The prevalence of computed tomography-defined leaflet thrombosis in intra- versus supra-annular transcatheter aortic valve prostheses

Hypoattenuated Leaflet Thickening After Implantation of the ACURATE neo or the ACURATE neo2 Transcatheter Heart Valve

Subclinical leaflet thrombosis, identified as hypoattenuated leaflet thickening (HALT) on cardiac computed tomography scan, has been observed after transcatheter aortic valve replacement (TAVR). However, data on HALT after the implant of the supra-annular ACURATE neo/neo2 prosthesis are limited. This study aimed to determine the prevalence and risk factors for the development of HALT after TAVR with the ACURATE neo/neo2. A total of 50 patients who received the ACURATE neo/neo2 prosthesis were prospectively enrolled. Patients underwent a contrast-enhanced multidetector row cardiac computed tomography scan at before, after, and 6 months after TAVR. At the 6-month follow-up, HALT was detected in 16% (8 of 50 patients). These patients had a lower implant depth of the transcatheter heart valve (8 ± 2 mm vs 5 ± 2 mm, p = 0.001), less calcified native valve leaflets, a better expansion of the frame at the level of the left ventricular outflow tract, and were less often hypertensive. Thrombosis of the sinus of Valsalva occurred in 18% (9/50). There was no difference in the anticoagulation regimen between patients with and without thrombotic findings. In conclusion, HALT was present in 16% of patients at 6 months follow-up, patients presenting with HALT had a lower implant depth of the transcatheter heart valve, and HALT was detected in patients on oral anticoagulation therapy.

Computed tomography imaging for subclinical leaflet thrombosis following surgical and transcatheter aortic valve replacement

Subclinical leaflet thrombosis (LT) may occur following surgical and transcatheter aortic valve replacement. Computed tomography (CT) has become an established imaging modality to diagnose subclinical LT following bioprosthetic aortic valve replacement. Even so, there is a limited (but growing) experience in utilizing CT imaging for this indication. This review emphasizes a systematic approach to acquiring and analysing CT imaging for subclinical LT, highlighting evidence surrounding clinical sequelae of subclinical LT and anti-thrombotic implications following diagnosis.

Effect of Native Aortic Leaflet Geometry Modification on Transcatheter Aortic Valve Neo-sinus and Aortic Sinus Flow: An In-vitro Study

PURPOSE

Leaflet thrombosis is a potentially fatal complication after transcatheter aortic valve replacement (TAVR). Blood flow stagnation in the neo-sinus and aortic sinuses are associated with increased thrombus severity. Native aortic leaflet modification may be a potential strategy to improve the neo-sinus and aortic sinus fluid dynamics. However, limited data exist on the effect of leaflet geometry modification on the flow within the neo-sinus and aortic sinus regions. We evaluate the effect of aortic leaflet modification on the neo-sinus and aortic sinus flow stagnation after simulated TAVR.

METHODS

Particle image velocimetry measurements were performed under nominal (5 LPM) and low (2.5 LPM) cardiac output conditions for an intact leaflet (control) case, and 3 modified leaflet geometries. Aortic leaflet geometry modification via leaflet splay was simulated with increasing splay geometry (leaflet splay distance: 5 mm-narrow, 10 mm-medium, and 20 mm-wide).

RESULTS

Leaflet geometry modification influenced flow features throughout the cardiac cycle, at both cardiac outputs, and allowed for flow communication between the neo-sinus and aortic sinus regions compared to the control. In the aortic sinus, flow stagnation reduced by over 64% at 5LPM, and over 36% at 2.5LPM for all simulated modified leaflet geometries compared to the control. However, only the medium and wide splay geometries enabled a reduction in neo-sinus flow stagnation compared to the control case.

CONCLUSIONS

These findings suggest that aortic leaflet geometry modification (of at least 10 mm leaflet splay distance) may reduce flow stasis and potentially decrease valve thrombosis risk.

