Gerson Rosenberg

The LionHeart LVD-2000 : a completely implanted left ventricular assist device for chronic circulatory support

Management of patients with end-stage cardiac disease remains a vexing problem. Limitations in medical management and a fixed supply of donor organs for cardiac transplant have a continued impact on this growing population of patients. Mechanical circulatory support has proved very successful as a means of bridging patients to cardiac transplant when all medical options have been exhausted. The development of a chronic system of circulatory support has been underway at the Pennsylvania State University for nearly 30 years. These efforts have been recently merged with the industrial partnership with Arrow International toward the development of the LionHeart LVD-2000 (Arrow International, Reading, PA) completely implanted left ventricular support system. We present an overview of the system, details of implantation, a review of preclinical studies, and a synopsis of the first European implants. Early results have demonstrated the system to be safe, effective, and reliable. Transcutaneous energy transmission and the compliance chamber have been validated.

Relative blood damage in the three phases of a prosthetic heart valve flow cycle.

Blood flow through a prosthetic heart valve operating in a ventricular assist device can be subdivided into three phases: a) forward flow through an open valve, b) rapid valve closure, and c) regurgitant back flow through a closed valve. Recent studies of fluid stresses in the Penn State Electric Left Ventricular Assist Device (PS LVAD) operating under physiologic conditions indicate that Reynolds stresses of possibly hemolytic magnitude may exist in the valve area. Although several studies have been made of the fluid stresses seen in forward flow through an open valve, few have looked at valve closure or backflow, and none have related these stresses directly to blood damage. In this study, novel in vitro blood flow loops were developed to allow for the separate analysis of the three flow phases of a Bjork-Shiley monostrut Delrin disk valve operating in a PS LVAD. Forward flow through fully open aortic and mitral valves and backflow through closed valves are studied separately in flow loops driven by a roller pump with the LVAD acting as a valve housing and compliance vessel. Valve closure is investigated with a PS LVAD operating in a low volume mock circulatory loop characterized by cavitation potential through stroboscopic videography of this mock loop, using saline as the working fluid. Rate of hemolysis, characterized by the index of hemolysis, IH, is determined for each of the three flow loops charged with fresh porcine blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Major factors in the controversy of pulsatile versus nonpulsatile flow during acute and chronic cardiac support.

During the past 50 years, the controversy over the benefits of pulsatile versus nonpulsatile flow in cardiac surgery has not been solved.1 A detailed investigation in all published literature reveals that in a majority of publications, the investigators could not show any differences between perfusion modes during acute or chronic cardiac support. However, in more than 20 articles, it appears clear that pulsatile flow causes significantly less vital organ injury and systemic inflammation during cardiopulmonary bypass (CPB) procedures and chronic cardiac circulatory support.1–23 To the best of our knowledge, there is not a single publication that clearly shows the benefits of nonpulsatile perfusion over pulsatile perfusion in acute or chronic clinical or animal settings. The pro-nonpulsatile flow investigators can only claim that there is no difference between perfusion modes, whereas the pro-pulsatile investigators have documented clear benefits.1–23 The objective of this editorial is to examine the major causes for this continuing controversy and suggest potential solutions to end it. Following are the two major causes for the controversy, and both are valid for acute or chronic settings.

An electrically powered total artificial heart. Over 1 year survival in the calf

An electric motor driven orthotopic artificial heart was implanted in a 110 kg female Holstein calf as part of a series of 12 such implants intended to demonstrate the in vivo durability and compatibility of the device. The device uses pusher plates set into motion by a reversing brushless DC motor and roller screw to alternately eject two cylindrical sac type blood pumps. The pumps use Bjork-Shiley Delrindisc convexo-concave or monostrut valves. The left pump provides an 88-90 ml dynamic stroke volume. Woven Dacron grafts and polyurethane coated Dacron/Lycra cuffs are used to attach the device to the major arteries and atria, respectively. A polyurethane conduit and anchoring skin button bring motor wires percutaneously to an extracorporeal controller. The controller provides balanced cardiac output sensitive to atrial or aortic pressures, without operator intervention. The system is hermetically sealed and uses a simple compliance sac to maintain thoracic pressure between the pumps. The calf recovered uneventfully from surgery and thrived thereafter. She was killed on the 388th post-operative day because of worsening cardiac insufficiency. The previous three operative survivors in this series lived 131, 134, and 204 days. These results indicate the devices good potential for durability and body compatibility.

Quantification of perfusion modes in terms of surplus hemodynamic energy levels in a simulated pediatric CPB model.

