In Vitro PET Imaging of a Miniature Ventricular Assist Device.

UNLABELLED: Interactions between the life-sustaining ventricular assist devices and diagnostic therapies must be carefully considered to decrease the risk of inaccurate diagnostic imaging or pump failure. METHODS: The MVAD(®) pump, currently under investigational use, was tested for interaction with radiotracers in an in vitro flow-loop study. The radiotracers (18)F-sodium fluoride and (18)F-FDG were injected into a closed loop to determine the feasibility of direct imaging of the MVAD(®) pump in a PET scanner. RESULTS: No real-time changes were observed in pump operation, and there were no statistical differences in pump parameters (power consumption, speed, and estimated flow rate) between the baseline and circulation conditions. In addition, no effect was observed on any external components, including the permissive-action-link controller and the batteries powering the device. Imaging of the internal pump components was possible, with obscuration observed only in the portion of the pump where the spinning impeller is located. Retention of radiotracer in the pump components after circulation was minimal (<1%). CONCLUSION: PET imaging is an attractive diagnostic tool for patients with a ventricular assist device and may have additional utility outside its current use, detection of infection.

Evaluation of a ventricular assist device: stability under x-rays and therapeutic beam attenuation.

Improved outcomes and quality of life of heart failure patients have been reported with the use of left ventricular assist devices (LVADs). However, little information exists regarding devices in patients undergoing radiation cancer treatment. Two HeartWare Ventricular Assist Device (HVAD) pumps were repeatedly irradiated with high intensity 18 MV x-rays to a dosage range of 64-75 Gy at a rate of 6 Gy/min from a radiation oncology particle accelerator to determine operational stability. Pump parameter data was collected through a data acquisition system. Second, a computerized tomography (CT) scan was taken of the device, and a treatment planning computer estimated characteristics of dose scattering and attenuation. Results were then compared with actual radiation measurements. The devices exhibited no changes in pump operation during the procedure, though the titanium components of the HVAD markedly attenuate the therapy beam. Computer modeling indicated an 11.8% dose change in the absorbed dosage that was distinctly less than the 84% dose change measured with detectors. Simulated and measured scattering processes were negligible. Computer modeling underestimates pretreatment dose to patients when the device is in the field of radiation. Future x-ray radiation dosimetry and treatment planning in HVAD patients should be carefully managed by radiation oncology specialists.

Evaluation of a ventricular assist device system: stability in a proton beam therapy.

Inadequate research exists regarding testing of a ventricular assist device (VAD) for susceptibility to radiation damage. Specifically, minimal data are available to radiation oncologists prescribing treatment plans for patients with an implanted VAD. As the number of implanted devices increases, patients requiring radiation at tissue sites near or at the device will increase. The purpose of this study is to provide the first analysis of radiation effects of proton beams on VADs. Five left VAD (LVAD) pumps (HeartWare Inc., Miami Lakes, FL) were exposed to proton beam radiation at a calibrated dose rate of 5 Gy/min up to a cumulative dose of 70 Gy. The Heartware LVAD pump recorded parameters including power (W), speed (revolutions/min), and estimated flow (L/min). Analysis of collected data after each irradiation found no deviation in pump parameters from baseline values. The Heartware LVAD pump exhibited no change in device function when directly irradiated by a high energy proton beam. Secondary neutron fluence created in the proton beam during irradiation had no effect on external components including the system controller and batteries powering the Heartware LVAD.

Evaluation of new Forcefield technology: reducing platelet adhesion and cell coverage of pyrolytic carbon surfaces.

INTRODUCTION: Platelet adhesion and activation are a significant source of clinical complications. Preventing foreign surface-platelet interaction may improve biocompatibility of implantable medical devices. This study evaluated efficacy of novel technique for electrically modifying surface of conductive biomaterial and attaching blood components to prevent thrombogenesis. Specifically, this new surface modification technology, Forcefield (ATS Medical, Inc, Minneapolis, Minn), was designed to prevent platelet adhesion on pyrolytic carbon. A modulated low-voltage current is directly applied to pyrolytic carbon surfaces to stimulate adherence of a layer of charged proteins from circulating blood components that is resistive to platelet deposition. METHODS: Feasibility of Forcefield technology was tested in line with cardiopulmonary bypass circuit in patients undergoing standard cardiac surgery (n = 6). Forcefield treatment was applied to segment of pyrolytic carbon with 15 minutes (n = 3) and 30 minutes (n = 3) of electrically stimulated exposure time, and resulting segments were compared with untreated pyrolytic carbon segment. Platelet adhesion confluence was then quantified by scanning electron microscopy. RESULTS: Confluence of the Forcefield-treated pyrolytic carbon segments (3.3% ± 2.2%) was significantly reduced relative to untreated pyrolytic carbon control segments (81.7% ± 24%, P < .001). There were no discernible differences in cell confluence with Forcefield-treated segments as function of exposure time (15 or 30 minutes). CONCLUSIONS: Forcefield technology may enable modification of pyrolytic carbon surfaces to prevent platelet adhesion and thrombogenesis of implanted medical devices, including heart valves, stents, catheters, and ventricular assist devices, and may eliminate the need for anticoagulant and antiplatelet therapies.

Platelet activation in heart failure patients supported by the HeartMate II ventricular assist device.

