Heart Motion Prediction Based on Adaptive Estimation Algorithms for Robotic Assisted Beating Heart Surgery

Robotic assisted beating heart surgery aims to allow surgeons to operate on a beating heart without stabilizers as if the heart is stationary. The robot actively cancels heart motion by closely following a point of interest (POI) on the heart surface-a process called Active Relative Motion Canceling (ARMC). Due to the high bandwidth of the POI motion, it is necessary to supply the controller with an estimate of the immediate future of the POI motion over a prediction horizon in order to achieve sufficient tracking accuracy. In this paper, two least-square based prediction algorithms, using an adaptive filter to generate future position estimates, are implemented and studied. The first method assumes a linear system relation between the consecutive samples in the prediction horizon. On the contrary, the second method performs this parametrization independently for each point over the whole the horizon. The effects of predictor parameters and variations in heart rate on tracking performance are studied with constant and varying heart rate data. The predictors are evaluated using a 3 degrees of freedom test-bed and prerecorded in-vivo motion data. Then, the one-step prediction and tracking performances of the presented approaches are compared with an Extended Kalman Filter predictor. Finally, the essential features of the proposed prediction algorithms are summarized.

Preload sensitivity in cardiac assist devices

With implantable cardiac assist devices increasingly proving their effectiveness as therapeutic options for end-stage heart failure, it is important for clinicians to understand the unique physiology of device-assisted circulation. Preload sensitivity as it relates to cardiac assist devices is derived from the Frank-Starling relationship between human ventricular filling pressures and ventricular stroke volume. In this review, we stratify the preload sensitivity of 17 implantable cardiac assist devices relative to the native heart and discuss the effect of preload sensitivity on left ventricular volume unloading, levels of cardiac support, and the future development of continuous-flow total artificial heart technology.

Functional mitral regurgitation: modern concepts for ventricular geometry reshaping

Functional mitral valve regurgitation (MR), a condition affecting millions of primarily elderly patients worldwide, is associated with poor clinical outcomes. Functional MR has traditionally been considered a disorder of regional or global left ventricular (LV) remodeling secondary to myocardial disease, in which anatomically normal leaflets fail to coapt adequately. The primary mechanisms of MR are mitral annular dilatation and leaflet restriction secondary to LV remodeling. Although annuloplasty is commonly used to correct valve incompetence, the effects of altered ventricular mechanics on MR need to be specifically addressed. This review focuses on current concepts of geometric reconfiguration of the LV and mitral-ventricular apparatus to reduce MR.

Effect of epivascular cardiac autonomic nerve stimulation on cardiac function

BACKGROUND

The cardiac plexus contains sympathetic and parasympathetic cardiac nerves. Our goal was to assess the hemodynamic and functional effects of stimulating the cardiac autonomic nervous system (CANS) at the epivascular surfaces of the cardiac plexus. Although CANS therapy to modulate cardiovascular function has drawn widespread interest, research has focused only on stimulating parasympathetic or sympathetic nerves, not both at once.

METHODS

Using general anesthesia and an open-chest surgical procedure, 12 dogs received epivascular stimulation of the cardiac plexus. A bipolar electrode was placed between the right pulmonary artery (PA) and the ascending aorta, with the stimulation frequency/pulse width held constant (20 Hz/4 ms) and the voltage varied (10-50 V). Left ventricular (LV) pressure-volume loops and hemodynamic data were recorded with and without stimulation.

RESULTS

In all dogs, aortic and LV systolic pressures, maximum rate of change of LV pressure, and LV stroke work increased (p<0.0001), as did cardiac output (2.9±1.0-0.4±1.0 L/min; p=0.001), end-systolic elastance (1.2±0.4-1.5±0.5 mm Hg/mL; p=0.0001), preload recruitable stroke work (30.1±11.0-39.3±7.8 mm Hg; p=0.003), and LV ejection fraction (p=0.012). Systemic vascular resistance increased slightly (p=0.04), and pulmonary vascular resistance decreased (p=0.01). Mean heart rate and pulmonary arterial, central venous, and left atrial pressures remained unchanged (p>0.1).

CONCLUSIONS

In contrast to inotropic drugs, epivascular CANS stimulation induced a significant and selective increase in LV contractility with no increase in heart rate.