Structural analysis of regional transcatheter aortic valve underexpansion and its implications for subclinical leaflet thrombosis

Subclinical leaflet thrombosis has been increasingly recognized following transcatheter aortic valve replacement (TAVR). Determining the risk factors is vital in preventing clinical leaflet thrombosis and ensuring long-term value durability. Clinical data have indicated that regional stent under-expansion of transcatheter aortic valves (TAVs), particularly self-expanding devices, may be associated with an increased risk of subclinical leaflet thrombosis. This study aimed to determine the effects of regional TAV frame under-expansion on leaflet kinematics, leaflet structural characteristics, and explore its impact on the likelihood of leaflet thrombosis. In this study, mild and moderate regional frame under-expansion of a 26-mm CoreValve were examined using experimental testing and computational simulations. The results indicated that regional TAV frame under-expansion impairs leaflet kinematics and reduces the range of motion in leaflets with an angle less than 120°. The reduced range of motion can increase blood stasis on the surface of the TAV leaflets. The results also demonstrated that regional frame under-expansion induced localized high-stress regions in the leaflets close to the fixed boundary edge. The increased mechanical stress can lead to accelerated tissue degeneration. The study improves our understanding of the effects of regional stent under-expansion in TAVR. Post-procedural balloon dilatation of self-expanding TAVs can potentially be advantageous in reducing leaflet distortion and normalizing leaflet stress distribution. Large-scale, prospective, and well-controlled studies are needed to further investigate regional TAV frame under-expansion effects on subclinical leaflet thrombosis and long-term valve durability.

Biomechanics of Transcatheter Aortic Valve Replacement Complications and Computational Predictive Modeling

Transcatheter aortic valve replacement (TAVR) is a rapidly growing field enabling replacement of diseased aortic valves without the need for open heart surgery. However, due to the nature of the procedure and nonremoval of the diseased tissue, there are rates of complications ranging from tissue rupture and coronary obstruction to paravalvular leak, valve thrombosis, and permanent pacemaker implantation. In recent years, computational modeling has shown a great deal of promise in its capabilities to understand the biomechanical implications of TAVR as well as help preoperatively predict risks inherent to device-patient-specific anatomy biomechanical interaction. This includes intricate replication of stent and leaflet designs and tested and validated simulated deployments with structural and fluid mechanical simulations. This review outlines current biomechanical understanding of device-related complications from TAVR and related predictive strategies using computational modeling. An outlook on future modeling strategies highlighting reduced order modeling which could significantly reduce the high time and cost that are required for computational prediction of TAVR outcomes is presented in this review paper. A summary of current commercial/in-development software is presented in the final section.

Prosthesis Geometrical Predictors of Leaflet Thrombosis Following Transcatheter Aortic Valve Replacement With Intra-Annular Prostheses

OBJECTIVE

To determine the association between prosthesis geometry with leaflet thrombosis (LT).

BACKGROUND

Leaflet thrombosis following transcatheter aortic valve replacement (TAVR) is a recognised entity. The association between prosthesis geometry with LT is unclear but maybe a potential modifiable factor in its prevention.

METHODS

Patients who received an intra-annular TAVR prosthesis and were prospectively planned to undergo post-procedural computed tomography (CT) imaging were included. Leaflet thrombosis was defined as at least 50% restricted leaflet motion on CT. Prosthesis expansion and eccentricity was measured at prosthesis inflow, annulus and outflow levels. Prosthesis misalignment was defined as the average angle deviation between native and prosthesis leaflet commissure, greater than 30°.

RESULTS

Prevalence of LT was 13.7% in 117 patients. None of the patients with LT were on anticoagulation therapy. Patients with LT had reduced prosthesis annular expansion (89.4±5.2% vs 97.0±4.4%, p<0.01), greater prosthesis misalignment (81.3% vs 48.5%, p=0.02) and deeper implants (6.3±1.7 mm vs 4.3±1.5 mm, p<0.01). Threshold for the presence of LT on ROC analysis was an implant depth of 5.7 mm (AUC [area under curve]=0.81). Independent predictors of LT were annular under-expansion (Odds ratio [OR] 1.4, 95% confidence interval [CI] 1.2-1.7, p=0.03) prosthesis misalignment (OR 6.8, 95%CI 1.1-45.5, p=0.04) and implant depth (OR 1.9, 95%CI 1.1-3.2, p=0.03). Anticoagulation therapy was a protective factor (OR 0.2; 95%CI 0.1-0.4, p<0.01).

CONCLUSION

Geometrical predictors of LT post intra-annular TAVR were reduced prosthesis expansion at the annular level, lower implant depth and greater prosthesis misalignment. These factors may be important considerations during procedural planning for TAVR.

