T. Sloane Guy

Live transference of surgical subspecialty skills using telerobotic proctoring to remote general surgeons

BACKGROUNDnCertain clinical environments, including military field hospitals or rural medical centers, lack readily available surgical subspecialists. We hypothesized that telementoring by a surgical subspecialist using a robotic platform is feasible and can convey subspecialty knowledge and skill to a remotely located general surgeon.nnnSTUDY DESIGNnEight general surgery residents evaluated the effect of remote surgical telementoring by performing 3 operative procedures, first unproctored and then again when teleproctored by a surgical subspecialist. The clinical scenarios consisted of a penetrating right ventricular injury requiring suture repair, an open tibial fracture requiring external fixation, and a traumatic subdural hematoma requiring craniectomy. A robotic platform consisting of a pan-and-tilt camera with laser pointer attached to an overhead surgical light with integrated audio allowed surgical subspecialists the ability to remotely teleproctor residents. Performance was evaluated using an Operative Performance Scale. Satisfaction surveys were given after performing the scenario unproctored and again after proctoring.nnnRESULTSnOverall mean performance scores were superior in all scenarios when residents were proctored than when they were not (4.30 +/- 0.25 versus 2.43 +/- 0.20; p < 0.001). Mean performance scores for individual metrics, including tissue handling, instrument handling, speed of completion, and knowledge of anatomy, were all superior when residents were proctored (p < 0.001). Satisfaction surveys showed greater satisfaction and comfort among residents when proctored. Proctored residents believed the robotic platform facilitated learning and would be feasible if used clinically.nnnCONCLUSIONSnThis study supports the use of surgical teleproctoring in guiding remote general surgeons by a surgical subspecialist in the care of a wounded patient in need of an emergency subspecialty operation.

Valve-in-Valve Implantation Using a Novel Supravalvular Transcatheter Aortic Valve: Proof of Concept

BACKGROUNDnTranscatheter valve implantation within degenerated bioprostheses is a potentially promising treatment for high-risk surgical patients. Clinical experience is limited; however, we have shown in vitro that currently available transcatheter aortic valve sizes did not provide acceptable hemodynamics in small bioprostheses. The objective of this study was to develop a new transcatheter valve that would provide good hemodynamics within degenerated bioprostheses.nnnMETHODSnSupravalvular transcatheter valves were created using a Dacron covered stainless steel stent at the base and trileaflet pericardial leaflets in an open stent above the bioprosthesis. The transcatheter valves were implanted within 19-, 21-, and 23-mm Carpentier-Edwards Perimount bioprostheses with simulated degeneration using BioGlue to achieve a mean pressure gradient of 50 mm Hg. Hemodynamics of valve-in-valve implantation were studied in a pulse duplicator.nnnRESULTSnSupravalvular transcatheter valves successfully relieved bioprosthetic stenosis. Acceptable hemodynamics were achieved with a significant reduction in mean pressure gradient of 54.0 +/- 3.5 to 9.2 +/- 6.3 mm Hg in 23-mm bioprostheses (p < 0.001), from 49.3 +/- 3.1 to 14.4 +/- 4.7 mmHg (p < 0.001) in 21 mm, and from 53.9 +/- 3.8 to 28.3 +/- 9.8 mm Hg (p = 0.013) in 19-mm bioprostheses. Effective orifice area after valve-in-valve implantation increased significantly and was comparable to rereplacement with the same size bioprosthesis.nnnCONCLUSIONSnValve-in-valve implantation was performed using a novel supravalvular transcatheter valve, which successfully relieved bioprosthetic stenosis. The hemodynamics were comparable with standard surgical valve replacement. Further studies are required to assess device safety and efficacy in patients.

