Validation and applications of indexed aortic prosthetic valve areas calculated by Doppler echocardiography

Functional hemodynamic assessment of the 21-mm and 23-mm CarboMedics Top Hat aortic prosthetic valve

Between 1993 and 1996 the CarboMedics Top Hat supraannular aortic valve was implanted in 41 patients at the Wessex Cardiothoracic Centre (age, 39 to 74 years; mean, 61.3+/-8.9 years). Comparisons of annular dimensions made at surgery indicate that conventional annular valve replacement would have required at least a size smaller valve. This was particularly marked when a prosthetic mitral valve was in place. Operative mortality was 2.4%. There were also three late deaths. Echocardiography before and after symptom-limited treadmill testing has been performed in 21 patients. The mean time to follow-up was 16.1 months. The Doppler-derived indices of forward flow pre- and postexercise were expressed as mean+/-standard deviation. For 23-mm valves the values were: peak valve gradient 21.43+/-7.46 mm Hg and 35.86+/-14.4 mm Hg, aortic valve area 1.13+/-0.39 cm2 and 1.24+/-0.54 cm2. For 21-mm valves the values were: peak valve gradient 24.84+/-8.2 mm Hg and 31.29+/-5.84 mm Hg, aortic valve area 1.08+/-0.44 cm2 and 0.95 +/-0.2 cm2. The Top Hat valve has a good hemodynamic profile at rest and during exercise. Surgical considerations make it particularly useful in patients with a small aortic annulus and in patients undergoing combined aortic and mitral valve replacement.

Hemodynamic performance of the 21-mm St. Jude BioImplant prosthesis using dobutamine Doppler echocardiography

This study examines the hemodynamic performance of small size St. Jude BioImplant aortic prostheses using dobutamine echocardiography. Eleven patients (3 women, mean age 75 years) who had undergone aortic valve replacement with a size 21-mm St. Jude BioImplant aortic prostheses at 10.8 +/- 5.1 months (SD) previously were studied. Dobutamine infusion was started at a rate of 5 microg/kg/min and increased to 10 microg/kg/min, and subsequently to 20 microg/kg/min at 15-minute intervals. Pulsed and continuous-wave Doppler studies were performed at rest and at the end of each stage. Effective orifice area, mean gradient, and the performance index across each prosthesis were calculated and cardiac output was determined by Doppler measurement of flow in the left ventricular outflow tract. Stress dobutamine increased heart rate and cardiac output by 51% and 56%, respectively (both p <0.0001), and the mean transvalvular gradient increased from 30.1 +/- 7.5 mm Hg at rest to 49.3 +/- 11.5 mm Hg at maximum stress (p <0.0005). The performance index increased progressively from 0.29 +/- 0.05 at rest to 0.40 +/- 0.10 at maximum stress (p <0.0005). Regression modeling analyses demonstrated that the maximum stress gradient was independent of all variables except the resting gradient (p = 0.03). Body surface area had no effect on the changes in cardiac output, effective orifice area, or transprosthetic gradient at maximum stress. Thus, these data demonstrate that the size 21-mm St. Jude BioImplant prosthesis exhibits suboptimal hemodynamic performance with transvalvular gradients consistent with mild to moderate aortic stenosis, both at rest and under stress conditions.

Evaluation of normal hemodynamic profile of CarboMedics prosthetic valves by Doppler echocardiography

The authors investigated 163 CarboMedics bileaflet prosthetic valves--81 mitral prostheses (MP), and 82 aortic prostheses (AP)--to determine acceptable pressure gradients across normally functioning prostheses and effective mitral valve orifice (MVO) area by Doppler echocardiography. In MP, the mean gradient was 3.6+/-1.7 mm Hg, peak transmitral gradient was 8.7+/-3.7 mm Hg, and mean effective valve area was 2.3+/-0.7 cm2. There was a significant overlap in mean and peak transaortic gradients even with valves of the same size. In AP, the mean gradient was 14.7+/-5.1 mm Hg and peak pressure gradient was 26.1+/-8.2 mm Hg. They observed a weak inverse correlation between valve size and gradients in AP. Mean and peak pressure gradients tended to be higher with smaller valve sizes, but differences were statistically significant (P < 0.5) only when they compared the smallest vs the largest valves. Trivial to mild regurgitation was detected in 28.4% of MP and 54.8% of AP. From the data they conclude that CarboMedics valves offer relatively little resistance to forward flow, both in the mitral and aortic positions, and their hemodynamic profile is comparable to that of the St. Jude bileaflet valves described in published literature.

