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

Secondary TR makes up the remaining 90% of TR in adults and results from right ventricular remodeling
in the presence of an otherwise normal TV. Etiologies are diverse and include chronic atrial fibrillation,
pulmonary hypertension, left ventricular failure, left to right shunts, right ventricular infarcts, and
[28]
cardiomyopathies . Secondary TR is associated with papillary muscle displacement, and dilatation
and remodeling of the TV annulus, leading to tethering or tenting of the TV leaflets and progressive RV
dysfunction.

CLINICAL IMPACT OF TR
It is estimated that about 1.6 million Americans have moderate to severe TR, while only about 8000 will
undergo TV surgery annually [3,28] . TV surgery carries a high risk of mortality compared to other cardiac
operations: overall in-hospital mortality from isolated TV repair has been reported at around 8.5%,
remaining stable over the past decade; this is compared to the 1%-5% mortality expected with isolated
repair of any of the other three main cardiac valves [11,12] . This is likely reflective of the late referral of these
patients, such that, by the time of surgical evaluation, they often have systemic manifestations of right
heart failure (i.e., coagulopathy, hepatic dysfunction, and renal failure). This is in contrast to the paradigm
for intervention on left-sided valves, which is to repair or replace before the onset of structural changes to
[9]
the heart .

TIMING AND METHODS OF TRICUSPID INTERVENTION
The 2014 American College of Cardiology/American Heart Association valvular heart disease guidelines
strongly recommend isolated TV surgery in severe symptomatic tricuspid stenosis, recommend isolated
TV surgery in patients with severe TR who do not respond to medical therapy, and recommend isolated
[9]
TV surgery in asymptomatic patients with severe TR and at least moderate RV dilation or dysfunction .
Despite these recommendations, there remains a large disparity between the number of affected patients
and the number surgically repaired [11,12] . It has been suggested that early surgery should be considered
in severe TR with RV dilation before the onset of symptoms [6,14] . There are currently no significant
published data on an accurate way to assess the TV and RV to determine the potential clinical evolution or
recommend the timing of intervention for isolated TR.

Various surgical methods have been applied to repair of the TV, including leaflet augmentation, suture
annuloplasty, and the “clover” technique of suturing the center-point of each of the tricuspid leaflets
[29]
together . The most common method of open surgical repair is ring annuloplasty, whereby a prosthetic,
incomplete ring is sutured to the tricuspid annulus to decrease annular size, restore leaflet coaptation,
[29]
and prevent further annular enlargement [Figure 2A] . Because of the high-risk nature of open tricuspid
surgery, and the general presence of comorbid conditions among patients with TR, significant interest
exists in percutaneous options for tricuspid repair. Methods to deploy the MitraClip (a percutaneous clip
designed for mitral valve repair) in the tricuspid position have yielded positive initial results, and work is
[30]
ongoing to design and test dedicated tricuspid clips and deployment devices [Figure 2B] .

INCIDENCE OF RV FAILURE AFTER REPAIR AND NEED FOR MECHANICAL RV SUPPORT
The RV is more sensitive to changes in preload and afterload than is the LV [31,32] . RV function can
deteriorate in context of alterations in preload or afterload, or direct alterations of RV contractility due
to infarction or ischemia. Importantly, acute increases in afterload are especially poorly tolerated by the
thin-walled RV. Regardless of surgical or percutaneous repair type, correction of moderate to severe TR
results in sudden exposure of the RV to increased afterload when the valve becomes competent. In patients
with limited RV reserve, this can result in acute postoperative RV failure, a unique management challenge
[33]
associated with increased complications and death after tricuspid surgery . The risk of RV dysfunction
is higher in the setting of structural remodeling (RV dilation) and/or high pulmonary vascular resistance,