When specifically looking at functional TR, it is very important to assess annular dilatation (>40 mm is abnormal), the height of coaptation of the tricuspid leaflets from the valve annular plane (>8 mm is abnormal), the tenting area (>6 cm² is abnormal), the presence or absence of edge-to-edge coaptation of the valve leaflets, and the regurgitant jet area. To evaluate the functional TR with 2D-TTE, in at least 2 orthogonal planes. For example; the RV inflow view, apical or subcostal views are the preferred planes to assess TR jet [3].

Color and Spectral Doppler are the main echocardiographic modalities to qualitatively and quantitatively assess the severity and impact of TR, while color Doppler evaluation of the presence and size of the TR jet in the RA is primarily utilized to qualitatively assess its severity [15]. The functional TR jet is usually central and is classified as either mild, if the area occupying of the TR jet in the RA is <5 cm², or severe, if the regurgitant area is >10 cm² [5]. There are major limitations, in that the color jet is only a mean velocity map and is influenced by many factors, the foremost of which is the ability to accurately image the TR jet, as well as hemodynamic state of the patient. In an attempt to improve the quantification of the TR color jet as a marker of severity, the recent ACC/AHA guidelines in 2014 have emphasized utilizing the vena contracta (VC) – a measurement of the width of the high velocity regurgitant jet on the atrial side of the tricuspid apparatus – as a marker of severity. VC is usually imaged in apical four-chamber view at an adapted Nyquist limit, with narrow sector scan with zoom in mode for better temporal resolution [16]. Average measurement of VC > 6.5 mm is usually associated with severe TR (Fig. 20.1).

It is easy to understand how there are limitations with this method, especially if there are multiple TR jets present or if the orifice is elliptical, not circular. In an attempt to further semi-quantitate the assessment of the severity of TR by echocardiographic Doppler, the PISA, or Proximal Isovelocity Surface Area radius, has also been utilized. While this has been widely applied to assessing the severity of mitral regurgitation, it has not been proven to be useful or reproducible in the evaluation of TR. The apical four-chamber view and the parasternal long- and short-axis views are recommended. Eccentric TR jets may limit the ability of an accurate radius of PISA to be measured. But, currently, most believe that a PISA radius of >9 mm at Nyquist limit is indicative of significant TR. Recently, many have emphasized trying to accurately quantitate TR by measuring an effective regurgitant orifice (ERO), but again, the variability and reproducibility of these measurements is difficult. An ERO area >40 mm² is suggestive of severe TR (Fig. 20.2). A simple way of evaluating severity of TR is to evaluate the presence of systolic flow reversal in the hepatic vein – also an indication of severe TR [17].

Spectral Doppler has been utilized to evaluate the flow velocity of the TR jet. From this, one can calculate RV and PA systolic pressures. The key measurement, though, is to get an accurate TR jet velocity profile, as this may vary, not only from acoustic window utilized (parasternal position versus apical position), but also from the direction of interrogation of the TR jet by the continuous wave Doppler. Saying that, it is widely utilized as a calculation of RV and, hence, PA systolic pressure, even though it does have limitations. For accurate calculation of right RV or PA systolic pressures it is important to appropriately estimate RA pressure. Various methods are utilized to estimate RA pressure based upon the size of the IVC, as well as the ability to show inspiratory collapse. Mutlak et al. noted that elevated PA systolic pressures are associated with more severe TR [18].

RV function can be assessed in four-chamber view by measuring end-diastolic area and the end-systolic area to calculate the RV fractional area change [3]. RV function is also analyzed by tricuspid annular plane systolic excursion (TAPSE), as well as tissue evaluation of the tricuspid annulus (S’). All of these measurements are utilized in clinical practice, but have important limitations in both proper acquisition of images, as well as proper measurements. TTE with strain analysis of RV function has shown promise at being able to accurately evaluate global RV function, but has not been widely clinically utilized [19, 20]. Measurements of RA size and dimension give some insight into the chronicity of the functional TR [20].

Doppler parameters have also been utilized to evaluate pulmonary vascular resistance (PVR), which is especially important when trying to evaluate patients who have adult congenital heart disease or congestive heart failure. PVR is directly related to the trans pulmonary pressure gradient and inversely related to trans pulmonary flow and can be measured noninvasively by Doppler when there is suspected elevation of the right-sided pressures, known or suspected increase inflow across the pulmonary valve, or any high output situation. The easiest way to measure that is by using an algorithm, whereby the ratio of tricuspid regurgitant velocity divided by the Velocity Time Integral (VTI) in the RV outflow tract is assessed and if that ratio exceeds 0.2, then it is suspected that one might have increased PVR. Spectral Doppler can also be utilized to evaluate flow parameters in the RV outflow tract. Being able to calculate a RV VTI does allow for the assessment of mean PA pressures. Importantly, the shape of the RV outflow tract pulse wave Doppler tracing gives a qualitative assessment of the presence or absence of PH, but being able to calculate RV outflow tract VTI may be very important to assess the functional reserve of the RV [21].