OBJECTIVE: Thromboembolic events have been observed in heart failure (HF) patients supported by long-term mechanical circulatory support (MCS) devices. It has been hypothesized that these adverse events may be the result of platelet activation associated with high rotational speeds common to axial flow pumps. In this study, markers of platelet activation were investigated in HF patients supported by a HeartMate II left ventricular assist device (LVAD). METHODS: The study group consisted of 34 HF patients supported by a HeartMate II axial flow LVAD implanted for destination therapy (DT). This patient population was 94% male (31 M, 3 F), supported by LVAD for 30 to 723 days (average 268 days), and with an anticoagulation regimen of Coumadin (0-8 mg daily dose) and aspirin (0-325 mg daily dose). Platelet adhesion markers (soluble P-selectin and solube CD40 ligand), platelet count (PC), hematocrit (Hct), and creatinine (Cr) were measured. RESULTS: The soluble P-selectin marker was within normal platelet activity limits for all end points. The soluble CD40 ligand marker indicated platelet inactivity for all end points. Despite high shear stresses associated with a high-speed axial flow pump, the HeartMate II had no discernable effect on platelet activation. Current clinical doses of aspirin also appear to have little effect on platelet activation. Platelet count, hematocrit, and creatinine were normal in these patients over duration of support. CONCLUSIONS: There were no discernable changes in platelet activation markers soluble P-selectin and soluble CD40 ligand in HF patients support by HeartMate II LVAD independently of length of support, anti-platelet, and anti-coagulation regimens.

Reducing the effects of the systemic inflammatory response to cardiopulmonary bypass: can single dose steroids blunt systemic inflammatory response syndrome?

The use of cardiopulmonary bypass (CPB) is associated with the development of a significant systemic inflammatory response syndrome (SIRS) which can affect patient outcomes. Multiple pathways are involved in initiating and maintaining SIRS. We studied whether a single dose of steroids (dexamethasone) after the induction of anesthesia could blunt the SIRS from CPB. A prospective, randomized, double-blinded, placebo control trial of 28 patients (13 study vs. 15 control). The study group received 100 mg of dexamethasone whereas the control group received sterile saline. Inclusion criteria were the following: elective coronary artery bypass grafting, less than 80 years old, normal ejection fraction, no acute myocardial infarction. Serum levels of C3a, interleukin (IL)-6, and plasma norepinephrine (PNE) were measured after intubation, 30 minutes after initiation of CPB, 24 and 72 hours after termination of bypass. The study group demonstrated significantly lower levels of IL-6 (p = 0.0005) at 24 hours and PNE (p = 0.05) at 72 hours post-CPB. There were no differences in the C3a levels between the groups. No infections occurred in either group. A single dose of dexamethasone reduces IL-6 and PNE levels associated with CPB. Despite the significant reductions in IL-6 and PNE, there was no effect on clinical outcomes. Additional studies are needed to demonstrate a clinically significant effect on patient outcomes.

Improvement in early oxygen uptake kinetics with left ventricular assist device support.

Sustained myocardial recovery and reversal of heart failure has been reported with the use of left ventricular assist devices (LVADs). However, clinical predictors of sustained recovery have not been clearly defined, and little information exists regarding exercise improvement in LVAD patients. Therefore, we sought to determine whether peripheral oxygen delivery and utilization were improved with LVAD support. Eleven patients with available pre- and post-LVAD cardiopulmonary exercise (CPX) data were studied retrospectively. Five patients received a HeartMate XVE for destination therapy (DT) and six patients received a Thoratec PVAD pneumatic LVAD for bridge-to-recovery (BTR). Oxygen uptake kinetics was assessed by fitting a single exponential function to the VO2 response. There was a significant improvement in several key parameters of cardiac performance including peak VO2, VO2 at anaerobic threshold (AT), oxygen kinetics as measured by mean response time (MRT), and oxygen deficit during LVAD support. Oxygen deficiency improved from 0.29 +/- 0.16 ml/kg to 0.16 +/- 0.06 ml/kg (p = 0.023), as did MRT 68 +/- 47.7 seconds to 35.8 +/- 13.3 seconds (p = 0.046) with LVAD support. Improved oxygen kinetics suggests improved peripheral utilization of oxygen, and may offer an additional clinical parameter to predict the likelihood of sustained recovery.

Destination therapy: safety and feasibility of national and international travel.

Results for Destination Therapy (DT) continue to improve with advanced technology, better patient selection, and experienced clinical management. Quality of life for these patients is an important component of the overall success of DT, and traveling is becoming more common. We reviewed our experience with long-distance travel in our DT population. All patients implanted with a left ventricular assist device for DT were followed prospectively. Long-distance travel was considered to be >200 miles, one way from their homes. There were 15 patients (14 men) with an average age of 66 years (range, 30-82) who traveled a combined total of 40 long-distance trips. Four trips were international (Spain, Canada (2), and Puerto Rico), 35 within the continental U.S., and one to Hawaii. The average one way distance traveled was 925 miles with a range of 218-4256 miles. The average time away from home was 8.3 days (range, 2-30). Patients traveled by airplane (17), car (23), and one trip included a 5 day cruise. Five complications occurred: driveline trauma, delay of reentry into the United States, missed flight, red heart alarm from bearing wear, and dehydration. All patients returned home safely for routine follow-up. Long-distance travel is possible for DT patients. Anticipating potential problems and careful planning is necessary for safe national and international travel.