Publications by authors named "Richard W Bianco"

37 Publications

Establishing Background Pathologic Changes of Valve Replacement Surgery in Sheep.

Cardiovasc Eng Technol 2021 Jul 14. Epub 2021 Jul 14.

Experimental Surgical Services Laboratory, Department of Surgery, University of Minnesota, Minneapolis, MN, 55455, USA.

Purpose: Sheep are the standard preclinical model for assessing safety of novel replacement heart valves, yet the anatomic and pathologic effects of invasive surgery, including those involving cardiopulmonary bypass (CPB), are unknown. Thus, we aimed to determine the gross, hematologic and biochemical effects of sham mitral and aortic replacement valve procedures in sheep to establish a useful control for evaluation of novel replacement valves.

Methods: Six control sheep were examined without any surgical intervention. Six sham mitral valve replacements (MVR) and six sham aortic valve replacements (AVR) were performed on 12 sheep. Complete blood counts and serum biochemistry were performed throughout the study. Sheep were sacrificed with a necropsy performed at 90 days.

Results: Renal infarcts (RIs) were the most frequently observed lesion, averaging 4.7 in control sheep, 2.5 with MVR and 5.8 with AVR. The number of infarcts strongly correlated with total estimated area of infarcted kidney (r = .84, p < .01). Additional cardiac interventions were significantly correlated with increased numbers of RIs (r = .85, p < .01). There was no correlation between number of RIs and time on CPB, or between AVR and MVR procedures.

Conclusion: The sheep model for AVR and MVR requires invasive surgery and CPB, which are associated with background anatomic and pathologic changes, especially in cases with additional surgical cardiac interventions. These findings serve as a critical control for future evaluation and development of novel replacement valves in order to distinguish device-related safety issues from expected outcomes of the surgical procedure and normal background changes in sheep.
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http://dx.doi.org/10.1007/s13239-021-00563-6DOI Listing
July 2021

New Model for the Assessment of Transcatheter Aortic Valve Replacement Devices in Sheep.

J Invest Surg 2020 Dec 28:1-10. Epub 2020 Dec 28.

Experimental Surgical Services Laboratory, Department of Surgery, University of Minnesota, Minneapolis, Minnesota, USA.

Background: Transcatheter aortic valve replacement (TAVR) is an effective therapy in treating high-risk patients suffering from aortic stenosis. Animal models used to evaluate safety and efficacy of TAVR devices prior to clinical use lack a stenotic aortic annulus, a critical impediment to long-term TAVR device evaluation. We sought to create a reproducible model of aortic stenosis using a modified aortic annuloplasty (MAA) procedure in sheep, followed by deployment and long-term evaluation of TAVR devices using this model.

Methods: Twelve sheep underwent the MAA procedure and were recovered. Transthoracic echocardiography (TTE) was used to monitor changes in the aortic annulus in the postoperative period. At 60 days post-MAA, Test group animals were anesthetized for TAVR insertion and Control animals underwent a necropsy. Test animals were recovered following TAVR insertion and observed for a postoperative period of 140 days.

Results: Twelve sheep survived the annuloplasty procedure and the 60-day recovery period. Gross examination of seven Control group animals revealed the implanted annuloplasty ring segments formed hard protrusions into the aortic annulus. Five sheep in the Test group underwent successful deployment of Abbott's experimental TAVR device without evidence of migration. Examination at 140 days post-TAVR insertion showed all devices tightly anchored within the modified aortic annulus.

Conclusions: The MAA procedure creates stenotic segments in the aortic annulus with adequate rigidity for anchorage and long-term evaluation of TAVR devices. This represents the first model that successfully mimics human aortic stenosis and provides a clinically relevant TAVR deployment platform for long-term evaluation in sheep.
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http://dx.doi.org/10.1080/08941939.2020.1864796DOI Listing
December 2020

Porcine Model of the Arterial Switch Operation: Implications for Unique Strategies in the Management of Hypoplastic Left Ventricles.

Pediatr Cardiol 2021 Mar 30;42(3):501-509. Epub 2020 Nov 30.

Cardiovascular Division, Department of Medicine, University of Minnesota Medical School, Minneapolis, MN, USA.

There are no reports on the performance of the arterial switch operation (ASO) in a normal heart with normally related great vessels. The objective of this study was to determine whether the ASO could be performed in a healthy animal model. Cardiopulmonary bypass (CPB) and coronary translocation techniques were used to perform ASO in neonatal piglets or a staged ASO with prior main pulmonary artery (PA) banding. Primary ASO was performed in four neonatal piglets. Coronary translocation was effective with angiograms confirming patency. Piglets could not be weaned from CPB due to right ventricle (RV) dysfunction. To improve RV function for the ASO, nine piglets had PA banding. All survived the procedure. Post-banding RV pressure increased from a mean of 20.3 ± 2.2 mmHg to 36.5 ± 7.3 mmHg (p = 0.007). At 58 ± 1 days post-banding, piglets underwent cardiac MRIs revealing RV hypertrophy, and RV pressure overload with mildly reduced RV function. Catheterization confirmed RV systolic pressures of 84.0 ± 6.7 mmHg with LV systolic pressure 83.3 ± 6.7 mmHg (p = 0.43). The remaining five PA banded piglets underwent ASO at 51 ± 0 days post-banding. Three of five were weaned from bypass with patent coronary arteries and adequate RV function. We were able to successfully perform an arterial switch with documented patent coronary arteries on standard anatomy great vessels in a healthy animal model. To our knowledge this is the first time this procedure has been successfully performed. The model may have implications for studying the failing systemic RV, and may support a novel approach for management of borderline, pulsatile left ventricles.
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http://dx.doi.org/10.1007/s00246-020-02507-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7990748PMC
March 2021

Anisotropic Polytetrafluoroethylene Cardiovascular Conduits Spontaneously Expand in a Growing Lamb Model.

