Possible Subclinical Leaflet Thrombosis in Bioprosthetic Aortic Valves

Transcatheter Aortic Valve Replacement: Comprehensive Review and Present Status

Aortic stenosis is the most common valvular heart disease in the developed world. About 7% of the population over age 65 years suffers from degenerative aortic stenosis. The prognosis of patients with symptomatic severe aortic stenosis is dismal without valve replacement. Even though the American College of Cardiology recommends aortic valve replacement to treat this condition as a class I recommendation, approximately one third of these patients over the age of 75 years are not referred for surgery. Typically, this is from concern about prohibitive surgical risk associated with patient frailty, comorbidities, age, and severe left ventricular dysfunction. The advent in France of transcatheter aortic valve replacement has raised the hope in the United States for an alternative, less invasive treatment for aortic stenosis. Two recent trials-the Placement of AoRTic TraNscathetER Valve Trial Edwards SAPIEN Transcatheter Heart Valve (Partner) and the CoreValve US Pivotal-have established transcatheter aortic valve replacement as the preferred approach in patients who are at high or prohibitive surgical risk. The more recently published Partner 2 trial has shown the feasibility of transcatheter aortic valve replacement in intermediate-surgical-risk patients as well. With a profile that promises easier use and better valve performance and delivery, newer-generation valves have shown their potential for further improvement in safety profile and overall outcomes. We review the history and status of this topic.

Trial design: Rivaroxaban for the prevention of major cardiovascular events after transcatheter aortic valve replacement: Rationale and design of the GALILEO study

BACKGROUND

Optimal antithrombotic treatment after transcatheter aortic valve replacement (TAVR) is unknown and determined empirically. The direct factor Xa inhibitor rivaroxaban may potentially reduce TAVR-related thrombotic complications and premature valve failure.

DESIGN

GALILEO is an international, randomized, open-label, event-driven, phase III trial in more than 1,520 patients without an indication for oral anticoagulation who underwent a successful TAVR (ClinicalTrials.govNCT02556203). Patients are randomized (1:1 ratio), 1 to 7days after a successful TAVR, to either a rivaroxaban-based strategy or an antiplatelet-based strategy. In the experimental arm, subjects receive rivaroxaban (10mg once daily [OD]) plus acetylsalicylic acid (ASA, 75-100mg OD) for 90days followed by rivaroxaban alone. In the control arm, subjects receive clopidogrel (75mg OD) plus ASA (as above) for 90days followed by ASA alone. In case new-onset atrial fibrillation occurs after randomization, full oral anticoagulation will be implemented with maintenance of the original treatment assignment. The primary efficacy end point is the composite of all-cause death, stroke, myocardial infarction, symptomatic valve thrombosis, pulmonary embolism, deep venous thrombosis, and systemic embolism. The primary safety end point is the composite of life-threatening, disabling, and major bleeding, according to the Valve Academic Research Consortium definitions.

CONCLUSIONS

GALILEO will test the hypothesis that a rivaroxaban-based antithrombotic strategy reduces the risk of thromboembolic complications post-TAVR with an acceptable risk of bleeding compared with the currently recommended antiplatelet therapy-based strategy in subjects without need of chronic oral anticoagulation.

On the Mechanics of Transcatheter Aortic Valve Replacement

Transcatheter aortic valves (TAVs) represent the latest advances in prosthetic heart valve technology. TAVs are truly transformational as they bring the benefit of heart valve replacement to patients that would otherwise not be operated on. Nevertheless, like any new device technology, the high expectations are dampened with growing concerns arising from frequent complications that develop in patients, indicating that the technology is far from being mature. Some of the most common complications that plague current TAV devices include malpositioning, crimp-induced leaflet damage, paravalvular leak, thrombosis, conduction abnormalities and prosthesis-patient mismatch. In this article, we provide an in-depth review of the current state-of-the-art pertaining the mechanics of TAVs while highlighting various studies guiding clinicians, regulatory agencies, and next-generation device designers.

