Right-Sided Valvular Disease and Pulmonary Hypertension
Pulmonic Valve Major structural abnormalities of the PV are relatively rare. Pulmonic stenosis (PS) is usually congenital in origin and resembles congenital AS in many respects. The stenotic valve does not open fully and exhibits characteristic thickening and systolic doming on 2D imaging (Fig. 15–85). M-mode recordings of the PV often show a large a wave, since RV diastolic pressure is often so high and PA pressure so low that the atrial "kick" is sufficient to open the PV. Doppler interrogation reveals turbulent flow distal to the valve, and CW measurements can be used to calculate gradients and valve areas with the Bernoulli and continuity equations much as in aortic stenosis.179
Although severe pulmonic regurgitation (PR) is rare, mild PR is common and appears as a flame shaped flow disturbance in the RV outflow tract (RVOT) in diastole. Many individuals have trivial PR on color Doppler examination; this is a physiologic, normal variant (Fig. 15–86). Hemodynamically significant PR is uncommon; when present, it is usually due to congenital heart disease, valvular tumors, endocarditis, or carcinoid heart disease (Chap. 59). The echocardiographic grading of PR is semiquantitative, based on the density of the CW envelope, area of the color Doppler jet, and width of the jet at the valve.180 The PR pressure half-time by CW Doppler may be shorter with more severe PR, but this is not as well investigated as in the case of AR. Measurements derived from the CW Doppler recording also provide estimates of end-diastolic PA pressure using the Bernoulli equation, as follows:
Tricuspid Valve Tricuspid stenosis (TS) is usually rheumatic in origin, and coexistent mitral and aortic valvular disease is the rule. Congenital or acquired (nonrheumatic) causes of TS are quite uncommon. On rare occasions, TS may be caused by carcinoid heart disease or by leaflet adhesions to permanent pacemaker leads. Because of the large size of the tricuspid annulus, obstruction by masses, even multiple vegetations, is unlikely to cause stenosis (Chap. 69). Regardless of the etiology, diastolic doming of the valve leaflets suggests stenosis.182 CW Doppler interrogation is also helpful and mimics the findings of MS (high diastolic velocity with prolonged pressure half-time).182 The pressure half-time equation used to calculate the area of the MV orifice cannot be applied directly to the TV, and large studies comparing Doppler echocardiography with right heart catheterization in TS are not available. Tricuspid regurgitation (TR) is much more common than TS, and, like PR, is present to a mild degree in many normal individuals (Chap. 59). Hemodynamically significant TR may be caused by endocarditis, rheumatic valvular disease, pulmonary hypertension (PH), congenital heart disease (for example, Ebstein's anomaly), carcinoid heart disease, flail TR leaflet (which can occur as a complication of cardiac trauma or endomyocardial biopsy), and TV prolapse. Echocardiographic findings in TR generally mirror those found in MR. Although 2D imaging can detect abnormalities associated with TR—such as incomplete leaflet coaptation, flail leaflet, and right-sided chamber enlargement—the technique cannot accurately quantify TR grade. Doppler echocardiography, especially color-flow mapping, has become the procedure of choice to detect TR and has reasonable accuracy for semiquantitation of severity.183 As with MR, the severity of TR can be estimated by regurgitant jet area, ratio of jet area to right atrial area, and size of proximal flow convergence zones (Fig. 15–31). Doppler interrogation of the hepatic vein is also useful, as systolic flow reversal within the vein suggests severe TR184 (Fig. 15–87). Peak RV (and PA) pressure can be estimated using measurements of peak TR velocity by CW Doppler (see "The Bernoulli Equation," above). If necessary, intravenous echocardiographic contrast agents can be injected to accentuate the TR Doppler jet and facilitate more accurate measurements of PA pressure.181
Right Ventricular Function and Pulmonary Hypertension RV enlargement and PH can be diagnosed and assessed by echocardiography185 (Fig. 15–88A and B). Because of the asymmetric and crescentic shape of the RV, accurate volume calculations are difficult. Nonetheless, 2D imaging provides useful general information regarding RV size and function. In the apical four-chamber view, the RV should appear somewhat smaller than the LV; therefore RV enlargement can be diagnosed qualitatively when the RV's cross-sectional area exceeds that of the LV. RV chamber area measurements in the apical four-chamber imaging plane can also be compared to standardized normal values. Although not well standardized, measurements of RV wall thickness can be performed from the parasternal view; a value of 5 mm is generally accepted as the upper limit of normal.185 Systolic motion of the RV free wall and LV lateral wall toward the interventricular septum should be similar and roughly symmetric in normal situations. Asymmetric hypokinesis of the RV free wall indicates RV dysfunction. RV volume overload can lead to RVH, chamber enlargement, and, in advanced stages, depressed RV systolic function. TR can result from or cause RV overload, and the TR Doppler velocity allows estimation of the peak RV systolic pressure. The interventricular septum also becomes abnormal in RV overload and tends to flatten or even bulge toward the LV (Fig. 15–89). The pattern of septal movement can help distinguish between volume and pressure overload: in pure volume overload, the RV diastolic pressure may equal or exceed that of the LV, while the systolic pressure of the LV greatly exceeds that of the RV. Therefore the interventricular septum flattens during diastole and returns to its normal curvature during systole.186 With RV pressure overload, however, the abnormally high RV pressures persist through the entire cardiac cycle and the interventricular septum remains deformed during both systole and diastole.186
The hallmark of PH by Doppler echocardiography is a high-velocity TR jet in the absence of PS. Peak TR jet velocity can be converted to peak systolic PA pressure as follows:
where CVP = central venous pressure. In the setting of severe PH, the main PA and the inferior vena cava are often dilated. If RA pressure is elevated, the inferior vena cava (IVC) does not decrease in diameter with inspiration as normally expected. M-mode examination of the PV in PH may show a characteristic W-shaped motion of the valve leaflet during systole187 (Fig. 15–90) and loss of the normal a dip caused by partial opening of the valve during atrial contraction. The loss of the a wave is probably due to the large pressure difference between the RV and PA during late diastole and the resulting inability of the atrial contraction to partially open the PV. The midsystolic closure of the valve and partial reopening in late systole (sometimes called the flying W) may be caused by elevated pulmonary vascular resistance and oscillation of a pressure wavefront within the PA.188 Characteristic pulsed-wave Doppler abnormalities in PH include a decrease in the velocity-time integral of flow through the PV (secondary to depressed RV stroke volume) and a shortening of the acceleration time (measured from beginning of flow through the PV to peak velocity). The acceleration time (in milliseconds) can be used to estimate the mean PA pressure as: Mean PA pressure = 80 – (acceleration time/2)
Interestingly, RVH and severe PH affect LV diastolic filling characteristics, possibly through septal effects (or by relative underfilling of the left ventricle). Diastolic "abnormal relaxation" patterns of LV filling (E < A) are common in severe PH, and LV diastolic function often returns to normal if PH is reversed.189 Several groups have attempted to differentiate various etiologies of PH with echocardiography. Although some reports have suggested some utility of echo in this regard, the diagnostic accuracy is insufficient to recommend its routine use. Pulmonic regurgitation is also common in the setting of PH and is usually well recorded by pulsed Doppler. As discussed above, the end-diastolic PR velocity can be used to estimate PA end-diastolic pressure by the Bernoulli equation. |
