Biomedical subjects

Daniel Tamez

Publications and source records attributed to Daniel Tamez.

6 recordsLinked to original sources

PubMed2004

Preclinical assessment of a trileaflet mechanical valve in the mitral position in a calf model.

BACKGROUND: The bileaflet valve is currently the mechanical replacement valve of choice. Though durable, it does not closely mimic native valve hemodynamics and remains potentially thrombogenic. METHODS: Prototype trileaflet valves (T1 and T2) were implanted in the mitral position in calves. Group I calves received either a T1 valve (n = 12) or a control bileaflet valve (n = 5); Group II, either a T2 valve (n = 7) or a control bileaflet valve (n = 5). Valve function, perivalvular leakage, and transvalvular pressure gradients were evaluated. Also, long-term prototype leaflet wear was evaluated in vivo in one Group I calf (502 days) and two Group II calves (385 and 366 days). Calves were euthanized and necropsied at study termination, and major organs weighed and examined. RESULTS: Valve function was excellent and hematologic parameters remained normal in all calves that survived to study termination. Mean peak transvalvular pressure gradients were 10 +/- 7 mm Hg for T1 valves, 6 +/- 3 mm Hg for T2 valves, and 12 +/- 4 mm Hg for bileaflet control valves. Clinically insignificant valvular regurgitation was observed in both prototypes. Explanted valves showed no thrombus-impaired leaflet motion, except in two T1-fitted calves and one T2-fitted calf. Major organs showed no evidence of clinically significant thromboembolic events. There were no other significant differences between the results of experimental and control groups. CONCLUSIONS: Prototype trileaflet valves performed safely and effectively in the mitral position in calves, even without long-term anticoagulation. This warrants their evaluation as an equivalent alternative to bileaflet valves.

Animals↗

PubMed2004

Preclinical hemodynamic assessment of a new trileaflet mechanical valve in the aortic position in a bovine model.

BACKGROUND AND AIM OF THE STUDY: The hemodynamic characteristics of a new trileaflet mechanical heart valve (TTV) (TriFlo Inc., Costa Mesa, CA, USA) in the aortic position were evaluated in a bovine model. The TTV was designed to combine the durability of mechanical heart valves with the central flow characteristics of a bioprosthesis. METHODS: Using nine calves, the native aortic valve was replaced with a 21-mm TTV (n = 6) or a St. Jude Medical (SJM) valve (n = 3). Hemodynamic values were assessed with echocardiography at implantation and with catheterization at explantation. All calves underwent a necropsy, followed by gross pathology and light microscopy studies. RESULTS: The mean implant duration was 159 +/- 55 days for the TTV and 102 +/- 67 days for the SJM valve. Immediately before euthanasia, the peak and mean pressure gradients were respectively 35 +/- 14 and 24 +/- 9 mmHg for the TTV, and 100 +/- 72 and 59 +/- 38 mmHg for the SJM valve (p = 0.03). Two of the SJM-valve animals were electively sacrificed after showing symptoms of aortic stenosis. At necropsy, all nine valves were free from thrombi, pannus, occlusive tissue, or mechanical impairment of leaflet motion. The prematurely sacrificed SJM-valve animals had concentric myocardial hypertrophy consistent with severe functional aortic stenosis. CONCLUSION: The significantly higher gradients and left ventricular hypertrophy in the SJM-valve animals were related to a smaller effective orifice area, which precluded adaptation to increasing transvalvular volumes in the growing animal. This problem was not seen with the TTV, which performed hemodynamically as well as the SJM valve. The high transvalvular gradients seen with the SJM valve at study end may suggest that the hemodynamic characteristics of the TTV may be superior, though additional studies are needed to confirm this.

Animals↗

PubMedDate not supplied

Biventricular support with the Jarvik 2000 axial flow pump: a feasibility study.

Patients with congestive heart failure who are supported with a left ventricular assist device (LVAD) may experience right ventricular dysfunction or failure that requires support with a right ventricular assist device (RVAD). To determine the feasibility of using a clinically available axial flow ventricular assist device as an RVAD, we implanted Jarvik 2000 pumps in the left ventricle and right atrium of two Corriente crossbred calves (approximately 100 kg each) by way of a left thoracotomy and then analyzed the hemodynamic effects in the mechanically fibrillated heart at various LVAD and RVAD speeds. Right atrial implantation of the device required no modification of either the device or the surgical technique used for left ventricular implantation. Satisfactory biventricular support was achieved during fibrillation as evidenced by an increase in mean aortic pressure from 34 mm Hg with the pumps off to 78 mm Hg with the pumps generating a flow rate of 4.8 L/min. These results indicate that the Jarvik 2000 pump, which can provide chronic circulatory support and can be powered by external batteries, is a feasible option for right ventricular support after LVAD implantation and is capable of completely supporting the circulation in patients with global heart failure.