Mechanical Properties of Surgical Glues Used in Aortic Root Replacement

BACKGROUNDnSurgical glues are used in mechanical, stentless bioprosthetic, and homograft aortic root replacements to seal and reinforce anastomotic suture lines. The aortic root normally undergoes substantial physiologic dilation and may be affected by the stiffness of applied sealants. We determined the material properties of four common commercial glues, comparing them with known properties of aortic root replacements.nnnMETHODSnSamples of BioGlue (CryoLife, Inc, Kennesaw, GA), CoSeal (Baxter Healthcare International, Palo Alto, CA), Tisseel (Baxter Healthcare Corp, Glendale, CA), and Crosseal (OMRIX Biopharmaceuticals, Inc, New York, NY) sealants underwent biaxial tensile testing. A Hookean strain energy function was fit to the stress-strain response of each sample, and the Youngs modulus was obtained for comparison of material stiffness.nnnRESULTSnSealants demonstrate a relatively linear response to loading; mean elastic moduli for BioGlue (3,122.04 +/- 1,639.68 kPa), CoSeal (100.02 +/- 67.60 kPa), Tisseel (102.59 +/- 41.13 kPa), and Crosseal (53.56 +/- 32.59 kPa) varied greatly. CoSeal and Tisseel have no significant difference in stiffness (p = 0.897) while Crosseal is more compliant than Tisseel (p = 0.004) and CoSeal (p = 0.055). BioGlue is stiffer than CoSeal, Tisseel, and Crosseal (p < 0.001). Furthermore, BioGlue is much stiffer than cited properties of Dacron grafts, glutaraldehyde-fixed porcine roots, and human aortic tissue. However, CoSeal and Tisseel are much more compliant than the aortic root conduits.nnnCONCLUSIONSnBioGlue is much less compliant than the other sealants studied and materials available for aortic root replacement. A surgeons choice of glue should be determined by stiffness as well as sealant efficacy. Sealants with greater stiffness than aortic root replacement material may restrict normal physiologic dilation and cause anastomotic strictures.

Migration forces of transcatheter aortic valves in patients with noncalcific aortic insufficiency

OBJECTIVEnTranscatheter aortic valves have been successfully implanted into the calcified leaflets of patients with severe aortic stenosis. However, their stability in patients with noncalcified aortic insufficiency is unknown. Similar to thoracic and abdominal aortic stent grafts, transcatheter aortic valves are subjected to antegrade ejection forces during systole. However, retrograde migration forces into the left ventricle are also generated by the diastolic pressure gradient across the closed valve. It has been suggested that leaflet calcification anchors the prosthesis, and measurements of migration forces should be considered before clinical trials in noncalcified aortic insufficiency. The objective of this study was to use computational fluid dynamics simulations to quantify forces that could potentially dislodge the prosthesis.nnnMETHODSnA computational fluid dynamics model was developed to simulate systolic flow through a geometric mesh of the aortic root and transcatheter aortic valves. Hemodynamic measurements were made at discrete moments during ejection. Unsteady control volume analysis was used for calculations of force on the mesh.nnnRESULTSnResults of the simulation indicate that a total force of 0.602 N acts on the transcatheter aortic valves during systole, 99% of which is in the direction of axial flow. The largest contributor to force was the dynamic pressure gradient through the transcatheter aortic valves. This antegrade force is approximately 10 times smaller than the retrograde force (6.01 N) on the closed valve during diastole.nnnCONCLUSIONnOur model simulated systolic flow through a transcatheter aortic valve and demonstrated migration into the left ventricle to be of greater concern than antegrade ejection.

Computational fluid dynamics simulation of transcatheter aortic valve degeneration.