J Invest Surg 2020 Aug 14:1-7. Epub 2020 Aug 14.

Experimental Surgical Services Laboratory, Department of Surgery, University of Minnesota, Minneapolis, Minnesota, USA.

Background: Insertion of conduits from the right ventricle (RV) to the pulmonary artery (PA) is a commonly used technique for repair of congenital heart defects. The vast majority of infants and children will require reoperation and/or re-intervention to replace the conduit. Some children may require multiple reoperations, with the risk of death and morbidity increasing significantly with each subsequent operation. We evaluated the feasibility and performance of a relatively novel anisotropic conduit for cardiovascular repair in the growing lamb model.

Materials And Methods: Lambs were allocated into a control ( = 3) or test ( = 4, anisotropic) conduit group. Control conventional polytetrafluoroethylene (PTFE) conduits or test anisotropic expanded PTFE (ePTFE) based test conduits measuring 10-11 mm in diameter were sewn as interpositional grafts in the main pulmonary artery (MPA) and followed up to 6 months. Clinical and echocardiographic evaluations were performed monthly with hemodynamic and angiographic assessment at 3 and 6 months.

Results: Control conduits did not expand, all 3 animals developed one or more adverse events including tachypnea, ascites, inappetence, lethargy, and mortality due to severe right heart failure and significantly higher peak trans-conduit gradients (48.5 ± 5.1 p = 0.02). The test conduits spontaneously expanded up to 14.8 ± 0.8 mm in diameter, no adverse events were observed in any animals and trans-conduit gradients were significantly lower (27.0 ± 8.3, p = 0.02).

Conclusions: Anisotropic ePTFE conduits can be safely implanted in growing lambs with stable hemodynamics. This spontaneously expanding anisotropic conduit may represent a novel approach to congenital heart repairs that would avoid the need for reoperation or multiple operations.
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http://dx.doi.org/10.1080/08941939.2020.1805056DOI Listing
August 2020

Feasibility Study of Catheter-Based Interventions for Anisotropic Expanded Polytetrafluoroethylene Cardiovascular Conduits in a Growing Lamb Model.

J Invest Surg 2020 Jul 20:1-7. Epub 2020 Jul 20.

Experimental Surgical Services Laboratory, Department of Surgery, University of Minnesota, Minneapolis, MN, USA.

Background: Cardiovascular repair in children often requires implant of conduits which do not have growth potential and will require reoperation. In the current study we sought to determine the feasibility of catheter-based interventions of anisotropic conduits inserted as interposition grafts in the main pulmonary artery (MPA) of growing lambs.

Methods: Lambs underwent interpositional implant of either an anisotropic expanded polytetrafluoroethylene (ePTFE) (Test) conduit or conventional PTFE (Control) conduit. In the postoperative period, lambs were anesthetized and underwent catheter-based interventions consisting of hemodynamic and angiographic data collection, balloon dilation and/or stenting of the conduit at 3, 6 or 9 month postoperative time point.

Results: At 3 months, control lambs showed significant increases in right ventricular pressures and trans-conduit gradients in comparison to test lambs. Test conduit diameters were significantly larger compared to controls due to spontaneous radial expansion of the anisotropic conduit. Balloon dilation of test conduits at 3 and 6 months showed a reduction in RV pressure and statistically significant improvement in the RV outflow tract gradient as well as significant increase in graft diameter, compared to both control and pre-dilation conditions. Furthermore, the test conduit diameter increased significantly compared to the pre-balloon and control conditions at each time point. Necropsy of test conduits showed no evidence of tears, perforations, or clot and smooth interiors with well-healed anastomoses.

Conclusions: Anisotropic conduits implanted as interposition grafts in the MPA show spontaneous expansion, and can safely and effectively undergo catheter-based interventions, with significant increases in graft diameter occurring after balloon dilation.
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http://dx.doi.org/10.1080/08941939.2020.1795324DOI Listing
July 2020

Pilot study investigating the feasibility of mitral valve repair without aortic cross-clamping and cardioplegia.

Can J Vet Res 2020 Apr;84(2):159-162

Veterinary Medical Center North, University of Minnesota, 1365 Gortner Avenue, St. Paul, Minnesota 55108, USA (Gordon-Evans); University of Minnesota Medical School, 420 Delaware Street SE, Mayo Mail Code 195, Minneapolis, Minnesota 55455, USA (Carney, Lahti, Bianco).

There is evidence that perfusing the heart with a heart and lung machine is less injurious than cross-clamping the aorta and administering cardioplegia during cardiac surgery. Although mitral valve replacement has been carried out without aortic cross-clamping and cardioplegia, it has been stated that cross-clamping is necessary in order to maintain visualization and a motionless surgical field for mitral valve repair. The purpose of this study was to determine the surgical feasibility of mitral valve repair without cross-clamping the aorta and using cardioplegia. Our hypothesis was that a completely bloodless and motion-free field would not be necessary to carry out mitral valve repair with annuloplasty and synthetic chordae tendineae sutures. Papillary muscles, chordae tendineae, annulus, and mitral valve leaflets were all readily visualized. Chordae tendineae sutures were used and annuloplasty was conducted without visual obstruction or motion interference. Our results show that mitral valve repair is feasible without cross-clamping the aorta and using cardioplegia.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7088510PMC
April 2020

A geometrically adaptable heart valve replacement.

Sci Transl Med 2020 02;12(531)

Department of Cardiac Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.