Aortic and mitral valve replacement with reconstruction of the intervalvular fibrous body

OBJECTIVE

The intervalvular fibrous body between the aortic and mitral valves can be damaged by infective endocarditis, degenerative calcification, or multiple previous heart valve operations, making double valve replacement difficult. We have managed this problem by approaching the aortic and mitral valves through the aortic root and the dome of the left atrium. After excising the aortic valve, the diseased fibrous body, and the mitral valve, we suture a properly tailored patch of Dacron fabric or bovine pericardium to the lateral and medial fibrous trigones and to the aortic root, reestablishing the aortic and mitral anuli. A prosthetic mitral valve is implanted and a separate patch is used to close the left atriotomy before implantation of a prosthetic aortic valve. This study was undertaken to determine the efficacy of this operation.

METHODS

Forty-three patients underwent reconstruction of the intervalvular fibrous body during aortic and mitral valve replacement because of infective endocarditis with abscess in 14 patients, extensive calcification in 9, lack of fibrous tissue because of multiple previous operations in 10, and to enlarge the aortic and mitral anuli in 10. The group comprised 18 men and 25 women with a mean age of 58 +/- 12 years. Thirty-two patients had had one or more previous heart valve replacements. All patients were in New York Heart Association functional classes III and IV, and 9 patients were in shock before the operation.

RESULTS

Seven operative deaths occurred (16%). Early prosthetic valve endocarditis developed in two patients and necessitated reoperation. Follow-up extended from 4 to 108 months, with a mean of 38 months. No patient was lost to follow-up. Six late deaths occurred. The actuarial survival at 6 years was 56% +/- 6%. A Doppler echocardiographic study revealed normal prosthetic valve function and anatomically intact anuli in all 30 long-term survivors.

CONCLUSIONS

Reconstruction of the intervalvular fibrous body during aortic and mitral valve replacement is a satisfactory operative approach in patients with complex valve annular pathology.

Aortic valve replacement with patch enlargement of the aortic annulus

BACKGROUND

Aortic annulus enlargement has long been advocated for the placement of valve prostheses larger than otherwise would have been possible. Little information exists, however, on the short- and long-term outcome of this surgical procedure.

METHODS

We performed a retrospective review of 530 patients enrolled in a registry for patients who underwent aortic valve replacement using the Hancock II bioprosthesis and were followed up prospectively over the course of 11 years at a single institution. In an effort to avoid prosthetic valve-patient mismatch, the aortic annulus was enlarged in 98 patients (18%). Short- and long-term outcome was analyzed.

RESULTS

Enlargement of the aortic annulus during aortic valve replacement increased the operative mortality rate from 3.5% to 7.1%, but this difference did not reach statistical significance (p = 0.10). The long-term survival of patients who had annulus enlargement was similar to that of patients who did not. Because there were differences in the clinical profile of patients who had annulus enlargement and those who did not, a case-control study was carried out. This study showed similar long-term survival, freedom from valve-related and cardiac death, and combined end points in the two groups of patients.

CONCLUSION

Aortic annulus enlargement increased the operative mortality of aortic valve replacement. However, patients who underwent enlargement of a small aortic annulus had long-term survival and freedom from cardiac and valve-related death comparable to those of patients who received larger aortic prostheses.

Extent and pattern of regression of left ventricular hypertrophy in patients with small size CarboMedics aortic valves

OBJECTIVE

To assess the extent and pattern of regression of left ventricular hypertrophy after valve replacement for aortic stenosis, we studied 26 patients receiving either 19 or 21 mm CarboMedics valves (group I, 13 patients) or either 23 or 25 mm CarboMedics valves (group II, 13 patients). The studies were done before the operation and after 3 years, and results were compared with those of 10 control patients.