OBJECTIVESnStudied under clinical trials, transcatheter aortic valves (TAV) have demonstrated good short-term feasibility and results in high-risk surgical patients with severe aortic stenosis. However, their long-term safety and durability are unknown. The objective of this study is to evaluate hemodynamic changes within TAV created by bioprosthetic leaflet degeneration.nnnMETHODSnComputational fluid dynamics (CFD) simulations were performed to evaluate the hemodynamics through TAV sclerosis (35% orifice reduction) and stenosis (78% orifice reduction). A three-dimensional surface mesh of the TAV within the aortic root was generated for each simulation. Leaflets were contained within an open, cylindrical body without attachment to the sinus commissures representing the stent. A continuous surface between the annulus and TAV excluded the geometry of the native calcified leaflets and prevented paravalvular leak. Unsteady control volume analysis throughout systole was used to calculate leaflet shear stress and total force on the TAV.nnnRESULTSnSclerosis increased total force on the TAV by 63% (0.602-0.98 N). Advancement of degeneration from sclerosis to stenosis was accompanied by an 86% increase in total force (1.82 N) but only a 32% increase in peak wall shear stress on the leaflets. Of the total force exerted on the TAV, 99% was in the direction of axial flow. Shear stresses on the TAV were greatest during peak systolic flow with stress concentrations on the tips of the leaflets. In the normal TAV, the aortic root geometry and physiologic flow dominate location and magnitude of shear stress. Following leaflet degeneration, the specific geometry of the stenosis dictates the profile of axial velocity leaving the TAV and shear stress on the leaflets. A dramatic increase in peak leaflet shear stress was observed (115 Pa stenosis vs. 87 Pa sclerosis and 29 Pa normal).nnnCONCLUSIONSnCFD simulations in this study provide the first of its kind data quantifying hemodynamics within stenosed TAV. Stenosis leads to significant forces of TAV during systole; however, diastolic forces predominate even with significant stenosis. Substantial changes in peak shear stress occur with TAV degeneration. As the first implanted TAV begin to stenose, the authors recommend watchful examination for device failure.

Energy Loss Due to Paravalvular Leak With Transcatheter Aortic Valve Implantation

BACKGROUNDnMild to moderate paravalvular leaks commonly occur after transcatheter aortic valve (TAV) implantation. Current TAVs match and may exceed hemodynamic performance of surgically implanted bioprostheses based on pressure gradient and effective orifice area. However, these hemodynamic criteria do not account for paravalvular leaks. We recently demonstrated that TAV implantation within 23 mm Perimount bioprostheses (Edwards Lifesciences, Irvine, CA) yields similar hemodynamics to the 23 mm Perimount valve. However, mild paravalvular leakage was seen after TAV implantation. The present study quantifies energy loss during the entire cardiac cycle to assess the impact of TAV paravalvular leaks on the ventricle.nnnMETHODSnFour TAVs designed to mimic the 23 mm SAPIEN valve (Edwards Lifesciences) were created. Transvalvular energy loss of 19, 21, and 23 mm Carpentier-Edwards bioprostheses were obtained in vitro within a pulse duplicator as a hemodynamic baseline (n = 4). The 23 mm TAVs were subsequently implanted within the 23 mm bioprostheses to assess energy loss due to paravalvular leak.nnnRESULTSnThe 23 mm bioprosthesis demonstrated the least energy loss (213.25 +/- 31.35 mJ) compared with the 19 mm (330.00 +/- 36.97 mJ, p = 0.003) and 21 mm bioprostheses (298.00 +/- 37.25 mJ, p = 0.008). The TAV controls had similar energy loss (241.00 +/- 30.55 mJ, p = 0.17) as the 23 mm bioprostheses. However, after TAV implantation, total energy loss increased to 365.33 +/- 8.02 mJ significantly exceeding the energy loss of the 23 mm bioprosthesis (p < 0.001). Due to mild TAV paravalvular leakage, 39% of energy loss occurred during diastole.nnnCONCLUSIONSnSubstantial energy loss during diastole occurs due to TAV paravalvular leakage. In the presence of mild paravalvular leakage, TAV implantation imposes a significantly higher workload on the left ventricle than an equivalently sized surgically implanted bioprosthesis.