Progress on the design and development of the continuous-flow total artificial heart

Cleveland Clinic's continuous-flow total artificial heart has one motor and one rotating assembly supported by a hydrodynamic bearing. The right hydraulic output is self regulated by passive axial movement of the rotating assembly to balance itself with the left output. The purpose of this article is to present progress in four areas of development: the automatic speed control system, self-regulation to balance right/left inlet pressures and flows, hemolysis testing using calf blood, and coupled electromagnetics (EMAG) and computational fluid dynamics (CFD) analysis. The relationships between functions of motor power and speed, systemic flow, and systemic vascular resistance (SVR) were used for the sensorless speed control algorithm and demonstrated close correlations. Based on those empirical relationships, systemic flow and SVR were calculated in the system module and showed good correlation with measured pump flow and SVR. The automatic system adjusted the pump's speed to obtain the target flow in response to the calculated SVR. Atrial pressure difference (left minus right atrial pressure) was maintained within ±10 mm Hg for a wide range of SVR/pulmonary vascular resistance ratios, demonstrating a wide margin of self-regulation under fixed-speed mode and 25% sinusoidally modulated speed mode. Hemolysis test results indicated acceptable values (normalized index of hemolysis <0.01 mg/dL). The coupled EMAG/CFD model was validated for use in further device development.

Implantable continuous-flow right ventricular assist device: lessons learned in the development of a cleveland clinic device

Although the need for right ventricular assist device (RVAD) support for right ventricular failure after the implantation of a continuous-flow left ventricular assist device has decreased, right ventricular failure still occurs in as many as 44% of patients after continuous-flow left ventricular assist device insertion. Cleveland Clinic's DexAide continuous-flow RVAD was implanted in 34 calves during the course of its development. This review discusses lessons learned in the design and development of an implantable continuous-flow RVAD that are drawn from the results of these in vivo studies, our clinical experience with RVAD support, and a review of previously published reports on clinical RVAD use.

Novel epicardial off-pump device for mitral regurgitation: acute evaluation

OBJECTIVE

This study evaluates the ability of a novel epicardial annuloplasty device Mitral Touch (MAQUET Cardiovascular LLC, San Jose, CA, USA) to reduce functional mitral regurgitation (MR) in a rapid ventricular pacing-induced dilated cardiomyopathy model in dogs.

METHODS

A median sternotomy was performed in 13 dogs after MR induction by rapid ventricular pacing (230 beats/min for an average of 35.6 + or - 12.8 days). Two-dimensional epicardial echocardiographic and haemodynamic measurements were performed to evaluate the baseline MR grade, the septal-lateral (S-L) dimension of the mitral annulus, mitral valve (MV) geometry and left ventricular function. The Mitral Touch was implanted by sliding the anterior arm onto the floor of the transverse sinus and positioning the posterior arm just apical to the atrioventricular groove on the left ventricular posterolateral wall. The 24-mm-long device was implanted in eight dogs, the 27-mm-long device in four and the 30-mm standard length device in one. MR grade, S-L dimension and haemodynamics data acquisition were immediately rechecked after device implantation.

RESULTS

All implantations, which took only approximately 30s to deploy, were performed on beating hearts without cardiopulmonary bypass. In one early case, after extended manipulation with undersized devices, an atrial laceration was created and bleeding occurred. Design changes were made to eliminate this complication. The MR grade was significantly (p=0.003) reduced from 3.1 + or - 1.1 at baseline to 1.4 + or - 0.8 after device implantation. The S-L dimension at end of systole was also significantly (p=0.001) reduced from 2.7 + or - 0.4 cm at baseline to 2.3 + or - 0.3 cm after device implantation (% reduction: 15.1 + or - 10.6%). The mitral valve coaptation length was significantly (p=0.0001) increased from 0.36 + or - 0.11 cm to 0.50 + or - 0.08 cm, and the mitral valve tethering area was significantly (p=0.0003) decreased from 1.36 + or - 0.38 cm(2) to 0.81 + or - 0.29 cm(2) after Mitral Touch implantation.

CONCLUSIONS

This new epicardial device was effective in significantly reducing MR and S-L dimensions acutely on the beating heart without requiring the use of cardiopulmonary bypass. Further studies are necessary to confirm the long-term maintenance of MR and S-L reductions.

In vivo biocompatibility evaluation of a new resilient, hard-carbon, thin-film coating for ventricular assist devices

The purpose of this study was to evaluate in vivo the biocompatibility of BioMedFlex (BMF), a new resilient, hard-carbon, thin-film coating, as a blood journal bearing material in Cleveland Heart's (Charlotte, NC, USA) continuous-flow right and left ventricular assist devices (RVADs and LVADs). BMF was applied to RVAD rotating assemblies or both rotating and stator assemblies in three chronic bovine studies. In one case, an LVAD with a BMF-coated stator was also implanted. Cases 1 and 3 were electively terminated at 18 and 29 days, respectively, with average measured pump flows of 4.9 L/min (RVAD) in Case 1 and 5.7 L/min (RVAD) plus 5.7 L/min (LVAD) in Case 3. Case 2 was terminated prematurely after 9 days because of sepsis. The sepsis, combined with running the pump at minimum speed (2000 rpm), presented a worst-case biocompatibility challenge. Postexplant evaluation of the blood-contacting journal bearing surfaces showed no biologic deposition in any of the four pumps. Thrombus inside the RVAD inlet cannula in Case 3 is believed to be the origin of a nonadherent thrombus wrapped around one of the primary impeller blades. In conclusion, we demonstrated that BMF coatings can provide good biocompatibility in the journal bearing for ventricular assist devices.

