Tofy Mussivand

Left ventricular assist devices as bridge to heart transplantation in congestive heart failure with pulmonary hypertension.

Severe pulmonary hypertension (PH) has been considered a significant contraindication to cardiac transplantation. Ongoing clinical experience, however, has shown that temporary support using left ventricular assist devices (LVADs) in these patients can result in significant reductions in PH. A comprehensive review of the available literature regarding the use of LVADs in heart failure patients with PH was conducted. The existing literature to date supports the use of LVADs in heart failure patients with PH and demonstrates that significant reductions in PH in these patients can be achieved. This subsequently allows for safe and effective cardiac transplantation in patients who were previously excluded from this modality. For heart failure patients with severe PH, the use of LVADs can provide significant benefits by significantly reducing PH and allowing subsequent staged transplantation.

A transcutaneous energy and information transfer system for implanted medical devices.

During the last four decades there has been a rapid increase in the development and usage of medical devices. Currently, there are more than 500,000 devices on the market and 25,000 new devices enter the market each year. Many medical devices are now designed to be implantable (pacemakers, defibrillators, circulatory assist devices, artificial hearts, cochlear implants, neuromuscular stimulators, biosensors, etc.). Almost all of the active devices (those that perform work) and many of the passive devices (those that do not perform work) require a source of power. In addition, these devices need to be monitored and controlled, which can be accomplished by utilizing remote communication methods. A transcutaneous energy transfer system combined with a remote communications system has been developed and evaluated in vitro and in vivo (bovine, porcine, and human cadaver experiments). The energy transfer system can deliver up to 60 W with power transfer efficiencies between 60 and 83%. An automatically tuned, resonant frequency tracking method is used to obtain optimum power transfer over a range of operating conditions. The remote communications system can transfer digital data bidirectionally through intact skin at rates up to 9600 baud. The system transmits information by frequency modulating an 890 nm infrared carrier signal. The system has demonstrated satisfactory performance during multicenter evaluation with ventricular assist and total artificial heart devices. Design improvements have been identified, which will be implemented to produce an optimized system for energy transfer to and remote communications with various implantable medical devices.

Fluid dynamic optimization of a ventricular assist device using particle image velocimetry.

Thrombus formation and resulting thromboembolism are major risks that can impede the widespread use of ventricular assist devices (VADs). Adverse flow patterns (turbulence and stasis) have been implicated in thrombogenesis. This study focuses on optimization of VAD geometry, port orientation, and fluid dynamics to reduce thrombus formation. Particle image velocimetry with cross-correlation was performed using Amberlite particles suspended in distilled water. The transparent VADs were illuminated by halogen lamps. Four different VADs were tested in an iterative approach toward optimization. A peak shear stress of 9,100 dynes/cm2 was noted in the first configuration immediately after the end of systole at the outlet port. Modifications in chamber geometry, port diameters and orientation, and valve enclosure design yielded shear stresses in the two subsequent geometries of 5,100 dynes/cm2 and 1,900 dynes/cm2, respectively. For the third iteration, a region of stasis occurred during the transition between the inlet port and the blood chamber. Further modifications were implemented, including a reduction in port diameters and further smoothing of the port entry region. This eliminated stasis and yielded a maximum shear level of 4,100 dynes/cm2. In conclusion, optimization was achieved through geometric modification of the VAD, thus minimizing adverse flow conditions.

Development of an autotuned transcutaneous energy transfer system.

A transcutaneous energy transfer (TET) system has been developed to power implanted devices such as heart assist devices, artificial hearts, defibrillators, and electrical stimulators. The TET system transfers power by electromagnetic induction without the need for percutaneous leads. For ease of implantation and patient comfort, it is desirable to use TET coils that are as small as possible. One problem encountered with TET designs that use small coils is a high sensitivity to coil electromagnetic coupling caused by changes in separation. These changes can result from variation in tissue thickness between subjects and from displacement of the coils that can occur during breathing and general body movement. Changes in coil coupling result in similar changes in the resonant frequency of the TET transformer, which can reduce power transfer and efficiency. The EVAD TET system was designed to address this problem by incorporating a technique for automatically tuning the power driver stage of the transformer. The system is able to deliver maximum output power of approximately 60 watts at a coil separation of 5 mm, falling to approximately 45 watts at a coil separation of 15 mm. The system can deliver a maximum efficiency of 75-80%; reducing to approximately 60% and 60 watts. The results presented demonstrate the systems ability to compensate for variations in coil separation by resonant frequency tracking. This has optimized power transfer throughout the required range of coil coupling conditions.