Autopsy after transcatheter aortic valve implantation

Autopsy after transcatheter aortic valve implantation (TAVI) is a new field of interest in cardiovascular pathology. To identify the cause of death, it is important to be familiar with specific findings related to the time interval between the procedure and death. We aimed to provide an overview of the autopsy findings in patients with TAVI in their medical history divided by the timing of death with specific interest in the added value of autopsy over a solely clinically determined cause of death. In 8 European centres, 72 cases with autopsy reports were available. Autopsies were divided according to the time interval of death and reports were analysed. In 32 patients who died ≤72 h postprocedure, mortality resulted from cardiogenic or haemorrhagic shock in 62.5 and 34.4%, respectively. In 31 patients with mortality >72 h to ≤30 days, cardiogenic shock was the cause of death in 51.6% followed by sepsis (22.6%) and respiratory failure (9.7%). Of the nine patients with death >30 days, 88.9% died of sepsis, caused by infective endocarditis in half of them. At total of 12 patients revealed cerebrovascular complications. Autopsy revealed unexpected findings in 61.1% and resulted in a partly or completely different cause of death as was clinically determined. Autopsy on patients who underwent TAVI reveals specific patterns of cardiovascular pathology that clearly relate to the time interval between TAVI and death and significantly adds to the clinical diagnosis. Our data support the role of autopsy including investigation of the cerebrum in the quickly evolving era of cardiac device technology.

Superhemophobic titania nanotube array surfaces for blood contacting medical devices

Appropriate hemocompatible response for blood-contacting medical devices is necessary to prevent device failure.

PARTNER 2A & SAPIEN 3: TAVI for intermediate risk patients

Transcatheter aortic valve implantation (TAVI) is currently indicated for patients with severe symptomatic aortic stenosis who are unfit for surgery or when the surgical risk is high. Thanks to the increasing experience of surgeons, better patient selection, and substantial improvements in device technology, the procedure is now being performed with excellent outcomes and a progressively lower rate of complications. As a result, the cut-off threshold to implant a transcatheter valve is gradually moving toward lower risk patients. However, this is not supported by strong evidence from rigorous large clinical trials. The PARTNER 2A and SAPIEN 3 trials were conducted to address this gap in our knowledge.

In Vitro Hydrodynamic Assessment of a New Transcatheter Heart Valve Concept (the TRISKELE)

This study presents the in vitro hydrodynamic assessment of the TRISKELE, a new system suitable for transcatheter aortic valve implantation (TAVI), aiming to mitigate the procedural challenges experienced with current technologies. The TRISKELE valve comprises three polymeric leaflet and an adaptive sealing cuff, supported by a novel fully retrievable self-expanding nitinol wire frame. Valve prototypes were manufactured in three sizes of 23, 26, and 29 mm by automated dip-coating of a biostable polymer, and tested in a hydrodynamic bench setup in mock aortic roots of 21, 23, 25, and 27 mm annulus, and compared to two reference valves suitable for equivalent implantation ranges: Edwards SAPIEN XT and Medtronic CoreValve. The TRISKELE valves demonstrated a global hydrodynamic performance comparable or superior to the controls with significant reduction in paravalvular leakage. The TRISKELE valve exhibits enhanced anchoring and improved sealing. The valve is currently under preclinical investigation.

Transcatheter Aortic Valve Implantation Compared With Surgical Aortic Valve Replacement in Low-Risk Patients

BACKGROUND

The proven efficacy of transcatheter aortic valve implantation (TAVI) in high-risk patients is leading to the expansion of its indications toward lower-risk patients. However, this shift is not supported by meaningful evidence of its benefit over surgical aortic valve replacement (SAVR). This analysis aims to describe outcomes of TAVI versus SAVR in low-risk patients.