Congenital heart valve disease has life-threatening consequences that warrant early valve replacement; however, the development of a growth-accommodating prosthetic valve has remained elusive. Thousands of children continue to face multiple high-risk open-heart operations to replace valves that they have outgrown. Here, we demonstrate a biomimetic prosthetic valve that is geometrically adaptable to accommodate somatic growth and structural asymmetries within the heart. Inspired by the human venous valve, whose geometry is optimized to preserve functionality across a wide range of constantly varying volume loads and diameters, our balloon-expandable synthetic bileaflet valve analog exhibits similar adaptability to dimensional and shape changes. Benchtop and acute in vivo experiments validated design functionality, and in vivo survival studies in growing sheep demonstrated that mechanical valve expansion accommodated growth. As illustrated in this work, dynamic size adaptability with preservation of unidirectional flow in prosthetic valves thus offers a paradigm shift in the treatment of heart valve disease.
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http://dx.doi.org/10.1126/scitranslmed.aay4006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7425635PMC
February 2020

Preclinical Assessment of Cardiac Valve Substitutes: Current Status and Considerations for Engineered Tissue Heart Valves.

Front Cardiovasc Med 2019 7;6:72. Epub 2019 Jun 7.

Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, United States.

Tissue engineered heart valve (TEHV) technology may overcome deficiencies of existing available heart valve substitutes. The pathway by which TEHVs will undergo development and regulatory approval has several challenges. In this communication, we review: (1) the regulatory framework for regulation of medical devices in general and substitute heart valves in particular; (2) the special challenges of preclinical testing using animal models for TEHV, emphasizing the International Standards Organization (ISO) guidelines in document 5840; and (3) considerations that suggest a translational roadmap to move TEHV forward from pre-clinical to clinical studies and clinical implementation.
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http://dx.doi.org/10.3389/fcvm.2019.00072DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6566127PMC
June 2019

Rodents Versus Pig Model for Assessing the Performance of Serotype Chimeric Ad5/3 Oncolytic Adenoviruses.

Cancers (Basel) 2019 Feb 8;11(2). Epub 2019 Feb 8.

Division of Basic and Translational Research, Department of Surgery, University of Minnesota, Minneapolis, 55455 MN, USA.

Oncolytic adenoviruses (Ad) are promising tools for cancer therapeutics. Most Ad-based therapies utilize species C serotypes, with Adenovirus type 5 (Ad5) most commonly employed. Prior clinical trials demonstrated low efficiency of oncolytic Ad5 vectors, mainly due to the absence of Ad5 primary receptor (Coxsackie and Adenovirus Receptor, CAR) on cancer cells. Engineering serotype chimeric vectors (Ad5/3) to utilize Adenovirus type 3 (Ad3) receptors has greatly improved their oncolytic potential. Clinical translation of these infectivity-enhanced vectors has been challenging due to a lack of replication permissive animal models. In this study, we explored pigs as a model to study the performance of fiber-modified Ad5/3 chimeric vectors. As a control, the Ad5 fiber-unmodified virus was used. We analyzed binding, gene transfer, replication, and cytolytic ability of Ad5 and Ad5/3 in various non-human cell lines (murine, hamster, canine, porcine). Among all tested cell lines only porcine cells supported active binding and replication of Ad5/3. Syrian hamster cells supported Ad5 replication but showed no evidence of productive viral replication after infection with Ad5/3 vectors. Transduction and replication ability of Ad5/3 in porcine cells outperformed Ad5, a phenomenon often observed in human cancer cell lines. Replication of Ad5 and Ad5/3 was subsequently evaluated in vivo in immunocompetent pigs. Quantitative PCR analyses 7 days post infection revealed Ad5 and Ad5/3 DNA and replication-dependent luciferase activity in the swine lungs and spleen indicating active replication in these tissues. These studies demonstrated the flaws in using Syrian hamsters for testing serotype chimeric Ad5/3 vectors. This is the first report to validate the pig as a valuable model for preclinical testing of oncolytic adenoviruses utilizing Adenovirus type 3 receptors. We hope that these data will help to foster the clinical translation of oncolytic adenoviruses including those with Ad3 retargeted tropism.
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http://dx.doi.org/10.3390/cancers11020198DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6406826PMC
February 2019

The Hancock® Valved Conduit for Right Ventricular Outflow Tract Reconstruction in Sheep for Assessing New Devices.

J Heart Valve Dis 2017 07;26(4):472-480

Division of Experimental Surgery, Department of Surgery, University of Minnesota School of Medicine, Minneapolis, Minnesota, USA. Electronic correspondence:

Background And Aim Of The Study: Xenograft conduits have been used successfully to repair congenital heart defects, but are prone to failure over time. Hence, in order to improve patient outcomes, better xenografts are being developed. When evaluating a conduit's performance and safety it must first be compared against a clinically available control in a large animal model. The study aim was to evaluate a clinically available xenograft conduit used in right ventricular outflow tract (RVOT) reconstruction in a sheep model.

Methods: RVOT reconstruction was performed in 13 adult and juvenile sheep, using the Medtronic Hancock® Bioprosthetic Valved Conduit (Hancock conduit). The method had previously been used on patients, and a newly modified variant termed 'RVOT Extraction' was employed to facilitate the surgical procedure. Animals were monitored over predetermined terms of 70 to 140 days. Serial transthoracic echocardiography, intracardiac pressure measurements and angiography were performed. On study completion the animals were euthanized and necropsies performed.

Results: Two animals died prior to their designated study term due to severe valvular stenosis and distal conduit narrowing, respectively. Thus, 11 animals survived the study term, with few or no complications. Generally, maximal and mean transvalvular pressure gradients across the implanted conduits were increased throughout the postoperative course. Among 11 full-term animals, seven conduits were patent with mild or no pseudointimal proliferation and with flexible leaflets maintaining the hemodynamic integrity of the valve.

Conclusions: RVOT reconstruction using the Hancock conduit was shown to be successful in sheep, with durable and efficient performances. With its extensive clinical use in patients, and ability for long-term use in sheep (as described in the present study) it can be concluded that the Hancock conduit is an excellent control device for the evaluation of new xenografts in future preclinical studies.
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July 2017

Dabigatran versus warfarin after mechanical mitral valve replacement in the swine model.

J Invest Surg 2012 Jun;25(3):150-5

Department of Surgery, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.

