Performance of a stentless xenograft aortic bioprosthesis up to four years after implantation

Impact of Stentless Aortic Valves on Left Ventricular Function and Hypertrophy: Current Best Available Evidence

Past four decades have seen a gradual evolution in aortic valve replacement surgery. The ideal valve substitute should combine central flow, low transvalvular gradient, low thrombogenicity, durability, easy availability, resistance to infection, freedom from anticoagulation, and easy implantability. Although there are several types of valves available to replace the diseased aortic valve-autograft, allograft, xenograft, mechanical, and bioprosthetic valves-none is ideal. On one end of the spectrum is the pulmonary autograft, which comes closest to achieving these goals, but creates a double valve procedure for single valve disease, while on the other end are the mechanical valves and stented tissue valves, which allow easy "off the shelf" availability as well as easy implantability but are limited by the potential drawback of causing intrinsic obstruction to some extent because of the space occupied by the stent and sewing ring. Stentless xenograft aortic valves have been developed as a compromise between these ends of the valve spectrum. Stentless aortic valves have been reported to provide more physiologic hemodynamic behavior and cause more timely and thorough regression of ventricular hypertrophy. This review article attempts to evaluate current best available evidence from randomized controlled trials to assess the impact of stentless aortic valves on left ventricular function and hypertrophy.

The effect of sizing on the hydrodynamic parameters of the Medtronic freestyle valve in vitro

BACKGROUND

An in vitro model has been established to investigate the effect of sizing on the hydrodynamic characteristics and leaflet motion of the Medtronic Freestyle valve.

METHODS

The valves were tested in fresh porcine aortic roots. Two or three different sizes of valves were implanted in the same aortic root one after the other. The compliance of the fresh aortic and the composite roots was measured in the pressure range of 0 to 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and degree of regurgitation were measured and the effective orifice area and performance index were calculated. Leaflet motion was recorded on video.

RESULTS

The fresh aortic roots dilated by average 39.4% as the hydrostatic pressure rose from 0 to 120 mm Hg. Implantation of the Medtronic Freestyle valve did not change the distensibility of the aortic root significantly. The sizing protocol did not affect significantly the hydrodynamic performance. However, a significantly lower open leaflet bending deformation was found in the undersized valves. Regurgitation was found only at 2-mm undersized valves.

CONCLUSIONS

Leaflet motion of the Medtronic Freestyle valve in vitro was best if 1 mm undersized, and this may be beneficial to long-term durability.

Hemodynamic Comparison by Doppler Echocardiography of Valves in the Aortic Position: Value of the Continuity Equation to Assess Prosthetic Dysfunction

In 281 patients, we used Doppler echocardiography to compare the hemodynamic performance of different aortic prosthetic valves at three postoperative stages and investigated the value of the continuity equation in diagnosing aortic prosthetic obstruction. A baseline study was performed in 163 patients, a 5 +/- 2-month follow-up study was performed in 103 patients, and a 15 +/- 5-month follow-up study was performed in 65 patients. From baseline to the second study, left ventricular diastolic diameter, heart rate, and maximum (MG) and mean Doppler-derived gradient (MeG) decreased significantly, and left ventricular shortening fraction, systolic blood pressure, stroke volume, and prosthetic valvular area (PVA) increased significantly. No changes were found between the second and third studies. Thus, noninvasive hemodynamic values at the time of follow-up are reported in 171 patients: 86 with Björk-Shiley Monostrut, 27 with Carbomedics, 11 with Medtronic-Hall, 18 with Hancock modified, and 29 with Toronto valve bioprosthesis. Patients implanted with the Toronto had a larger prosthetic size (Monostrut 23 +/- 2 mm, Carbomedics 23 +/- 3 mm, Medtronic-Hall 23 +/- 2 mm, Hancock 23 +/- 2 mm, Toronto 25 +/- 2 mm, P < 0.01) despite a similar body surface area. MeG and MG were lower (MeG [in mmHg] Monostrut 12 +/- 5, Carbomedics 14 +/- 6, Medtronic-Hall 19 +/- 6, Hancock 11 +/- 4, Toronto 7 +/- 5; P < 0.01 between Toronto and all others), and PVA was greater (Monostrut 2.0 +/- 0.7 cm(2), Carbomedics 1.8 +/- 0.8 cm(2), Medtronic-Hall 1.6 +/- 0.7 cm(2), Hancock 1.7 +/- 0.5 cm(2), Toronto 2.2 +/- 0.9 cm(2); P < 0.01 between Toronto and Carbomedics, Medtronic-Hall, and Hancock), even compared with the same sizes in the other valves. A PVA of 0.9 cm(2) or less and MeG of 28 mmHg or more identified prosthetic obstruction with 100% sensitivity and 99% specificity. Hemodynamics change significantly from the early to the late postoperative state. The Toronto valve stentless porcine bioprostheses performs hemodynamically better than other valves. PVA measurement using the continuity equation may accurately identify prosthetic obstruction.