METHODS

Left ventricular end-diastolic and end-systolic diameters and volumes, ejection fraction and fractional shortening, and interventricular septum and posterior wall thickness were measured. The ratio between interventricular septum and posterior wall thickness, the ratio between left ventricular wall thickness and left ventricular chamber radius, and the left ventricular mass were then calculated.

RESULTS

At follow-up there was a significant reduction in the left ventricular mass, interventricular septum, and posterior wall thickness for both patient groups (p < 0.01). However, only the posterior wall thickness reached normal values; the interventricular septum and the left ventricular mass indices were still significantly greater than in the control group (p < 0.01). Because of the incomplete regression of interventricular septal hypertrophy, the ratio between interventricular septum and posterior wall thickness was similar between both patient groups but it was significantly higher than in control subjects (p < 0.01). The ratio between wall thickness and chamber radius did not decrease significantly in group II patients, in whom it remained above the control values.

CONCLUSION

Having a bileaflet aortic prosthesis of one size larger did not seem to significantly influence the pattern and the extent of regression of left ventricular hypertrophy after an intermediate period of follow-up.

Dynamic evaluation of the 21-mm Medtronic Intact aortic bioprosthesis by dobutamine echocardiography

BACKGROUND

High residual transvalvular gradients have been reported with the use of small Medtronic Intact aortic valve prostheses. The aim of this study was to evaluate the hemodynamic performance of 21-mm prostheses using dobutamine Doppler echocardiography.

METHODS

Ten patients (7 women; mean age, 79 years) who had undergone aortic valve replacement with 21-mm Medtronic Intact prostheses 19.1 +/- 9.9 (standard deviation) months previously were studied. Dobutamine infusion was started at a rate of 5 microg x kg(-1) x min(-1) and increased to 10 and 20 microg x kg(-1) x min(-1) at 15-minute intervals. Pulsed and continuous-wave Doppler studies were performed at rest and at the end of each stage. Effective orifice area, performance index, and discharge coefficient of each valve were calculated, and peak and mean velocity and pressure drop across the prostheses were measured. Cardiac output was determined by Doppler measurement of flow in the left ventricular outflow tract.

RESULTS

Dobutamine stress increased heart rate and cardiac output by 68% and 65%, respectively (both p < 0.005), and mean transvalvular gradient increased from 19.1 +/- 5.1 mm Hg at rest to 33.2 +/- 7.7 mm Hg at maximum stress (p < 0.0001). Regression analyses demonstrated that maximum-stress gradient was independent of all variables except resting gradients (p < 0.004). Body surface area had no effect on the changes in cardiac output, effective orifice area, or transprosthetic gradient at maximum stress.

CONCLUSIONS

These data show that the 21-mm Medtronic Intact aortic prosthesis exhibits acceptable hemodynamic performance. Transvalvular gradients remained within a clinically acceptable range, both at rest and at maximum stress. Moreover, overall hemodynamic performance suggests that patient-prosthesis mismatch is unlikely to be a problem of clinical importance when this prosthesis is used.

Hemodynamic performance of small aortic valve bioprostheses: is there a difference?

BACKGROUND

There is the potential for left ventricular outflow obstruction when small aortic valve bioprostheses are employed in normal-sized or large adults. It has been hoped that bovine pericardial valves would improve hemodynamic performance in the smaller tissue valve sizes.

METHODS

To determine in vivo hemodynamic performance of heterograft aortic valve prostheses, we analyzed echocardiographic data from patients receiving 21- or 23-mm Carpentier-Edwards pericardial, Medtronic Intact, and Carpentier-Edwards porcine bioprostheses. In addition, data from 19-mm Carpentier-Edwards pericardial valves were included for comparison of hemodynamic performance between valve sizes. Doppler echocardiography was performed in 151 patients within 2 weeks of operation. Left ventricular outflow gradient was derived from continuous Doppler measurements of flow velocity, and effective orifice area was calculated by the continuity equation.

