Initial Assessment of Mucosal Capture and Leak Pressure After Gastrointestinal Stapling in a Porcine Model.

BACKGROUND: Anastomotic leak is a leading cause of morbidity and mortality in gastrointestinal surgery. The serosal aspect of staple lines is commonly observed for integrity, but the mucosal surface and state of mucosa after firing is less often inspected. We sought to assess the degree of mucosal capture when using stapling devices and determine whether incomplete capture influences staple line integrity. METHODS: Porcine ileum was transected in vivo and staple lines were collected and rated for degree of mucosal capture on a 5-point scale from 1 (mucosa mainly captured on both sides) to 5 (majority of mucosa not captured). Mucosal capture was also assessed in ex vivo staple lines, and fluid leakage pressure and location of first leak was assessed. Stapling devices studied were Echelon Flex GST with 60-mm blue (GST60B) and green (GST60G) cartridges, and Medtronic EndoGIA Universal with Tri-Staple Technology™ with 60 mm medium (EGIA60AMT) reloads (purple). RESULTS: GST60B and GST60G staple lines produced significantly better mucosal capture scores than the EGIA60AMT staple lines (p < 0.001, in all tests). Compared to EGIA60AMT, leak pressures were 39% higher for GST60B (p < 0.001) and 23% higher for GST60G (p = 0.022). Initial staple line leak site was associated with incomplete mucosal capture 78% of the time. CONCLUSIONS: There are differences in degree of mucosal capture between commercial staplers, and the devices that produce better mucosal capture had significantly higher leak pressures. Further research is needed to determine the significance of these findings on staple line healing throughout the postoperative period.

Quantitative Imaging Assessment of an Alternative Approach to Surgical Mitral Valve Leaflet Resection: An Acute Porcine Study.

This study reports the initial in vivo use of a combined radiofrequency ablation and cryo-anchoring (RFC) catheter as an alternative to surgical mitral valve (MV) leaflet resection. Radiofrequency ablation thermally shrinks enlarged collagenous tissues, providing an alternative to leaflet resection, and cryo-anchoring provides reversible attachment of a catheter to freely mobile MV leaflets. Excised porcine MVs (n = 9) were tested in a left heart flow simulator to establish treatment efficacy criteria. Resected leaflet area was quantified by tracking markers on the leaflet surface, and leaflet length reductions were directly measured on echocardiography. Leaflet area decreased by 38 ± 2.7%, and leaflet length decreased by 9.2 ± 1.8% following RFC catheter treatment. The RFC catheter was then tested acutely in healthy pigs (n = 5) under epicardial echocardiographic guidance, open-chest without cardiopulmonary bypass, using mid-ventricular free wall access. Leaflet length was quantified using echocardiography. Quantitative assessment of MV leaflet length revealed that leaflet resection was successful in 4 of 5 pigs, with a leaflet length reduction of 13.3 ± 4.6%. Histological, mechanical, and gross pathological findings also confirmed that RFC catheter treatment was efficacious. The RFC catheter significantly reduces MV leaflet size in an acute animal model, providing a possible percutaneous alternative to surgical leaflet resection.

An Inflection Point Method for the Determination of Pulmonary Transit Time From Contrast Echocardiography.

OBJECTIVE: Indicator-dilution curves (IDCs) for the estimation of pulmonary transit times (PTTs) can be generated noninvasively using contrast echocardiography. Currently, these IDCs are analyzed by manual inspection, which is not feasible in a clinical setting, or fit to a statistical model to derive parameters of interest. However, IDCs generated from patients are frequently subject to significant low-frequency noise and recirculation artifacts that obscure the first-pass signal and render model fitting impractical or inaccurate. Thus, the objective of this paper was to develop alternative computational methods to determine PTT using noisy clinical data in which the signal decay is not adequately visible. METHODS: We report on a method that uses a model fit to the rise portion of the IDCs to determine the signal inflection point. Additionally, a signal truncation algorithm was developed that enables automated analysis of the IDCs. RESULTS: We compare PTTs derived from our inflection point method to those obtained by manual inspection in 25 patients (R(2) = 0.86) and to those obtained by mean transit time calculation following fitting to a local density random walk model (R(2) = 0.80) in a subset of this cohort. CONCLUSION: Combined with a signal truncation algorithm, the inflection point method provides robust, automated determination of PTT from noisy IDCs containing recirculation artifacts. SIGNIFICANCE: The inflection point method addresses the need for computational analysis of IDCs obtained from contrast echocardiograms that are not amenable to first-pass model fitting.