Echocardiographic assessment of aortic valve replacement with stentless porcine xenografts

Stentless porcine xenografts (SPXs) implanted in the aortic position have potential hemodynamic advantages over traditional valve prostheses because of the lack of a rigid stent. Twenty-four patients (mean age 59 years) who underwent aortic valve replacement with SPXs were studied by echocardiography early after and 26 +/- 10 months (range 8 to 40) after operation. Peak and mean gradients, as well as aortic valve area, did not change significantly from baseline (16.3 +/- 8 and 9.8 +/- 5.6 mm Hg, and 1.78 +/- 0.63 cm2, respectively) to follow-up study (12.5 +/- 5 and 7.7 +/- 3 mm Hg, and 1.8 +/- 0.65 cm2, respectively). At baseline, color flow Doppler imaging showed aortic valve regurgitation where the leaflets coapted centrally in 17 of 24 patients (trivial, n = 14; mild, n = 3). Besides the central leak, paravalvular regurgitation was seen in 4 patients (trivial, n = 3; mild, n = 1). At follow-up, 18 of 24 patients had aortic valve regurgitation (trivial, n = 11; mild, n = 6; and moderate, n = 1). New valvular regurgitation (graded as trivial, n = 2; mild, n = 2; and moderate, n = 1) was detected in 5 patients, and new paravalvular regurgitation (graded as mild) developed in 1 patient. Two patients underwent repeat operation for valve-related complications: (1) rupture of a valve cusp with acute pulmonary edema, and (2) fibrotic stenosis of the left coronary ostium with unstable angina. In conclusion, this study demonstrates good hemodynamic performance of the SPX in the aortic position.(ABSTRACT TRUNCATED AT 250 WORDS)

Perioperative assessment of aortic homograft, Toronto stentless valve, and stented valve in the aortic position

We investigated aortic valve hemodynamic performance and perioperative left ventricular function in 50 patients (mean [+/- SD] age, 64 +/- 9 years; 34 men, 16 women) undergoing elective aortic valve replacement, using an aortic homograft (n = 20), a Toronto stentless porcine valve (n = 20), or a stented bioprosthesis (n = 10), by transesophageal echocardiography combined with high-fidelity cavity pressure recordings and thermodilution cardiac output measurements. Thirty-nine patients had aortic stenosis; 11 had predominant regurgitation. Thirteen patients with concomitant coronary artery stenosis underwent grafting. Left ventricular mass index in all patients was 280 +/- 110 g/m2. The transvalvular pressure drop and energy consumption were significantly higher with stented than stentless valves (5 with aortic homograft and 11 with Toronto valve, with matched age and valve size; 20 +/- 12 versus 3 +/- 9 mm Hg; 21% +/- 13% versus 8% +/- 8%, both p < 0.01). However, there was no difference in these variables between the Toronto valve and the aortic homograft (3 +/- 12 versus 2 +/- 10 mm Hg; 5% +/- 14% versus 2% +/- 12%, both p > 0.05), although the Toronto valves (normalized to body surface area) were larger than the aortic homografts (14.4 +/- 1.9 versus 12.6 +/- 1.8 mm/m2, p < 0.01). There was no significant difference in left ventricular stroke volume index or stroke work index in the systemic circulation, either between stentless and stented valves or between aortic homografts and Toronto valves, although the cross-clamp time required to insert a stentless valve was 20 minutes longer than that for a stented valve.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcification of valved aortic allografts in rats: effects of age, crosslinking, and inhibitors

Experiments were carried out to investigate rat aortic allograft calcification using valved abdominal aortic allografts. Results indicated that this was a potentially useful model for investigating fresh allograft calcification, as well as mineralization of glutaraldehyde-crosslinked valved allografts. Valve cusp results, however, were not comparable to those noted in large animal or human studies, while aortic wall calcification was more comparable. Calcification inhibitor investigations demonstrated that nearly complete inhibition of the calcification of the aortic wall of glutaraldehyde-crosslinked allografts was achieved using a number of individual inhibitors, including controlled release diphosphonates, and pretreatment with either ferric chloride or aluminum chloride. However, aminopropanehydroxydiphosphonate pretreatment was not efficacious, and sodium dodecyl sulfate pretreatment was only partially effective for inhibiting the aortic wall calcification in the glutaraldehyde-crosslinked allografts. It is concluded that valved aortic allografts in rats provide a useful model for investigating aortic wall (but not valve cusp) calcification and its inhibition.

Stentless aortic bioprosthesis? The way forward: early experience with the Edwards valve

Tissue valve degeneration has been variably attributed to preservation and fixation methods. Additionally, a rigid valve ring might contribute to valve failure. The use of a nonstented porcine valve in the aortic position has clear hemodynamic advantages, and the lack of a stent may favorably influence long-term function. We have implanted stentless aortic valves (Prima valve) in 31 patients. There were 17 men. The mean age was 71.5 years (range, 50 to 83 years). After sculpturing of the sinuses the valve is positioned below the coronary arteries. Valve sizes ranged from 19 to 27 mm. There were no early or late deaths. Mean follow-up to date is 8.9 months (range, 4 weeks to 15 months). Early hemodynamic follow-up using Doppler echocardiography shows average peak systolic and mean gradients of 20.4 mm Hg and 8.6 mm Hg, respectively, at 4 weeks in 26 patients, with no significant change in 13 patients at 6 months. All patients are currently in New York Heart Association class I or II. Our early experience of stentless aortic valves shows them to be reliable with a satisfactory early hemodynamic profile. Their use in the elderly may conserve homografts for children and the young.