Transcatheter Aortic Valve Leaflet Thrombosis: Prevalence, Management, and Future Directions

PURPOSE OF REVIEW

We review the pathology, prevalence, diagnosis, hemodynamics, risk factors, prognosis, and treatment of leaflet thrombosis (LT), and suggest future directions in this field.

RECENT FINDINGS

The latest meta-analysis showed the prevalence of overall LT is 5.4% (clinical LT of 1.2% and subclinical LT of 15.1%). Either subclinical or clinical LT is not associated with risk of mortality; however, clinical LT is associated with increased risk of stroke. Although LT can be reduced by oral anticoagulation therapy (OAT), routine use of OAT as primary prevention for high-risk patients is not recommended due to increased risk of mortality. Four-dimensional computed tomography plays an important role in the diagnosis of LT and the accumulation of qualitative or qualitative assessments of hypoattenuated leaflet thickening would provide more clues to clarify effective OAT strategies. In addition, further studies are warranted to evaluate the efficacy of other anticoagulants in low-intermediate risk patients.

Effect of Leaflet Type and Leaflet-Stent Attachment Height on Transcatheter Aortic Valve Leaflet Thrombosis Potential

Transcatheter aortic valve replacement devices vary in leaflet material and in the height for which leaflets attach to the stented valve frame. Combinations of these features can influence leaflet dynamics, neo-sinus geometries, and fluid dynamics, thereby reducing or exacerbating the potential for blood flow stasis and leaflet thrombosis. To investigate these interconnected relationships, this study evaluated the effects of transcatheter valve leaflet type (porcine vs. bovine pericardium) and the leaflet-stent attachment height (low, mid, and high) on flow stasis and potential for leaflet thrombosis. Transcatheter valve models were manufactured and tested within an aortic simulator under pulsatile left heart hemodynamic conditions. Transvalvular hemodynamics, leaflet kinematics, and flow structures were evaluated by direct measurement, high-speed imaging, and two differing techniques of particle image velocimetry. Transcatheter valves with porcine pericardial leaflets were observed to be less stiff, exhibit a lesser resistance to flow, were associated with reduced regions of neo-sinus flow stasis, and superior sinus washout times. More elevated attachments of the leaflets were associated with less neo-sinus flow stasis. These initial results and observations suggest combinations of leaflet type and stent attachment height may reduce transcatheter aortic valve flow stasis and the potential for leaflet thrombosis.

Transcatheter Aortic Valve Implantation and Subclinical and Clinical Leaflet Thrombosis: Multimodality Imaging for Diagnosis and Risk Stratification

In recent years, the phenomenon of subclinical leaflet thrombosis (SLT) in patients who have undergone transcatheter aortic valve implantation has become increasingly relevant. Hypo-attenuating leaflet thickening and hypo-attenuation affecting motion diagnosed by CT are the hallmarks of SLT, and their incidence varies depending on the intensity of screening. Whether these phenomena are a surrogate for leaflet thrombosis reducing valve durability and increasing the risk of stroke is still a matter of debate. Uncertainty remains over the optimal antithrombotic therapy after TAVI and the best treatment strategy is still not confirmed. Ongoing and future trials will provide more evidence about the best strategy for the prevention and treatment of SLT.

The JenaValve pericardial transcatheter aortic valve replacement system to treat aortic valve disease

Transcatheter aortic valve replacement is a valuable alternative technique to surgery and the spectrum of therapy continues to evolve. The JenaValve Pericaridal transcatheter aortic valve replacement System allows prosthesis fixation in a native, noncalcified aortic annulus with a unique paper clip-like anchorage mechanism. The low rate of paravalvular leakage and permanent pacemaker implantation emphasizes the further widespread use of the JenaValve - despite the limited data available. In May 2021, a CE mark for the transfemoral implantation in both aortic regurgitation and aortic stenosis was granted. However, no data have been published so far. The ongoing ALIGN trials are expected to provide the pending long-term data.

Added value of 18F-FDG-PET/CT and cardiac CTA in suspected transcatheter aortic valve endocarditis

BACKGROUNDS

Transcatheter-implanted aortic valve infective endocarditis (TAVI-IE) is difficult to diagnose when relying on the Duke Criteria. Our aim was to assess the additional diagnostic value of 18F-fluorodeoxyglucose (18F-FDG) positron emission/computed tomography (PET/CT) and cardiac computed tomography angiography (CTA) in suspected TAVI-IE.