METHODS AND RESULTS

We compared the outcome after TAVI and SAVR of low-risk patients (European System for Cardiac Operative Risk Evaluation II [EuroSCORE II] <4%) included in the Observational Study of Effectiveness of SAVR-TAVI Procedures for Severe Aortic Stenosis Treatment (OBSERVANT) study. The primary outcome was 3-year survival. Secondary outcomes were early events and major adverse cardiac and cerebrovascular events at 3 years. Propensity score matching resulted in 355 pairs of patients with similar baseline characteristics. Thirty-day survival was 97.1% after SAVR and 97.4% after TAVI (P=0.82). Cardiac tamponade, permanent pacemaker implantation, major vascular damage, and moderate-to-severe paravalvular regurgitation were significantly more frequent after TAVI compared with SAVR. Stroke rates were equal in the study groups. SAVR was associated with higher risk of cardiogenic shock, severe bleeding, and acute kidney injury. At 3 years, survival was 83.4% after SAVR and 72.0% after TAVI (P=0.0015), whereas freedom from major adverse cardiac and cerebrovascular events was 80.9% after SAVR and 67.3% after TAVI (P<0.001).

CONCLUSIONS

In patients with low operative risk, significantly better 3-year survival and freedom from major adverse cardiac and cerebrovascular events were observed after SAVR compared with TAVI. Further studies on new-generation valve prostheses are necessary before expanding indications of TAVI toward lower-risk patients.

Incidence, Predictors, and Mid-Term Outcomes of Possible Leaflet Thrombosis After TAVR

OBJECTIVES

This study sought to clarify the incidence and predictors of hypoattenuated leaflet thickening (HALT) and mid-term outcomes after transcatheter aortic valve replacement.

BACKGROUND

HALT detected on multidetector computed tomography (MDCT) scanning raised concerns about possible subclinical leaflet thrombosis.

METHODS

We studied 70 of 100 consecutive patients from a single-center registry who underwent implantation with the Edwards SAPIEN-XT device. MDCT results, echocardiographic data, and laboratory findings obtained at the 6-month and 1-year follow-ups were analyzed.

RESULTS

Of 70 patients, MDCT scans revealed HALT in 1 patient (1.4%) at discharge, 7 (10.0%) at 6 months, and 10 (14.3%) at 1 year post-transcatheter aortic valve replacement cumulatively. The degree of leaflet immobility correlated with the HALT area on 4-dimensional MDCT (r = 0.68) on the basis of data from 10 patients. HALT was associated with male sex (70% vs. 25%; p = 0.008) and larger sinus of Valsalva (31.0 ± 2.0 mm vs. 28.6 ± 2.6 mm; p = 0.005). HALT was found in 3 of 49 patients with a 23-mm bioprosthesis and in 7 of 21 patients with a 26-mm bioprosthesis (6.1% vs. 33.3%; p = 0.006). D-dimer levels were significantly increased in the HALT group at the 6-month (2.3 μg/ml [interquartile range (IQR): 2.1 to 6.1 μg/ml] vs. 1.1 μg/ml [IQR: 0.8 to 2.2 μg/ml]; p = 0.002) and 1-year (2.7 μg/ml [IQR: 1.7 to 4.8 μg/ml] vs. 1.2 μg/ml [IQR: 0.9 to 2.1 μg/ml]; p = 0.006) follow-ups, despite no differences at discharge. The pressure gradient was decreased in the HALT group at the 1-year follow-up (8.3 ± 0.8 mm Hg vs. 11.1 ± 4.9 mm Hg; p = 0.005). After detecting HALT, additional anticoagulation therapy was not administered. Clinical outcomes, including all-cause mortality (0% vs. 1.7%; p = 1.00) and stroke (0% vs. 0%; p = 1.00), were similar between the groups.

CONCLUSIONS

HALT with reduced leaflet motion was not rare but usually subclinical. Valve hemodynamics and mid-term outcomes were uneventful even without additional anticoagulant therapy in our limited number of cases. Male sex, larger sinus and bioprosthesis size, and elevated D-dimer levels during follow-up were associated with this phenomenon.