Performance of extracorporeally adjustable ventricular assist device inflow cannula

PURPOSE

This study evaluated the feasibility and efficacy of a newly developed adjustable left ventricular assist device inflow cannula in a short-term calf model.

DESCRIPTION

In this inflow cannula, the angle between the cannula body and the inflow cannula tip can be altered extracorporeally by manipulating 2 externalized cables connected to the cannula. The cannula tip is adjustable in any plane to a maximum of ±15 degrees.

EVALUATION

After initial prototyping in 4 calf cadavers, a Cleveland Heart left ventricular assist device was implanted with the adjustable inflow cannula placed in the left ventricular apex and the outlet to the descending aorta. Under hypovolemic conditions, the angle of the cannula tip could be changed to induce varying degrees of ventricular suction and then eliminate it, as evidenced by recorded pump and native left ventricular flows. Epicardial echocardiography and fluoroscopy in the closed-chest condition documented extracorporeal adjustments of the inflow cannula position.

CONCLUSIONS

This extracorporeally adjustable inflow cannula was effective in preventing or controlling left ventricular suction.

Chest tube selection in cardiac and thoracic surgery: a survey of chest tube-related complications and their management

BACKGROUND

Blood accumulating inside chest cavities can lead to serious complications if it is not drained properly. Because life-threatening conditions can result from chest tube occlusion after thoracic surgery, large-bore tubes are generally employed to optimize patency.

AIMS

The aim of this study was to better define problems with current paradigms for chest drainage.

MATERIALS AND METHODS

A survey was conducted of North American cardiothoracic surgeons and specialty cardiac surgery nurses. A total of 108 surgeons and 108 nurses responded.

RESULTS

The survey revealed that clogging leading to chest-tube dysfunction is a major concern when choosing tube size. Of surgeons responding, 106 of 106 (100%) had observed chest tube clogging, and 93 of 106 (87%) reported adverse patient outcomes from a clogged tube. Despite techniques such as tube stripping, tapping, and squeezing, up to 51% of surveyed surgeons stated they are not satisfied with currently available tubes and procedures to avoid tube occlusion and some even forbid the stripping maneuver for fear of causing more bleeding by the negative pressures generated. In addition, respondents noted that patients experience increasing discomfort with increasing drain size.

DISCUSSION

The major reason surgeons choose large-diameter chest tubes is linked to concern about the suboptimal available methods to avoid and treat chest-tube clogging. Even though larger tubes are thought to be associated with more pain, physicians generally err on the side of caution to avoid clogging and insert tubes with larger diameters.

CONCLUSION

Results of this survey highlight the frequent problems with clogging with current postsurgical chest drainage systems and suggest the need for innovative solutions to avoid clogging complications and overcome clinician concern and patient pain.

Speed modulation of the continuous-flow total artificial heart to simulate a physiologic arterial pressure waveform

This study demonstrated the concept of using speed modulation in a continuous-flow total artificial heart (CFTAH) to shape arterial pressure waveforms and to adjust pressure pulsatility. A programmable function generator was used to determine the optimum pulsatile speed profile. Three speed profiles [sinusoidal, rectangular, and optimized (a profile optimized for generation of a physiologic arterial pressure waveform)] were evaluated using the CFTAH mock circulatory loop. Hemodynamic parameters were recorded at average pump speeds of 2,700 rpm and a modulation cycle of 60 beats per minute. The effects of varying physiologically relevant vascular resistance and lumped compliance on the hemodynamics were assessed. The feasibility of using speed modulation to manipulate systemic arterial pressure waveforms, including a physiologic pressure waveform, was demonstrated in vitro. The additional pump power consumption needed to generate a physiologic pulsatile pressure was 16.2% of the power consumption in nonpulsatile continuous-flow mode. The induced pressure waveforms and pulse pressure were shown to be very responsive to changes in both systemic vascular resistance and arterial compliance. This system also allowed pulsatile pulmonary arterial waveform. Speed modulation in the CFTAH could enable physicians to obtain desired pressure waveforms by simple manual adjustment of speed control input waveforms.

