Thrombosis of TAVI prosthesis—cause for concern or innocent bystander? A comment and review of currently available data

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.

A PEGylation method of fabricating bioprosthetic heart valves based on glutaraldehyde and 2-amino-4-pentenoic acid co-crosslinking with improved antithrombogenicity and cytocompatibility

With the development of diagnostic techniques, the incidence of bioprosthetic heart valve thrombosis (BHVT) is found to be seriously underestimated. Developing bioprosthetic heart valves (BHVs) that have good hemocompatibility without sacrificing other properties such as hydrodynamics and durability will be an effective strategy to alleviate BHVT. In this study, we developed a PEGylation method by co-crosslinking and subsequent radical polymerization. 2-amino-4-pentenoic acid was used to introduce carbon-carbon double bonds for glutaraldehyde crosslinked pericardia. Then poly (ethylene glycol) diacrylate (PEGDA) was immobilized on pericardia by radical polymerization. A comprehensive evaluation of the modified pericardia was performed including structural characterization, hemocompatibility, cytocompatibility, mechanical properties, component stability, hydrodynamic performance and durability of the BHVs. The modified pericardia significantly reduced platelet adhesion by more than 75% compared with traditional glutaraldehyde crosslinked pericardia. Cell viability in the modified pericardia group was nearly 5-fold higher than that in glutaraldehyde crosslinked pericardia. The hydrodynamic performance met the requirements of ISO 5840-3 under physiological aortic valve conditions and its durability was proved after 200 million cycles of accelerated fatigue test. In conclusion, PEGDA modified pericardia exhibited improved antithrombogenicity and cytocompatibility properties compared with glutaraldehyde crosslinked pericardia. STATEMENT OF SIGNIFICANCE: Bioprosthetic valve (BHV) implantation requires BHV to be structurally stable as well as biocompatible in vivo. Traditional glutaraldehyde crosslinking method prepared BHV suffers from severe cytotoxicity, thrombosis, and calcification. BHV modification methods that have simultaneously improved structural stability and biocompatibility were rarely reported. Here, we proposed a PEGylation method for BHV based on co-crosslinking strategy that could improve its structural stability as well as hemocompatibility. We take the advantage of high efficiency of glutaraldehyde crosslinking and demonstrate the feasibility and superiority of the PEGylated strategy, offering a promising option in glutaraldehyde-based BHV fabrication in the future.

Predictive Model for Thrombus Formation After Transcatheter Valve Replacement

PURPOSE

Leaflet thrombosis is a significant adverse event after transcatheter aortic valve (TAV) replacement (TAVR). The purpose of our study was to present a semi-empirical, mathematical model that links patient-specific anatomic, valve, and flow parameters to predict likelihood of leaflet thrombosis.

METHODS

The two main energy sources of neo-sinus (NS) washout after TAVR include the jet flow downstream of the TAV and NS geometric change in volume due to the leaflets opening and closing. Both are highly dependent on patient anatomic and hemodynamic factors. As rotation of blood flow is prevalent in both the sinus of Valsalva and then the NS, we adopted the vorticity flux or circulation (Г) as a metric quantifying overall washout. Leaflet thrombus volumes were segmented based on hypo-attenuating leaflet thickening (HALT) in post-TAVR patient's gated computed tomography. Г was assessed using dimensional scaling as well as computational fluid dynamics (CFD) respectively and correlated to the thrombosis volumes using sensitivity and specificity analysis.

RESULTS

Г in the NS, that accounted for patient flow and anatomic conditions derived from scaling arguments significantly better predicted the occurrence of leaflet thrombus than CFD derived measures such as stasis volumes or wall shear stress. Given results from the six patient datasets considered herein, a threshold Г value of 28.0 yielded a sensitivity and specificity of 100% where patients with Gamma < 28 developed valve thrombosis. A 10% error in measurements of all variables can bring the sensitivity specificity down to 87%.

CONCLUSION

A predictive model relating likelihood of valve thrombosis using Г in the NS was developed with promising sensitivity and specificity. With further studies and improvements, this predictive technology may lead to alerting physicians on the risk for thrombus formation following TAVR.

The Red Kangaroo pericardium as a material source for the manufacture of percutaneous heart valves

BACKGROUND

The kangaroo pericardium might be considered to be a good candidate material for use in the manufacture of the leaflets of percutaneous heart valves based upon the unique lifestyle. The diet consists of herbs, forbs and strubs. The kangaroo pericardium holds an undulated structure of collagen.

