Impact of Tricuspid Regurgitation on Outcomes After Transcatheter Mitral Valve Replacement.

Development of functional tricuspid regurgitation (TR) because of chronic mitral disease and subsequent heart failure is common. However, the effect of TR on clinical outcomes after transcatheter mitral valve replacement (TMVR) remains unclear. We aimed to evaluate the impact of baseline TR on outcomes after TMVR. This was a single-center, retrospective analysis of patients who received valve-in-valve or valve-in-ring TMVR between 2012 and 2022. Patients were categorized into none/mild TR and moderate/severe TR based on baseline echocardiography. The primary outcome was 3 years all-cause death and the secondary outcomes were in-hospital events. Of the 135 patients who underwent TMVR, 64 (47%) exhibited none/mild TR at baseline, whereas 71 (53%) demonstrated moderate/severe TR. There were no significant differences in in-hospital events between the groups. At 3 years, the moderate/severe TR group exhibited a significantly increased risk of all-cause death (adjusted hazard ratio 3.37, 95% confidence interval 1.35 to 8.41, p = 0.009). When patients with baseline moderate/severe TR were stratified by echocardiography at 30 days into improved (36%) and nonimproved (64%) TR groups, although limited by small sample size, there was no significant difference in 3-year all-cause mortality (p = 0.48). In conclusion, this study investigating the impact of baseline TR on clinical outcomes revealed that moderate/severe TR is prevalent in those who underwent TMVR and is an independent predictor of 3-year all-cause mortality. Earlier mitral valve intervention before the development of significant TR may play a pivotal role in improving outcomes after TMVR.

Transcatheter Myotomy to Reduce Left Ventricular Outflow Obstruction.

BACKGROUND: Left ventricular outflow tract (LVOT) obstruction is a source of morbidity in hypertrophic cardiomyopathy (HCM) and a life-threatening complication of transcatheter mitral valve replacement (TMVR) and transcatheter aortic valve replacement (TAVR). Available surgical and transcatheter approaches are limited by high surgical risk, unsuitable septal perforators, and heart block requiring permanent pacemakers. OBJECTIVES: The authors report the initial experience of a novel transcatheter electrosurgical procedure developed to mimic surgical myotomy. METHODS: We used septal scoring along midline endocardium (SESAME) to treat patients, on a compassionate basis, with symptomatic LVOT obstruction or to create space to facilitate TMVR or TAVR. RESULTS: In this single-center retrospective study between 2021 and 2023, 76 patients underwent SESAME. In total, 11 (14%) had classic HCM, and the remainder underwent SESAME to facilitate TMVR or TAVR. All had technically successful SESAME myocardial laceration. Measures to predict post-TMVR LVOT significantly improved (neo-LVOT 42 mm2 [Q1-Q3: 7-117 mm2] to 170 mm2 [Q1-Q3: 95-265 mm2]; P < 0.001; skirt-neo-LVOT 169 mm2 [Q1-Q3: 153-193 mm2] to 214 mm2 [Q1-Q3: 180-262 mm2]; P < 0.001). Among patients with HCM, SESAME significantly decreased invasive LVOT gradients (resting: 54 mm Hg [Q1-Q3: 40-70 mm Hg] to 29 mm Hg [Q1-Q3: 12-36 mm Hg]; P = 0.023; provoked 146 mm Hg [Q1-Q3: 100-180 mm Hg] to 85 mm Hg [Q1-Q3: 40-120 mm Hg]; P = 0.076). A total of 74 (97.4%) survived the procedure. Five experienced 3 of 76 (3.9%) iatrogenic ventricular septal defects that did not require repair and 3 of 76 (3.9%) ventricular free wall perforations. Neither occurred in patients treated for HCM. Permanent pacemakers were required in 4 of 76 (5.3%), including 2 after concomitant TAVR. Lacerations were stable and did not propagate after SESAME (remaining septum: 5.9 ± 3.3 mm to 6.1 ± 3.2 mm; P = 0.8). CONCLUSIONS: With further experience, SESAME may benefit patients requiring septal reduction therapy for obstructive hypertrophic cardiomyopathy as well as those with LVOT obstruction after heart valve replacement, and/or can help facilitate transcatheter valve implantation.

Transcatheter Paravalvular Leak Closure With Covered Stent Tract and Vascular Plug: Tootsie Roll Technique.