Animals↗

PubMedDate not supplied

Baseline hemodynamic and echocardiographic indices in anesthetized calves.

The experimental calf model is used to assess mechanical circulatory support devices and prosthetic heart valves. Baseline indices of cardiac function have been established for the normal awake calf but not for the anesthetized calf. Therefore, we gathered hemodynamic and echocardiographic data from 16 healthy anesthetized calves (mean age, 189.0 +/- 87.0 days; mean body weight, 106.9 +/- 32.3 kg) by cardiac catheterization and noninvasive echocardiography, respectively. Baseline hemodynamic data included heart rate (65 +/- 12 beats per minute), mean aortic pressure (113.5 +/- 17.4 mm Hg), left ventricular end-diastolic pressure (16.3 +/- 38.9 mm Hg), and mean pulmonary artery pressure (21.7 +/- 8.3 mm Hg). Baseline two-dimensional echocardiographic data included left ventricular systolic dimension (3.5 +/- 0.7 cm), left ventricular diastolic dimension (5.6 +/- 0.8 cm), end-systolic intraventricular septal thickness (1.7 +/- 0.2 cm), end-diastolic intraventricular septal thickness (1.2 +/- 0.2 cm), ejection fraction (63 +/- 10%), and fractional shortening (37 +/- 10%). Doppler echocardiography revealed a maximum aortic valve velocity of 0.9 +/- 0.5 m/s and a cardiac index of 3.7 +/- 1.1 L/minute/m2. The collected baseline data will be useful in assessing prosthetic heart valves, cardiac assist pumps, new cannulation techniques, and robotics applications in the anesthetized calf model and in developing calf models of various cardiovascular diseases.

Anesthetics, Dissociative↗

PubMedDate not supplied

Thrombogenicity of mechanical aortic valves in an animal model: site specific testing is crucial.

We evaluated a new trileaflet prosthesis and a control bileaflet prosthesis in the mitral and aortic positions in 27 calves. The prototype trileaflet valve (TV1) functioned satisfactorily in the mitral position (TV1m, n = 7) but later yielded thrombogenic complications in the aortic position (TV1a, n = 4). The valve was redesigned (TV2) and retested in the mitral (TV2m n = 4) and aortic (TV2a, n = 5) positions, along with control valves (Cm, n = 4; Ca, n = 3). At necropsy, the valves were graded on a scale of 0 (no visible thrombi) to 4 (thrombi greater than 5 mm and/or obstructed leaflets). The TV1m, TV2m, and Cm animals, respectively, had implant durations of 215+/-112, 140+/-63, and 159+/-89 days and thrombus grades of 0.71+/-0.76, 0.33+/-0.58, and 1.50+/-0.58. The TV1a, TV2a, and Ca animals had implant durations of 18+/-12, 159+/-61, and 108+/-62 days and thrombus grades of 2.75+/-1.00, 0.50+/-0.58, and 0.67+/-0.58 (p < .005; TV2a vs. TV1a). Three TV1a calves died early of valve related complications. A design irregularity, undetected in the mitral position but revealed in the aortic position, caused a high early mortality in the TV1a animals. Redesigning the prosthesis eliminated valve related mortality and significantly reduced the thrombus grade. Because satisfactory performance in the mitral position does not guarantee safety or efficacy in the aortic position, site specific preclinical testing is crucial for mechanical heart valves.

Animals↗

PubMedDate not supplied

Total heart replacement with dual centrifugal ventricular assist devices.

In an ovine feasibility study, we implanted two HeartMate-III centrifugal ventricular assist devices (VADs) for total heart replacement. With cardiopulmonary bypass support, both ventricles were transected at the atrioventricular groove, preserving a rim of ventricular tissue. The atrioventricular valves were excised, and the aorta and pulmonary artery were transected above the ventriculoarterial valves. An interatrial septal window was created by excising the foramen ovale. The VADs' sewing rings were attached to the left and right ventricular remnants, respectively. Outflow grafts were anastomosed to the aorta and pulmonary artery. The left VAD operated continuously at 4,500 rpm. Right VAD speed increased from 2,000 to 4,500 rpm in 500 rpm increments. Outflow graft flow, pressure, oxygen saturation, and shunt direction were recorded. The pulmonary artery to aortic ratio of flow and pressure increased from 0.26 and 0.15 (at 2,000 rpm) to 1.21 and 0.53, respectively (at 4,500 rpm). The interatrial shunt, which was right to left at lower right VAD speeds, progressed to bidirectional, then to left dominant as right VAD speed increased. Outflow-graft oxygen saturation was reflective of the shunt direction. In this acute experiment, total heart replacement with continuous flow VADs satisfactorily balanced left and right ventricular flows and preserved the physiologic circulatory response.

Animals↗