RESULTS

There were statistically significant differences in hemodynamic performance of different sized prostheses for each valve type (effective orifice area, p < 0.01; valvular gradient, p < 0.03). There were, however, no significant differences in effective orifice area or mean gradient for different valve types within each size category.

CONCLUSIONS

The in vivo hemodynamic performance of these three different aortic valve heterograft bioprostheses is similar. Patient-prosthesis mismatch with heterograft prostheses, as demonstrated by the indexed effective orifice area can be avoided by appropriate sizing and use of annular enlarging techniques when necessary.

Doppler echocardiographic assessment of normally functioning Starr-Edwards, carbomedics and Carpentier-Edwards valves in aortic position

Doppler echocardiography was performed in 168 normally functioning aortic prostheses to determine acceptable pressure gradients across the commonly used valves and to establish the relationship between valve size and gradients. There were 82 Carbomedics (C), 63 Starr-Edwards (SE), and 23 Carpentier-Edwards (CE) valves. Peak and mean gradients across the prostheses were measured by use of the simplified Bernoulli equation. CarboMedics valve had a lower peak and mean gradient than Starr-Edwards and Carpentier-Edwards valve (P < 0.05 when compared with Starr-Edwards). The authors observed a weak inverse correlation between valve size and peak and mean gradients in CarboMedics and Carpentier-Edwards valves but not in the Starr-Edwards valve. For the CarboMedics valve the peak pressure gradient (PPG) was 26.1 +/- 8.2 mm Hg and the mean pressure gradient (MPG) was 14.7 +/- 5.1 mm Hg; in Starr-Edwards valve the PPG was 32.8 +/- 9.1 mm Hg and the MPG was 19.5 +/- 5.6 mm Hg; in the Carpentier-Edwards valve the PPG was 28.7 +/- 10.1 mm Hg and the MPG was 16.1 +/- 5.2 mm Hg when size was not specified. The CarboMedics valves were noted to have a better hemodynamic profile in comparison with Starr-Edwards and Carpentier-Edwards prostheses.

Early in vivo experience with the Hemodynamic Plus St. Jude Medical heart valves in patients with narrowed aortic annulus

BACKGROUND

Small aortic orifice primarily resulted in heart prosthesis mismatch in a significant number of patients. The Hemodynamic Plus (HP) series of St. Jude Medical heart valves represents an interesting innovation, allowing a larger valve orifice area with an equivalent tissue annulus diameter.

METHODS

Hemodynamic characteristics of the 21-mm HP St. Jude Medical valve were prospectively compared with those of the standard 21-mm and 23-mm St. Jude Medical valves in three groups of 22 patients. Patients were selected from a database to be rigorously matched for age, sex, body surface area, functional class, underlying lesion, native valve opening area, left ventricular function, and preoperative peak and mean valve gradients. Postoperative evaluation (follow-up ranging from 3 to 24 months; mean, 11.5 months) included clinical examination and echocardiographic studies.

RESULTS

There was no operative mortality or significant perioperative complications. Short-term clinical follow-up was marked by a complete absence of valve-related complications. Presently, all but 1 patient in the 21-mm HP group and 2 in the 21-mm standard group are in New York Heart Association functional class I. Doppler echocardiography-derived mean and maximal pressure gradients were significantly lower in the 21-mm HP group (8.1 +/- 1.9 and 16.4 +/- 3.4 mm Hg) than in the 21-mm standard group (13.4 +/- 3.9 and 21.2 +/- 4.3 mm Hg; p = 0.002 and p = 0.0004, respectively), confirming the better hemodynamic performance already described in in vitro studies. Pressure gradients did not differ significantly between the 21-mm HP and the 23-mm standard groups. The 21-mm HP valve demonstrated the highest performance index; 0.66 +/- 0.08, compared with 0.49 +/- 0.09 for the 21-mm standard valve (p < 0.001) and 0.59 +/- 0.07 for the 23-mm standard valve (p < 0.001).

