Obstructic characteristics of Björk-Shiley, Hancock, and Lillehei-Kaster prosthetic mitral valves in the immediate postoperative period

Validation and applications of mitral prosthetic valvular areas calculated by Doppler echocardiography

Doppler echocardiography is used in the noninvasive evaluation of mitral valve prostheses using parameters heretofore validated primarily for native valves. Accordingly, this study was designed to examine the validity and relative usefulness of valve gradient and area measurements in a group of 26 patients (17 women, 9 men, mean age 62 +/- 8 years), 19 +/- 4 months after implantation of different sizes (25 to 31 mm) of a given type of bioprosthesis. Areas obtained with both the continuity equation, using stroke volume measured in the left ventricular outflow tract, and the pressure half-time method are compared to known prosthetic areas derived from an in vitro hydraulic model. Areas calculated by the continuity equation correlate well with in vitro areas (r = 0.82, standard error of the y estimate = 0.1 cm2, p less than 0.001), and are within the range of predicted in vitro values in 92% of cases. Areas derived by the pressure half-time method do not correlate with in vitro areas (r = 0.15, p greater than 0.3) or continuity equation areas (r = 0.23, p greater than 0.2), and are above the range of predicted values in 69% of cases. Correlations are also found between continuity equation areas and the peak and mean valvular gradients (r = 0.59, p less than 0.005 and r = -0.63, p less than 0.0005, respectively). Taking the effect of cardiac output on gradients into account results in projected relations between indexed prosthetic areas and the pressure gradients at rest and during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler measurement of cardiac output across prosthetic mitral valves

In 46 patients with a normal functioning mitral valve prosthesis (15 St. Jude, 19 Medtronic Hall, 12 Hancock) cardiac output was measured by pulsed Doppler echocardiography across the valve prosthesis. Simultaneously cardiac output was determined by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract (2.8 l/min-9.5 l/min). The prosthetic valve area was calculated using the pressure half-time method. Cardiac output was calculated by multiplying time-velocity integrals with the mitral valve area. Cardiac output measurements across the mitral prosthesis correlated significantly with thermodilution (r = 0.96, SEE = 0.400 l/min) and pulsed Doppler echocardiography flow measurements in the left ventricular outflow tract (r = 0.82, SEE = 0.679 l/min). The mean percent error of the Doppler transmitral flow measurement was 10.8%. Doppler transmitral flow underestimated cardiac output valves of more than 6.5 l/min in 6 of 7 patients. Cardiac output measurements across Hancock (SEE = 0.473 l/min) and St. Jude prostheses (SEE = 0.538 l/min) were more accurate than across Medtronic Hall prostheses (SEE = 0.847 l/min). Cardiac output can be calculated by pulsed Doppler echocardiography across normal functioning mitral prostheses. Due to the different flow dynamics the accuracy of cardiac output measurement depends on the prosthetic valve type. Reliable measurements of cardiac output can be performed across Hancock and St. Jude prostheses only. This method is limited in volume flow measurements across Medtronic Hall prostheses.

Limitations of Doppler ultrasound in the assessment of the function of prosthetic mitral valves

Pressure half time has been assumed to be a relatively flow-independent measure of orifice area, but it may also be influenced by atrial and ventricular factors. Pressure half time and peak left ventricular inflow velocity were measured by continuous wave Doppler ultrasound in 164 patients with normally functioning Carpentier-Edwards, Björk-Shiley, and Starr-Edwards mitral prostheses. Pressure half time was shorter in the Björk-Shiley than in the other value types and peak transmitral velocity was highest in the Starr-Edwards prostheses. These differences, however, were partly explained by coexistent differences in transmitral flow. Filling time accounted for 19% and stroke volume for 15% of the variance in pressure half time compared with only 5.6% for prosthetic design and 0.4% for annulus diameter when each of these variables was considered alone. The design of the prosthesis explained 18% of the variance in peak transmitral velocity, while cardiac output and annulus diameter did not contribute significantly. With Doppler ultrasound it is impossible to define reliable normal ranges for prosthetic function independently of atrial and ventricular function. Formulas for orifice area based on peak transmitral velocity and flow seem more likely to reflect the behaviour of normally functioning prostheses than those based on pressure half time.