A novel bioreactor for mechanobiological studies of engineered heart valve tissue formation under pulmonary arterial physiological flow conditions.

The ability to replicate physiological hemodynamic conditions during in vitro tissue development has been recognized as an important aspect in the development and in vitro assessment of engineered heart valve tissues. Moreover, we have demonstrated that studies aiming to understand mechanical conditioning require separation of the major heart valve deformation loading modes: flow, stretch, and flexure (FSF) (Sacks et al., 2009, "Bioengineering Challenges for Heart Valve Tissue Engineering," Annu. Rev. Biomed. Eng., 11(1), pp. 289-313). To achieve these goals in a novel bioreactor design, we utilized a cylindrical conduit configuration for the conditioning chamber to allow for higher fluid velocities, translating to higher shear stresses on the in situ tissue specimens while retaining laminar flow conditions. Moving boundary computational fluid dynamic (CFD) simulations were performed to predict the flow field under combined cyclic flexure and steady flow (cyclic-flex-flow) states using various combinations of flow rate, and media viscosity. The device was successfully constructed and tested for incubator housing, gas exchange, and sterility. In addition, we performed a pilot experiment using biodegradable polymer scaffolds seeded with bone marrow derived stem cells (BMSCs) at a seeding density of 5 × 10(6) cells/cm(2). The constructs were subjected to combined cyclic flexure (1 Hz frequency) and steady flow (Re = 1376; flow rate of 1.06 l/min (LPM); shear stress in the range of 0-9 dynes/cm(2) for 2 weeks to permit physiological shear stress conditions. Assays revealed significantly (P < 0.05) higher amounts of collagen (2051 ± 256 µg/g) at the end of 2 weeks in comparison to similar experiments previously conducted in our laboratory but performed at subphysiological levels of shear stress (<2 dynes/cm(2); Engelmayr et al., 2006, "Cyclic Flexure and Laminar Flow Synergistically Accelerate Mesenchymal Stem Cell-Mediated Engineered Tissue Formation: Implications for Engineered Heart Valve Tissues," Biomaterials, 27(36), pp. 6083-6095). The implications of this novel design are that fully coupled or decoupled physiological flow, flexure, and stretch modes of engineered tissue conditioning investigations can be readily accomplished with the inclusion of this device in experimental protocols on engineered heart valve tissue formation.

In vitro assessment of a combined radiofrequency ablation and cryo-anchoring catheter for treatment of mitral valve prolapse.

Percutaneous approaches to mitral valve repair are an attractive alternative to surgical repair or replacement. Radiofrequency ablation has the potential to approximate surgical leaflet resection by using resistive heating to reduce leaflet size, and cryogenic temperatures on a percutaneous catheter can potentially be used to reversibly adhere to moving mitral valve leaflets for reliable application of radiofrequency energy. We tested a combined cryo-anchoring and radiofrequency ablation catheter using excised porcine mitral valves placed in a left heart flow loop capable of reproducing physiologic pressure and flow waveforms. Transmitral flow and pressure were monitored during the cryo-anchoring procedure and compared to baseline flow conditions, and the extent of radiofrequency energy delivery to the mitral valve was assessed post-treatment. Long term durability of radiofrequency ablation treatment was assessed using statically treated leaflets placed in a stretch bioreactor for four weeks. Transmitral flow and pressure waveforms were largely unaltered during cryo-anchoring. Parameter fitting to mechanical data from leaflets treated with radiofrequency ablation and cryo-anchoring revealed significant mechanical differences from untreated leaflets, demonstrating successful ablation of mitral valves in a hemodynamic environment. Picrosirius red staining showed clear differences in morphology and collagen birefringence between treated and untreated leaflets. The durability study indicated that statically treated leaflets did not significantly change size or mechanics over four weeks. A cryo-anchoring and radiofrequency ablation catheter can adhere to and ablate mitral valve leaflets in a physiologic hemodynamic environment, providing a possible percutaneous alternative to surgical leaflet resection of mitral valve tissue.