BACKGROUND: Transcatheter closure of transcatheter heart valve (THV)-related paravalvular leak (PVL) is associated with a high failure rate with available devices due to the complex interaction of THV and aortic/mitral annulus. OBJECTIVES: This study reports on novel transcatheter techniques to treat PVL after THV. METHODS: The authors describe consecutive patients who underwent PVL closure after transcatheter aortic valve replacement (TAVR) or transcatheter mitral valve replacement (TMVR). A covered self-expanding stent (Viabahn) was deployed in the defect to create a seal between the THV and annulus. A vascular plug (Amplatzer Vascular Plug 2 [AVP2] or AVP4) was then deployed inside the covered stent to obliterate PVL. RESULTS: Eight patients with THV-related PVL were treated using this method (aortic [3 SAPIEN, 1 Evolut], mitral [2 SAPIEN-in-MAC (mitral annular calcification), 2 M3 TMVR). Various combinations of stents and plugs were used (5 mm × 2.5 cm Viabahn + 6 mm AVP4 [n = 2], 8 mm × 2.5 cm Viabahn + 10 mm AVP2 [n = 5], and 10 mm × 5.0 cm Viabahn + 12 mm AVP2 [n = 1]). All had technical success with immediate elimination of target PVL, without in-hospital complications. None had signs of postprocedure hemolysis. All patients were discharged alive (median 3.5 days [Q1-Q3: 1.0-4.8 days]). No residual PVL was seen at discharge, except for 1 patient with mild regurgitation due to another untreated PVL location. One patient died before 30 days due to complication of valve-in-MAC TMVR. In remaining patients, none had recurrence of PVL at 30 days. Symptoms decreased to NYHA functional class I/II in 6 patients. NYHA functional class III symptoms remained in 1 patient with mitral regurgitation awaiting subsequent valve replacement procedure. CONCLUSIONS: The technique of sequential deployment of a covered stent and vascular plug may effectively treat THV-related PVL.

Valve-in-Valve Transcatheter Aortic Valve Replacement During Second Trimester of Pregnancy.

Critical bioprosthetic aortic valve stenosis is a rare finding in the second trimester of pregnancy. We present the case of a successful valve-in-valve transcatheter aortic valve replacement in a 16-weeks-pregnant patient. We describe the significant role of the multidisciplinary heart team during preconception and pregnancy.

Hybrid Closure of Postinfarction Apical Ventricular Septal Defect Using Septal Occluder Device and Right Ventricular Free Wall: The Apical BASSINET Concept.

BACKGROUND: Postinfarction ventricular septal defect (VSD) is a catastrophic complication of myocardial infarction. Surgical repair still has poor outcomes. This report describes clinical outcomes after a novel hybrid transcatheter/surgical repair in patients with apical VSD. METHODS: Seven patients with postmyocardial infarction apical VSD underwent hybrid transcatheter repair via subxiphoid surgical access. A transcatheter occluder (Amplatzer Septal Occluder) with a trailing premounted suture was deployed through the right ventricular wall and through the ventricular septum into the left ventricular apex. The trailing suture was used to connect an anchor external to the right ventricular wall. Tension on the suture then collapses the right ventricular free wall against the septum and left ventricular occluder, thereby obliterating the VSD. Outcomes were compared with 9 patients who underwent surgical repair using either patch or primary suture closure. RESULTS: All patients had significant left-to-right shunt (Qp:Qs 2.5:1; interquartile range [IQR, 2.1-2.6] hybrid repair versus 2.0:1 [IQR, 2.0-2.5] surgical repair), and elevated right ventricular systolic pressure (62 [IQR, 46-71] versus 49 [IQR, 43-54] mm Hg, respectively). All had severely depressed stroke volume index (22 versus 21 mL/m2) with ≈45% in each group requiring mechanical support preprocedurally. The procedure was done 15 (IQR, 10-50) versus 24 (IQR, 10-134) days postmyocardial infarction, respectively. Both groups of patients underwent repair with technical success and without intraprocedural death. One patient in the hybrid group and 4 in the surgical group developed multiorgan failure. The hybrid group had a higher survival at discharge (86% versus 56%) and at 30 days (71% versus 56%), but similar at 1 year (57% versus 56%). During follow-up, 1 patient in each group required reintervention for residual VSD (hybrid: 9 months versus surgical: 5 days). CONCLUSIONS: Early intervention with a hybrid transcatheter/surgical repair may be a viable alternative to traditional surgery for postinfarction apical VSD.

