A pilot study for inducing chronic heart failure in calves by means of oral monensin

INTRODUCTION

Heart failure remains a major cause of mortality in the United States, despite advancing technologies, newer methods of treatment, and novel devices. To evaluate such novel devices, a large-animal model of chronic heart failure is critical in carrying out preclinical animal studies.

METHODS

We evaluated the efficacy of oral monensin in inducing stable heart failure in five Jersey calves. Various doses of monensin were administered. Hemodynamics, pressure-volume loops, echocardiographic measurements, extent of tissue perfusion, and histopathologic data were recorded before and after induction of heart failure.

RESULTS

Responses were variable in the animals. One experiment showed a significant decrease in cardiac output within one week, associated with simultaneous increases in left atrial pressure, central venous pressure, and mean pulmonary artery pressure. Left ventricular pressure-volume loops showed that the slope of the end-systolic pressure-volume relation decreased markedly between the baseline and terminal study, suggesting a decrease in contractility. Echocardiographic studies indicated a decrease in ejection fraction. Histopathologic analysis in cardiac tissue showed extensive fibrosis and necrosis.

CONCLUSION

We demonstrated the feasibility of inducing and maintaining severe yet stable heart failure for up to 3 weeks in a calf model by administration of oral monensin.

Use of zirconia ceramic in the DexAide right ventricular assist device journal bearing

Our aim was to evaluate the potential use of zirconium oxide (zirconia) as a blood journal bearing material in the DexAide right ventricular assist device. The DexAide titanium stator was replaced by a zirconia stator in several blood pump builds, without changing the remaining pump hardware components. In vitro pump performance and efficiency were evaluated at a predetermined pump speed and flow. Motor power consumption decreased by 20%, and DexAide battery life was extended to over 12 h on two fully charged batteries. The zirconia stator was also successfully evaluated in a severe start/stop test pre- and postexposure of the zirconia to accelerated simulated biologic aging. This study's outcomes indicated the advantages of zirconia as an alternate journal bearing material for the DexAide device.

In vivo acute performance of the Cleveland Clinic self-regulating, continuous-flow total artificial heart

BACKGROUND

The purpose of this study was to evaluate the acute in vivo pump performance of a unique valveless, sensorless, pulsatile, continuous-flow total artificial heart (CFTAH) that passively self-balances left and right circulations without electronic intervention.

METHODS

The CFTAH was implanted in two calves, with pump and hemodynamic data recorded at baseline over the full range of pump operational speeds (2,000 to 3,000 rpm) in 200-rpm increments, with pulsatility variance, and under a series of induced hemodynamic states created by varying circulating blood volume and systemic and pulmonary vascular resistance (SVR and PVR).

RESULTS

Sixty of the 63 induced hemodynamic states in Case 1 and 73 of 78 states in Case 2 met our design goal of a balanced flow and maximum atrial pressure difference of 10 mm Hg. The correlation of calculated vs measured flow and SVR was high (R(2) = 0.857 and 0.832, respectively), allowing validation of an additional level of automatic active control. By varying the amplitude of sinusoidal modulation of the speed waveform, 9 mm Hg of induced pulmonary and 18 mm Hg of systemic arterial pressure pulsation were achieved.

CONCLUSIONS

These results validated CFTAH self-balancing of left and right circulation, induced arterial flow and pressure pulsatility, accurate calculated flow and SVR parameters, and the performance of an automatic active control mode in an acute, in vivo setting in response to a wide range of imposed physiologic perturbations.

An innovative, sensorless, pulsatile, continuous-flow total artificial heart: device design and initial in vitro study

BACKGROUND

We are developing a very small, innovative, continuous-flow total artificial heart (CFTAH) that passively self-balances left and right pump flows and atrial pressures without sensors. This report details the CFTAH design concept and our initial in vitro data.

METHODS

System performance of the CFTAH was evaluated using a mock circulatory loop to determine the range of systemic and pulmonary vascular resistance (SVR and PVR) levels over which the design goal of a maximum absolute atrial pressure difference of 10 mm Hg is achieved for a steady-state flow condition. Pump speed was then modulated at 2,600 +/- 900 rpm to induce flow and arterial pressure pulsation to evaluate the effects of speed pulsations on the system performance. An automatic control mode was also evaluated.

