Axial flow pump support from the inferior vena cava to the pulmonary artery can prevent the substantial decrease of aortic flow and pressure associated with total cavopulmonary connection and can reverse its poor hemodynamics. This is a simple model that can be used to further evaluate the potential of mechanical support as a treatment option in failing Fontan circulation.
Total cavopulmonary connection (CPC) has a significant incidence of late failure due to increased systemic venous pressure and low cardiac output. Mechanical support could prevent failure by correcting hemodynamics. We established a model of inferior CPC using an axial flow pump (Thoratec HeartMate II, Thoratec Corp. Pleasanton, CA) in a group of ten 47-57 kg sheep and assessed hemodynamics and metabolism as a potential chronic treatment option for failed Fontan circulation. After pilot studies (n = 7), three animals underwent pump-supported inferior CPC to assess hemodynamic and metabolic responses. Pump inflow was connected to the inferior vena cava (IVC) and outflow to the main pulmonary artery. The IVC was ligated at the right atrium. Hemodynamic and biochemical parameters were recorded over four days. The first seven animals died from pump-related causes (graft kinking, three; pump thrombosis, one) or other causes (GI bleeding, one; suspected stroke, two). The subsequent three animals were electively euthanized on postoperative day four due to IRB requirements. Over the four day postoperative period, pump flow was 3.43 +/- 0.62 L/min and IVC pressure 4.05 +/- 3.21 mm Hg (mean +/- SD). Lactate levels remained normal. Low pressure and high-volume IVC flow was sustained by mechanical support. We will next attempt chronic pump implantation.
The primary objective of this study was to evaluate bearing wear during clinical use of the HeartMate II (HMII) left ventricular assist device. Bearings obtained from HMII pumps explanted after clinical use in the Destination Therapy and Bridge to Transplantation clinical trials were analyzed for wear using surface profilometry. Geometric profile variations measured on the inlet bearing ball were used to calculate the wear. Bearing wear was normalized to the total pump support duration to obtain an annualized bearing wear rate. Bearing life was estimated assuming a linear wear rate, as the time to reach a wear limit of 25 µm, which includes a 3× safety factor, to ensure that there is no contact between the rotor blades and the blood bore housing. One hundred and eighty-three bearings from left ventricular assist devices implanted in 181 patients were analyzed. Average age of the patients was 56.3 ± 14.6 years, 76% were male, 46% had an ischemic etiology of heart failure. Mean support duration for the pumps was 363 ± 349 days (median: 238, range: 1-1,621 days). Sixty pumps (33%) were explanted at heart transplantation, 20 (11%) after device replacement, 6 (3%) for ventricular recovery, 94 (51%) after patient death, and 3 (2%) were explanted for other reasons. Mean bearing wear was 0.59 ± 0.37 µm (median: 0.46 µm [5-95% interval: 0.25-1.48]). The median bearing wear rate for patients supported for at least 1 year was 0.30 [5-95% interval: 0.09-0.94] µm/yr. The 5-95% limits of the bearing wear rate corresponded to an estimated bearing life between 27 and 269 years. The pump having the highest bearing wear rate (1.46 µm/yr) had an estimated bearing life of at least 17 years. HMII bearing wear is extremely small, with an estimated bearing life well in excess of 17 years; it is not a limiting factor for long-term support with the HMII left ventricular assistive system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.