CONCLUSIONS

In vivo hemodynamic performance of the 21-mm HP valve corresponds closely to that of the 23-mm standard valve and is substantially better than that of the 21-mm standard valve. The 21-mm HP St. Jude Medical valve demonstrates excellent hemodynamic characteristics and can be recommended in normal-sized adult patients with narrow aortic root. This valve will minimize the need for aortic annulus enlargement.

Echocardiography and Doppler assessment of prosthetic heart valves with transesophageal echocardiography

This article examines the use of transesophageal echocardiography (TEE) in the assessment of prosthetic heart valves. A summary of the commonly used artificial valves and their physiologic regurgitant flow patterns, as identified by color Doppler imaging, is presented. The hemodynamic evaluation of prosthetic valve stenosis using Doppler techniques is reviewed, and the diagnostic utility of TEE in identifying the complications of cardiac prostheses is discussed.

Comparison of hemodynamic performances of St. Jude Medical and CarboMedics 21 mm aortic prostheses by means of dobutamine stress echocardiography

Dobutamine stress Doppler echocardiography was used to compare the hemodynamic performance of two small aortic bileaflet prostheses. Nineteen patients (14 female, mean age 64 years) who had undergone aortic valve replacement with 21 mm bileaflet valve prostheses (St. Jude Medical valve, n = 9, or CarboMedics valve, n = 10) were studied. Dobutamine infusion was started at a rate of 5 micrograms.kg-1.min-1 and increased to 10 and 20 micrograms.kg-1.min-1 at 15-minute intervals. Under maximum stress, heart rate and cardiac output increased by 70% and 120%, respectively, and mean arterial blood pressure decreased by 9%. Pulsed-wave and continuous-wave Doppler studies were performed at rest and at the end of each stage. Velocity ratio, effective orifice area, performance index, and discharge coefficient of the valve were calculated, and peak and mean velocities and pressure drops across the prostheses were measured. Dobutamine infusion produced similar increases in cardiac output in all patients. Effective orifice areas, discharge coefficients, and performance indexes were comparable for the two valve groups both at rest and maximum stress. Transvalvular velocities and pressure drops were also similar in the two valve groups. Transvalvular pressure drops were also comparable in patients with large body surface area. Dobutamine stress echocardiography is useful in the evaluation of the hemodynamic performance of prosthetic heart valves. St. Jude Medical and CarboMedics 21 mm prostheses have equally favorable hemodynamic performances in most patients under conditions of high cardiac output.

Evaluation of the hemodynamic performance of small CarboMedics aortic prostheses using dobutamine-stress Doppler echocardiography

BACKGROUND

The well-known correlation between prosthetic valve orifice area and transvalvular gradients has raised concerns about the presence of significant residual gradients when the size of the prosthesis that can be implanted is limited by the presence of a small aortic annulus.

METHODS

Dobutamine-stress Doppler echocardiography was used to evaluate the hemodynamic performance of small CarboMedics aortic prostheses (19 mm and 21 mm) in 18 patients (16 women; mean age, 64 years) who had undergone aortic valve replacement 23.5 +/- 19 months (standard deviation) previously. Dobutamine infusion was started at a rate of 5 micrograms.kg-1.min-2 and increased to 10 and 20 micrograms.kg-1.min-2 at 15-minute intervals. Pulsed and continuous wave Doppler studies were performed at rest and at the end of each stage. Effective orifice area, performance index, and discharge coefficient of both valves were calculated, and peak and mean velocity and pressure drop across the prostheses were measured.

RESULTS

Heart rate and cardiac output increased by 74% and 94%, respectively, and mean arterial blood pressure decreased by 9% at maximum stress. Effective orifice area, discharge coefficient, and performance index were comparable in both valve sizes at rest and maximum stress. Also, there was no significant difference in mean transvalvular pressure drop (gradient) for 19-mm and 21-mm prostheses at rest (8.1 +/- 8.4 and 4.8 +/- 3.8 mm Hg) or maximum stress (15.1 +/- 14.2 and 8.8 +/- 5.8 mm Hg, respectively). No significant correlation could be demonstrated between transvalvular pressure drop and patient's body surface area.