Physician-Modified Endograft-Facilitated Transcatheter Pulmonary Valve Replacement in Large Right Ventricular Outflow Tract.

BACKGROUND: Transcatheter pulmonary valve replacement (TPVR) in patients with a congenital or acquired abnormality resulting in enlarged right ventricular outflow tract (RVOT) is challenging and may preclude treatment with dedicated devices. We describe a technique using a physician-modified endograft to facilitate TPVR. METHODS: Six patients underwent physician-modified endograft-facilitated TPVR for severe symptomatic pulmonary insufficiency with enlarged RVOT. The fenestration was created in a commercially available endograft before implantation, which was then deployed from the dominant branch pulmonary artery into the RVOT, with the fenestration aligned with the ostium of the nondominant pulmonary artery. A covered stent was placed through the fenestration into the nondominant branch pulmonary artery, and a transcatheter heart valve was deployed within the endograft at the level of the original pulmonary valve. RESULTS: Four patients had tetralogy of Fallot, 1 had pulmonary atresia, and 1 had rheumatic valve disease. The RVOT/main pulmonary artery was severely enlarged (diameter, 44.2 [43.5-50.6] mm). All patients had reduced right ventricular (RV) function and dilated RVs (RV end-diastolic volume, 314 [235-316] mL). Successful endograft, covered stent, and transcatheter heart valve deployment were achieved in all cases without stent/valve embolization, vascular complications, or bleeding complications. At 30 days, 1 patient had mild pulmonary insufficiency, while others had none. The RV size measured by echocardiography was significantly reduced after TPVR (RV area, 34.4 [baseline] versus 29.0 [pre-discharge] versus 25.3 [30 days] cm2; P=0.03). During median follow-up of 221.5 (range, 29-652) days, there were no deaths or need for pulmonary valve reintervention. One patient developed severe tricuspid regurgitation due to entrapment of the anterior tricuspid leaflet by the endograft. The patient underwent successful tricuspid replacement and resection of the offending endograft with preservation of the pulmonary valve prosthesis. CONCLUSIONS: Simple fenestration of an off-the-shelf endograft and associated covered stent placement through the fenestration allows TPVR for patients with dysfunctional native or patch-repaired pulmonary valves and RVOT enlargement.

Feasibility of redo-TAVI in self-expanding Evolut valves: a CT analysis from the Evolut Low Risk Trial substudy.

BACKGROUND: Transcatheter aortic valve implantation in an existing transcatheter valve (redo-TAVI) pins the index valve leaflets in the open position (neoskirt), which can cause coronary flow compromise and limit access. Whether anatomy may preclude redo-TAVI in self-expanding Evolut valves is unknown. AIMS: We aimed to evaluate the anatomical feasibility of redo-TAVI by simulating implantation of a balloon-expandable SAPIEN 3 (S3) within an Evolut or an Evolut within an Evolut. METHODS: A total of 204 post-TAVI computed tomography (CT) scans from the Evolut Low Risk CT substudy were analysed. Five redo-TAVI positions were evaluated: S3-in-Evolut inflow-to-inflow, S3 outflow at Evolut nodes 4, 5, and 6, and Evolut-in-Evolut inflow-to-inflow. Univariable modelling identified pre-TAVI clinical characteristics, CT anatomical parameters, and procedural variables associated with coronary flow compromise using the neoskirt height and post-TAVI aortic root dimensions. RESULTS: The risk of coronary flow compromise was lowest when the S3 outflow was at Evolut node 4 (20%) and highest when at Evolut node 6 (75%). The highest likelihood of preserving coronary accessibility occurred with the S3 outflow at Evolut node 4. Female sex and higher body mass index were associated with a higher risk of coronary flow compromise, as were a smaller annulus diameter, lower sinus of Valsalva height and width, shorter coronary height, smaller sinotubular junction diameter, and shallower Evolut implant depth. CONCLUSIONS: The feasibility of redo-TAVI after Evolut failure is multifactorial and relates to the native annular anatomy, as well as the implantation depth of the index and second bioprostheses. Placement of an S3 at a lower Evolut position may reduce the risk of coronary flow compromise while preserving coronary access. CLINICALTRIALS: gov: NCT02701283.