The objective of this investigation was to compare pulsatile versus nonpulsatile perfusion modes in terms of surplus hemodynamic energy (SHE) levels during cardiopulmonary bypass (CPB) in a simulated neonatal model. The extracorporeal circuit consisted of a Jostra HL-20 heart-lung machine (for both pulsatile and nonpulsatile modes of perfusion), a Capiox Baby RX hollow-fiber membrane oxygenator, a Capiox pediatric arterial filter, 5 feet of arterial tubing and 6 feet of venous tubing with a quarter-inch diameter. The circuit was primed with a lactated Ringers solution. The systemic resistance of a pseudo-patient (mean weight, 3 kg) was simulated by placing a clamp at the end of the arterial line. The pseudo-patient was subjected to five pump flow rates in the 400 to 800 ml/min range. During pulsatile perfusion, the pump rate was kept constant at 120 bpm. Pressure waveforms were recorded at the preoxygenator, postoxygenator, and preaortic cannula sites. SHE was calculated by use of the following formula {SHE (ergs/cm3) = 1,332 [((∫ fpdt) / (∫ fdt)) – Mean Arterial Pressure]} (f = pump flow and p = pressure). A total of 60 experiments were performed (n = 6 for nonpulsatile and n = 6 for pulsatile) at each of the five flow rates. A linear mixed-effects model, which accounts for the correlation among repeated measurements, was fit to the data to assess differences in SHE between flows, pumps, and sites. The Tukey multiple comparison procedure was used to adjust p values for post hoc pairwise comparisons. With a pump flow rate of 400 ml/min, pulsatile flow generated significantly higher surplus hemodynamic energy levels at the preoxygenator site (23,421 ± 2,068 ergs/cm3 vs. 4,154 ± 331 ergs/cm3, p < 0.0001), the postoxygenator site (18,784 ± 1,557 ergs/cm3 vs. 3,383 ± 317 ergs/cm3, p < 0.0001), and the precannula site (6,324 ± 772 ergs/cm3 vs. 1,320 ± 91 ergs/cm3, p < 0.0001), compared with the nonpulsatile group. Pulsatile flow produced higher SHE levels at all other pump flow rates. The Jostra HL-20 roller pump generated significantly higher SHE levels in the pulsatile mode when compared with the nonpulsatile mode at all five pump flow rates.

Pulsed ultrasonic Doppler velocity measurements inside a left ventricular assist device.

In this study we have employed a single channel, pulsed ultrasonic Doppler velocimeter to measure instantaneous velocity distributions within the pumping chamber of a ventricular assist device. Instantaneous velocities have been decomposed into periodic mean and turbulent fluctuating components from which estimates of Reynolds stresses within the chamber and mean shear stresses along the wall of the chamber have been obtained. A review of the complete data set indicates a maximum value of the mean wall shear stress of 25 dynes/cm2 and a maximum Reynolds stress of 212 dynes/cm2. These values are lower than those measured distal to aortic valve prostheses in vitro and are well below levels known to damage blood components. Core flow patterns, wall washing patterns and flow stagnation points are also revealed.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and The Society of Thoracic Surgeons: Long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

An investigation of the in vivo stability of poly(ether urethaneurea) blood sacs

In this paper we investigate the biostability of a series of Biolon blood sacs that were utilized in electric total artificial hearts for time periods of up to 19 weeks. A battery of experimental probes, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), were used to characterize the bulk and surface properties of explanted and control blood sacs. Gel permeation chromatography (GPC) experiments showed that generally there was a dramatic increase in average molecular weight at longer implantation times. However, SEM and GPC observations suggest significant deterioration of the flex regions of right blood sacs after 17 weeks of service. XPS experiments indicated appreciable silicon and hydrocarbon concentrations on blood-contacting surfaces both before and after implantation, and we speculate as to their origin.

Permanent circulatory support systems at the Pennsylvania State University

Two systems which provide long-term circulatory support are described: the left ventricular assist system and the total artificial heart. These systems are based on the design of a pusher plate actuated blood pump, driven by a small brushless DC electric motor and rollerscrew driver. An implantable motor controller maintains suitable physiologic flow rates for both systems and controls left-right balance in the total artificial heart. Other parts of the system include an intrathoracic compliance chamber, transcutaneous energy and data transmission system, and internal and external batteries.<<ETX>>

In vivo performance of a transcutaneous energy transmission system with the Penn State motor driven ventricular assist device.

A transcutaneous energy transmission system (TETS) has been used to power the Penn State motor driven ventricular assist device in nine calf experiments, for a total of 316 days of cumulative in vivo experience. This is seen as an important step toward a completely implantable ventricular assist system and total artificial heart. The TETS converts an external 12 volt DC source via inductive coupling to a regulated 14 volt output voltage for use by the motor controller. A maximum output power of 70 watts is available. In calf experiments, the TETS output power averaged between 8 and 12 watts. The motor controller was not implanted in these experiments, awaiting further development of the miniaturized electronics. The TETS output was returned percutaneously to the external motor controller, allowing the TETS output to be monitored directly. System efficiency, from DC source to DC output, and including losses in 12 feet of cable, ranged from 55% to 70%, depending upon supply voltage, motor load, and degree of coil coupling. The subcutaneous coil was well tolerated, demonstrating only temporary, mild, superficial induration.