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Page 2 of 14 Morgan et al. Vessel Plus 2020;4:6 I http://dx.doi.org/10.20517/2574-1209.2019.32

the increasing incidence of atrial fibrillation and with use of mechanical devices such as pacemakers, and
[2,3]
it is currently estimated at around 1.6 million Americans . Population-based studies have determined
that isolated TR in the absence of other cardiac disease is a risk factor for death even when incidentally
identified on echocardiography. Further work has shown that, when controlling for other measures of
cardiac disease such as depressed left ventricular (LV) ejection fraction and elevated pulmonary artery
[4,5]
pressure, moderate to severe TR remains an independent risk factor for both morbidity and mortality .
Links between TR and increased mortality risk may stem from adverse right ventricle (RV) remodeling.
TR provides a nidus for progressive right ventricular dilation, volume overload, and ultimate right heart
[6]
contractile dysfunction . Supporting this is the finding that increasing severity of TR on imaging is associated
[4]
with markers of progressive RV dysfunction, such as RV dilation and increased right atrial pressure . The
greater the initial burden of TR in untreated patients, the more likely they are to progress over time, and the
[7]
greater the associated progression of RV dysfunction . Correspondingly, isolated severe TR is associated with
increased incidence of heart failure despite maximal medical therapy, a 3-4 × risk of major adverse cardiac
[8]
events, and a 2-3 × risk of death, after controlling for age and presence of other comorbid conditions . Despite
these sobering statistics, ideal management of moderate to severe TR remains unclear.

While surgical valve repair is the standard of care for patients with severe and symptomatic TR, it carries
with it a 2-5 × higher risk of mortality than surgery on other cardiac valves, and consequently repair of
isolated severe TR is rare [3,9-13] . Furthermore, because of the complex relationship between TR and RV
dysfunction, for a subset of patients with a clear indication for surgery, correction of TR results in florid
[6]
right heart failure, and can be fatal . At present, no predictive index exists to identify such patients
[14]
preoperatively . Because of the high morbidity and mortality rate of open tricuspid surgery, there is a
growing interest in minimally invasive therapies for the tricuspid valve (TV). However, while transcatheter
therapies for TR are evolving, they have lagged behind similar interventions for the aortic and mitral
[15]
valves, and have yet to be incorporated into routine clinical practice .
Advances in cardiac imaging have enabled high-resolution assessments of both the RV and TV, providing
improved assessment of both structure and function [9,14,16] . Computational models of the RV and TV are
underway to accurately represent the mechanical behavior of the right heart under varied conditions [17,18] .
The utility of this type of cardiac modeling has been previously demonstrated in the LV and mitral valve,
illuminating the effects of surgical procedures such as ring annuloplasty, MitraClip placement, and
surgical ventricular restoration [19-22] . Using these techniques to examine the TV will provide insight into
the mechanical effects of surgical repair and of novel transcatheter devices, leading to improved care of
this large group of patients with diseases of the “forgotten” valve.

RIGHT HEART ANATOMY
The right heart includes the right atrium (RA) and RV, separated by the TV. Deoxygenated venous blood
drains from the body into the RA, and is propelled forward into the RV during atrial systole; the TV then
acts as a one-way valve preventing regurgitant flow of blood back to the RA during ventricular systole, as
blood is ejected from the RV out to the pulmonary circulation to participate in oxygen and carbon dioxide
exchange.

TV ANATOMY
The TV is a unique and complex anatomic structure, in a dynamic relationship with the RA and
ventricle. The TV is the largest and most apically positioned of the four cardiac valves with a normal
orifice area of 7-9 cm 2[23] . The TV complex encompasses valve leaflet, papillary muscles, chordae, and
annular components. These components work in a well-coordinated symphony in order for the TV to