Background: Mechanical heart valve replacement is an absolute indication for anticoagulation. We report our experience comparing dabigatran to warfarin as thromboembolic prophylaxis after mechanical mitral valve replacement in the swine model.

Methods: Nineteen swine underwent mitral valve replacement with a regulatory approved, 27 mm mechanical valve. Two control groups consisted of three animals receiving no anticoagulation and five animals receiving warfarin (5 mg once a day [QD], adjusted to maintain international normalized ratio [INR] from 2.0 to 2.5). The experimental group consisted of 11 animals receiving dabigatran (20 mg/kg twice a day [BID]). The study period was 90 days. The primary outcome was animal mortality; secondary outcomes included presence of thrombus and bleeding complications.

Results: The experimental group had four full-term survivors (40.0%); there were no full-term survivors in either control group. The average length of survival was 50.3 days in the experimental group compared with 18.7 and 15.6 days for the no anticoagulation and warfarin groups, respectively (p = .017). Valve thrombus was observed in all study groups. Hemorrhagic complications were present in 40% of the warfarin group and 27% of the dabigatran group.

Conclusions: There was a significant mortality benefit to the use of dabigatran as thromboembolic prophylaxis when compared with warfarin in the setting of mechanical heart valve replacement in the swine model. There was also a decreased incidence of bleeding complications in the dabigatran group compared with the warfarin group. Valve thrombus was observed in all study groups. Any conclusions regarding the rate of thrombus formation are outside the scope of this study and merit further investigation.
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http://dx.doi.org/10.3109/08941939.2011.616256DOI Listing
June 2012

Use of large animals to assess human safety of heart valves and other medical devices.

J Invest Surg 2012 Feb;25(1):1-2

Department of Surgery, Surgical Research Laboratories, University of Minnesota, Minneapolis, Minnesota 55455, USA.

The use of large animals are critical for the evaluation of safety of human valves and other medical devices. Preclinical assessment includes many factors oriented at maximizing safety and performance. The final step of the device approval for patient's use goes through an exhaustive regulatory process to prevent clinical complications or any other close or distant injuries. The development of reproducible animal models, the better understanding of the implantation of medical devices and the follow through with specific clinical trials will complete the significant steps required for the evaluation of safety of human heart valves and other medical devices.
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http://dx.doi.org/10.3109/08941939.2011.648863DOI Listing
February 2012

Triglycidyl amine crosslinking combined with ethanol inhibits bioprosthetic heart valve calcification.

Ann Thorac Surg 2011 Sep;92(3):858-65

Division of Cardiology, The Children's Hospital of Philadelphia, and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA.

Background: One of the most important factors responsible for the calcific failure of bioprosthetic heart valves is glutaraldehyde crosslinking. Ethanol (EtOH) incubation after glutaraldehyde crosslinking has previously been reported to confer anticalcification efficacy for bioprostheses. The present studies investigated the anticalcification efficacy in vivo of the novel crosslinking agent, triglycidyl amine (TGA), with or without EtOH incubation, in comparison with glutaraldehyde.

Methods: The TGA crosslinking (±EtOH) was used to prepare porcine aortic valves for both rat subdermal implants and sheep mitral valve replacements, for comparisons with glutaraldehyde-fixed controls. Thermal denaturation temperature, an index of crosslinking, cholesterol extraction, and hydrodynamic properties were quantified. Explant endpoints included quantitative and morphologic assessment of calcification.

Results: Thermal denaturation temperatures after TGA were intermediate between unfixed and glutaraldehyde-fixed. EtOH incubation resulted in almost complete extraction of cholesterol from TGA or glutaraldehyde-fixed cusps. Rat subdermal explants (90 days) demonstrated that TGA-EtOH resulted in a significantly greater level of inhibition of calcification than other conditions. Thus, TGA-ethanol stent mounted porcine aortic valve bioprostheses were fabricated for comparisons with glutaraldehyde-pretreated controls. In hydrodynamic studies, TGA-EtOH bioprostheses had lower pressure gradients than glutaraldehyde-fixed. The TGA-ethanol bioprostheses used as mitral valve replacements in juvenile sheep (150 days) demonstrated significantly lower calcium levels in both explanted porcine aortic cusp and aortic wall samples compared with glutaraldehyde-fixed controls. However, TGA-EtOH sheep explants also demonstrated isolated calcific nodules and intracuspal hematomas.

Conclusions: The TGA-EtOH pretreatment of porcine aortic valves confers significant calcification resistance in both rat subdermal and sheep circulatory implants, but with associated structural instability.
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http://dx.doi.org/10.1016/j.athoracsur.2011.04.104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3265762PMC
September 2011

Internal aortic annuloplasty: a novel technique.

J Invest Surg 2011 ;24(5):222-6

Medical School, University of Minnesota, Minneapolis, USA.

Background: The purpose of this study was to define an experimental model and a reproducible surgical technique for the preclinical assessment of safety and biocompatibility of a novel intra-annular internal aortic annulus repair device.

Methods: Adult sheep were implanted with HAART Inc's 19 mm aortic annulus repair device via a transverse aortotomy using standard anesthetic, surgical, and cardiopulmonary bypass techniques. Animals were closely monitored throughout the study period until the time of elective sacrifice at 30 or 60 days.

Results: Six adult sheep, mean age 63.2 weeks, mean weight 68.8 kg, underwent aortic annuloplasty with a 19 mm annuloplasty frame. Five of the sheep remained stable until scheduled sacrifice. The primary outcome of this study was animal mortality. Early mortality was seen in only one animal (16.7%), due to a surgical complication. Mild-to-moderate aortic insufficiency was observed in all animals upon echocardiographic examination at the time of elective sacrifice.