Asymmetric Mechanical Properties of Porcine Aortic Sinuses

BACKGROUNDnAortic sinuses are crucial components of the aortic root and important for aortic valve function. Mathematical modeling of various aortic valve or root replacements requires tissue material properties, and those of the aortic sinuses are unknown. The aim of this study is to compare the biaxial mechanical properties of the individual porcine aortic sinuses.nnnMETHODSnSquare specimens, oriented in the longitudinal and circumferential directions, were excised from the left coronary, right coronary, and noncoronary porcine sinuses. Tissue thickness was measured, and specimens were subjected to equibiaxial mechanical testing. Stress-strain data corresponding to a 35% stretch were fitted to a Fung strain energy function. Tissue stiffness and anisotropy were compared at 0.3 strain.nnnRESULTSnThe circumferential direction was more compliant than the longitudinal one for left coronary (183.03 +/- 40.78 kPa versus 231.17 +/- 45.38 kPa, respectively; p = 0.04) and right coronary sinuses (321.74 +/- 129.68 kPa versus 443.49 +/- 143.59 kPa, respectively; p = 0.02) at 30% strain. No such differences were noted for noncoronary sinuses (331.74 +/- 129.68 kPa versus 415.98 +/- 191.38 kPa; p = 0.19). Left coronary sinus was also significantly more compliant than right and noncoronary sinuses. There were no differences between right coronary and noncoronary sinus tissues.nnnCONCLUSIONSnWe demonstrate that the material properties of the porcine aortic sinuses are not symmetric. The left coronary sinus is significantly more compliant than the remaining sinuses. Realistic modeling of the aortic root must take into account the asymmetric differences in tissue material properties of the aortic sinuses.

Comparison of Porcine Pulmonary and Aortic Root Material Properties

BACKGROUNDnThe pulmonary autograft remodels when subjected to systemic pressure and subsequent dilation can lead to reoperation. Inherent material property differences between pulmonary and aortic roots may influence remodeling but are currently unknown. The objective of this study was to determine stiffness across a wide range of strain and compare nonlinear material properties of corresponding regions of native aortic and pulmonary roots.nnnMETHODSnTissue samples from porcine aortic and pulmonary roots-sinuses and supravalvular artery distal to the sinotubular junction-were subjected to displacement-controlled equibiaxial stretch testing. Stress-strain data recorded were used to derive strain energy functions for each region. Stiffness from low to high strains at 0.15, 0.3, and 0.5 strain were determined for comparisons.nnnRESULTSnAortic and pulmonary roots exhibited qualitatively similar material properties; both had greater nonlinearity in the sinus than supravalvular artery. The pulmonary artery was significantly more compliant than the ascending aorta both circumferentially and longitudinally throughout the strain range (p < 0.03), except at high strain circumferentially (p = 0.06). However, no differences in stiffness were seen circumferentially or longitudinally between pulmonary and aortic sinuses (p > or = 0.3) until high strain, when the pulmonary sinuses were significantly stiffer (p < 0.05) in both directions.nnnCONCLUSIONSnDifferences in stiffness between porcine aortic and pulmonary roots are regionally specific, supravalvular artery versus sinus. These regional differences may impact the mode of remodeling to influence late autograft dilation.

Retrograde cerebral perfusion and delayed hyperbaric oxygen for massive air embolism during cardiac surgery.

We report a case of massive air embolism from a ventricular vent line during cardiac surgery successfully treated with emergent retrograde cerebral perfusion and delayed hyperbaric oxygen therapy. The etiologies of this rare but potentially devastating complication are discussed along with prevention and treatment options.

A simple correction for anomalous coronary arteries in adults

Although the risk of sudden death in children and young adults with anomalous coronary arteries arising from the wrong sinus of Valsalva is well described, the risk for older adults who present with such anatomy is unclear. Age greater than 30 years has been shown to impart a diminished risk of sudden death, although it can occur in older adults. Although simple coronary artery bypass for these patients has been described, the outcome can be hampered by competitive flow in the absence of concomitant coronary disease, and poor long-term patency can be expected. Other techniques include internal unroofing, either across the commissural post or not, with a possible effect on aortic valve function. We report a simple physiologic approach previously described in children and adolescents and now used in 2 cases of symptomatic adult patients with anomalous coronary arteries arising from the wrong sinus of Valsalva with an intra-arterial course between the pulmonary artery and aorta.