RESULTS

Using only passive self-regulation, pump flows were balanced and absolute atrial pressure differences were maintained at <10 mm Hg over a range of SVR (750 to 2,750 dyne.sec.cm(-5)) and PVR (135 to 600 dyne.sec.cm(-5)) values far exceeding normal levels. The magnitude of induced speed pulsatility affected relative left/right performance, allowing for an additional active control to improve balanced flow and pressure. The automatic control mode adjusted pump speed to achieve targeted pump flows based on sensorless calculations of SVR and CFTAH flow.

CONCLUSIONS

The initial in vitro testing of the CFTAH with a single, valveless, continuous-flow pump demonstrated its passive self-regulation of flows and atrial pressures and a new automatic control mode.

Human clinical fitting study of the DexAide right ventricular assist device

The DexAide right ventricular assist device (RVAD) has been developed as an implantable RVAD. The purpose of this study was to determine the final design and optimal anatomical placement of the DexAide RVAD when implanted simultaneously with either of two commercially available left ventricular assist devices (LVADs) in patients. A mock-up DexAide RVAD was used to assess configuration with each of two types of commercially available LVADs at the time of LVAD implantation in three human clinical cases. The pump body of the DexAide RVAD was placed either in the preperitoneal space or in the right thoracic cavity. The DexAide RVAD placed into the right thoracic cavity is suitable for use with the Novacor or HeartMate II LVADs. The results of this study will guide the finalization of the inflow cannula and optimal placement of the DexAide RVAD for human clinical trials.

Novel implantable device to detect cardiac allograft rejection

BACKGROUND

Allograft rejection remains the nemesis of solid organ transplantation. Soul Mate is a novel implantable wireless data transmission system that analyzes 9 intramyocardial electrogram parameters recorded from 4 or 6 configurations of 2 or 3 epicardial leads to detect allograft rejection. This study determined the ability of the Soul Mate to detect early rejection of transplanted hearts.

METHODS AND RESULTS

Five dogs underwent heterotopic cervical heart transplantation and simultaneous implantation of the Soul Mate's Cardiac Rejection Monitoring Device. Dogs were initially immunosuppressed, but subsequent drug discontinuation allowed allograft rejection to appear. Allograft biopsies were performed at regular intervals to determine rejection grade, which was compared to a calculated rejection score determined as percent change from baseline of values for each intramyocardial electrogram. There was significant correlation between the biopsy results and the evolution of 5 parameters. The strongest correlation (r=0.939; P<0.001) was obtained using the "general median" parameter from 4 configurations, assessed 1 day before the biopsy, with a sensitivity of 85.7% and a specificity of 100% compared to the myocardial biopsy results.

CONCLUSIONS

The Soul Mate allograft rejection monitoring system accurately detected transplanted heart rejection in a canine model noninvasively with continuous sampling. This proof-of-concept study suggests that the Soul Mate could be used to more intensely and more frequently monitor cardiac allografts for rejection.

Comparison of pulsatile and non‐pulsatile cardiopulmonary bypass on regional renal blood flow in sheep

OBJECTIVE

The purpose of the present study was to evaluate the effects of pulsatile cardiopulmonary bypass (CPB) on sheep regional renal blood flow by comparing pulsatile and non-pulsatile perfusion at two different flow rates.

DESIGN

Seven female Suffolk sheep were used and the animals were perfused with pulsatile and non-pulsatile CPB at flow rates of 60 and 100 ml/min/kg. Regional renal blood flow was measured by the colored microsphere method. General linear model ANOVA was performed to analyze the data.

RESULTS

Regional renal blood flow was significantly higher in both outer and middle cortices of pulsatile CPB compared with non-pulsatile CPB (outer cortex: pulsatile CPB, 381+/-192 ml/min/100 g, non-pulsatile CPB, 255+/-151 ml/min/100g, p=0.002; middle cortex: pulsatile CPB, 239+/-114 ml/min/100 g, non-pulsatile CPB, 176+/-80 ml/min/100 g, p=0.02). The increase of flow rate from 60 to 100 ml/min/kg improved renal cortical blood flow significantly.

