Characterization of Effective Orifice Areas of Mitral Prosthetic Heart Valves: An In-Vitro Study.

BACKGROUND: Reference values of hemodynamic parameters for the assessment of prosthetic heart valves are necessary, and ideally need to be provided by entities independent of the valve manufacturers. Thus, the study aim was to provide, in vitro, normal reference values of the effective orifice area (EOA) for different models and sizes of mitral prosthetic valve, and to assess the determinants of EOA and mean transvalvular pressure gradient (mTPG). METHODS: Four models of mechanical prostheses were tested (one mono-leaflet, three bi-leaflet) and four models of bioprostheses (two bovine pericardial, two porcine) on a double-activation pulsed duplicator that was specifically designed and optimized for assessing the hemodynamic performance of mitral prosthetic valves. The hemodynamic conditions were standardized and included for bioprostheses: two mitral flow volumes, three mean aortic pressures, two heart rates, and three E/A ratios. The EOAs were measured with Doppler echocardiography, using the same method (continuity equation) as was used in the clinical setting. Overestimation in term of EOA was defined according to guidelines as >0.25 cm2. RESULTS: EOA reference values were recorded. For mono-leaflet prostheses (Medtronic Hall 7700, size 25 to 31 mm) 2.29 and 3.49; for bi-leaflet prostheses (St. Jude Medical Master and Master HP, sizes 25 to 33 mm and On-X valve, sizes 27-29 mm) 1.34 and 4.74 cm2; for porcine bioprostheses (Medtronic Mosaic CINCH, sizes 25 to 31 mm and St. Jude Epic 100, sizes 25 to 33 mm) 1.35 and 3.56 cm2; for bovine pericardial bioprosthetic valves (Edwards Perimount 6900P and Magna Ease 7300, sizes 25 to 33 mm) 1.67 and 2.36 cm2. There were some discrepancies between the normal reference EOAs measured compared to those provided by the prosthesis manufacturers, or in published reports. The bioprosthetic EOAs were shown to be smaller than the manufacturers' values in 32% of valves (by an average of 0.57 ± 0.28 cm2) versus in 7% of valves when compared to values reported elsewhere (by an average of 0.43 ± 0.17 cm2). The relationship between EOA and internal orifice area (IOA) varied according to the type of prosthesis. The EOA was close to the IOA in mechanical valves (regression slopes 0.87-0.99) but was much smaller than the IOA in bioprosthetic valves (slopes 0.25-0.30). The EOA was influenced by prosthesis diameter, prosthesis stent diameter and height, while the mTPG was influenced by EOA and heart rate. CONCLUSIONS: The present study has provided normal reference values of EOAs for several frequently used mitral prostheses. This information may be helpful for identifying and quantifying prosthetic valve dysfunction and prosthesis-patient mismatch.

Clinical interpretation standards and quality assurance for the multicenter PET/CT trial rubidium-ARMI.

UNLABELLED: Rubidium-ARMI ((82)Rb as an Alternative Radiopharmaceutical for Myocardial Imaging) is a multicenter trial to evaluate the accuracy, outcomes, and cost-effectiveness of low-dose (82)Rb perfusion imaging using 3-dimensional (3D) PET/CT technology. Standardized imaging protocols are essential to ensure consistent interpretation. METHODS: Cardiac phantom qualifying scans were obtained at 7 recruiting centers. Low-dose (10 MBq/kg) rest and pharmacologic stress (82)Rb PET scans were obtained in 25 patients at each site. Summed stress scores, summed rest scores, and summed difference scores (SSS, SRS, and SDS [respectively] = SSS-SRS) were evaluated using 17-segment visual interpretation with a discretized color map. All scans were coread at the core lab (University of Ottawa Heart Institute) to assess agreement of scoring, clinical diagnosis, and image quality. Scoring differences greater than 3 underwent a third review to improve consensus. Scoring agreement was evaluated with intraclass correlation coefficient (ICC-r), concordance of clinical interpretation, and image quality using κ coefficient and percentage agreement. Patient (99m)Tc and (201)Tl SPECT scans (n = 25) from 2 centers were analyzed similarly for comparison to (82)Rb. RESULTS: Qualifying scores of SSS = 2, SDS = 2, were achieved uniformly at all imaging sites on 9 different 3D PET/CT scanners. Patient scores showed good agreement between core and recruiting sites: ICC-r = 0.92, 0.77 for SSS, SDS. Eighty-five and eighty-seven percent of SSS and SDS scores, respectively, had site-core differences of 3 or less. After consensus review, scoring agreement improved to ICC-r = 0.97, 0.96 for SSS, SDS (P < 0.05). The agreement of normal versus abnormal (SSS ≥ 4) and nonischemic versus ischemic (SDS ≥ 2) studies was excellent: ICC-r = 0.90 and 0.88. Overall interpretation showed excellent agreement, with a κ = 0.94. Image quality was perceived differently by the site versus core reviewers (90% vs. 76% good or better; P < 0.05). By comparison, scoring agreement of the SPECT scans was ICC-r = 0.82, 0.72 for SSS, SDS. Seventy-six and eighty-eight percent of SSS and SDS scores, respectively, had site-core differences of 3 or less. Consensus review again improved scoring agreement to ICC-r = 0.97, 0.90 for SSS, SDS (P < 0.05). CONCLUSION: (82)Rb myocardial perfusion imaging protocols were implemented with highly repeatable interpretation in centers using 3D PET/CT technology, through an effective standardization and quality assurance program. Site scoring of (82)Rb PET myocardial perfusion imaging scans was found to be in good agreement with core lab standards, suggesting that the data from these centers may be combined for analysis of the rubidium-ARMI endpoints.