CONCLUSIONS

These data show that 19-mm and 21-mm CarboMedics aortic prostheses exhibit equally favorable hemodynamic performance with minimal pressure gradient, both at rest and under stress conditions.

Substitution of left ventricular outflow tract diameter with prosthesis size is inadequate for calculation of the aortic prosthetic valve area by the continuity equation

It remains uncertain whether prosthetic ring size should be used interchangeably with measured left ventricular outflow tract (LVOT) diameter in the continuity equation to estimate the aortic prosthetic valve area by transthoracic Doppler echocardiography. To determine the difference in area caused by this substitution, the area of the prosthetic valve was calculated in 143 patients with aortic bioprostheses by use of the standard continuity equation with the measured LVOT diameter (LVOT method) and then with the bioprosthetic size (size method). Compared with known in vitro prosthetic valve areas, the LVOT method (r = 0.86; standard error of the estimate +/- 0.16 cm2; p < 0.001) was more accurate than the size method (r = 0.74; standard error of the estimate +/- 0.40 cm2; p < 0.001). The prosthetic valve area estimated by the size method overestimated the area estimated by the LVOT method by an average of 15% +/- 23% (p < 0.001). This difference in area between the two methods has increased with the interval since implantation of the bioprosthesis (p = 0.01). It is concluded that prosthetic size should not be used instead of LVOT diameter during calculation of aortic prosthetic valve area. This restriction is particularly important in patients with older bioprosthesis.

Echocardiographic assessment of artificial heart valves: British Society of Echocardiography position paper

Images

Postoperative Doppler echocardiographic evaluation in different sizes of Medtronic-Hall, Biocor and Carpentier-Edwards S.A.V. prosthetic aortic valves

Doppler echocardiography was performed on 108 patients 4-15 days after implantation of a Medtronic-Hall, Biocor or Carpentier-Edwards S.A.V. prosthetic aortic valve because of aortic stenosis. Significant correlation was found between the in vitro (maker-declared) and the Doppler-estimated effective prosthetic valve orifice area (r = 0.70, p < 0.01). Doppler-estimated prosthetic valve orifice area, but not transprosthetic blood velocities, discriminated between different sizes of Medtronic-Hall and Biocor valves. The effective orifice area in these valves was 57% of the in vitro area, but in Carpentier-Edwards valves it was only 43%. Transprosthetic blood velocity was inversely related to orifice area in men, but not in women, who also had longer duration of systole and better preservation of systolic left ventricular function. The data suggest that the effective prosthetic valve areas found in patients are significantly smaller than the experimental in vitro areas. Prosthesis size and type, anatomic and hemodynamic variables and gender are important in Doppler estimation of effective valve area.

Quantitative hemodynamics by Doppler echocardiography: a noninvasive alternative to cardiac catheterization

Doppler echocardiography has greatly enhanced the information provided by two-dimensional echocardiography. By providing information concerning pressure gradients, intracardiac pressures, volumetric flow, and diastolic filling of the heart, most hemodynamic information that in the past could be obtained only from cardiac catheterization can now be provided accurately and noninvasively by Doppler echocardiography. Future developments in instrument technology and understanding of the various Doppler velocity curves should further aid in the ability to obtain a complete, noninvasive hemodynamic assessment of the patient with cardiac disease.

Echocardiographic description of the CarboMedics bileaflet prosthetic heart valve

OBJECTIVES

The aim of this study was to describe the echocardiographic appearance of the normal CarboMedics prosthesis in the aortic and mitral positions.

BACKGROUND

Echocardiography is the standard method of assessing prosthetic valves. However, new valve designs may still be marketed without an accompanying echocardiographic description. The CarboMedics prosthesis is in widespread use, but few noninvasive hemodynamic data have been published.

METHODS

Echocardiography was performed in 147 patients with a total of 96 normally functioning CarboMedics prostheses in the aortic position and 75 in the mitral position; in 24 patients, valves were implanted in both positions. The following variables were measured: peak and mean transvalvular velocities, peak and mean instantaneous gradient estimated from the modified Bernoulli equation, aortic acceleration slope, pressure half-time, transvalvular flow and effective orifice area using the continuity equation. Patterns of regurgitation were observed by transthoracic study in all valves and by transesophageal study in selected mitral valve prostheses.