CONCLUSION

The regional renal blood flow was significantly higher in both outer and middle cortices of pulsatile CPB compared with the non-pulsatile CPB.

Comparative study of heart rate variability between healthy human subjects and healthy dogs, rabbits and calves

Several studies have been performed to assess heart rate variability (HRV) in several species such as humans, dogs, pigs, calves, rabbits and rats. However, haemodynamic parameters are totally different in each animal, and optimal animal models for studying HRV corresponding to human HRV are still unclear. The purpose of this study was to assess HRV in human subjects and to compare those HRV data with canine, bovine and rabbit HRV data. The heart rate in the human subjects (62.8 ± 7.4 bpm) was significantly lower than that in dogs (124.2 ± 18.8 bpm, P < 0.001), calves (73.4 ± 10.5 bpm, P < 0.05), and rabbits (217.3 ± 21.5 bpm, P < 0.001). The low-frequency waves (LF) (57.9 ± 65.8 ms2/Hz) and high-frequency waves (HF) (33.8 ± 49.1 ms2/Hz) in rabbits were significantly lower than human LF (1216.3 ± 1220.7 ms2/Hz, P < 0.05) and HF (570.9 ± 581.3 ms2/Hz, P < 0.05). Dogs and calves showed similar LF (991.1 ± 646.1 ms2/Hz and 547.0 ± 256.9 ms2/Hz, respectively), HF (702.1 ± 394.1 ms2/Hz and 601.0 ± 666.6 ms2/Hz, respectively) and LF/HF (2.0 ± 1.3 and 2.5 ± 1.9, respectively) when compared with the human data. The present study shows that dogs and calves revealed similar HRV values as those which relate to humans. Large deviation of the HRV values in rabbits compared with humans might be considered when conducting animal studies using those animals to reflect human clinical situations.

Median sternotomy approach for chronic bovine experiments

Lateral thoracotomy is the traditional surgical approach for preclinical animal testing of various ventricular assist devices. Median sternotomy, however, is regarded from a functional standpoint as the most appropriate approach for cardiac surgical procedures, particularly for device implantation. The purpose of this study was to evaluate the outcomes of performing a median sternotomy in chronic bovine studies. Three chronic studies using the sternotomy approach were performed. Surgical access was compared to the lateral thoracotomy approach used in three other animal experiments. Postoperative speed of recovery, pain management, sternotomy incision, and monitoring line exit site healing and infection were also evaluated. With sternotomy, better surgical access to all cardiac chambers and great vessels and more room for device placement were achieved. The recovery time was similar to that using the lateral thoracotomy approach, with no additional difficulties observed in standing or recumbency and no need for increased pain management. At the time of autopsy, the sternum was well healed without any sign of infection. In conclusion, these studies showed that a median sternotomy can be used successfully for chronic bovine studies. This approach will be used for our future biventricular assist device implantation surgeries.

Development of DexAide right ventricular assist device: update II

The DexAide right ventricular assist device (RVAD) is a magnetically and hydrodynamically levitated implantable centrifugal pump. Recent progress includes 1) redesign of the inflow/outflow conduits, which yielded two successful 3-month experiments, 2) development of alternative journal bearing materials, and 3) completion of an 18-month duration of in vitro endurance testing. Verification testing of the RVAD electronics has been completed, and a prototype biventricular assist device (BVAD) system has been tested. Acute DexAide/CorAide BVAD implantations via median sternotomy in two calves documented BVAD control algorithms and anatomical fit. A drug-induced chronic calf heart failure model, currently under development in our laboratory, resulted in a successful BVAD implantation in a calf with heart failure. Our future plans are to complete in vitro and in vivo validation of alternative bearing materials, perform preclinical DexAide in vivo and in vitro reliability studies, and obtain Food and Drug Administration (FDA) approval for an Investigational Device Exemption to conduct a clinical pilot study. In conclusion, two successful 3 month in vivo experiments and an 18-month in vitro endurance test were completed. After final bearing material selection, the DexAide design will be "frozen" so that preclinical systems can be manufactured. BVAD experiments using a chronic heart failure model are in progress.