A Comparison of Thirty-Day Clinical and Echocardiographic Outcomes of Patients Undergoing Transcatheter vs. Surgical Aortic Valve Replacement for Native Aortic Insufficiency.

OBJECTIVES: We aim to compare in-hospital and 30-day outcomes of transcatheter aortic valve replacement (TAVR) versus surgical aortic valve replacement (SAVR) for native aortic insufficiency (AI). BACKGROUND: TAVR is increasingly used off-label in patients with AI deemed high risk for SAVR. There is a paucity of data comparing TAVR and SAVR with current commercially available TAVR devices. METHODS: A single-center, retrospective cohort study of patients undergoing TAVR or SAVR for native AI between 2014 and 2020 was performed. Data were obtained from the Society of Thoracic Surgeons (STS) Adult Cardiac Surgery Database, Transcatheter Valve Therapy (TVT) registry, and chart review. In-hospital and 30-day outcomes are reported. RESULTS: Of 125 total patients, 91 underwent SAVR and 34 underwent TAVR. The TAVR group had a higher STS predictive risk of mortality (PROM) (TAVR = 3.96 %, SAVR = 1.25 %, p < 0.0001). In the postoperative period, the SAVR group had higher rates of new-onset atrial fibrillation (20.9 % vs. 0 %, p < 0.001), while the TAVR group had higher rates of complete heart block requiring permanent pacemaker implantation (20.6 % vs. 2.2 %, p < 0.001). There was no difference in in-hospital or 30-day mortality, stroke, myocardial infarction, residual AI, or repeat valve intervention. CONCLUSIONS: Despite higher STS PROM and more comorbidities, patients who underwent TAVR for AI had similar in-hospital and 30-day outcomes as patients who underwent SAVR for AI. These results support TAVR in selected high-risk patients with AI, with the knowledge that pacemaker needs may be higher than patients undergoing SAVR.

Transcatheter Mitral Valve Repair in a Tricuspid Atresia Patient With Potts and Glenn Shunts.

Our patient was a 50-year-old woman with tricuspid atresia who had undergone palliation with a Potts shunt to the left pulmonary artery as an infant and a classic Glenn shunt to the right pulmonary artery as a young child. Under general anesthesia, she underwent transcatheter edge-to-edge repair of the mitral valve for severe symptomatic mitral regurgitation. (Level of Difficulty: Advanced.).

Evolving computed tomography angiography for aortic valve replacement: Optimizing transcatheter and surgical therapies.

Transcatheter aortic valve replacement (TAVR) has transformed the treatment of aortic stenosis and pre-procedure planning relies heavily on advanced imaging. Multidetector computed tomography angiography, the "TAVR CT," facilitates essential planning steps of measuring the aortic root for valve sizing and feasibility and assessment of potential access vessels, making it the guideline gold standard in preprocedural TAVR work up. This Impact of Advanced Imaging Techniques on Cardiac Surgery article will examine the development of TAVR CT, illustrate the current impact and utility, and highlight potential areas of future growth. Clinicians who keep informed of these changes and can become proficient with TAVR CT analyses will offer patients the most optimal results and fuel future therapeutic growth.

Echocardiographic Imaging of the Tricuspid Valve: Preprocedural Planning and Intraprocedural Guidance.

Transcatheter tricuspid valve (TV) interventions have increased dramatically in recent years. TV imaging is challenging in many respects. Given the TV's anatomic complexity, multimodality imaging, which is centered on echocardiography (echo), plays a significant part in planning and execution of these interventions. With the help of echo-guided imaging, pathophysiologic mechanisms for TV disease are better understood, and thus, appropriate valve intervention can be strategized. Novel devices for the TV continue to be developed, and thus, intraprocedural echo imaging will continue to evolve in the days ahead.

Use of transesophageal echocardiography for transcatheter valve-in-valve implantation for patients with prior bioprosthetic surgical aortic, mitral, tricuspid, and pulmonic valves.