Conclusions: Of the six animals that underwent aortic annuloplasty, there was one early death due to surgical complication. The remaining five subjects were clinically stable at the time of elective sacrifice. Any conclusions regarding the cause of the observed aortic insufficiency are beyond the scope of this feasibility study but would need to be fully evaluated in the preclinical assessment of any internal aortic annuloplasty device. We have shown that we have developed a reproducible surgical technique in a physiologically appropriate model for the preclinical assessment of internal aortic annulus repair devices.
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http://dx.doi.org/10.3109/08941939.2011.575916DOI Listing
December 2011

Transmural atrial fibrosis after epicardial and endocardial argon-powered CryoMaze ablation.

J Card Surg 2011 Mar;26(2):240-3

Experimental Surgical Services, University of Minnesota, Minneapolis, Minnesota, USA.

Background: The CryoMaze procedure is usually limited to endocardial ablation under cardio-pulmonary bypass. Epicardial ablation is considered inferior as endocardial islets of atrial tissue could theoretically remain viable, protected from cryoinjury by epicardial fat and endocardial circulating warm blood. Novel argon-powered cryoprobes with lower ablation temperatures have recently become available. It is unclear if these instruments can reliably induce transmural atrial fibrosis by epicardial cryoablation on the beating heart.

Methods: Ten sheep were divided into two equal groups. CryoMaze ablations were applied using an argon-powered cryoprobe with an ablation temperature of -185°C. In the control group, standardized ablations (n = 50) were applied endocardially under cardiopulmonary bypass. In the experimental group, corresponding ablations (n = 50) were applied epicardially on the beating heart. Postoperatively the animals were monitored for 30 days. At necropsy, the lesions were explanted and analyzed histologically for evidence of transmural fibrosis.

Results: Two animals in the control group and one animal in the experimental group died prematurely. Autopsy of the remaining animals showed that all lesions (n = 70) had retained their structural integrity. In the control group, histology demonstrated transmural fibrosis in 94% (28/30) of the endocardially applied lesions. In the experimental group, histology demonstrated transmural fibrosis in 95% (38/40) of the epicardially applied lesions. Statistical analysis revealed no significant difference between the two groups (p = 0.96).

Conclusion: Argon-powered epicardial cryoablation on the beating heart is as efficient in inducing transmural fibrosis as the traditional technique of endocardial ablation under cardio-pulmonary bypass.
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http://dx.doi.org/10.1111/j.1540-8191.2011.01214.xDOI Listing
March 2011

Evaluation of aortic root and valve calcifications by multi-detector computed tomography.

J Heart Valve Dis 2009 Nov;18(6):662-70

University of Florida, Department of Radiology, P.O. Box 100374, Gainesville, Florida 32610-0374, USA.

Background And Aim Of The Study: In percutaneous aortic valve replacement (AVR), whilst calcifications are used as landmarks in fluoroscopic placement of the stent, they may also complicate stent placement. In response to this problem, the study aim was to examine severe aortic root calcification by using multi-detector computed tomography (MDCT), to better understand the pathology complicating percutaneous valve placement.

Methods: In 33 patients with severe aortic stenosis and scheduled for surgery, the 'inner orifice' and 'outer fibrous' annulus diameter and area (with and without calcification) were measured, in addition to the distances of the calcifications and coronary ostia from the annulus, using by ECG-gated 64-slice MDCT. Aortic root calcification was evaluated as minimal (< 25% of total circumference), mild (25-50%), moderate (50-75%), and severe (75-100%).

Results: The inner orifice annulus area was 5.9 +/- 1.9 cm2 (range: 1.4-10.1 cm2), while the outer fibrous area was 7.5 +/- 1.8 cm2 (range: 4.7-11.5 cm2). The proximal-to-distal extent of valve calcification from the annulus in the mid-center of leaflets was 0.8 +/- 0.26 cm. In 36% of patients, valvular calcification extended +/- 3 mm within the coronary-ostium level. The distance of the coronary ostia from the annulus was variable, with a mean of 1.3 +/- 0.35 cm (range: 0.6-2.4 cm) for the left coronary artery. In 42% of patients, a 'low coronary ostium' (< or = 1.1 cm), and in 6% a 'critical-low-coronary ostium' (< or = 8 mm) was identified. Annulus calcification was present in 100% of cases, but the severity varied widely (severe 50%, moderate 35%, mild 15%). In 36% of cases, the aortic annulus calcification extended caudally into the membranous part of the interventricular septum (and thus into the left ventricular outflow tract), and in 42% of cases (n = 14) into the anterior mitral valve leaflet.

Conclusion: The present results indicated that cardiac MDCT may qualify as a primary pre-procedural imaging modality to select patients for percutaneous AVR, based on the measurement and characterization of the aortic root and valve calcification. In comparison to echocardiography, CT will reduce--if not eliminate--difficulties in visualizing the aortic orifice area in heavily calcified valves. Furthermore, knowledge of the exact location of calcific deposits provides a distinct advantage to the fluroscopist for precise placement of the percutaneous aortic valve. Likewise, knowledge of the coronary arteries orifice in relation to the valve plane is critical to prevent inadvertent coronary artery occlusion, and would clearly be beneficial when planning future valve designs.
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November 2009

Perfusion preservation of the donor heart: basic science to pre-clinical.

J Extra Corpor Technol 2009 Sep;41(3):140-8

Department of Surgery, Experimental Surgical Services, University of Minnesota, Minneapolis, Minnesota, USA.

As a consequence of technology improvements and refinement, perfusion of the donor heart has moved from the research laboratory to clinical studies. Multiple investigators are currently leading pre-clinical trials of devices using perfusion preservation, and one device is now in European clinical trials. One major problem with the donor heart is the high metabolism relative to other organs, and depletion of ATP leads rapidly to acidosis and necrosis of the myocardium. Two techniques in development to address the issue are normothermic and hypothermic perfusion. This review examines the current issues regarding donor heart preservation and techniques of preclinical evaluation necessary for regulatory approval.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4679948PMC
September 2009

A novel alternative placement site and technique for totally implantable vascular access ports in non-human primates.