RESULTS

For the aortic valve prostheses, estimated mean gradient ranged between 6 and 19 mm Hg. Effective area differed markedly among the anulus diameters (p < 0.001), with a mean value of 1 cm2 for the 19-mm valve and 2.6 cm2 for the 29-mm valve. For the mitral valve prostheses, mean gradient ranged from 3 to 7 mm Hg. There were a total of four washing leaks, one on either side of each pivotal point, and these lasted throughout systole or diastole. One jet was commonly more prominent than the other three.

CONCLUSIONS

The CarboMedics prosthesis offered relatively little resistance to forward flow except at small anulus diameters. The washing jets were prominent and would be easy to misdiagnose as a sign of paraprosthetic regurgitation.

Assessing prosthetic heart valve function. Value of Doppler echocardiography and patient/prosthetic valve identity and follow-up card

Doppler echocardiography is being used increasingly in the follow-up of patients with valvular heart prostheses because it provides unique hemodynamic information about flow through prosthetic valves. A baseline checkup about 3 months after implantation is now recommended. We therefore now supply each patient with an identity and follow-up card for each particular prosthesis.

Hemodynamic evaluation by Doppler echocardiography of small (less than or equal to 21 mm) prostheses and bioprostheses in the aortic valve position

To assess resting hemodynamics of an unselected group of patients with prostheses or bioprostheses sized less than or equal to 21 mm implanted into the aortic valve position during a 7-year period, 46 of 50 eligible patients were examined by Doppler echocardiography. The valves were Carpentier-Edwards (CE) supraannular 21 mm (n = 8), Medtronic-Hall (MH) 20 mm (n = 8) and 21 mm (n = 21), and the rest (n = 9) were other valves with only 1 to 3 patients in each group. Gradients, valve areas and dimensionless obstruction indexes (ratio of subvalvular/valvular velocities and velocity time integrals) were compared. By analysis of variance, gradients did not differ significantly between the CE supraannular 21 mm, the MH 20 and 21 mm prostheses (peak/mean 25 +/- 8/14 +/- 5, 31 +/- 13/16 +/- 6 and 25 +/- 10/13 +/- 5 mm Hg; p = not significant). Only 2 patients had a mean gradient greater than 25 mm Hg. The valve area was slightly larger for the MH 21 mm group compared with the CE supraannular 21 mm group (1.34 +/- 0.15 vs 1.16 +/- 0.14 cm2, p less than 0.05). The dimensionless obstruction indexes did not differ (CE supraannular 21 mm 0.36 +/- 0.07/0.40 +/- 0.07 (velocities/velocity time integrals), MH 20 mm 0.40 +/- 0.12/0.47 +/- 0.12, MH 21 mm 0.38 +/- 0.05/0.44 +/- 0.06; p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical experience with the zero-pressure-fixed Medtronic Intact bioprosthetic valve

The Medtronic Intact porcine valve bioprosthesis was inserted in 219 patients between 1983 and 1990. Mean patient age was 52 years and mean follow up 33.3 months. There was only one example of structural valve degeneration at 25 months, giving an actuarial freedom of 99% at 6 years. Reoperation was performed in 7 patients. Freedom from reoperation was 93% at 6 years, from infective endocarditis 96%, from thrombo-embolism 91% and from valve-related complications 86%. Doppler echocardiography revealed non-significant incompetence in 8 instances and mild leaflet thickening of 5 valves. Valve gradients and areas were unchanged between two Doppler studies 2 years apart of valves in the mitral position, and were reduced in valves in the aortic position from 17 +/- 5.2 mmHg to 13 +/- 2.8 mmHg (P = 0.02). These medium-term results are considered very encouraging. The theoretical considerations underlying the use of zero-pressure glutaraldehyde fixation, which is the technique used for the Intact valve, are detailed elsewhere in this issue [1]. The Intact valve is treated with toluidine blue as a calcium-retarding agent and is mounted on a Dacron-covered acetyl copolymer (Celcon) stent with flexible posts. The normal profile of the porcine aortic valve is maintained.