Failed attempts and improvement strategies in peripheral intravenous catheterization.

BACKGROUND Access to peripheral veins is necessary for sample collection, transfusion and infusion of fluids or medications. The peripheral intravenous catheterization (PIVC) procedure is the introduction of a short catheter into a peripheral vein and can be problematic, leading to multiple failed attempts. PURPOSE To analyze scientific literature regarding difficulties in establishing peripheral intravenous access and improvement strategies. METHOD A literature search was undertaken and secondary references were retrieved from the papers obtained from the initial search. A total of 128 papers published from 1975 to 2011 were reviewed. RESULTS The first attempt of PIVC fails in 12-26% of adults and 24-54% of children. Factors associated with the currently utilized PIVC success include: (1) patients characteristics such as age, gender, race, weight/BMI, co-existing medical conditions and skin/vein characteristics, (2) procedure related factors such as the insertion site and catheter caliber, and (3) the operators expertise. Strategies to improve PIVC success include: (1) bedside techniques such as venodilation, vascular visualization and vein entry indication, (2) pain management and (3) engagement of expert health care providers. CONCLUSION Bedside techniques have shown more improvement in PIVC success rates as opposed to pain management. Expert health care providers have shown higher performance levels with regard to the difficult cases of PIVC.

Cardiac Transplantation After Mechanical Circulatory Support: A Canadian Perspective

BACKGROUND To assess the relative efficacy of cardiac transplantation after mechanical circulatory support with a variety of support systems, we analyzed our consecutive series of patients who had and did not have mechanical support before transplantation. METHODS A review of 209 patients undergoing cardiac transplantation from 1984 to May 1995 was performed. Group 1 consisted of 110 patients who were maintained on oral medications while awaiting transplantation, and group 2 consisted of 60 patients who required intravenous inotropic support. Group 3 included 39 patients who had transplantation after mechanical circulatory support for cardiogenic shock. The indication for device implantation was acute onset of cardiogenic shock in 38 patients and deterioration while awaiting transplantation in 1 patient. The support systems were an intraaortic balloon pump in 13 (subgroup 3A), a ventricular assist device in 7 (subgroup 3B), and a total artificial heart in 19 patients (subgroup 3C). RESULTS After transplantation, infection was more common in group 3 (56%) than in group 1 (28%) or group 2 (32%) (p = 0.005). Survival to discharge was lower for group 3 (71.7%) than for group 1 (90.9%) or 2 (88.3%) (p = 0.009). For mechanically supported patients, survival to discharge was 84.6% in subgroup 3A, 71.4% in subgroup 3B, and 63.1% in subgroup 3C (p = not significant). CONCLUSIONS Transplantation after mechanical support offers acceptable results in this group of patients for whom the only alternative is certain death. Patient selection and perioperative management remain the challenge to improving these results.

Transcutaneous energy transfer with voltage regulation for rotary blood pumps.

Rotary blood pumps often require a constant operating voltage. To meet this requirement and to eliminate the need for percutaneous leads, a voltage-regulated transcutaneous energy transfer (TET) system has been developed. Voltage regulation is achieved by using a transcutaneous infrared feedback control loop operating on a 890 nanometer (nm) wavelength. In vitro testing of the system developed has shown that output voltage can be maintained to within 0.2 V of nominal (14.5 V) for delivered powers up to 50 watts (W) and coil separations of between 3 and 10 mm. Power transfer efficiencies were determined to be from 68% to 72% over the tested range of coil separations and output currents from 1.5 to 3.6 amperes (A). This system has demonstrated acceptable performance in regulating output voltage while transferring power inductively without using percutaneous connections. By integrating this type of TET system with an implanted rotary blood pump, the quality of life for the device recipient could be improved.