J Med Primatol 2009 Jun 10;38(3):204-12. Epub 2009 Feb 10.

Schulze Diabetes Institute, Department of Surgery, University of Minnesota, Minneapolis, MN, USA.

Background: Two novel approaches to implanting a central venous catheter port in non-human primates (NHPs) using peripheral insertion are presented and compared.

Methods: Sixty vascular access port (VAP) implants were attempted in 52 NHPs by saphenous vein puncture (n = 20) or saphenous vein cutdown (n = 40).

Results: Fifty eight procedures were successful. Eighteen of 20 VAPs were successfully placed using saphenous vein puncture, and 40 of 40 using saphenous vein cutdown. There were no significant differences between procedures. Mean implantation times were similar between groups. At explant or study endpoint, all 58 VAPs were patent.

Conclusions: Vascular access port implantation by saphenous vein puncture or saphenous vein cutdown is safe and effective in NHPs. It is less invasive than conventional procedures, has fewer complications, provides outstanding patency, and reduces surgery time. Furthermore, it allows for cooperative in-homecage VAP use, minimizing handling stress. We recommend these refined methods for long-term vascular access in NHPs.
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http://dx.doi.org/10.1111/j.1600-0684.2009.00340.xDOI Listing
June 2009

Intermittent antegrade cardioplegia: isolated heart preservation with the Asporto heart preservation device.

Prog Transplant 2008 Jun;18(2):127-33

University of Minnesota, Minneapolis, USA.

Background: A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

Objective: To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

Materials And Methods: Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n = 13) or 15.6 (0.6) hours (n = 11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n = 9) given a single antegrade dose, were compared with hearts (group 2, n = 8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

Results: Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P = .00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) (P = .0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

Conclusion: Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.
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http://dx.doi.org/10.7182/prtr.18.2.044435h811qw0326DOI Listing
June 2008

Development of a sheep model of atrial fibrillation for preclinical prosthetic valve testing.

J Heart Valve Dis 2007 May;16(3):314-23

Experimental Surgical Services, Department of Surgery, University of Minnesota, Minneapolis, MN 55455, USA.

Currently, prosthetic heart valve testing is performed on animal models with no underlying cardiovascular pathologies. Unfortunately, unforeseen adverse events may occur when heart valves tested in animals in normal sinus rhythm are implanted in patients suffering from arrhythmias. For example, the Medtronic Parallel valve functioned well in pre-clinical testing, but a high rate of thromboembolic complications appeared when the valve was placed in patients with atrial fibrillation (AF). Given the increasing number of patients afflicted with AF, an animal model of the disorder is needed to more accurately predict a valve's function in the clinical setting. Among methods available for inducing AF, electrophysiological pacing is the most practiced, but the challenges associated with pacing have led to the development of alternative methods of inducing AF These methods include gene transfer and a pharmacologic approach with acetylcholine and catecholamines. Finally, although stem cells have been widely investigated in terms of their therapeutic benefits, the use of their well-reported pro-arrhythmic behavior shows great promise for the development of an AF model in sheep. Such a model would have the potential for detecting adverse outcomes with mechanical heart valves before implantation in the clinical setting.
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May 2007

Administration of tauroursodeoxycholic acid (TUDCA) reduces apoptosis following myocardial infarction in rat.

Am J Chin Med 2007 ;35(2):279-95

Department of Surgery, Experimental Surgical Services, University of Minnesota, Minneapolis, MN 55455, USA.

Black bear bile has been used in traditional Chinese medicine to treat liver and eye related illnesses for centuries. A major constituent of bile is ursodeoxycholic acid (UDCA). Recent analysis of the cellular effects of UDCA and its taurine conjugate tauroursodeoxycholic acid (TUDCA) have demonstrated their antiapoptotic properties through regulation of Bcl-2 family and survival signaling proteins (Bax, Bad, phosphatidylinositol-3-kinase). In this study, we tested the hypothesis that TUDCA administered to rats prior to a myocardial infarction (MI) would exhibit anti-apoptotic effects and improve cardiac function. Prior to ligation of the left anterior descending (LAD) coronary artery, TUDCA (50 mg/ml, 400 mg/kg, IV) or PBS was administered to rats. Animals were sacrificed 24 hours after ligation for terminal transferase-mediated dUTP-digoxigenin nick end-labeling (TUNEL) and caspase-3 activity to assess apoptosis. Additional TUDCA or PBS treated rats underwent pre-operative,1 and 4 week transthoracic ultrasounds to assess heart function by quantification of shortening fraction (SF) and infarct area. TUNEL labeling of the cardiac tissue revealed a significant reduction in apoptotic cells in rats given TUDCA prior to ischemic injury (p = 0.05). In support of reducing apoptosis, caspase-3 activity in the TUDCA treated animals also decreased (p = 0.02). By 4 weeks, a significantly smaller infarct area was present in the TUDCA group compared to the PBS group (0.05 vs. 0.13 cm(2), p = NS) and there was also an improvement in SF. The results provide evidence for TUDCA as a viable treatment for reducing apoptosis in a model of myocardial infarction. Additional studies will distinguish the functional result of improved cell survival following infarction, suggesting the potential for clinical application of this anti-apoptotic drug in treatment of acute MI.
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http://dx.doi.org/10.1142/S0192415X07004813DOI Listing
September 2007

A comparison of myocardial perfusion and rejection in cardiac transplant patients.

Int J Cardiovasc Imaging 2007 Oct 6;23(5):575-82. Epub 2007 Jan 6.

Department of Surgery, Experimental Surgical Services, University of Minnesota, MMC 220, 420 Delaware Street SE, Minneapolis, MN 55455, USA.

Introduction: Although histological evaluation of the cardiac tissue is the current gold standard for evaluation of rejection, we hypothesized that cardiac perfusion MRI is a safe non-invasive method that correlates tissue blood flow changes with biopsy proven rejection in the cardiac transplant patient.

