title: Assessment of small-diameter aortic mechanical prostheses: physiological relevance of the Doppler gradient, utility of flow augmentation, and limitations of orifice area estimation.
abstract: BACKGROUND
  Noninvasive assessment of functionally stenotic small-diameter aortic mechanical prostheses is complicated by theoretical constraints relating to the hemodynamic relevance of Doppler-derived transprosthetic gradients. To establish the utility of Doppler echocardiography for evaluation of these valves, 20-mm Medtronic Hall and 19-mm St Jude prostheses were studied in vitro and in vivo.
  
  
  RESULTS
  Relations between the orifice transprosthetic gradient (equivalent to Doppler), the downstream gradient in the zone of recovered pressure (equivalent to catheter), and fluid mechanical energy losses were examined in vitro. Pressure-flow relations across the 2 prostheses were evaluated by Doppler echocardiography in vivo. For both types of prosthesis in vitro, the orifice was higher than the downstream gradient (P<0.001), and fluid mechanical energy losses were as strongly correlated with orifice as with downstream pressure gradients (r2=0.99 for both). Orifice and downstream gradients were higher and fluid mechanical energy losses were larger for the St Jude than the Medtronic Hall valve (all P<0.001). Whereas estimated effective orifice areas for the 2 valves in vivo were not significantly different, model-independent dynamic analysis of pressure-flow relations revealed higher gradients for the St Jude than the Medtronic Hall valve at a given flow rate (P<0.05).
  
  
  CONCLUSIONS
  Even in the presence of significant pressure recovery, the Doppler-derived gradient across small-diameter aortic mechanical prostheses does have hemodynamic relevance insofar as it reflects myocardial energy expenditure. Small differences in function between stenotic aortic mechanical prostheses, undetectable by conventional orifice area estimations, can be identified by dynamic Doppler echocardiographic analysis of pressure-flow relations.
authors.affiliation: Noninvasive Cardiac Imaging Laboratory, University of Chicago Medical Center, Ill, USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Marcus
authors.forename: R S
authors.initials: RS
authors.lastname: Heinrich
authors.forename: J
authors.initials: J
authors.lastname: Bednarz
authors.forename: S
authors.initials: S
authors.lastname: Lupovitch
authors.forename: J
authors.initials: J
authors.lastname: Abruzzo
authors.forename: R
authors.initials: R
authors.lastname: Borok
authors.forename: B
authors.initials: B
authors.lastname: Vandenberg
authors.forename: R E
authors.initials: RE
authors.lastname: Kerber
authors.forename: W
authors.initials: W
authors.lastname: Piccione
authors.forename: A P
authors.initials: AP
authors.lastname: Yoganathan
authors.forename: R M
authors.initials: RM
authors.lastname: Lang
mesh_terms: D001024:Aortic Valve Stenosis / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D001783:Blood Flow Velocity; D001807:Blood Vessel Prosthesis / Q000592:standards*; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology; D002316:Cardiotonic Agents / Q000008:administration & dosage; D004280:Dobutamine / Q000008:administration & dosage; D004452:Echocardiography; D006801:Humans; D008955:Models, Cardiovascular; D011312:Pressure; D013314:Stress, Mechanical; D017211:Treatment Failure
chemical_list: D002316:Cardiotonic Agents; D004280:Dobutamine