A Calf Model for Left Ventricular Centrifugal Mechanical Assist

Retrospective analysis of adverse events in preclinical ventricular assist device experiments

Ventricular assist devices (VADs) are a widely acceptable therapeutic option for patients with end-stage heart failure. Data from preclinical animal trials provide important information about the efficacy, biocompatibility, and functioning of these devices. However, animal experiments have several limitations that may significantly affect outcomes even after implanting a properly functioning device. This retrospective analysis was performed to analyze, at explant, adverse events associated with VADs during the animal phase of testing. Data were collected from 141 VAD experiments performed in cattle that had received 11 different types of devices. A total of 294 adverse events were documented. Inflow cannula problems were cited in 79 implants (56%) and pump-related issues in 55 cases (39%). Adverse events associated with connectors were found in 53 implants (38%). Adverse events directly having to do with the animals represented only 17 implants (12%) in this series. These findings suggest that preclinical testing needs to place greater emphasis on the entire VAD system. In support of these results, human clinical data seem to indicate that actual VAD failure is rarely a cause for premature device removal.

Perioperative management of calves undergoing implantation of a left ventricular assist device

OBJECTIVE

To describe perioperative management of calves that underwent left lateral thoracotomy, aortic cross-clamping, partial left heart bypass and implantation of a left ventricular assist device.

SAMPLE POPULATION

A total of 43 healthy castrated male calves, weighing 121 +/- 24 kg.

RESULTS

Diazepam (mean +/- SD, 0.26 +/- 0.07 mg/kg), ketamine (5.9 +/- 2.17 mg/kg) and isoflurane were used in the anesthetic management of calves undergoing implantation of a left ventricular assist device in the descending thoracic aorta. Other adjunctive agents administered were fentanyl (11 +/- 5.4 microg/kg), lidocaine (4.9 +/- 3.19 mg/kg), bupivacaine (0.75%) and butorphanol (0.49 +/- 0.13 mg/kg). None of the calves regurgitated at induction or during intubation. A tube was used to drain the rumen and prevent bloat during the procedure. Partial left heart bypass was used to perfuse the caudal half of the body during the period of aortic cross clamp and device implantation. Initial mean systemic blood pressure was 96 +/- 25 mm Hg, and pressures measured in the auricular artery increased during aortic cross-clamping and bypass. Vasoconstrictor therapy was required to treat caudal arterial hypotension during the procedure in 9 calves. Mean systemic arterial pressures returned to baseline values by the end of the anesthetic period. Initial mean pulmonary arterial pressures (PAP) were 22 +/- 3 mm Hg. A significant but transient increase in pulmonary arterial pressure occurred after both heparin and protamine administration.

CONCLUSIONS

The described anesthetic protocol was effective for thoracotomy and implantation of an intra-aortic left ventricular assist device in normal calves. Partial left ventricular bypass was a useful adjunct during the period of aortic cross clamp. The doses of heparin and protamine administered were effective. Responsibility to monitor oxygenation of the cranial half of the animal continues during the bypass period as hypoxemia due to pulmonary dysfunction will not be detected by the perfusionist.

Centrifugal pumps: description of devices and surgical techniques

BACKGROUND

Because of simplicity of application, universal access, and low cost, centrifugal pumps are commonly used for short-term mechanical cardiac assist. Indications and techniques for application of this technology continue to evolve.

METHODS

The clinical experience with 151 patients undergoing centrifugal mechanical cardiac assist at the University of Missouri-Columbia has been reviewed. We have compared commonly available centrifugal pumping systems in vitro and in vivo for characteristics that might distinguish them.

RESULTS

Centrifugal pumps have been found to be well suited for use in surgery on the thoracic aorta, for extracorporeal membrane oxygenation and for postcardiotomy cardiac mechanical assist. Complications associated with centrifugal mechanical assist are predictable and common but potentially can be reduced by improved surgical techniques and anticoagulation strategies. In vitro and in vivo experimentation with available centrifugal pumps reveals nuances characteristic of each of the devices.

CONCLUSIONS

All centrifugal pumps presently available are less destructive to blood cellular elements compared with roller pumps. With familiarity, all can function satisfactorily for short-term mechanical assist with no compelling evidence that favors any particular centrifugal pump system clinically available. Centrifugal pumps are ideally suited for left heart bypass during surgery on a thoracic aorta and for short-term application as may be required for postcardiotomy mechanical assist. Centrifugal pump technology should be part of the armamentarium of all cardiothoracic surgeons.