METHODS

A multicenter retrospective analysis was performed in all patients who underwent 18F-FDG-PET/CT and/or CTA with suspected TAVI-IE. Patients were first classified with Duke Criteria and after adding 18F-FDG-PET/CT and CTA, they were classified with European Society of Cardiology (ESC) criteria. The final diagnosis was determined by our Endocarditis Team based on ESC guideline recommendations.

RESULTS

Thirty patients with suspected TAVI-IE were included. 18F-FDG-PET/CT was performed in all patients and Cardiac CTA in 14/30. Using the Modified Duke Criteria, patients were classified as 3% rejected (1/30), 73% possible (22/30), and 23% definite (7/30) TAVI-IE. Adding 18F-FDG-PET/CT and CTA supported the reclassification of 10 of the 22 possible cases as "definite TAVI-IE" (5/22) or "rejected TAVI-IE" (5/22). This changed the final diagnosis to 20% rejected (6/30), 40% possible (12/30), and 40% definite (12/30) TAVI-IE.

CONCLUSIONS

Addition of 18F-FDG-PET/CT and/or CTA changed the final diagnosis in 33% of patients and proved to be a valuable diagnostic tool in patients with suspected TAVI-IE.

How to Image and Manage Prosthesis-Related Complications After Transcatheter Aortic Valve Replacement

PURPOSE OF REVIEW

In this review, we provide an overview of potential prosthesis - related complications after transcatheter aortic valve replacement, their incidences, the imaging modalities best suited for detection, and possible strategies to manage these complications.

RECENT FINDINGS

Therapy for severe aortic valve stenosis requiring intervention has increasingly evolved toward transcatheter aortic valve replacement over the past decade, and the number of procedures performed has increased steadily in recent years. As more and more centers favor a minimalistic approach and largely dispense with general anesthesia and intra-procedural imaging by transesophageal echocardiography, post-procedural imaging is becoming increasingly important to promptly detect dysfunction of the transcatheter valve and potential complications. Complications after transcatheter aortic valve replacement must be detected immediately in order to initiate adequate therapeutic measures, which require a profound knowledge of possible complications that may occur after transcatheter aortic valve replacement, the imaging modalities best suited for detection, and available treatment options.

Clinical predictors and sequelae of computed tomography defined leaflet thrombosis following transcatheter aortic valve replacement at medium-term follow-up

BACKGROUND

The clinical predictors and sequelae of leaflet thrombosis (LT) following transcatheter aortic valve replacement (TAVR) is still unclear. Therefore, our aim was to determine the clinical predictors and sequelae at mid-term follow-up of computed tomography (CT)-defined LT following TAVR.

METHODS AND RESULTS

We performed a prospective evaluation with a 320-multislice CT following TAVR for the presence of LT, defined as hypo-attenuated leaflet thickening (HALT). Four-dimensional CT image-rendering was performed to determine the presence of reduced leaflet motion (RELM). 172 patients [89 (51.7%) male, mean age 82.8 ± 5.7 years] treated with commercially available TAVR device (Lotus 54%, CoreValve 32% and Sapien 3 14%) were included, with median CT-scan at 6.0 weeks post-TAVR. Prevalence of HALT was 14.0% (24 cases) and RELM was 9.8% (17 cases). On multivariate analysis, patients with HALT were less prescribed oral anticoagulation (OAC) (OR 9.9), received larger TAVR prostheses (OR 5.7) and higher rates of moderate-severe para-valvular regurgitation (PVR) (OR 16.3). There was no difference in clinical outcomes at a median follow-up of 2.3 years. Patients with RELM had significantly higher transvalvular gradients after discharge when compared to those without RELM.

CONCLUSIONS

Absence of OAC, large TAVR prostheses and moderate-severe PVR were predictors for LT. Transvalvular gradients were higher in patients that developed RELM but not HALT. Further studies are warranted to determine the long-term impact of LT on TAVR durability. Prevalence of different sub-types of CT-defined LT (HALT and RELM) and the clinical predictors of developing LT following TAVR. CT computed tomography, HALT hypo-attenuated leaflet thickening, LT leaflet thrombosis, RELM reduced leaflet motion, TAVR transcatheter aortic valve replacement.