Long-Term Valve Performance of TAVR and SAVR: A Report From the PARTNER I Trial

OBJECTIVES

The aim of this study was to evaluate the long-term performance of transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR) through longitudinal echocardiographic analysis.

BACKGROUND

The long-term performance of the SAPIEN TAVR is not well-described. Therefore, we examined the hemodynamic and valvular profile of the SAPIEN TAVR over 5 years.

METHODS

All patients receiving TAVR or SAVR with first post-implant (FPI) and 5-year echoes were analyzed for aortic valve (AV) peak velocity, AV mean gradient, AV area, peak left ventricular (LV) outflow tract and in-stent velocities, Doppler velocity index, aortic regurgitation (AR), LV mass index, stroke volume index, and cardiac index. The FPI and 5-year data were compared using a paired t test or McNemar's analyses.

RESULTS

There were 86 TAVR and 48 SAVR patients with paired FPI and 5-year echocardiograms. Baseline characteristics were similar between groups. The AV area did not change significantly 5 years after TAVR (p = 0.35). The AV mean gradient also remained stable: 11.5 ± 5.4 mm Hg at FPI to 11.0 ± 6.3 mm Hg at 5 years (p = 0.41). In contrast, the peak AV and LV outflow tract velocities decreased (p = 0.03 and p = 0.008, respectively), as did in-stent velocity (p = 0.015). Correspondingly, the TAVR Doppler velocity index was unchanged (p = 0.07). Among TAVR patients, there was no change in total AR (p = 0.40), transvalvular AR (p = 0.37), or paravalvular AR (p = 0.26). Stroke volume index and cardiac index remained stable (p = 0.16 and p = 0.25, respectively). However, there was a significant regression of LV mass index (p < 0.0001). The longitudinal evaluation among SAVR patients revealed similar trends. There was a low rate of adverse events among TAVR and SAVR patients alive at 5 years.

CONCLUSIONS

Longitudinal assessment of the PARTNER I trial (THE PARTNER TRIAL: Placement of AoRTic TraNscathetER Valve Trial) demonstrates that valve performance and cardiac hemodynamics are stable after implantation in both SAPIEN TAVR and SAVR in patients alive at 5 years. (THE PARTNER TRIAL: Placement of AoRTic TraNscathetER Valve Trial; NCT00530894).

Anticoagulant independent mechanical heart valves: viable now or still a distant holy grail

Valvular heart disease remains a large public health problem for all societies; it attracts the attention of public health organizations, researchers and governments. Valve substitution is an integral part of the treatment for this condition. At present, the choice of valve prosthesis is either tissue or mechanical. Tissue valves have become increasingly popular in spite of unresolved problems with durability, hemodynamics, cost and need for anticoagulation therapy. As a consequence, mechanical valve innovation has virtually ceased; the last successful mechanical design is 25 years old. We postulate that with improved technology, knowledge and experience gained over the last quarter century, the best possible solution to the problem of valve substitution can be achieved with a mechanical valve that is anticoagulant independent, durable, hemodynamically and cost efficient. At present, it is possible to design, test and produce a valve that can accomplish these goals.

Course of early subclinical leaflet thrombosis after transcatheter aortic valve implantation with or without oral anticoagulation

BACKGROUND

After transcatheter aortic valve implantation, early leaflet thickening, presumably reflecting thrombus, has recently been described on computed tomography angiography (CTA) in ~10% of the patients. We sought to investigate the impact of the antithrombotic regimen on the course of leaflet thickening.

METHODS

The study comprised 51 patients with leaflet thickening. Based on the time period, patients without an established indication for anticoagulation were put on phenprocoumon plus clopidogrel for at least 3 months or on dual antiplatelet therapy with aspirin and clopidogrel. Follow-up CTAs were evaluated for leaflet restriction, assessed by four-point-grading score, and maximal thickness.