Valve-in-valve (ViV) transcatheter procedures are the preferred option for redo valve replacement in patients who otherwise would be high risk for surgery. Transesophageal echocardiography (TEE) is an integral imaging modality for both peri-procedural and intra-procedural guidance during transcatheter ViV replacement. When intentional leaflet laceration is needed, such as with the BASILICA (Bioprosthetic or native Aortic Scallop Intentional Laceration to prevent Iatrogenic Coronary Artery obstructions during TAVR) or LAMPOON (Laceration of the Anterior Mitral valve leaflet to Prevent left ventricular Outlet ObstructioN) procedures, TEE is critical to proper guidewire positioning and achieving a successful laceration. In this paper we detail the role of TEE in ViV transcatheter valve replacement in patients with prior surgical aortic, mitral, tricuspid, and pulmonic valves.

Balloon-Augmented Leaflet Modification With Bioprosthetic or Native Aortic Scallop Intentional Laceration to Prevent Iatrogenic Coronary Artery Obstruction and Laceration of the Anterior Mitral Leaflet to Prevent Outflow Obstruction: Benchtop Validation and First In-Man Experience.

BACKGROUND: Bioprosthetic or native aortic scallop intentional laceration to prevent iatrogenic coronary artery obstruction (BASILICA) and laceration of the anterior mitral leaflet to prevent outflow obstruction (LAMPOON) reduce the risk of coronary and left ventricular outflow obstruction obstruction during transcatheter aortic valve replacement and transcatheter mitral valve replacement. Despite successful laceration, BASILICA or LAMPOON may fail to prevent obstruction caused by inadequate leaflet splay in patients having challenging anatomy such as very small valve-to-coronary distance, diffusely calcified, rigid leaflets, or undergoing transcatheter aortic valve replacement inside existing transcatheter aortic valve replacement. We describe a novel technique of balloon-augmented (BA) leaflet laceration to enhance leaflet splay. METHODS: We measured the incremental leaflet splay from BA-BASILICA in vitro. From November 2019 to March 2021, 16 patients underwent BA-BASILICA and 4 BA-LAMPOON at 3 centers. RESULTS: BA-BASILICA increased benchtop leaflet tip splay 17%, maximum splay angle 30%, and splay area 23%, resulting in a more rounded apex and larger effective area. Sixteen patients at risk for inadequate BASILICA leaflet splay, including 4 transcatheter aortic valve replacement inside existing transcatheter aortic valve replacement, underwent BA-BASILICA. All had successful leaflet laceration. One had coronary obstruction requiring immediate orthotopic stenting. Two underwent elective orthotopic coronary stenting through the transcatheter valve cells for leaflet prolapse without coronary ischemia. There were no deaths during the procedure or at 30 days. Four patients at risk for inadequate anterior mitral leaflet splay underwent BA-LAMPOON. All had successful target leaflet laceration without left ventricular outflow obstruction obstruction or procedural death. One died within 30 days. CONCLUSIONS: BA leaflet laceration enhances leaflet splay in vitro and may allow transcatheter aortic valve replacement and transcatheter mitral valve replacement in patients otherwise ineligible for traditional BASILICA or LAMPOON due to challenging anatomy. Graphic Abstract: A graphic abstract is available for this article.

The Art of SAPIEN 3 Transcatheter Mitral Valve Replacement in Valve-in-Ring and Valve-in-Mitral-Annular-Calcification Procedures.

The SAPIEN 3 is the only transcatheter heart valve commercially available for compassionate transcatheter mitral valve replacement in patients with previous mitral surgical rings and mitral annular calcification (valve in ring [VIR] and valve in mitral annular calcification [VIM]). Reported outcomes have been inconsistent or poor. The review provides an overview of the authors' approach to achieve largely consistent results despite the intrinsic limitations of SAPIEN 3 VIM and VIR. The approach includes bedside modifications of the valve implant, the delivery system, and of the cardiac substrate itself. Until purpose-built devices are readily available, VIR and VIM procedures will require aggressive multidisciplinary cooperation, meticulous planning and execution, and postprocedure management by experienced, high-volume operators.

Electrosurgical Detachment of MitraClips From the Anterior Mitral Leaflet Prior to Transcatheter Mitral Valve Implantation.