Rationale and design of the ADAPT-TAVR trial: a randomised comparison of edoxaban and dual antiplatelet therapy for prevention of leaflet thrombosis and cerebral embolisation after transcatheter aortic valve replacement

INTRODUCTION

Optimal antithrombotic strategy following transcatheter aortic valve replacement (TAVR) is still unknown. We hypothesised that the direct factor Xa inhibitor edoxaban can potentially prevent subclinical leaflet thrombosis and cerebral embolisation compared with conventional dual antiplatelet therapy (DAPT) in patients undergoing TAVR.

METHODS AND ANALYSIS

The ADAPT-TAVR trial is an international, multicentre, randomised, open-label, superiority trial comparing edoxaban-based strategy and DAPT strategy in patients without an indication for oral anticoagulation who underwent successful TAVR. A total of 220 patients are randomised (1:1 ratio), 1-7 days after successful TAVR, to receive either edoxaban (60 mg daily or 30 mg daily if patients had dose-reduction criteria) or DAPT using aspirin (100 mg daily) plus clopidogrel (75 mg daily) for 6 months. The primary endpoint was an incidence of leaflet thrombosis on four-dimensional, volume-rendered cardiac CT imaging at 6 months post-TAVR. The key secondary endpoints were the number of new lesions and new lesion volume on brain diffusion-weighted MRI and the changes in neurological and neurocognitive function assessment between immediate post-TAVR and 6 months of study drug administration. Detailed clinical information on thromboembolic and bleeding events were also assessed.

ETHICS AND DISSEMINATION

Ethic approval has been obtained from the Ethics Committee/Institutional Review Board of Asan Medical Center (approval number: 2017-1317) and this trial is also approved by National Institute of Food and Drug Safety Evaluation of Republic of Korea (approval number: 31511). Results of this study will be disseminated in scientific publication in reputed journals.

TRIAL REGISTRATION NUMBER

NCT03284827.

In-Vitro Assessment of the Effects of Transcatheter Aortic Valve Leaflet Design on Neo-Sinus Geometry and Flow

Transcatheter aortic valve (TAV) leaflet thrombosis is a clinical risk with potentially fatal consequences. Studies have identified neo-sinus flow stasis as a cause of leaflet thrombosis. Flow stasis is influenced by the TAV leaflets, which affect the local fluid dynamics in the aortic sinus and neo-sinus. This study evaluated the effects of TAV leaflet features on the neo-sinus flow as a measure of leaflet thrombosis risk. Five TAVs of varied leaflet length and insertion height were tested in a simulator. Hydrodynamics and leaflet kinematics through en-phase imaging were quantified. Velocity fields were assessed using high-speed particle image velocimetry. Regions of flow stasis and particle residence times (PRTs) were quantified. TAVs with shorter leaflet length exhibited larger orifice areas and lower transvalvular pressure gradients. Shorter leaflet length and increased leaflet insertion TAVs additionally exhibited lower neo-sinus PRTs (0.44 ± 0.21 vs 2.83 ± 0.48 cycles, p < 0.05) and higher neo-sinus peak velocities (0.15 ± 0.009 vs 0.07 ± 0.005 m/s, p < 0.05) than TAVs with longer leaflet length and lower leaflet insertion. The average neo-sinus volume positively correlated with PRT(r = 0.810, p < 0.001), and extent of flow stasis (r = 0.682, p < 0.05). These results suggest that a small neo-sinus volume may reduce flow stagnation and particle residence, potentially reducing the risk of leaflet thrombosis. We propose that leaflet design features might be proactively controlled in the design of future transcatheter aortic valves.

The role of four-dimensional computed tomography in transcatheter aortic valve replacement prosthesis endocarditis with concurrent leaflet thrombosis: a case report

Background

Transcatheter aortic valve replacement (TAVR) is becoming increasingly utilized for the treatment of severe aortic valvular heart disease. Infective endocarditis of TAVR is rare but associated with higher mortality and morbidity. The potential for leaflet thrombosis following TAVR is also becoming increasingly recognized. Diagnosis of these conditions on echocardiography can be challenging due to prosthesis artefact.

Case summary

An 84-year-old man with a previous transcatheter aortic valve replacement presented with a febrile illness and bacteraemia. Transthoracic and transoesophageal echocardiography demonstrated high transvalvular gradients with features of prosthesis endocarditis, though leaflet morphology could not be fully assessed due to prosthesis artefact. Four-dimensional computed tomography revealed hypo-attenuated leaflet thickening with reduced leaflet motion, consistent with prosthesis leaflet thrombosis. The patient was successfully treated with antibiotics and anticoagulation, with resolution of the infection and normalization of the transvalvular gradient after 6 weeks.

