dimensional echocardiographic evaluation
The normal pulmonic valve is a semilunar valve composed of three cusps, similar to the aortic valve. It is inserted into the pulmonary artery annulus distal to the right ventricular outflow tract (RVOT). When viewed with two-dimensional (2D) echocardiography, typically only one or two cusps are seen simultaneously. Visualization of the entire pulmonic valve is more difficult; however, dilation of the pulmonary artery may at times permit an en face evaluation.
Optimal visualization of the pulmonic valve is typically achieved from a parasternal short-axis view at the base of the heart at the level of the aortic valve. The main pulmonary artery and bifurcation into the right and left pulmonary arteries may also be visualized in this view. The right ventricular “outflow” view can also be obtained in the parasternal long axis with cranial angulation toward the right shoulder; however, evaluation of the pulmonic valve in this view is highly dependent on body habitus. The pulmonic valve can also be evaluated in the subcostal view; with anterior angulation the entire RVOT can often be visualized, including the pulmonic valve leaflets. Using M-mode echocardiography from a parasternal approach, the motion of the pulmonic valve can be recorded. The characteristic appearance of the pulmonic valve motion on M-mode (“flying W” pattern) can be found in the presence of pulmonary hypertension and can provide indirect evidence of other right heart pathology.
Transesophageal echocardiography can also be used to evaluate the pulmonic valve. The views that maximize visualization of the pulmonic valve include (1) the pulmonary artery bifurcation view in the upper esophagus with a transducer angle between 0 and 30 degrees; (2) the mid-esophageal short-axis view with a 40- to 60-degree transducer angle and counterclockwise rotation; (3) in a transgastric location with the transducer angle between 0 and 20 degrees—the RVOT and pulmonic valve will come into view with anteflexion and/or right flexion, as well as at 90 to 110 degrees with clockwise rotation; and (4) when evaluating the aorta in the upper esophagus—the pulmonary artery and pulmonic valve can be visualized if the transducer angle is between 70 and 90 degrees.
Three-dimensional echocardiographic evaluation
The pulmonic valve can be visualized by cropping a full-volume dataset obtained using three-dimensional (3D) transthoracic imaging from the parasternal outflow window or 3D transesophageal view obtained from the right ventricular coronal window. Because of the location of the pulmonic valve, image acquisition is challenging and may not add to the information obtained using 2D imaging.
Doppler echocardiographic evaluation
Color Flow Doppler
Detection of PR relies almost exclusively on color flow Doppler imaging ( Fig. 124.1 ). A diastolic retrograde jet in the RVOT, beginning at the line of leaflet coaptation and directed toward the right ventricle, is diagnostic of PR. Regurgitant jets seen with structurally normal pulmonic valves are usually very small, spindle or flame-shaped, and originate centrally from the pulmonic leaflet coaptation site. Jets less than 10 mm in length are considered trivial, whereas larger jets have been associated with an increased severity of PR and underlying structural heart disease. However, jet length is highly dependent on the driving pressure gradient between the pulmonary artery and the right ventricle. When compared with measurements during right heart catheterization, it has been found that as the end-diastolic pressure gradient increases between the pulmonary artery and right ventricle, there is an increase in regurgitant jet area and jet length obtained from color flow mapping. , However, these studies also found that there can be considerable overlap among different grades of regurgitation, especially after repair of congenital heart disease such as tetralogy of Fallot. Alternatively, vena contracta width may be a more accurate method to evaluate PR severity by color Doppler. , This may be especially true in cases of severe PR, where equalization of diastolic pulmonary artery and right ventricular pressures occurs early in diastole and the regurgitant color jet area and length can be brief. In this situation, the large width of the vena contracta and findings on spectral Doppler are integral to estimating the severity of PR. Although appreciated qualitatively, it is important to note that standards for PR vena contracta width have not been established.
Continuous Wave Doppler
Using continuous-wave Doppler and imaging though the RVOT, across the pulmonic valve, and into the main pulmonary artery, a spectral profile above the baseline in diastole is visualized in the presence of PR ( Fig. 124.2 ). A faint Doppler signal with a slow diastolic decay is consistent with relatively mild PR, whereas severe PR is associated with a dense Doppler signal and a steep decay slope. In a study comparing continuous wave Doppler with pulmonary angiography for the quantification of PR severity, a pressure half-time of 100 msec had a sensitivity of 93% and specificity of 93% for the identification of severe PR. A rapid deceleration rate, while consistent with more severe regurgitation, is influenced by several factors, including right ventricular diastolic properties and filling pressures. In severe PR, a rapid equalization of right ventricular and pulmonary artery pressures can occur before the end of diastole with a resultant intense “to and fro” signal in the shape of a sine wave with termination of flow in mid-to-late diastole (see Fig. 124.2 ).
Patients in sinus rhythm may have a late diastolic interruption of flow in the Doppler signal that is indicative of atrial systole. The end-diastolic flow velocities of PR can also be used to calculate the end-diastolic pressure gradient between the pulmonary artery and right ventricle using the modified Bernoulli equation and adding an estimate of right atrial pressure (RAP) :
Pulmonary artery diastolic pressure PADP = RAP + 4 PR Velocity end – diastole 2