FINDINGS

The anticoagulation and the dual antiplatelet therapy group comprised 29 and 22 patients, respectively. After a median of 86 days, we obtained follow-up CTAs in 22 patients on anticoagulation and in 16 patients on dual antiplatelet therapy. Leaflet thickening progressed in 11 on dual antiplatelet therapy, but always regressed onanticoagulation. The course of leaflet restriction and maximal thickness was significantly different between the two groups (P < 0.001): in the dual antiplatelet therapy group, maximal thickness increased by a mean of 1.37 ± 1.67 mm (P = 0.005) and leaflet restriction score by a median 1[quartiles 0;2] (P = 0.013), whereas in the anticoagulation group, maximal thickness regressed by 2.57 ± 1.52 mm (P < 0.001) and leaflet restriction score decreased by 1[-4;0] (P = 0.001). After a median of 91 days after discontinuation of anticoagulation, CTA performed in ten patients revealed a significant recurrent increase in leaflet restriction score and maximal thickness (P = 0.023, P = 0.007). In the entire cohort, changes in leaflet restriction correlated significantly with changes in transvalvular pressure gradients (r = 0.511, P < 0.001).

INTERPRETATION

The course of leaflet restriction was fundamentally different depending on the presence or absence of anticoagulation, with consistent regression under phenprocoumon, but mostly progression under antiplatelet therapy alone. Changes in leaflet restriction were associated with changes in transvalvular pressure gradients.

Transcatheter Aortic Valve Replacement: State of the Art and Future Directions

Transcatheter aortic valve replacement (TAVR) is a transformational and rapidly evolving treatment for patients with aortic stenosis who require valve replacement. Novel technological advancements have made this percutaneous minimally invasive therapy a first-line treatment for many patients at extreme risk for conventional cardiac surgery. New devices and improvements in existing devices have reduced procedural complications, and scientific trials are investigating the role of TAVR in lower-risk aortic stenosis populations, in patients with aortic regurgitation, and in patients with bicuspid aortic valve disease. Finally, there is intense interest in identifying patients in whom the risk-benefit ratio of TAVR is not favorable and should not be performed.

Fluid-Structure Interaction Study of Transcatheter Aortic Valve Dynamics Using Smoothed Particle Hydrodynamics

Computational modeling of heart valve dynamics incorporating both fluid dynamics and valve structural responses has been challenging. In this study, we developed a novel fully-coupled fluid-structure interaction (FSI) model using smoothed particle hydrodynamics (SPH). A previously developed nonlinear finite element (FE) model of transcatheter aortic valves (TAV) was utilized to couple with SPH to simulate valve leaflet dynamics throughout the entire cardiac cycle. Comparative simulations were performed to investigate the impact of using FE-only models vs. FSI models, as well as an isotropic vs. an anisotropic leaflet material model in TAV simulations. From the results, substantial differences in leaflet kinematics between FE-only and FSI models were observed, and the FSI model could capture the realistic leaflet dynamic deformation due to its more accurate spatial and temporal loading conditions imposed on the leaflets. The stress and the strain distributions were similar between the FE and FSI simulations. However, the peak stresses were different due to the water hammer effect induced by the fluid inertia in the FSI model during the closing phase, which led to 13-28% lower peak stresses in the FE-only model compared to that of the FSI model. The simulation results also indicated that tissue anisotropy had a minor impact on hemodynamics of the valve. However, a lower tissue stiffness in the radial direction of the leaflets could reduce the leaflet peak stress caused by the water hammer effect. It is hoped that the developed FSI models can serve as an effective tool to better assess valve dynamics and optimize next generation TAV designs.

Transcatheter aortic valves produce unphysiological flows which may contribute to thromboembolic events: An in-vitro study

PURPOSE

Transcatheter aortic valve implantation (TAVI) has been associated with large incidence of ischemic events, whose sources are still unclear. In fact, sub-acute complications cannot be directly related to the severity of the calcification in the host tissues, nor with catheter manipulation during the implant. A potential cause could be local flow perturbations introduced by the implantation approach, resulting in thrombo-embolic consequences. In particular, contrary to the surgical approach, TAVI preserves the presence of the native leaflets, which are expanded in the paravalvular space inside the Valsalva sinuses. The purpose of this study is to verify if this configuration can determine hemodynamic variations which may promote blood cell aggregation and thrombus formation.

