Effect of prosthetic aortic valve design on the Doppler-catheter gradient correlation: an in vitro study of normal St. Jude, Medtronic-Hall, Starr-Edwards and Hancock valves. - Baumgartner,H.; Khan,S.; DeRobertis,M.; Czer,L.; Maurer,G. (J Am Coll Cardiol, 1992)