MATERIAL AND METHOD

A Red Kangaroo was obtained after a traffic fatality and the pericardium was dissected. Four compasses were cut from four different sites: auricular (AUR), atrial (ATR), sternoperitoneal (SPL) and phrenopericardial (PPL). They were investigated by means of scanning electron microscopy, light microscopy and transmission electron microscopy.

RESULTS

All the samples showed dense and wavy collagen bundles without vascularisation from both the epicardium and the parietal pericardium. The AUR and the ATR were 150±25μm thick whereas the SPL and the PPL were thinner at 120±20μm. The surface of the epicardium was smooth and glistening. The filaments of collagen were well individualized without any aggregation, but the banding was poorly defined and somewhat blurry.

CONCLUSION

This detailed morphological analysis of the kangaroo pericardium illustrated a surface resistant to thrombosis and physical characteristics resistant to fatigue. The morphological characteristics of the kangaroo pericardium indicate that it represents an outstanding alternative to the current sources e.g., bovine and porcine. However, procurement of tissues from the wild raises supply and sanitary issues. Health concerns based upon sanitary uncertainty and reliability of supply of wild animals remain real problems.

Oral Anticoagulant Therapy for Early Post-TAVI Thrombosis

While transcatheter aortic valve implantation (TAVI) is now the accepted treatment option of choice for patients presenting with severe symptomatic aortic stenosis who are deemed to be inoperable or of high surgical risk, there have been concerns regarding the risk of early valve failure and durability. One potential limitation is the occurrence of early post-TAVI thrombosis. Whilst the incidence of obstructive transcatheter heart valve (THV) thrombosis is <1 %, with technological advances in imaging, it is increasingly apparent that the overall true incidence is likely to be much higher with between 7-40 % of patients observed to have appearances strongly suggestive of asymptomatic subclinical THV thrombosis. This short review discusses the diagnosis of early THV thrombosis and the role of anticoagulation therapy for the management of these patients.

The Fluid Mechanics of Transcatheter Heart Valve Leaflet Thrombosis in the Neosinus

BACKGROUND

Transcatheter heart valve (THV) thrombosis has been increasingly reported. In these studies, thrombus quantification has been based on a 2-dimensional assessment of a 3-dimensional phenomenon.

METHODS

Postprocedural, 4-dimensional, volume-rendered CT data of patients with CoreValve, Evolut R, and SAPIEN 3 transcatheter aortic valve replacement enrolled in the RESOLVE study (Assessment of Transcatheter and Surgical Aortic Bioprosthetic Valve Dysfunction With Multimodality Imaging and Its Treatment with Anticoagulation) were included in this analysis. Patients on anticoagulation were excluded. SAPIEN 3 and CoreValve/Evolut R patients with and without hypoattenuated leaflet thickening were included to study differences between groups. Patients were classified as having THV thrombosis if there was any evidence of hypoattenuated leaflet thickening. Anatomic and THV deployment geometries were analyzed, and thrombus volumes were computed through manual 3-dimensional reconstruction. We aimed to identify and evaluate risk factors that contribute to THV thrombosis through the combination of retrospective clinical data analysis and in vitro imaging in the space between the native and THV leaflets (neosinus).

RESULTS

SAPIEN 3 valves with leaflet thrombosis were on average 10% further expanded (by diameter) than those without (95.5±5.2% versus 85.4±3.9%; P<0.001). However, this relationship was not evident with the CoreValve/Evolut R. In CoreValve/Evolut Rs with thrombosis, the thrombus volume increased linearly with implant depth (R²=0.7, P<0.001). This finding was not seen in the SAPIEN 3. The in vitro analysis showed that a supraannular THV deployment resulted in a nearly 7-fold decrease in stagnation zone size (velocities <0.1 m/s) when compared with an intraannular deployment. In addition, the in vitro model indicated that the size of the stagnation zone increased as cardiac output decreased.

CONCLUSIONS

Although transcatheter aortic valve replacement thrombosis is a multifactorial process involving foreign materials, patient-specific blood chemistry, and complex flow patterns, our study indicates that deployed THV geometry may have implications on the occurrence of thrombosis. In addition, a supraannular neosinus may reduce thrombosis risk because of reduced flow stasis. Although additional prospective studies are needed to further develop strategies for minimizing thrombus burden, these results may help identify patients at higher thrombosis risk and aid in the development of next-generation devices with reduced thrombosis risk.