title: Use of dobutamine stress echocardiography in assessing mechanical aortic prostheses: comparison with exercise echocardiography.
abstract: OBJECTIVE
  Relatively high resting flow velocities are occasionally seen in asymptomatic patients with apparently normal mechanical aortic prostheses. Doppler echocardiography in conjunction with bicycle exercise or dobutamine have been used to 'unmask' symptoms or abnormal hemodynamics in these patients. The aim of this study was to compare the Doppler-derived hemodynamic response to exercise and to dobutamine in patients with normally functioning mechanical aortic prostheses.
  
  
  METHODS
  Bicycle ergometry (from 200-400 kg x m/min) and dobutamine (from 5-40 micrograms/kg/min) in conjunction with Doppler echocardiography were performed in 25 asymptomatic patients (21 men, four women; mean age 61 years) with mechanical aortic prostheses (range: 19 mm to 27 mm) who had normal resting hemodynamics and normal left ventricular function. Aortic valve area (continuity equation) and maximal instantaneous and mean gradients were estimated at rest and at peak stress.
  
  
  RESULTS
  Target heart rate was achieved in 10/25 (40%) patients with exercise, and in 21/25 (84%) with dobutamine (p < 0.005). At peak stress, exercise induced a 25% increase in peak flow velocity, a 55% increase in valve gradients, and no significant change in valve area. In comparison, dobutamine induced a 48% increase in peak flow velocity, a 105% increase in valve gradients, and also no significant change in valve area. The flow velocity and pressure gradients at peak stress were significantly higher with dobutamine than with exercise.
  
  
  CONCLUSIONS
  In normally functioning aortic valve prostheses, the target heart rate can be reached more often with dobutamine than with supine bicycle exercise. Despite significant increase in the transvalvular gradients, the valve area remained unchanged. The clinical significance of exercise or dobutamine in symptomatic patients with mechanical prostheses is yet to be proven.
authors.affiliation: Department of Medicine/Cardiology, The University of Texas Health Science Center at San Antonio 78284-7872, USA.
authors.forename: M
authors.initials: M
authors.lastname: Zabalgoitia
authors.forename: K
authors.initials: K
authors.lastname: Kopec
authors.forename: L
authors.initials: L
authors.lastname: Oneschuk
authors.forename: W
authors.initials: W
authors.lastname: Linn
authors.forename: C J
authors.initials: CJ
authors.lastname: Herrera
authors.forename: R A
authors.initials: RA
authors.lastname: O'Rourke
mesh_terms: D000328:Adult; D000368:Aged; D001021:Aortic Valve; D001705:Bioprosthesis; D002316:Cardiotonic Agents; D002319:Cardiovascular System / Q000000981:diagnostic imaging / Q000503:physiopathology; D004280:Dobutamine; D015150:Echocardiography, Doppler / Q000379:methods*; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006350:Heart Valve Prosthesis; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D016683:Supine Position
chemical_list: D002316:Cardiotonic Agents; D004280:Dobutamine