Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience

Structural abnormalities after aortic root replacement with stentless xenograft

OBJECTIVE

In complex and high-risk aortic root disease, the porcine Freestyle stentless bioprosthesis (Medtronic Inc, Minneapolis, Minn) is an important surgical treatment option. We aimed to determine prevalence and clinical effect of structural and functional abnormalities after full-root Freestyle implantation.

METHODS

Our cross-sectional 2-center study combined with clinical follow-up included 253 patients with full-root Freestyle bioprostheses implanted from 1999 to 2017. Patients underwent transthoracic echocardiography (TTE) and contrast-enhanced, electrocardiogram-gated 4-dimensional cardiac computed tomography (4DCT) at median age 70 (interquartile range, 62-75) years. After 4DCT, clinical follow-up continued throughout 2018. Median follow-up was 3.3 years before 4DCT and 1.4 years after.

RESULTS

We identified abnormalities in 46% of patients, including pseudoaneurysms (n = 32; 13%), moderate or severe coronary ostial stenosis (n = 54; 21%), and moderate-severe leaflet thickening or reduced leaflet motion (n = 51; 20%). TTE only identified 1 patient with pseudoaneurysm. After 4DCT, the unadjusted hazard ratio for surgical reintervention among patients with abnormal 4DCT was 4.2 (95% confidence interval, 1.2-15.3), in all, 10% required a reintervention. 4DCT abnormalities were associated with a statistically nonsignificant increased risk of death, stroke, or myocardial infarction (hazard ratio obtained using Cox proportional hazards regression analysis, 2.4; 95% confidence interval, 0.7-7.6). In all, 4.0% died, 3.6% had a myocardial infarction, and 2.0% had a stroke.

CONCLUSIONS

Structural and functional abnormalities of the aortic root are frequent after Freestyle implantation and TTE appears to be insufficient for follow-up. Abnormalities might be associated with increased risk of reintervention and potentially adverse clinical outcomes. Longer follow-up and larger study populations are needed to further clarify the clinical implications of abnormalities identified with 4DCT.

Myocardial ischaemia caused by bilateral coronary ostial stenosis from pseudointimal membranes in a full root freestyle valve: a case report

Background

Coronary artery ostial stenosis is a rare but well-known complication to aortic root replacement. The occurrence of this complication in patients with the Medtronic Freestyle bioprosthesis is poorly described. We report a case of late bilateral coronary ostial stenosis due to pseudointimal membranes within a Medtronic Freestyle bioprosthesis, resulting in acute coronary syndrome.

Case summary

In 2013, a 43-year-old male patient received a Medtronic Freestyle bioprosthesis as a full aortic root implantation due to endocarditis with root abscess. Preoperative coronary angiography was normal. The patient, who had no previous symptoms of coronary ischaemia, presented with severe chest pain and acute coronary syndrome in 2017. Coronary angiography and electrocardiogram-gated contrast-enhanced cardiac computed tomography showed bilateral coronary ostial stenosis. The patient was successfully treated with coronary artery bypass grafting. Intraoperative inspection revealed pseudointimal membranes covering the coronary ostia. Histology showed fibro-intimal thickening with areas of inflamed granulation tissue.

Discussion

Bilateral coronary ostial stenosis is a severe, potentially life-threatening condition, and a possible complication to implantation of the Medtronic Freestyle bioprosthesis as a full root. The phenomenon may occur late and should be distinguished from arteriosclerotic coronary artery disease.

Influence of Age on Longevity of a Stentless Aortic Valve

BACKGROUND

The longevity of a stentless valve in a younger population (20-60 years old) is unknown.

METHODS

From 1992 to 2015, 1947 patients underwent aortic valve/root replacement for aortic stenosis, insufficiency, root aneurysm, or aortic dissection with stentless bioprostheses (median size, 26 mm). At operation 105 patients were <40 years old, 528 were 40 to 59, 860 were 60 to 74, and 454 were ≥75 years. The data were obtained through chart review, administered surveys, and the National Death Index.

RESULTS

The 30-day mortality rate was 2.6%. During follow-up 807 patients (41%) died before reoperation, 993 (51%) were alive without reoperations because of deterioration, and 113 patients (5.8%) underwent reoperation for structural valve deterioration. After adjusting death and reoperation for non-structural valve deterioration causes as competing risks, the cumulative incidence of reoperation was significantly different between the younger groups (<40, 40-59) and the older groups (60-74, ≥75; P < .0001) but not inside the younger (<40 vs 40-59) or older (60-74 vs ≥75) group. The significant hazard ratio of reoperation for <40 versus ≥75 years of age was 12, <40 versus 60 to 74 was 4, 40 to 59 versus 60 to 74 was 3, and 40 to 59 versus ≥75 was 9 (P ≤ .01). The 10- and 15-year survival in the entire cohort was 53% and 29%, respectively.

CONCLUSIONS

The stentless aortic valve provides satisfactory durability as a conduit for aortic valve/root replacement for patients who prefer a bioprosthesis. However it should be judiciously considered for patients younger than 60 years because of an increased incidence of reoperation for structural valve deterioration.

Morphometrical and biomechanical analyses of a stentless bioprosthetic valve: an implication to avoid potential primary tissue failure

OBJECTIVES

Stentless bioprosthetic valves provide hemodynamic advantages over stented valves as well as excellent durability. However, some primary tissue failures in bioprostheses have been reported. This study was conducted to evaluate the morphometrical and biomechanical properties of the stentless Medtronic Freestyle™ aortic root bioprosthesis, to identify any arising problem areas, and to speculate on a potential solution.

METHODS

The three-dimensional heterogeneity of the stentless bioprosthesis wall was investigated using computed tomography. The ascending aorta and the right, left, and non-coronary sinuses of Valsalva were resected and examined by an indentation test to evaluate their biomechanical properties.

RESULTS

The non-coronary sinus of Valsalva was significantly thinner than the right sinus of Valsalva (p < 0.01). Young's modulus, calculated as an indicator of elasticity, was significantly greater at the non-coronary sinus of Valsalva (430.7 ± 374.2 kPa) than at either the left (190.6 ± 70.6 kPa, p < 0.01) or right sinuses of Valsalva (240.0 ± 56.5 kPa, p < 0.05).

CONCLUSIONS

Based on the morphometrical and biomechanical analyses of the stentless bioprosthesis, we demonstrated that there are differences in wall thickness and elasticity between each sinus of Valsalva. These differences suggest that the non-coronary sinus of Valsalva is the most vulnerable and at greater risk of tissue failure. The exclusion of the non-coronary sinus of Valsalva may be beneficial to mitigate the long-term risks of tissue failure in the stentless bioprosthesis.