Doppler color flow mapping in the evaluation of prosthetic mitral and aortic valve function

Doppler color flow mapping and color-guided conventional Doppler studies were performed on 119 patients with 126 prosthetic valves (mitral alone in 60, aortic alone in 52 and both mitral and aortic in 7 patients) within 2 weeks of the catheterization study or surgery, or both. The mean pressure gradients derived by color-guided continuous wave Doppler ultrasound correlated well with those obtained at catheterization for both the tissue and mechanical mitral and aortic prostheses (r = 0.85 to 0.87). For the effective prosthetic orifice areas, better correlation with catheterization results were obtained with the tissue mitral (r = 0.94) and tissue aortic (r = 0.87) prostheses than with the mechanical mitral (r = 0.79) and mechanical aortic (r = 0.76) prostheses. The maximal width of the color flow signals at their origin from the tissue mitral prostheses also correlated well with the effective prosthetic orifice area at catheterization (r = 0.81). Doppler color flow mapping identified prosthetic valvular regurgitation with a sensitivity and specificity of 89% and 100%, respectively, for the mitral and 92% and 83% for the aortic prostheses. There was complete agreement between the Doppler color flow mapping and angiographic grading of the severity of prosthetic valvular regurgitation in 90% of mitral and 73.5% of the aortic regurgitant prostheses with under- or overestimation by greater than 1 grade in only two cases. Valvular and paravalvular regurgitation was correctly categorized by Doppler color flow mapping in relation to the surgical findings in 94% of the mitral and 80.5% of the aortic prostheses.

Six month postoperative hemodynamics of the Hancock heterograft and the Björk-Shiley prosthesis: results of a Veterans Administration cooperative prospective randomized trial

In a Veterans Administration Cooperative Study involving 13 medical centers, 575 patients undergoing single valve replacement were prospectively randomized to receive either the standard Björk-Shiley prosthesis or the Hancock porcine heterograft (with a modified orifice for sizes 23 and smaller). The hemodynamic data in the 268 patients who underwent cardiac catheterization an average of 6 months (range 3 to 12) postoperatively are reported. Statistical analyses were performed on valve sizes 23, 25 and 27 in the aortic position, and 29, 31 and 33 in the mitral position. A wide variation was observed in mean pressure gradient and calculated orifice area in both valve types within all sizes in both the aortic and the mitral positions. In the aortic position, the Björk-Shiley prosthesis tended to have a lower pressure gradient and larger calculated orifice area than the Hancock heterograft, but the differences in gradient between the two valve types were significant only in the larger-sized valves. The difference in calculated area between the two valve types was not significant within each valve size. In the mitral position, there were no differences in gradient and calculated orifice area between the two types of prostheses. The postoperative cardiac index, regurgitant volume, pulmonary artery systolic and mean pressures, left ventricular end-diastolic pressure, left ventricular ejection fraction and left ventricular end-diastolic volume index did not differ in patients receiving the Björk-Shiley prosthesis from values in patients receiving the Hancock heterograft. Hence, the overall hemodynamic performance of both types of valves is remarkably similar. The choice between these two prostheses should, therefore, be governed not by the hemodynamic performance, but by other factors such as valve durability, risk of anticoagulation and incidence of valve-related complications.

Normal values of prosthetic valve Doppler echocardiographic parameters: a review

Doppler echocardiography plays an important role in the evaluation of patients with prosthetic valves. The evaluation of flow velocities across prosthetic valves is more complicated compared with native valves, and flow velocities are specific for various types, positions, and sizes of prostheses. Because all prosthetic valves are at least mildly stenotic and a significant proportion is regurgitant, information regarding normally functioning prosthetic valves is important. Eighteen studies resulting in data on 1105 patients with normally functioning prosthetic valves were reviewed. Significant differences among the various types and sizes of prosthetic valves were found in both the aortic and mitral positions. The results are summarized in tables and figures that can be used for reference in a clinical laboratory.