The once and future state of percutaneous mitral valve repair.

There has been a great deal of interest in percutaneous mitral valve repair techniques in recent years, with several devices undergoing animal testing and clinical trials. Percutaneous annuloplasty and leaflet repair devices are currently in development, and while safety rates have generally been equal or superior to conventional surgical techniques, efficacy has been suboptimal. Most current percutaneous mitral valve repair devices can only reduce regurgitant volumes by approximately 20-40%, but these reductions may be enough to treat high-risk patients, including the elderly and those with comorbidities, who are otherwise ineligible for surgery. An analysis of how these devices alter the geometry and mechanics of the mitral valve apparatus can provide insight into long-term efficacy and durability and may lead to improvements in the reduction of mitral regurgitation. In the future, multiple percutaneous techniques may be utilized in combination to increase overall efficacy. In this article, we report on percutaneous mitral valve repair techniques with published clinical or animal data.

Development of a simultaneous cryo-anchoring and radiofrequency ablation catheter for percutaneous treatment of mitral valve prolapse.

Mitral valve prolapse (MVP) is one subtype of mitral valve (MV) disease and is often characterized by enlarged leaflets that are thickened and have disrupted collagen architecture. The increased surface area of myxomatous leaflets with MVP leads to mitral regurgitation, and there is need for percutaneous treatment options that avoid open-chest surgery. Radiofrequency (RF) ablation is one potential therapy in which resistive heating can be used to reduce leaflet size via collagen contracture. One challenge of using RF ablation to percutaneously treat MVP is maintaining contact between the RF ablation catheter tip and a functioning MV leaflet. To meet this challenge, we have developed a RF ablation catheter with a cryogenic anchor for attachment to leaflets in order to apply RF ablation. We demonstrate the effectiveness of the dual-energy catheter in vitro by examining changes in leaflet biaxial compliance, thermal distribution with infrared (IR) imaging, and cryogenic anchor strength. We report that 1250 J of RF energy with cryo-anchoring reduced the determinant of the deformation gradient tensor at systolic loading by 23%. IR imaging revealed distinct regions of cryo-anchoring and tissue ablation, demonstrating that the two modalities do not counteract one another. Finally, cryogenic anchor strength to the leaflet was reduced but still robust during the application of RF energy. These results indicate that a catheter having combined RF ablation and cryo-anchoring provides a novel percutaneous treatment strategy for MVP and may also be useful for other percutaneous procedures where anchored ablation would provide more precise spatial control.

Superparamagnetic iron oxide (SPIO) labeling efficiency and subsequent MRI tracking of native cell populations pertinent to pulmonary heart valve tissue engineering studies.

The intimal and medial linings of the pulmonary artery consist largely of vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), respectively. The migration of these cell types to a potential tissue-engineered pulmonary valve (TEPV) implant process is therefore of interest in understanding the valve remodeling process. Visualization and cell tracking by MRI, which employs hypointense contrast achievable through the use of superparamagnetic iron oxide (SPIO) microparticles to label cells, provides a method in which this can be studied. We investigated the SPIO labeling efficiency of human VECs and VSMCs, and used two- and three-dimensional gradient echo sequences to track the migration of these cells in agar gel constructs. Protamine sulfate (4.5 µg/mL) was used to enhance SPIO uptake and was found to have no influence on cell viability or proliferation. MRI experiments were initially performed using a 9.4-T scanner. The results demonstrated that the spatial positions of hypointense spots were relatively unchanged over 12 days. Subsequent MR experiments performed at 7 T demonstrated that three-dimensional imaging provided the best spatial resolution to assess cell fate. R(2)* maps were bright in SPIO cell-encapsulated gels in comparison with unlabeled counterparts. Signal voids were ruled out as hypointense regions owing to the smooth exponential decay of T(2)* in these voxels. As a next step, we intend to use the SPIO cell labeling and MR protocols established in this study to assess whether hemodynamic stresses will alter the vascular cell migratory patterns. These studies will shed light on the mechanisms of vascular remodeling after TEPV implantation.