The tale of functional tricuspid regurgitation: when atrial fibrillation is the villain

This editorial refers to ‘Tricuspid valve geometry and right heart remodeling: insights into the mechanism of atrial functional tricuspid regurgitation’, by H. Utsunomiya et al., pp. 1068--1078. Atrial fibrillation (AF) is the most common sustained arrhythmia, affecting ∼33 million people worldwide and contributes to significant patient morbidity and mortality.1 The prevalence of AF is increasing due to ageing of the population, and its true prevalence is likely higher given that many individuals remain undiagnosed. A large proportion of AF patients (63.5% in EORP-AF Registry)2 have valvular heart disease (VHD). This association is justified by the fact that the volume and/or pressure overload caused by VHD promote atrial remodelling and stretching, and thus may lead to AF development.3 The fact that the causal relationship between VHD and AF is actually bidirectional is largely unknown. Indeed, AF can cause by itself functional mitral regurgitation (AF-MR) and tricuspid regurgitation (AF-TR) due to atrial and annular dilation,4,5 despite normal ventricular size and function. Both AF-MR and AF-TR, when haemodynamically significant, may play a role in heart failure (HF) development in AF patients, worsening their prognosis and functional capacity. Utsunomyia et al.6 provide unique perspectives on the geometric changes of tricuspid valve (TV) apparatus and right chambers in AF-TR. They analysed echocardiographic data from 23 patients with severe symptomatic AF-TR and compared their features with 28 patients with ventricular functional tricuspid regurgitation (VF-TR) in sinus rhythm and 10 controls. A comprehensive imaging protocol included 2D transthoracic echocardiography (2DTTE) and 3D transoesophageal echocardiography acquisitions obtained within the same day. The methodology applied to study the TV complex represents one of the strengths of this study, as it addressed all its components. Besides the TV leaflets and annulus (TA) geometry, the authors assessed the spatial position of papillary muscle (PM) tips using a 3D co-ordinate reference (X-Y-Z), as well as the right ventricular (RV) volumes by 3DTEE and the vena contracta area as markers of functional tricuspid regurgitation (FTR) severity. Finally, the authors also looked at the orientation (α°) of the major TA axis with respect to the direction of interatrial septum, reflecting the main direction of TA expansion. The rationale of α° index stems from the authors’ observation that a more posterior orientation of TA major axis is common in AF patients and associated with higher likelihood of TA diameter underestimation by 2DTTE in FTR.7 Patients with AF-TR had larger annuli with more posterior orientation and less leaflet tethering, despite having similar vena contracta area, compared with VF-TR. When projected on an X-Y annular plane, the anterior and posterior PM tips were closer and medial PM tip was farther from TA centre in AF-TR patients, as they showed more prominent annular dilation than VF-TR patients. Conversely, VF-TR patients had larger leaflet tethering and end-systolic RV volumes, and greater displacement of PM tips towards the RV apex compared to AF-TR patients. Further stratification into severe vs. massive/torrential AF-TR showed that greater volume overload and RV remodelling lead to larger leaflet tethering and PM apical displacement. The apically-directed displacement of PM tips was independently correlated with leaflet tethering angles in AF-TR at multivariable analysis. AF-TR was associated with larger right atrial (RA) volumes than VF-TR, although the single-plane algorithm employed might have underestimated RA size.8,9Three-dimensional TTE would have allowed a more accurate assessment of RA remodelling, a key player in AF-TR pathophysiology. However, RA volume and its ratio with RV end-systolic volume were independent correlates of TA area and orientation.6 This confirms previous reports that TA area correlates more closely with RA than with RV size.4,10,11 The quantification of TA and tenting volume was performed by adapting the software dedicated for mitral valve analysis, which provides a 3D model of the valve in mid-systolic frame. This off-label use required a complex semi-automated analysis (i.e. 20 landmarks for annulus and ≤22 intersections/patient for leaflets). The availability of automated software dedicated for TV with minimal user input will allow to analyse larger amounts of data in multicentre settings and to implement these measurements in routine clinical studies. Also, the possibility to obtain a static TV 3D model in any desired frame and to track it during systole and diastole will enable a better understanding of TA geometry and mechanics.12 Indeed, when using such prototype software, it was evident that the largest TA area occurs at end-diastole, not at mid-systole.10 As TA is a dynamic structure showing variable linear dimensions depending on the 2DTTE view used and the measurement timing,13 future studies will need to address the impact of TA 3D area measurement timing on patient outcome and indication for therapeutic interventions. The investigators are to be commended for their efforts to elucidate the AF-TR pathophysiology and to increase awareness about its potential clinical impact.6,7 Their work—despite the small sample size with retrospective analysis from a tertiary centre with potential referral bias—is thought provoking and timely. In fact, current guidelines and reviews addressing AF outcomes do not mention AF-MR or AF-TR, and VHD guidelines do not differentiate AF-TR from the classical form of TR due to RV remodelling (VF-TR), despite these two entities may require different management approaches. Severe AF-TR may be more suitable than VF-TR for transcatheter repair procedures, as it exhibits more severe annular dilation with minimal or no apparent tethering (Figure 1).4 On the other hand, too late intervention when AF-TR is massive/torrential might bring less benefit, as these patients had significant RV remodelling with consequent leaflet tethering and large coaptation gap. By promoting progressive RA and RV remodelling, AF-TR may also limit the success of ablation and cardioversion procedures.4 Tricuspid valve geometry by 3D transthoracic echocardiography in three illustrative cases, i.e. severe ventricular functional tricuspid regurgitation (VF-TR) compared to severe and torrential atrial functional tricuspid regurgitation (AF-TR). Tricuspid valve geometry by 3D transthoracic echocardiography in three illustrative cases, i.e. severe ventricular functional tricuspid regurgitation (VF-TR) compared to severe and torrential atrial functional tricuspid regurgitation (AF-TR). Prospective multicentre studies are needed to address the many questions that arise with this ‘new’ entity: which is the true prevalence of AF-TR among AF patients and in the general population? which are the distinctive features and management options between the patients with AF that develop AF-TR and the (more prevalent) patients with VF-TR that develop AF? will rhythm vs. rate control strategy going to be affected by AF-TR evidence5? which is the outcome of interventional repair for AF-TR vs. VF-TR? etc. As the incidence of AF is rising and its association with HF portends worse prognosis than each of the two conditions separately, the interest in the AF-TR will clearly remain high and practice-changing evidence is expected to emerge from large-scale studies. Conflict of interest: none declared. The opinions expressed in this article are not necessarily those of the Editors of European Heart Journal - Cardiovascular Imaging, the European Heart Rhythm Association or the European Society of Cardiology.