Analysis of Doppler-obtained velocity curves in functional evaluation of mechanical prosthetic valves in the mitral and aortic positions

A total of 145 patients with 160 mechanical prostheses of the Björk-Shiley or Starr-Edwards type (15 with double mitral plus aortic valves) underwent clinical and Doppler echocardiography analysis. In the mitral position (85 valves) 10 patients with valve-related symptoms, calculated prosthetic area less than or equal to 1 cm2, or mean transprosthetic gradient greater than 10 mm Hg by Doppler echocardiography were predefined as abnormal. Seven patients had operations, and prosthetic obstruction was confirmed in all. All patients had higher pulmonary pressures (p less than 0.001) before valve replacement. Clinical presentation was variable; however, all those with proved prosthetic thrombosis had a fulminant course and distinctive velocity curves on Doppler. In the 75 patients predefined as normal, calculated valve area (2.3 +/- 0.6 cm2, mean +/- SD, range 1.3 to 3.7 cm2) and mean gradient (4.9 +/- 1.7 mm Hg, range 1.5 to 9.5 mm Hg) were widely spread and were independent of prosthetic size greater than or equal to 27 mm. Clinically 37 of 75 patients were moderately to severely limited. Mean gradient above 5 mm Hg was associated with a higher incidence of chronic atrial fibrillation (p less than 0.05), significant tricuspid regurgitation, failure of the right side of the heart, and significant functional limitation (p less than 0.02 for all). In the aortic position (75 valves) peak gradients were 28.2 +/- 15 mm Hg (8 to 80 mm Hg). Mean gradients were 18 +/- 9.6 mm Hg (6.5 to 46.5 mm Hg). Averaged gradients derived from the average of peak and late systolic gradients were 22.4 +/- 12.7 mm Hg (6 to 62 mm Hg). In all five abnormal patients (two with endocarditis and three with hemodynamic decompensation) but also in 18 of 70 clinically normal valves, peak gradients were greater than or equal to 36 mm Hg (ranges 36 to 65 mm Hg in both). Gradients were unrelated to symptoms or to the duration of the valve in situ (3 weeks to 20 years). Gradients correlated with prosthetic size (r = 0.57) and were higher (p less than 0.001) across small (19 to 23 mm) versus large (25 to 31 mm) valves. Regurgitation was present in 40% of the mitral prostheses. It was detected in 32% of the mitral prostheses defined as normal and was estimated as mild in most. Aortic regurgitation was present in all five abnormal aortic prostheses, significant in four, and in 26 of the valves (37%) defined as normal, significant in two.(ABSTRACT TRUNCATED AT 400 WORDS)

Validation of continuous-wave Doppler echocardiographic measurements of mitral and tricuspid prosthetic valve gradients: a simultaneous Doppler-catheter study