OBJECTIVES: The aim of this study was to test the hypothesis that transcatheter electrosurgery might allow intentional detachment of previously placed MitraClip(s) from the anterior leaflet to recreate a single mitral orifice for transcatheter mitral valve implantation (TMVI), leaving the retained MitraClip(s) securely fastened to the posterior leaflet and without interfering with the mitral bioprosthesis. BACKGROUND: Patients with severe mitral regurgitation or stenosis despite edge-to-edge mitral repair with the MitraClip typically have few therapeutic options because the resultant double orifice precludes TMVI. Transcatheter electrosurgery may allow detachment of failed MitraClip(s) from the anterior leaflet to recreate a single orifice for TMVI. METHODS: This was a single-center, 5-patient, consecutive, retrospective observational cohort. Patients underwent transcatheter electrosurgical laceration and stabilization of failed MitraClip(s) to recreate a single orifice, leaving the MitraClip(s) securely fastened to the posterior leaflet. Subsequently, patients underwent TMVI with an investigational device, the Tendyne mitral bioprosthesis, on a compassionate basis. Patients were followed up to 30 days. RESULTS: MitraClip detachment from the anterior leaflet and Tendyne implantation were successful in all patients. All patients survived to discharge. All patients were discharged with grade 0 central mitral regurgitation. Two patients had moderate perivalvular mitral regurgitation that did not require reintervention. During the follow-up period of 30 days, there were no deaths, cases of valve dysfunction, or reintervention. There was no evidence of erosion or bioprosthetic valve dysfunction attributable to the retained MitraClip(s) still attached to the posterior leaflet. CONCLUSIONS: Transcatheter electrosurgical detachment of failed MitraClips from the anterior leaflet followed by TMVI is technically feasible and safe at 30 days. Longer term study is needed to determine the clinical benefit of this approach and new algorithms for TMVI sizing following electrosurgical laceration and stabilization of a failed MitraClip to avoid perivalvular leak.

Omission of Heart Transplant Recipients From the Appropriate Use Criteria for Revascularization and the Ramifications on Heart Transplant Centers.

Importance: Guidelines endorse routine coronary angiography and percutaneous coronary intervention (PCI) to screen for and treat cardiac allograft vasculopathy in heart transplant recipients. However, the current Appropriate Use Criteria for Revascularization (AUC-R) do not recognize prior heart transplant as a unique PCI indication. Whether this affects rates of rarely appropriate (RA) PCIs is unknown. Objective: To assess the rate of RA PCI procedures in heart transplant recipients and how it pertains to hospital PCI appropriateness metrics and pay-for-performance scorecards. Design, Setting, and Participants: This observational study used National Cardiovascular Data Registry CathPCI Registry data on all patients undergoing elective PCIs from 96 Medicare-approved heart transplant centers from quarter 3 of 2009 to quarter 2 of 2017. The data were analyzed in July 2018. Exposures: Prior heart transplant. Main Outcomes and Measures: Rates of RA elective PCIs in heart transplant recipients compared with nonrecipients and hospital rates of RA PCI before vs after exclusion of heart transplant recipients using paired t tests. In a subset of heart transplant centers participating in the Anthem Blue Cross and Blue Shield's Quality-In-Sights Hospital Incentive Program (Q-HIP), we compared the change in Q-HIP scorecards before vs after excluding heart transplant recipients. Results: Of 168 802 participants, 123 124 (72.9%) were men, 137 457 were white, and the mean (SD) age was 66.3 (11.4) years. Of 168 802 elective PCIs performed in heart transplant centers, 1854 (1.1%) were for heart transplant recipients. Heart transplant recipients were less likely to have ischemic symptoms (14.6% vs 61.4%, P < .001), had lower rates of antecedent stress testing (15.0% vs 58.4%, P < .001), and had higher RA PCI rates (66.0% vs 16.9%, P < .001) compared with nonrecipients. In heart transplant centers, the absolute difference in RA rates (before vs after excluding transplant recipients) was directly associated with the proportion of PCIs performed in heart transplant recipients (r = 0.91; P < .001). In the subset of heart transplant centers participating in Q-HIP during the 2016 and 2017 calendar years, 8 of 20 (40%) and 8 of 16 centers (50%), respectively, could have benefited from a change in their Q-HIP scorecards if their RA PCI rates excluded transplant recipients. Conclusions and Relevance: Two-thirds of PCIs in heart transplant recipients were deemed RA by the AUC-R. The failure of the AUC-R to consider prior heart transplant as a unique PCI indication may lead to inflated RA PCI rates with the potential for affecting quality reporting and pay-for-performance metrics in heart transplant centers.