Hemodynamic evaluation of the CarboMedics prosthetic heart valve in the aortic position: comparison of noninvasive and invasive techniques

Seventy-three patients with a CarboMedics aortic bileaflet valve prosthesis were examined by Doppler ultrasonography, and 27 of them were also assessed by transseptal catheterization. The ultrasonic mean systolic gradient was 17.1 +/- 5.6 mm Hg for valve size 19 mm, falling gradually with increasing valve size to 6.8 +/- 2.5 mm Hg for size 27 mm. The catheter mean systolic gradient was consistently smaller than the ultrasonic gradient (4.3 +/- 4.8 mm Hg), but Tobit regression analysis showed a significant association between the two methods. In all patients both methods revealed negligible to small amounts of retrograde leakage, which is assumed to be a normal finding for this valve. The effective flow areas of the valves calculated from the ultrasonic data were similar to the in vitro calculated flow areas. The hemodynamic potential of this valve is therefore completely utilized in vivo. The effective orifice area corrected for body surface area increased with increasing valve size, which demonstrates a moderate valve-patient mismatch.

The zero pressure fixed medtronic intact porcine valve: clinical results over a 6-year period, including serial echocardiographic assessment

Between 1983 and 1990, 219 patients had 224 Medtronic Intact porcine valves inserted. There were 94 aortic, 110 mitral, and 20 tricuspid valve replacements. The mean patient age was 52 years. Mean follow-up was 33.3 months and was 97.7% complete. There was only one example of structural valve degeneration occurring at 25 months, giving an actuarial freedom of 99% at 6 years. Reoperation was performed in seven patients. At 6 years, actuarial survival was 71%, freedom from infective endocarditis 96%, freedom from thromboembolism 91%, freedom from reoperation 93%, and freedom from valve-related complications 86%. Doppler echocardiography was performed in 48 of the 70 patients operated upon between August 1983 and October 1986 and who remained alive at the current review. Their follow-up averaged 4.7 (3-6.7) years. The results were compared to a similar examination performed in 1987 by the same operator. No patient had significant regurgitation. Valve gradients and areas remained the same in the two studies in the mitral position (3.8 +/- 1.33 mmHg) and the mean aortic gradient had reduced from 17 +/- 5.2 mmHg in 1987 to 13 +/- 2.8 mmHg in the current study (p = 0.02). These medium-term results are considered encouraging.

Doppler echocardiographic study of porcine bioprosthetic heart valves in the aortic valve position in patients without evidence of cardiac dysfunction

To study the natural history of the hemodynamic performance of bioprosthetic heart valves, Doppler echocardiograms were recorded in a group of clinically stable patients at 2 and 5 years after replacement of native aortic valves with bioprosthetic valves. Eighteen patients completed a 2-year and 26 patients a 5-year follow-up examination. The effective orifice areas of identical models of bioprosthetic valves (Hancock II) were determined in vitro in a left-sided heart pulse duplicator system. In vivo Doppler-derived effective orifice areas were compared with the in vitro measurements for the same valve size. At both the 2- and 5-year follow-up examinations, the Doppler-derived effective orifice area was significantly less than the in vitro area (p less than 0.0001 at each interval). Ten of 16 valves evaluated serially decreased greater than 0.20 cm2 in the Doppler-derived effective orifice area between studies. The mean decrease in effective orifice area in valves evaluated serially was 0.25 +/- 0.29 cm2 (p less than 0.005). The peak transaortic gradient increased from 21 +/- 6 to 27 +/- 8 mm Hg (p less than 0.01). The mean transaortic gradient increased from 12 +/- 4 to 15 +/- 7 mm Hg (p less than 0.05). It is concluded that serial Doppler echocardiographic studies demonstrate a deterioration in the hemodynamic performance of bioprosthetic valves over time in patients with no symptoms or signs of valvular dysfunction and that Doppler echocardiography may be useful for identifying subclinical bioprosthetic valvular dysfunction.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.