For patients with stenotic native valves, the modified Bernoulli equation (delta P = 4V2) may be applied to Doppler-measured transvalvular velocities to yield an accurate estimate of transvalvular gradients. Although it would be useful if the same approach could be used for those with stenotic prosthetic valves, no previous study has validated the Doppler technique in this setting. We therefore recorded simultaneous continuous-wave Doppler flow profiles and transvalvular manometric gradients in 12 catheterized patients in whom all atrial and ventricular pressures were directly measured (transseptal left atrial catheterization and transthoracic ventricular puncture were performed where necessary). A total of 13 prostheses were studied: 11 mitral (seven porcine, three Starr-Edwards, and one Björk-Shiley) and two tricuspid (one porcine and one Björk-Shiley). The Doppler-determined mean gradient was calculated as the mean of the instantaneous gradients (delta P = 4V2) at 10 msec intervals throughout diastole. The correlation of simultaneous Doppler (DMG) and manometric mean gradients (MG) for the whole group (n = 13) demonstrated a highly significant relationship (MG = 1.07 DMG + 0.28; r = .96, p = .0001). The correlation was equally good for porcine valves alone (n = 8) (MG = 1.06 DMG + 0.55; r = .96, p = .001) and for mechanical valves alone (n = 5) (MG = 1.06 DMG - 0.04; r = .93, p = .02). In a subset of patients without regurgitation (n = 8), prosthetic valve areas were estimated by two Doppler methods originally described by Holen and Hatle, as well as by the invasive Gorlin method. As expected from theoretical considerations, a close correlation was not demonstrated between results of the Gorlin method and those of either Hatle's Doppler method (r = .65, fp = NS) or Holen's method (r = .14, p = NS). Comparison of the results of the two Doppler methods yielded a somewhat closer correlation (r = .73, p less than or equal to .05). These results suggest that in patients with disk-occluder, ball-occluder, and porcine prosthetic valves, Doppler estimates of transvalvular gradients are virtually identical to those obtained invasively.

Non-invasive assessment by Doppler ultrasound of 155 patients with bioprosthetic valves: a comparison of the Wessex porcine, low profile Ionescu-Shiley, and Hancock pericardial bioprostheses

One hundred and fifty five patients with 167 bioprosthetic valves (68 Wessex porcine, 54 Hancock pericardial, and 45 low profile Ionescu-Shiley pericardial valves) were studied by Doppler ultrasound. Valve gradients were calculated from the mitral and aortic flow velocities by the modified Bernoulli equation. Mean mitral gradients were significantly smaller across the Ionescu-Shiley valves than across the Wessex porcine or Hancock pericardial valves. Mitral pressure half time was, however, significantly longer in the Hancock pericardial than in the Wessex porcine or Ionescu-Shiley valves. No significant differences were seen among the groups of aortic bioprostheses, though the comparable size of Wessex porcine valves showed significantly higher gradients. Bioprosthetic regurgitation was detected in 13 of 103 mitral and 11 of 59 aortic valves, though it was suspected clinically in only 12 mitral and six aortic bioprostheses. Doppler ultrasound is a repeatable non-invasive method of acquiring haemodynamic information in vivo from a variety of bioprostheses and it can detect bioprosthetic regurgitation at an early stage.

Doppler echocardiographic evaluation of Hancock and Björk-Shiley prosthetic values

Doppler echocardiographic characteristics of normally functioning Hancock and Björk-Shiley prostheses in the mitral and aortic positions were studied in 50 patients whose valvular function was considered normal by clinical evaluation. Doppler studies were also performed in 46 patients with suspected malfunction of Hancock and Björk-Shiley valves and who subsequently underwent cardiac catheterization. Mean gradients were estimated for both mitral and aortic valve prostheses and valve area was calculated for the mitral prostheses. Doppler prosthetic mitral valve gradient and valve area showed good correlation with values obtained with cardiac catheterization (r = 0.93 and 0.97, respectively) for both types of prosthetic valves. The correlation coefficient (r = 0.93) for mean prosthetic aortic valve gradient was also good, although Doppler echocardiography overestimated the mean gradient at lower degrees of obstruction. Regurgitation of Hancock and Björk-Shiley prostheses in the mitral and aortic positions was correctly diagnosed. These results suggest that Doppler echocardiography is a reliable method for the characterization of normal and abnormal prosthetic valve function.

