Structural evaluation of porcine heart valve prostheses with radiofrequency ultrasound

Background: Bioprosthetic heart valve use is limited by progressive degener ation. Early degenerative changes are often occult, making assessment of ti ssue integrity difficult. Ultrasound tissue characterization may detect alt erations in tissue structure and allow early detection of leaflet degenerat ion. Methods: Using a modified echocardiographic unit (Acuson), radiofreque ncy (R-F) integrated backscatter amplitude (IBA) (f/RF/dt) was measured in 38 leaflets from nine explanted and six control porcine valves. Regions of interest in each leaflet were studied using four ultrasound frequencies. Ra diographic gray scale mean and leaflet thickness were measured at each regi on of interest. Percent collagen and mineral were calculated for each regio n of interest using color-image processing of histologic sections and compa red to IBA. Results: IBA values for control vs. explanted leaflets were (me an value +/- standard deviation): 8.2 +/- 4.69 dB vs. - 4.7 +/- 4.64dB at 7 .0 MHz; -5.8 +/- 4.34 dB vs. -3.1 +/- 5.34 dB at 5.0 MHz; -3.8 +/- 3.38 dB vs. -2.1 +/- 3.18 dB at 3.5 MHz; and -9.0 +/-4.58 dB vs. - 7.1 +/- 4.25 dB at 2.5 MHz. Collagen content was 27.7 +/- 8.50% vs. 33.2 +/- 10.90%, minera l content was 0.1 +/- 0.10% vs. 2.1 +/- 4.30%, and radiographic gray scale mean was 150.6 +/- 1.96 vs. 145.3 +/- 5.14 for control vs. explanted leafle ts, respectively. For control and explanted leaflets IBA, collagen content, mineral content, and radiographic gray scale mean were different (control vs. explanted P < 0.05). Leaflet thickness was also noted to be different b etween the two groups. IBA was different among explanted leaflets with low, medium, and high mineral content. Conclusion: IBA was found to be a useful technique to differentiate normal from explanted porcine prosthetic valves in vitro. This method may be useful in the serial assessment of bioprosthe tic leaflet degenerative properties in vivo. (C) 2001 Elsevier Science Inc. All rights reserved.