Discussion

Echocardiography should be the first-line investigation for assessing leaflet morphology in suspected prosthetic valve endocarditis or leaflet thrombosis but its accuracy may be limited by artefact. Our case highlights that four-dimensional computed tomography provides further evaluation of prosthesis leaflet morphology/motion, providing valuable diagnostic information.

Novel Perspective for Antithrombotic Therapy in TAVI

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While surgical aortic valve replacement (SAVR) was for years the only available treatment for symptomatic aortic stenosis, the introduction of transcatheter aortic valve implantation (TAVI) in 2002 and the improvement of its technical aspects in the following years, has holistically changed the synchronous therapeutic approach of aortic valve stenosis. Recent evidence has expanded the indication of TAVI from high to lower surgical risk populations with symptomatic aortic stenosis. The administration of antithrombotic therapy periprocedurally and its maintenance after a successful TAVI is crucial for the prevention of complications and affects postprocedural survival. Randomized controlled trials investigating the appropriate combination and the duration of antithrombotic treatment after TAVI are for the moment scarce. This review article sheds light on the underlying pathogenetic mechanisms contributing in periprocedural TAVI thrombotic complications and discuss the efficacy of current antithrombotic policies as evaluated in randomized trials.

Clinical Valve Thrombosis and Subclinical Leaflet Thrombosis Following Transcatheter Aortic Valve Replacement: Is There a Need for a Patient-Tailored Antithrombotic Therapy?

Transcatheter aortic valve replacement (TAVR) has become an established therapeutic option for patients with symptomatic, severe aortic valve stenosis at increased surgical risk. Antithrombotic therapy after TAVR aims to prevent transcatheter heart valve (THV) thrombosis, in which two different entities have to be recognized: clinical valve thrombosis and subclinical leaflet thrombosis. In clinical valve thrombosis, obstructive thrombus formation leads to an increased transvalvular gradient, often provoking heart failure symptoms. Subclinical leaflet thrombosis is most often an incidental finding, characterized by a thin layer of thrombus covering the aortic side of one or more leaflets; it is also referred to as Hypo-Attenuating Leaflet Thickening (HALT) as described on multi-detector computed tomography (MDCT) imaging. This phenomenon may also affect leaflet motion and is then classified as Hypo-Attenuation affecting Motion (HAM). Even in case of HAM, the transvalvular pressure gradient remains within normal range and does not provoke heart failure symptoms. Whereas, clinical valve thrombosis requires treatment, the clinical impact and need for intervention in subclinical leaflet thrombosis is still uncertain. Oral anticoagulant therapy protects against and resolves both clinical valve thrombosis and subclinical leaflet thrombosis; however, large-scale randomized clinical trials studying different antithrombotic strategies after TAVR are still under way. This review article summarizes the currently available data within the field of transcatheter aortic valve/leaflet thrombosis and discusses the need for a patient tailored antithrombotic approach.

Bioprosthetic Valve Thrombosis

Degenerative valve disease is on the rise with greater than 100,000 valve operations performed in the US alone per year. The majority of those procedures employ tissue bioprostheses to avoid the attendant risk of anticoagulation, especially in the elderly. Though traditionally this approach has been considered a superior option to avoid anticoagulation, more recent analyses have demonstrated a significant incidence of previously unrecognized thrombosis associated with bioprosthetic valves, especially with the more recent advent of the transcatheter aortic valve replacement implantations. Bioprosthetic valve thrombosis is a major cause of either acute or indolent bioprosthetic valve degeneration, and often has an elusive presentation causing delayed recognition and treatment. The literature has extensively addressed the risks and benefits of anticoagulation following bioprosthetic valve replacement to prevent bioprosthetic valve thrombosis (BPVT), without conclusive evidence-based recommendations. The duration of anticoagulation following an episode of BPVT is unclear, and lifelong anticoagulation has been suggested. The increasing use of transcatheter aortic valve replacement as an alternative to surgical aortic valve replacement in various risk groups has introduced new challenges with regards to valve thrombosis, which have been poorly studied with regards to optimal treatment and prevention. The increasing use of valve-in-valve procedures is expected to bring on further uncharted challenges.