Mechanical circulatory devices for the treatment of heart failure.

AbstractBackground: During the last four decades substantial efforts have been made in the development of effective mechanical circulatory devices. Since the first clinical utilization in the 1960s, the field has gone from the stage of clinical experimentation to that of a valid and effective heart failure treatment alternative. Experience gained during the short‐term use of these devices, typically as a bridge to cardiac transplantation, has led to increased expectations of devices capable of long‐term or permanent support to be used as a permanent treatment for end‐stage heart failure patients. This article reviews the history, current state of the art, and future of the field of mechanical circulatory devices. Methods: Mechanical circulatory devices can be classified into three major categories: (1) total artificial hearts, (2) pulsatile ventricular assist devices, and (3) nonpulsatile ventricular assist devices. The most widely used devices have been the pulsatile ventricular assist devices with more than 5,800 reported cases, whereas the use of total artificial hearts has been limited to less than 350 reported cases. Nonpulsatile devices have been used clinically, but only in short‐term cases (i.e., hours and days), whereas the pulsatile devices have been used in the long‐term application, with patients supported for weeks, months, and in a small number of cases, years. The technological evolution of these devices has gone from large, extra‐corporeal systems designed to keep the patient alive in the intensive care unit (ICU) until a donor organ could be found, to portable devices that allow the patient to be mobilized outside of the hospital setting. Results: The clinical experience with mechanical circulatory devices as a bridge to cardiac transplantation has saved the lives of thousands of patients. Exciting new research discoveries related to recovery of native heart function during extended circulatory support have provided new hope for many more patients. Additional research efforts currently underway are being tested at various laboratories around the world and will soon provide the next generation of systems. These new systems will offer the recipients an unparalleled quality of life with minimal limitations on daily activities. The progress in this field has reached the point where circulatory support will soon be considered a valid long‐term or permanent therapy and an elective to transplantation.

Development of a Mathematical Model of the Human Circulatory System

A mathematical lumped parameter model of the human circulatory system (HCS) has been developed to complement in vitro testing of ventricular assist devices. Components included in this model represent the major parts of the systemic HCS loop, with all component parameters based on physiological data available in the literature. Two model configurations are presented in this paper, the first featuring elements with purely linear constitutive relations, and the second featuring nonlinear constitutive relations for the larger vessels. Three different aortic compliance functions are presented, and a pressure-dependent venous flow resistance is used to simulate venous collapse. The mathematical model produces reasonable systemic pressure and flow behaviour, and graphs of this data are included.

Totally implantable intrathoracic ventricular assist device

BACKGROUND A totally implantable, intrathoracic electrohydraulic ventricular assist device (EVAD) is being developed for permanent use or as a bridge to transplantation. METHODS The blood pump with 70-mL nominal stroke volume, volume displacement chamber, reversible turbine, internal electronics and infrared diaphragm position sensor are combined in one compact unit (unified system). The size and geometry are based on human anatomic measurements and fluid dynamic studies. A transcutaneous energy transfer powers the system and recharges the implantable nickel-cadmium battery pack. Autotuning circuitry optimizes energy transfer efficiency over a range of transcutaneous energy transfer coil spacings and misalignments. An infrared diaphragm position sensor detects end-systole and diastole points. RESULTS In vitro and acute in vivo tests have demonstrated flow rates greater than 6 L/min. The transcutaneous energy transfer system demonstrated power transfer efficiencies of 60% to 80% for power demands from 5 to 60 W. Thirteen systems are currently undergoing durability testing; one has run for more than 750 days failure-free. The system recently sustained circulation in an acute calf implantation for 96 hours. CONCLUSIONS Results of the in vitro and in vivo testing to date have demonstrated that the developed system can function effectively as a totally implantable ventricular assist device. Chronic in vivo evaluation is planned.