Phasic coronary blood flow patterns in dogs vs. pigs: an acute ischemic heart study

BACKGROUND

Canine and porcine hearts have been widely used to investigate diagnoses, interventions, and surgical therapies for ischemic heart disease. Dogs and pigs are known to vary with regard to the anatomic distribution of their coronary arteries. However, the mechanisms of these differences and the differing phasic coronary blood flow patterns between the two species are not well characterized.

MATERIAL/METHODS

Phasic coronary blood flow patterns and hemodynamic data were analyzed using three flow probes placed around the left anterior descending (LAD), left circumflex (LCX), and right coronary (RCA) arteries in both canine and porcine models.

RESULTS

Systolic left ventricular pressure, arterial pressure, and systemic vascular resistance in dogs were higher than in pigs. Likewise, total coronary blood flow, LAD flow, and LCX flow were higher in dogs than in pigs. LCX flow was higher in dogs, but RCA flow was higher in pigs. Diastolic fraction and diastolic/systolic peak velocity ratio of the LAD, LCX, and RCA showed no significant differences at baseline between dogs and pigs. Systolic LAD flow in dogs decreased after the creation of an LAD stenosis, whereas systolic LAD flow in pigs increased.

CONCLUSIONS

Coronary blood flow patterns in dogs and pigs are quite different. These findings are potentially relevant to understanding the physiology of myocardial blood perfusion in dogs and pigs with ischemic heart disease.

Reduced pulsatility induces periarteritis in kidney: role of the local renin-angiotensin system

OBJECTIVE

The need for pulsatility in the circulation during long-term mechanical support has been a subject of debate. We compared histologic changes in calf renal arteries subjected to various degrees of pulsatile circulation in vivo. We addressed the hypothesis that the local renin-angiotensin system may be implicated in these histologic changes.

METHODS AND RESULTS

Sixteen calves were implanted with devices giving differing degrees of pulsatile circulation: 6 had a continuous flow left ventricular assist device (LVAD); 6 had a continuous flow right ventricular assist device (RVAD); and 4 had a pulsatile total artificial heart (TAH). Six other calves were histologic and immunohistochemical controls. In the LVAD group, the pulsatility index was significantly lower (0.28 +/- 0.07 LVAD vs 0.56 +/- 0.08 RVAD, vs 0.53 +/- 0.10 TAH; P < 0.01), and we observed severe periarteritis in all cases in the LVAD group. The number of angiotensin II type 1 receptor-positive cells and angiotensin converting enzyme-positive cells in periarterial areas was significantly higher in the LVAD group (angiotensin II type 1 receptor: 350 +/- 139 LVAD vs 8 +/- 6 RVAD, vs 3 +/- 2 TAH, vs 3 +/- 2 control; P < .001; angiotensin-converting enzyme: 325 +/- 59 LVAD vs 6 +/- 4 RVAD, vs 6 +/- 5 TAH, vs 3 +/- 1 control; P < .001).

CONCLUSIONS

The reduced pulsatility produced by a continuous flow LVAD implantation induced severe periarteritis in the kidneys. The local renin-angiotensin system was up-regulated in the inflammatory cells only in the continuous flow LVAD group.

Innovative, replaceable heart valve: concept, in vitro study, and acute in vivo study

The purpose of this study was to evaluate the feasibility of our innovative, replaceable heart valves that can be easily detached from the sewing ring at the time of repeat replacement. The prototype devices consist of the base magnet ring assembly and the valve magnet ring assembly that utilize magnetic coupling force for the locking mechanism. Magnetic coupling strength was evaluated in vitro. Prototype bioprosthetic valves were implanted acutely in three sheep to confirm the feasibility of the replaceable mitral valve. The static separation force of prototype size #25 was 12.5 lb, meeting the design goal. In situ attachment and detachment of the valve magnet ring assembly from the base magnet ring assembly were very easily accomplished in all animals. The magnetic coupling did not decouple even under extremely high left ventricular pressures. We have demonstrated the feasibility of this innovative concept of a replaceable mitral valve.