Materials And Methods: In a retrospective study from 1984-2001, 83 patients underwent 135 MR Gd-DTPA imaging studies. In 8 patients (9%), biopsies graded 2 or higher (by ISHLT criteria) provided evidence of rejection. Patients were age and sex matched to 11 non-rejected controls for imaging analysis. Time-signal intensity curves generated for a mid-ventricle LV short axis slice during rest and adenosine stress allowed determination of myocardial blood flow (MBF, ml/min/gm). ROC curve analysis by SPSS allowed estimation of sensitivity and specificity.

Results: At rest, there was no difference in MBF between patients with prior rejection vs. those without (1.18 +/- 0.26 vs. 1.16 +/- 0.29). At stress there was a decrease in MBF for patients with prior rejection episodes (3.27 +/- 0.74) compared to no rejection (3.60 +/- 0.72), P = 0.067). The area under the ROC curve was 0.82, with specificity and sensitivity of 75% and 81%, respectively.

Conclusion: This study suggests that perfusion MR imaging can be used in assessing the cardiac transplant patient for rejection related microvascular changes. The high specificity and sensitivity recorded from the ROC curve illustrates the potential utility of this diagnostic test for future studies.
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http://dx.doi.org/10.1007/s10554-006-9184-6DOI Listing
October 2007

In-vivo experience with the Triflo trileaflet mechanical heart valve.

J Heart Valve Dis 2006 Nov;15(6):791-9

University of Minnesota, Department of Surgery, Experimental Surgical Services, Minneapolis 55455, USA.

Background And Aim Of The Study: The in-vivo performance of the Triflo trileaflet mechanical valve was evaluated in an ovine model. The aim of long-term follow up was to gather site-specific performance data demonstrating device safety, as required for regulatory approval of this new valve design, prior to its use in clinical trials.

Methods: The Triflo trileaflet valve was implanted in 26 sheep using 29-mm mitral (n=8; animal body weight 63.3 +/- 10.3 kg, age 112.0 +/- 30.7 weeks) or 21-mm aortic mechanical valves (n=19; body weight 73.0 +/- 4.36 kg, age 112.6 +/- 23.6 weeks) using standard techniques. Animals were allocated to 150- or 365-day survival cohorts. The 150-day cohort was further subdivided into mitral valve (n=6) and aortic valve (n=11) implants. The 365-day cohort was organized into aortic (n=7) and mitral (n=2) implants. Angiography, echocardiography, and pathology were performed to assess valve performance.

Results: Angiographically monitored pressure measurements for the trileaflet mitral valve at 150 and 365 days were within established ranges in terms of mean aortic pressure, systolic and diastolic aortic pressure, and left ventricular end-diastolic pressure. In animals receiving a mitral valve the transvalvular gradient was 3.5 +/- 0.71 mmHg at 365 days, and 0.2 +/- 0.4 mmHg at 150 days. The Triflo mitral valve had only mild (physiologic) regurgitation. Cardiac output was within normal limits in animals receiving the Triflo valve in the aortic position. Laboratory values reflected no ongoing infection or destruction of blood cells as a result of device implantation. No significant abnormality was noted at necropsy in any animal, except for evidence of thromboembolic events in the kidneys (4-20%). Pathological evaluation was reflected by mild to moderate fibrous tissue formation at the inflow orifice (n=15), and minimal growth was observed in the outflow tract of one valve. This was consistent with that seen in sheep implanted with a standard St. Jude Medical bileaflet valve.

Conclusion: The study results showed the Triflo valve to perform to safety levels comparable with those of the standard St. Jude Medical bileaflet design, when implanted in the aortic and mitral positions. Additional analysis of historic control data suggested that the trileaflet valve design may offer a reduction in outflow tract obstruction by allowing for a greater effective orifice area index when compared to an equal-sized-orifice bileaflet valve. Notably, the Triflo valve was associated with a statistically significant reduction in myocardial hypertrophy, further reducing the potential for patient-prosthesis mismatch. Overall, the Triflo valve appeared to more closely emulate the hemodynamic properties of the native tissue valve than the traditional bileaflet design. Hence, the trileaflet design may offer the function of a tissue valve while retaining the durability of the mechanical valve.
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November 2006

Rat intubation and ventilation for surgical research.

J Invest Surg 2006 Jul-Aug;19(4):267-74

Cellular and Integrative Physiology Graduate Program, Department of Physiology, University of Minnesota, 321 Church Street SE, Minneapolis, MN 55455, USA.

Effective outcomes in cardiothoracic surgical research using rodents are dependent upon adequate techniques for intubation and mechanical ventilation. Multiple methods are available for intubation of the rat; however, not all techniques are appropriate for survival studies. This article presents a refinement of intubation techniques and a simplified mechanical ventilation setup necessary for intrathoracic surgical procedures using volatile anesthetics. The procedure is defined and complications of the procedure are elucidated that provide a justification for animal numbers needed for initiating new studies. Lewis rats weighing 178-400 g (287 +/- 44) were anesthetized using Enflurane and intubated with a 16-G angiocatheter using transillumination. Mechanical ventilation (85 bpm, 2.5 mL TV, enflurane 1.5-2%) maintained adequate sedation for completion of an intrathoracic procedure. Complications of the intubation and ventilation included mortality from anesthetic overdose, intubation difficulty, pneumothorax, traumatic extubation, and ventilation disconnection. Anesthetic agents and their related effects on the rat heart and reflexes are compared. This article also underscores the importance of refinement, reduction, and replacement in the context of cardiothoracic surgery using rodent models.
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http://dx.doi.org/10.1080/08941930600778297DOI Listing
September 2006

Preoperative predictors for postoperative problems in heart transplantation: psychiatric and psychosocial considerations.

