title: Pressure gradients across bileaflet aortic valves by direct measurement and echocardiography.
abstract: BACKGROUND
  Pressure gradients calculated from echo-cardiography after aortic valve replacement are commonly much higher than would be expected from in vitro measurements.
  
  
  METHODS
  The mean, peak-to-peak, and maximal gradients across bileaflet aortic prostheses (St. Jude Medical) were measured invasively in 52 patients at high and low heart rate, cardiac index, and stroke volume. One week after operation the gradients were calculated from a standard transthoracic echocardiogram (delta p = 4v2(2)). In a second study 3 to 12 months later, gradients were calculated using the standard, simplified Bernoulli equation, and with the equation considering subvalvular flow velocities (delta p = 4(v2(2-)v1(2)). Invasive and echocardiographic measurements were matched and compared.
  
  
  RESULTS
  Invasively measured mean gradients for 21 to 29-mm valves ranged from 7.4 +/- 4.9 to 4.3 +/- 1.6 mm Hg at systolic flow rates from 11.3 +/- 0.7 to 16.2 +/- 1.8 L.min-1.m-2. Mean echocardiographic gradients were 15.1 +/- 4.5 to 7.5 +/- 2.2 mm Hg (p < 0.001) with the standard method, and 10.5 +/- 1.9 to 5.6 +/- 1.5 mm Hg when considering the subvalvular flow velocity (p < 0.001).
  
  
  CONCLUSIONS
  Mean gradients across bileaflet prostheses are generally low, even in small valves and with high systolic flow. The correlation of the invasive in vivo with in vitro gradients is good. Standard echocardiography overestimates gradients across bileaflet heart valves and high gradients are not due to valve dysfunction. Gradients obtained by echocardiography considering the subvalvular flow velocity correlate better to invasively measured and in vitro gradients.
authors.affiliation: Clinic for Cardiac Surgery, Triemli Hospital Zürich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Laske
authors.forename: R
authors.initials: R
authors.lastname: Jenni
authors.forename: M
authors.initials: M
authors.lastname: Maloigne
authors.forename: G
authors.initials: G
authors.lastname: Vassalli
authors.forename: O
authors.initials: O
authors.lastname: Bertel
authors.forename: M I
authors.initials: MI
authors.lastname: Turina
mesh_terms: D000328:Adult; D000368:Aged; D001021:Aortic Valve / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D001022:Aortic Valve Insufficiency / Q000503:physiopathology / Q000601:surgery; D001024:Aortic Valve Stenosis / Q000503:physiopathology / Q000601:surgery; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002302:Cardiac Output; D002404:Catheterization; D015150:Echocardiography, Doppler; D005260:Female; D006339:Heart Rate; D006350:Heart Valve Prosthesis; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D011312:Pressure; D013318:Stroke Volume; D017725:Ventricular Pressure