RESUMO
Current generation continuous flow assist devices to operate at a fixed speed, which limits preload response and exercise capacity in left ventricular assist device (LVAD) patients. A feedback control system was developed to automatically adjust pump speed based on direct measurements of ventricular loading using a custom cannula tip with an integrated pressure sensor and volume-sensing conductance electrodes. The input to the control system is the integral of the left ventricular (LV) pressure versus conductance loop (PGA) over each cardiac cycle. The feedback control system adjusts pump speed based on the difference between the measured PGA and the desired PGA. The control system and cannula tip were tested in acute ovine studies (n = 5) using the HeartMate II LVAD. The preload response of the control system was evaluated by partially occluding and releasing the inferior vena cava using a vessel loop snare. The cannula tip was integrated onto a custom centrifugal flow LVAD and tested in a 14-day bovine study. The control system adjusted pump support to maintain constant ventricular loading: pump speed increased (decreased) following an increase (decrease) in preload. This study demonstrated in vivo the Starling-like response of an automatic pump control system based on direct measurements of LV loading.
Assuntos
Coração Auxiliar , Animais , Bovinos , Humanos , Cânula , Ventrículos do Coração , Ovinos , Pressão VentricularRESUMO
Mechanical circulatory support for children under 6 years of age remains a challenge. This article describes the preclinical status and the results of recent animal testing with the Penn State Infant Left Ventricular Assist Device (VAD). The objectives have been to 1) demonstrate acceptably low thromboembolic risk to support Food and Drug Administration approval, 2) challenge the device by using minimal to no anticoagulation in order to identify any design or manufacturing weaknesses, and 3) improve our understanding of device thrombogenicity in the ovine animal model, using multicomponent measurements of the coagulation system and renal ischemia quantification, in order to better correlate animal results with human results.The Infant VAD was implanted as a left VAD (LVAD) in 18-29 kg lambs. Twelve LVAD and five surgical sham animals were electively terminated after approximately 30 or 60 days. Anticoagulation was by unfractionated heparin targeting thromboelastography R times of 2x normal (n = 6) or 1x normal (n = 6) resulting in negligible heparin activity as measured by anti-Xa assay (<0.1 IU/ml). Platelet inhibitors were not used.There were no clinically evident strokes or evidence of end organ dysfunction in any of the 12 electively terminated LVAD studies. The degree of renal ischemic lesions in device animals was not significantly different than that found in five surgical sham studies, demonstrating minimal device thromboembolism.In summary, these results in a challenging animal test protocol support the conclusion that the Penn State Infant VAD has a low thromboembolic risk and may allow lower levels of anticoagulation.