METHODS

The study was performed in vitro, on idealized models of the patient anatomy before and after TAVI, reproducing a range of physiological operating conditions on a pulse duplicator. The fluid dynamics in the Valsalva sinuses was analyzed and characterized using phase resolved Particle Image Velocimetry.

RESULTS

Comparison of the flow downstream the valve clearly indicated major alterations in the fluid mechanics after TAVI, characterized by unphysiological conditions associated with extended stagnation zones at the base of the sinuses.

CONCLUSION

The prolonged stasis observed in the Valsalva sinuses for the configuration modelling the presence of transcatheter aortic valves provides a fluid dynamic environment favourable for red blood cell aggregation and thrombus formation, which may justify some of the recently reported thromboembolic and ischemic events. This suggests the adoption of anticoagulation therapies following TAVI, and some caution in the patients׳ selection.

Complementary role of cardiac CT in the assessment of aortic valve replacement dysfunction

Aortic valve replacement is the second most common cardiothoracic procedure in the UK. With an ageing population, there are an increasing number of patients with prosthetic valves that require follow-up. Imaging of prosthetic valves is challenging with conventional echocardiographic techniques making early detection of valve dysfunction or complications difficult. CT has recently emerged as a complementary approach offering excellent spatial resolution and the ability to identify a range of aortic valve replacement complications including structural valve dysfunction, thrombus development, pannus formation and prosthetic valve infective endocarditis. This review discusses each and how CT might be incorporated into a multimodal cardiovascular imaging pathway for the assessment of aortic valve replacements and in guiding clinical management.

Anticoagulation After Heart Valve Replacement or Transcatheter Valve Implantation

Valvular heart disease is prevalent and represents a significant contributor to cardiac morbidity and mortality. Several options for valve replacement exist, including surgical replacement and transcatheter valve implantation. Prosthetic valves lead to increased risk of thromboembolic disease; therefore, antithrombotic therapy after valve replacement is indicated. For patients with mechanical prostheses, indefinite vitamin K antagonist and antiplatelet therapy are the mainstays of treatment. There is no consensus regarding optimal antithrombotic therapy after bioprosthetic valve replacement, although vitamin K antagonist therapy of varying duration in addition to antiplatelet therapy is recommended by guidelines. Dual-antiplatelet therapy is commonly used after transcatheter valve implantation; however, alternative antithrombotic regimens are being studied. Further studies are needed to identify the optimal regimen, intensity, and duration of antithrombotic therapy after surgical bioprosthetic valve replacement and transcatheter valve implantation.

Anticoagulation for prosthetic heart valves: unresolved questions requiring answers

PURPOSE OF REVIEW

The efficacy of anticoagulation for valvular prostheses is the result of a delicate balance between the risk of thromboembolic (TE) events and bleeding. Here, we review data on anticoagulation for valve prostheses with a focus on clinical trials that address key unanswered questions.

RECENT FINDINGS

There are several unanswered questions in the field of prosthetic valve anticoagulation, including: optimal TE prophylaxis in the short term for bioprostheses, optimal TE prophylaxis following transcatheter aortic valve implantation, the safety and efficacy of lower levels of anticoagulation with the bileaflet mechanical prosthesis, the role of aspirin for patients with mechanical prostheses, and the management of anticoagulation for mechanical valves in pregnancy. Other areas of study include the role, if any, of nonwarfarin oral anticoagulants for prosthetic TE prophylaxis as well as self-INR monitoring. Finally, we briefly mention studies of newer anticoagulants, such as novel vitamin K antagonists and antisense oligonucleotides, that are on the horizon.

SUMMARY

Optimal antithrombotic management is a key issue for patients with valvular prostheses, and the publication of recent trials has provided much-needed guidance. We highlight areas of progress, in addition to the major unanswered questions for which well-designed, prospective clinical trials are forthcoming.