Effective orifice diameter: a new sizing parameter of surgical valve prostheses to inform valve selection.

Background: The labeled sizes of surgical valve prostheses and their discordance with the physical internal valve orifice sizes has long been a controversy in the cardiac surgery community, leading many to believe it to be a contributing factor in prosthesis-patient mismatch following valvular replacement surgery. In an attempt to address this issue, the International Organization for Standardization (ISO) 5840-2:2021 standard for surgical valve prostheses recommends that a new sizing parameter, namely, the effective orifice diameter, be provided in labeling by all manufacturers as an indicator of the true flow-passing capacity of a prosthetic valve. Methods: The ISO Cardiac Valves Working Group conducted a multi-laboratory round-robin study to investigate whether the effective orifice diameter of a prosthetic surgical valve could be derived repeatably and reproducibly through steady forward-flow testing. A total of seven valve models, each with multiple sizes, were tested, including a mechanical heart valve and multiple biological heart valves. Results: The round-robin study confirmed that the steady forward-flow test had good intra-laboratory repeatability and inter-laboratory reproducibility in deriving the effective orifice diameters of surgical valve prostheses. On average, among the participating laboratories, the experimentally derived effective orifice diameter of a prosthetic heart valve was 3-12 mm smaller than its labeled size. Conclusions: The effective orifice diameter provides better characterization of the hydrodynamic characteristics of a surgical valve prosthesis and can be derived using a validated steady forward-flow test method. This new sizing parameter will soon be adopted by surgical valve manufacturers and provided in device labeling to inform valve selection by surgeons.

In-Vitro Pulsatile Flow Testing of Prosthetic Heart Valves: A Round-Robin Study by the ISO Cardiac Valves Working Group.

PURPOSE: Hydrodynamic performance testing is one of the core in vitro assessments required by the ISO 5840 series of standards for all prosthetic heart valves. A round-robin study carried out in 2005 in accordance with ISO 5840:2005 revealed significant variabilities in prosthetic heart valve hydrodynamic performance measurements among the participating laboratories. In order to re-examine the inter-laboratory variability based on the "state-of-the-art" under ISO 5840-1 and 5840-2:2015, the ISO Cardiac Valve Working Groups decided in 2016 to repeat the round-robin study. METHODS: A total of 13 international laboratories participated in the study. The test valves were chosen to be the St. Jude Medical Masters Series mechanical valves (19 mm aortic, 25 mm aortic, 25 mm mitral, and 31 mm mitral), which were circulated among the laboratories. The testing was conducted according to a common test run sequence, with prespecified flow conditions. RESULTS: The study revealed improved, yet still significant variability among different laboratories as compared to the 2005 study. The coefficient of variation ranged from 7.7 to 21.6% for the effective orifice area, from 10.1 to 32.8% for the total regurgitant fraction, and from 14.7 to 45.5% for the mean transvalvular pressure gradient. CONCLUSIONS: The study revealed the ambiguities in the current versions of the ISO 5840 series of standards and the shortcomings of some participating laboratories. This information has allowed the ISO Working Group to incorporate additional clarifying language into the ISO 5840-1, -2, and -3 standards that are currently under revision to improve in vitro assessments. The results presented here can also be used by the testing laboratories to benchmark pulse duplicator systems and to train and certify testing personnel.

Extraction of pulmonary vascular compliance, pulmonary vascular resistance, and right ventricular work from single-pressure and Doppler flow measurements in children with pulmonary hypertension: a new method for evaluating reactivity: in vitro and clinical studies.

BACKGROUND: Current evaluation of pulmonary hypertension (PH) in children involves measurement of pulmonary vascular resistance (PVR); however, PVR neglects important pulsatile components. Pulmonary artery (PA) input impedance and ventricular power (VP) include mean and pulsatile effects and have shown promise as alternative measures of vascular function. Here we report the utility of pulsed-wave (PW) Doppler-measured instantaneous flow and pressure measurements for estimation of input impedance and VP and use this method to develop a novel parameter: reactivity in compliance. METHODS AND RESULTS: An in vitro model of the general pulmonary vasculature was used to obtain impedance and VP, measured by PW Doppler and a reference flow meter. The method was then tested in a preliminary clinical study in subjects with normal PA hemodynamics (n=4) and patients with PH undergoing reactivity evaluation (8 patients; 23 data points). In vitro results showed good agreement between the impedance spectra computed from both flow-measurement methods. Excellent correlation was seen in vitro between actual resistance and the zero-frequency (Z(o)) impedance value (r2=0.984). Excellent agreement was also found between Z(o) and PVR in the clinical measurements (y=1.075x+0.73; r=0.993). Furthermore, total VP and VP/cardiac output increased significantly with hypertension (128.73 to 365.91 mW and 2.42 to 6.69 mW x mL(-1) x s(-1), respectively). The first-harmonic value of impedance (Z1) was used as a measure of compliance reactivity; older patients exhibited markedly less compliance reactivity than did younger patients. CONCLUSIONS: Input impedance and VP calculated from Doppler measurements and a single-catheter pressure measurement provide comprehensive characterization of PH and reactivity.

Use of intravascular ultrasound to measure local compliance of the pediatric pulmonary artery: in vitro studies.

BACKGROUND: The accurate measurement of local pulmonary artery compliance in pediatric pulmonary hypertension is an important step toward further understanding the biomechanical and hemodynamic aspects of the disease. The emergence of intravascular ultrasound (IVUS) imaging techniques promises the ability to make such measurements clinically. However, the use of IVUS for compliance measurements has not been validated. Furthermore, confusion exists regarding the most appropriate method to measure compliance. METHODS: This study validated IVUS measurements against a laser micrometer standard for 4 elastic tubes of varying compliance. Two methods of quantifying local compliance were explored: The pressure-strain modulus (E(p)), (E(p)(g/cm(2)) = DeltaP x R(d)/DeltaR (Where DeltaP is pulse pressure, R(d) is diastolic radius, and DeltaR is systolic minus diastolic radii) and the dynamic compliance (C(dyn)), (C(dyn)(%/100 mm Hg) = [DeltaD/(DeltaP x D(d))] x 10(4) Where DeltaD is systolic minus diastolic diameters and D(d) is diastolic diameter. RESULTS: IVUS diameter measurements agreed well with laser micrometer data although slight overestimation (mean = 3.67% +/- 2.78%) was present. Mean values of E(p) ranged from 353.3 g/cm(2) to 2676.0 g/cm(2); mean C(dyn) values ranged from 5.7% diametric change/100 mm Hg to 39.5% diametric change/100 mm Hg for all tube models. Although mean values of E(p) and C(dyn) could be distinguished among the various tubes, the extremely large measurement uncertainty for E(p) precluded statistical differentiation. The uncertainty in E(p) increased inversely with the diametric change, indicating a potential limitation of E(p) associated with stiffening arteries. CONCLUSIONS: We conclude that C(dyn) is a more robust mean of quantifying pediatric pulmonary artery compliance, especially as arteries stiffen with chronic pulmonary hypertension.