Hemodynamic differentiation of pathologic and physiologic stenosis in mitral porcine bioprostheses

Porcine bioprostheses are physiologically stenotic valves. Degenerative calcification leading to pathologic stenosis is an increasingly recognized serious late complication of mitral valve replacement with a porcine bioprosthesis. Hemodynamic differentiation of pathologic from physiologic stenosis is important for identification of porcine bioprosthetic valve dysfunction. In 42 patients with a normal Hancock porcine bioprosthesis (standard model, sizes 27 to 33 mm), mean diastolic flow (65 to 461 ml/s), mean gradient (2.0 to 13.4 mm Hg) and effective orifice area (1.1 to 4.4 cm2) were determined at rest, during epicardial pacing (90, 110 and 130/min) and with isoproterenol infusion. A statistically significant increase in mean gradient occurred with increases in flow and decreases in valve size (p less than 0.05). Effective orifice area increased significantly as flow rate increased and as valve size increased (p less than 0.05). These measurements were compared with those in 16 patients with pathologically confirmed porcine bioprosthetic valve stenosis: 8 patients with reoperation (1.1% per patient-year) 3 to 8.5 years after mitral valve replacement and 8 previously reported abnormal cases. Stenotic failure rate was inversely related to valve size (2.1, 1.4, 0.5 and 0% per patient-year for sizes 27 to 33 mm). Stenotic and normal bioprostheses were not accurately differentiated on the basis of a single value for gradient or effective orifice area. A mathematical model that related flow to the square root of the mean gradient allowed complete separation of stenotic from normal prosthetic valve function, after valve size was accounted for and normal confidence limits were established (r = 0.74 to 0.94, sizes 27 to 33, p less than 0.0001). The effective orifice area-flow relation did not provide accurate differentiation of abnormal from normal function. Thus, normal mitral bioprostheses have significant transvalvular gradients whose magnitude depends on flow. Risk of stenotic failure is increased in the smaller valves, which have a larger gradient at implantation. Differentiation of pathologic from physiologic stenosis cannot be made on the basis of a single value for gradient or effective orifice area. Accurate hemodynamic differentiation is achieved by relating mean gradient to mean diastolic flow rate and valve size.

Determination of pressure gradient in the Hancock mitral valve from noninvasive ultrasound Doppler data

The accuracy with which the pressure gradient in the Hancock mitral valve can be determined from noninvasive ultrasound Doppler data was explored in a study of eight adult patients. The mean manometric pressure gradient (delta PM) was determined by performing simultaneous left atrial and left ventricular catheterization. The mean diastolic pressure gradient was also determined from noninvasive ultrasound data (delta PU). Identical cardiac cycles were used to compare delta PM and delta PU. In the eight patients delta PM ranged from 3.0 to 9.0 mmHg and cardiac output from 3.7 to 5.5 l/min. The difference delta PM-delta PU was 0.3 +/- 0.9 mmHg (mean +/- SD). The results thus indicated that noninvasive ultrasound can determine the mean diastolic gradient in the Hancock mitral valve with an accuracy which approaches that attained with conventional manometric methods.

Determination of pre- and postoperative flow obstruction in patients undergoing closed mitral commissurotomy from non-invasive ultrasound Doppler data and cardiac output

A non-invasive ultrasound Doppler system and indwelling thermodilution catheter system were used to determine the pre- and postoperative mitral flow obstruction in eight adults undergoing closed mitral commissurotomy. The effective valve area (Ae) was used as a measure of the obstruction. In the eight patients Ae was 1.08 +/- 0.34(SD) cm. 2 preoperatively and increased to 1.71 +/- 0.43(SD) cm. 2 postoperatively. The technique used in the investigation appears useful for the evaluation of surgical procedures designed to reduce the mitral flow obstruction.

An ultrasound Doppler technique for the noninvasive determination of the pressure gradient in the Björk-Shiley mitral valve

The accuracy in determining the pressure gradient in the Björk-Shiley mitral implant from noninvasive ultrasound Doppler data was explored in nine adult patients. Manometric and ultrasound data were collectd simultaneously, and identical diastolic periods were used to compare the manometric gradient (delta Pm) with the gradient obtained from ultrasound data (delta Pu). In the nine patients the mean diastolic value of delta Pm ranged from 2-12.5 mm Hg and the difference between the mean diastolic values of delta Pm and delta Pu was 0.3 +/- 1.0 mm Hg(SD). The results of the investigation indicated that the method is accurate and reliable in the nonivasive determination of the mean diastolic gradient in the Björk-Shiley mitral implant.