• Raffael Amacher, Alberto Weber, Henriette Brinks, Shannon Axiak, Antonio Ferreira, Lino Guzzella, Thierry Carrel, James Antaki, and Stijn Vandenberghe.
• Institute for Dynamic Systems and Control, ETH Zurich, Zurich, Switzerland. raffael.amacher@idsc.mavt.ethz.ch
• J. Thorac. Cardiovasc. Surg.. 2013 Sep 1;146(3):710-7.

ObjectiveCurrent pulsatile ventricular assist devices operate asynchronous with the left ventricle in fixed-rate or fill-to-empty modes because electrocardiogram-triggered modes have been abandoned. We hypothesize that varying the ejection delay in the synchronized mode yields more precise control of hemodynamics and left ventricular loading. This allows for a refined management that may be clinically beneficial.MethodsEight sheep received a Thoratec paracorporeal ventricular assist device (Thoratec Corp, Pleasanton, Calif) via ventriculo-aortic cannulation. Left ventricular pressure and volume, aortic pressure, pulmonary flow, pump chamber pressure, and pump inflow and outflow were recorded. The pump was driven by a clinical pneumatic drive unit (Medos Medizintechnik AG, Stolberg, Germany) synchronously with the native R-wave. The start of pump ejection was delayed between 0% and 100% of the cardiac period in 10% increments. For each of these delays, hemodynamic variables were compared with baseline data using paired t tests.ResultsThe location of the minimum of stroke work was observed at a delay of 10% (soon after aortic valve opening), resulting in a median of 43% reduction in stroke work compared with baseline. Maximum stroke work occurred at a median delay of 70% with a median stroke work increase of 11% above baseline. Left ventricular volume unloading expressed by end-diastolic volume was most pronounced for copulsation (delay 0%).ConclusionsThe timing of pump ejection in synchronized mode yields control over left ventricular energetics and can be a method to achieve gradual reloading of a recoverable left ventricle. The traditionally suggested counterpulsation is not optimal in ventriculo-aortic cannulation when maximum unloading is desired.Copyright © 2013 The American Association for Thoracic Surgery. Published by Mosby, Inc. All rights reserved.

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