Prog Transplant 2005 Sep;15(3):276-82

University of Minnesota, Minneapolis, MN, USA.

The psychiatric and psychosocial evaluation of the heart transplant candidate can identify particular predictors for postoperative problems. These factors, as identified during the comprehensive evaluation phase, provide an assessment of the candidate in context of the proposed transplantation protocol. Previous issues with compliance, substance abuse, and psychosis are clear indictors of postoperative problems. The prolonged waiting list time provides an additional period to evaluate and provide support to patients having a terminal disease who need a heart transplant, and are undergoing prolonged hospitalization. Following transplantation, the patient is faced with additional challenges of a new self-image, multiple concerns, anxiety, and depression. Ultimately, the success of the heart transplantation remains dependent upon the recipient's ability to cope psychologically and comply with the medication regimen. The limited resource of donor hearts and the high emotional and financial cost of heart transplantation lead to an exhaustive effort to select those patients who will benefit from the improved physical health the heart transplant confers.
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September 2005

Evaluation of perfusion and viability in hypothermic non-beating isolated porcine hearts using cardiac MRI.

Int J Cardiovasc Imaging 2006 Apr 25;22(2):243-51. Epub 2005 Oct 25.

Department of Physiology, University of Minnesota, MMC 195, 420 Delaware Street S.E., Minneapolis, MN 55455, USA.

The donor heart undergoes degradation during hypothermic storage. An assessment of donor heart preservation is typically done with histological or biochemical methods that are not feasible in the clinical setting. We describe a method to study the donor heart using cardiac perfusion MRI that is potentially feasible for clinical use. Standard cardiectomy was performed in the pig model and the hearts were stored in normal saline at 5 degrees C. Imaging was performed by using a rapid gradient-echo sequence (FLASH) with saturation-recovery preparation for T1-weighting in the short axis and horizontal long axis views. Approximately 80 serial images were acquired at a rate of 1/s during administration of 0.006 mmol/ml Gd-DTPA (500 ml, 1 l/min). Signal intensity vs. time curves were generated for each heart and slice imaged and compared to a 0.006 mmol/ml Gd-DTPA reference. H&E stained biopsies of the LV, RV, and septum were also obtained. The mean duration of heart storage (N=10) was 8.8 h (range 4.2-19.2 h). Histologically, no differences were seen in H&E stained biopsies among hearts at different storage times. However cardiac MRI revealed a decrease in perfusion units in each subsequent heart tested after 4.2 h. (R=0.49). Average peak up-slope was used as a surrogate measure for flow capacity through the microvasculature and peak contrast enhancement was used as a measurement of viable microvasculature. The 4 h heart had 83% peak contrast enhancement of the reference standard, as compared to 44% for the 19.2 h heart. The decrease in peak enhancement is directly related to the duration of storage time. No correlation of peak up-slope of the intensity curve to storage time was found. This new application of cardiac MRI in the donor heart is applicable to: (1) assessing marginal hearts, (2) evaluating donor heart preservation techniques, and (3) correlating pre- to post-transplant viability.
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http://dx.doi.org/10.1007/s10554-005-9015-1DOI Listing
April 2006

The current state of in-vivo pre-clinical animal models for heart valve evaluation.

J Heart Valve Dis 2005 May;14(3):423-32

University of Minnesota Department of Surgery, Experimental Surgical Services and the Lillehei Heart Institute, Minneapolis 55455, USA.

For over 30 years, animal models have remained a central critical component in the pre-clinical safety evaluation of prosthetic heart valves developed for use in humans. Though many advances have been made in valve design, no ideal replacement prosthesis has yet been developed. As a result, valve manufacturers continue to address issues relating to thrombogenicity, structural integrity, fluid dynamics and calcification in their designs. Many animal models have been developed to examine these issues, including dog, pig, calf and sheep, yet no standard model has been accepted. Recently, the International Standard Organization has provided guidelines in document 5840 to address cardiovascular implants. The aim of this report is to provide a summary of the current state of pre-clinical valve evaluation in animals. Changes in ISO 5840 will be addressed that have occurred between 1998 and the present date, and the role of current available animal models. The aim also is to provide rational guidance in the selection of appropriate animal models to match the purpose of valve implantation studies.
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May 2005

Cardiac MRI in the isolated porcine heart reveals possible etiology of sudden right heart failure following heart transplantation.

Int J Cardiovasc Imaging 2004 Dec;20(6):493-6

Department of Physiology, University of Minnesota, Minneapolis, MN 55455, USA.

Occurrence of immediate post-transplant heart failure in the cardiac transplant recipient is typically attributed to elevated pulmonary vascular resistance, however other etiologies may play a role. At the completion of the transplant, free air, which has collected in the donor heart, is vented via an aortotomy. Free air may rise into the right coronary artery and obstruct reperfusion of the right ventricle. Cardiac perfusion MRI may offer a method of non-invasively determining the presence of air embolus. The objectives in the pilot study were to identify steps in the donor process where free air could enter into the aortic root causing obstruction of perfusion of the coronary arteries. A change in surgical technique could then be used to eliminate a portal of entry and cardiac perfusion MRI could validate the technique. Standard cardiectomy was compared to a variation in technique in two animals. Pulmonary vein ligation was completed in the experimental model before completion of cardiectomy. Both hearts were isolated and imaged using T1-weighted FLASH sequence and gadolinium contrast via the aortic root. Cardiac perfusion MRI imaging of the heart with the unligated pulmonary vein revealed evidence of air embolus and no perfusion of the right coronary artery compared to the ligated heart. Anatomically, the right coronary artery is anterior in the mediastinum compared to the left coronary artery. Air emboli preferentially rise into the right coronary and can obstruct flow into the right heart. Cardiac perfusion MRI offers an effective method to evaluate the isolated pre-transplant heart for perfusion defects.
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http://dx.doi.org/10.1007/s10554-004-1690-9DOI Listing
December 2004
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