title: A novel non-invasive method to assess aortic valve opening in HeartMate II left ventricular assist device patients using a modified Karhunen-Loève transformation.
abstract: BACKGROUND
  Thrombus formation on or near the aortic valve has been reported in HeartMate II (Thoratec, Pleasanton, CA) left ventricular assist device (LVAD) patients whose aortic valves do not open. With an akinetic valve, thrombogenesis is more likely. Thrombus formation may lead to neurologic events, placing the patient at greater risk. Aortic valve stenosis and/or regurgitation have also been observed with akinetic aortic valves. Assessing aortic valve opening is crucial when optimizing rotations per minute (rpm) to minimize embolic risk and aortic valve stenosis but presently relies solely on echocardiography, intermittent decreases in rpms to force aortic valve opening, and monitoring of pulse pressure. We hypothesized the electrical current waveforms of the HeartMate II would reveal whether the aortic valve was opening due to pressure changes in the left ventricle to allow for continuous monitoring and control of aortic valve opening ratios.
  
  
  METHODS
  Electrical HeartMate II current waveforms of patients from 2008 to 2009 that were recorded at the time of echocardiograph procedures were analyzed using a modified Karhunen-Loève transformation with a training set of electrical waveforms from 8,860 HeartMate II electrical current recordings from 2001 to 2009.
  
  
  RESULTS
  The study included 6 patients. The electrical current magnitude of the projection of the electrical current waveforms onto the training set's eigenvectors was statistically significantly greater in 4 of the 6 patients when the aortic valve was closed, confirmed by echocardiography. The 2 patients who did not have a large increase in the magnitude had mild aortic valve regurgitation.
  
  
  CONCLUSIONS
  Electrical current analysis for rotary non-pulsatile pumps is a means to develop a physiologic feedback algorithm for an auto-mode, which currently does not exist. Constant regulation and optimization of rotary non-pulsatile LVADs would minimize patients' risk for neurologic events and aortic valve stenosis.
authors.affiliation: Utah Artificial Heart Program, Intermountain Medical Center, Murray, Utah 84157, USA. coreyjbishop@gmail.com
authors.forename: Corey J
authors.initials: CJ
authors.lastname: Bishop
authors.forename: Nathan O
authors.initials: NO
authors.lastname: Mason
authors.forename: Abdallah G
authors.initials: AG
authors.lastname: Kfoury
authors.forename: Robert
authors.initials: R
authors.lastname: Lux
authors.forename: Sandi
authors.initials: S
authors.lastname: Stoker
authors.forename: Kenneth
authors.initials: K
authors.lastname: Horton
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Clayson
authors.forename: Brad
authors.initials: B
authors.lastname: Rasmusson
authors.forename: Bruce B
authors.initials: BB
authors.lastname: Reid
mesh_terms: D000465:Algorithms; D001021:Aortic Valve / Q000000981:diagnostic imaging / Q000503:physiopathology*; D001024:Aortic Valve Stenosis / Q000453:epidemiology / Q000503:physiopathology; D004452:Echocardiography; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods*; D025461:Feedback, Physiological / Q000502:physiology; D005583:Fourier Analysis; D006353:Heart-Assist Devices / Q000145:classification*; D006801:Humans; D012189:Retrospective Studies; D012307:Risk Factors; D016277:Ventricular Function, Left / Q000502:physiology