Complete mapping of the tricuspid valve apparatus using three-dimensional sonomicrometry

OBJECTIVE

Many surgeons consider the tricuspid valve to be a second-class structure. Our objective was to determine the normal anatomy and dynamic characteristics of the tricuspid valve apparatus in vivo and to discern whether this would aid the design of a tricuspid valve annuloplasty ring model.

METHODS

Sixteen sonomicrometry crystals were placed around the tricuspid annulus, at the bases and tips of the papillary muscles, the free edges of the leaflets, and the right ventricular apex during cardiopulmonary bypass in 5 anesthetized York Hampshire pigs. Animals were studied after weaning of cardiopulmonary bypass on 10 cardiac cycles of normal hemodynamics.

RESULTS

Sonomicrometry array localizations demonstrate the multiplanar shape of the tricuspid annulus. The tricuspid annulus reaches its maximum area (97.9 ± 25.4 mm(2)) at the end of diastole and its minimum area (77.3 ± 22.5 mm(2)) at the end of systole, and increases again in early diastole. Papillary muscles shorten by 0.8 to 1.5 mm (11.2%) in systole, and chordae tendineae straighten by 0.8 to 1.7 mm (11.4%) in systole.

CONCLUSIONS

The shape of the tricuspid annulus is a multiplanar 3-dimensional one with its highest point at the anteroseptal commissure and its lowest point at the posteroseptal commissure, and the anteroposterior commissure is in a middle plane in between. The tricuspid annulus area reaches its maximum during diastole and its minimum during systole. The papillary muscles contract by the same amount of chordal straightening. The optimal tricuspid annuloplasty ring may be a multiplanar 3-dimensional one that mimics the normal tricuspid annulus.

Introduction of fixed-flow mode in the DexAide right ventricular assist device

BACKGROUND

Although some continuous-flow left ventricular assist device algorithms have been created to respond to varying patient physiology, very little research has been conducted on control of right ventricular support in uni- or biventricular application. The purpose of this study was to develop and evaluate a simple and reliable fixed-flow algorithm for the DexAide right ventricular assist device (RVAD). This algorithm automatically adjusts speed to maintain a target flow while preventing ventricular suction when a requested target flow exceeds available tricuspid flow.

METHODS

Fixed-flow control mode was evaluated in 17 DexAide RVAD long-term bovine studies, with a duration ranging from 14 to 90 days (33 +/- 24 days). Targeted fixed-flow levels ranged from 4.0 to 6.5 liters/min. Data were monitored on an hourly basis. Pump-flow data were also recorded on a weekly basis to document the speed increment required to increase pump flow from 5 to 8 liters/min at 0.5-liter/min increments.

RESULTS

The fixed-flow control mode was evaluated for a total duration of 5,283 hours without complications related to pump flow or left/right circulation imbalance. The pump speed varied between 2,000 and 3,220 rpm to maintain the flow constant at each target level. The average absolute mismatch between the target flow and measured flow was 0.6 +/- 0.5 liter/min.

CONCLUSIONS

Fixed-flow control mode with a pre-determined maximum automatic pump speed can be used safely and effectively in the DexAide RVAD. It can provide target flows by adjusting the pump speed while monitoring pump-flow response to automatic speed increment requests.

In vivo evaluation of zirconia ceramic in the DexAide right ventricular assist device journal bearing

Zirconia is a ceramic with material properties ideal for journal bearing applications. The purpose of this study was to evaluate the use of zirconium oxide (zirconia) as a blood journal bearing material in the DexAide right ventricular assist device. Zirconia ceramic was used instead of titanium to manufacture the DexAide stator housing without changing the stator geometry or the remaining pump hardware components. Pump hydraulic performance, journal bearing reliability, biocompatibility, and motor efficiency data of the zirconia stator were evaluated in six chronic bovine experiments for 14-91 days and compared with data from chronic experiments using the titanium stator. Pump performance data including average in vivo pump flows and speeds using a zirconia stator showed no statistically significant difference to the average values for 16 prior titanium stator in vivo studies, with the exception of a 19% reduction in power consumption. Indices of hemolysis were comparable for both stator types. Results of coagulation assays and platelet aggregation tests for the zirconia stator implants showed no device-induced increase in platelet activation. Postexplant evaluation of the zirconia journal bearing surfaces showed no biologic deposition in any of the implants. In conclusion, zirconia ceramic can be used as a hemocompatible material to improve motor efficiency while maintaining hydraulic performance in a blood journal bearing application.