Entire Mitral Valve Reconstruction Using Porcine Extracellular Matrix: Adding a Ring Annuloplasty

PURPOSE

This study investigated the implications of inserting a flexible annuloplasty ring after reconstructing the entire mitral valve in a porcine model using a previously investigated tube graft design made of 2-ply small intestinal submucosa extracellular matrix (CorMatrix®).

METHODS

An acute model with eight 80-kg pigs, each acting as its own control, was used. The entire mitral valve was reconstructed with a 2-ply small intestinal submucosa extracellular matrix tube graft (CorMatrix®). Subsequently, a Simulus® flexible ring was inserted. The characterization was based on mitral annular geometry and valvular dynamics with sonomicrometry and echocardiography.

RESULTS

After adding the ring annuloplasty, the in-plane annular dynamics were more constant throughout the cardiac cycle compared to the reconstruction alone. However, the commissure-commissure distance was statistically significantly decreased [35.0 ± 3.4 mm vs. 27.4 ± 1.9 mm, P < 0.001, diff =  - 7.6 mm, 95% CI, - 9.8 to (-5.4) mm] after ring insertion, changing the physiological annular D-shape into a circular shape which created folds at the coaptation zone resulting in a central regurgitant jet on color Doppler.

CONCLUSION

We successfully reconstructed the entire mitral valve using 2-ply small intestinal submucosal extracellular matrix (CorMatrix®) combined with a flexible annuloplasty. The annuloplasty reduced the unphysiological systolic widening previously found with this reconstructive technique. However, the Simulus flex ring changed the physiological annular D-shape into a circular shape and hindered a correct unfolding of the leaflets. Thus, we do not recommend a flexible ring in conjunction with this reconstructive technique; further investigations are needed to discover a more suitable remodelling annuloplasty.

Clinical Characteristics, Incidences, and Mortality Rates for Type A and B Aortic Dissections: A Nationwide Danish Population-Based Cohort Study From 1996 to 2016

BACKGROUND

Population-based epidemiologic studies of aortic dissections (ADs) are needed. This study aimed to report clinical characteristics, incidences, and mortality rates for adult patients admitted to Danish hospitals with type A AD (TAAD) or type B AD (TBAD) from 1996 through 2016.

METHODS

We conducted a nationwide, population-based register study. All cases of AD registered with International Classification of Diseases, Tenth Revision codes in the Danish National Patient Registry at time of admission to a hospital with available medical records underwent validation. Data were merged between nationwide health registries including the cause of death registry. Patients with validated AD were matched 1:10 on sex and age with patients with hypertension from the general Danish population.

RESULTS

Of 5018 registered cases of AD, 4183 cases underwent review and 3023 (60.2%) were validated as AD. After exclusions, the distribution of validated TAAD and TBAD was 1620 (60.5%) and 1059 (39.5%; P<0.001), 67.5% and 67.0% of patients were men, and mean ages at dissection were 63.5±12.9 and 67.5±12.2 years (P<0.001), respectively. The most prevalent comorbidities for TAAD were hypertension (55.2%), thoracic aortic aneurysms (14.6%), and chronic obstructive pulmonary disease (13.1%); for TBAD, the most prevalent comorbidities were hypertension (64.1%), aortic aneurysms at any location (7.5% to 12.0%), and chronic obstructive pulmonary disease (15.7%). The overall mean annual incidence rate was 4.2/100 000 patient-years. Incidence was significantly higher for TAAD (2.2/100 000) compared with TBAD (1.5/100 000; P<0.001). The 30-day mortality rates for validated TAAD and TBAD were 22.0% and 13.9% (P<0.001), respectively, with no significant changes over time or between sexes. Adjusted 5-year overall mortality rates for TAAD and TBAD were hazard ratio 3.2 (2.9 to 3.5; P<0.001; aortic-related cause of death, 57.0%) and hazard ratio 2.1 (1.9 to 2.4; P<0.001; aortic-related cause of death, 42.8%), respectively, compared with the general hypertensive population. Among patients who survived 30 days from dissection, the adjusted 5-year overall mortality rates were hazard ratio 1.1 (1.0 to 1.3; P=0.12; aortic-related cause of death, 23.2%) and hazard ratio 1.4 (1.2 to 1.6; P<0.001; aortic-related cause of death, 25.6%) for TAAD and TBAD, respectively.

CONCLUSIONS

Hypertension, aortic aneurysms, and chronic obstructive pulmonary disease were the most prevalent comorbidities. The 30-day mortality frequencies were consistent over time with no significant differences between sexes. The 5-year mortality rate was higher for TAAD than TBAD. If the patient survived 30 days from dissection, the mortality rate for patients with TAAD was comparable with that of the general hypertensive population, but the mortality rate was significantly higher in patients with TBAD.

Annular and subvalvular dynamics after extracellular matrix mitral tube graft implantation in pigs

OBJECTIVES

Entire mitral valve reconstruction with an extracellular matrix tube graft is a potential candidate to overcome the current limitations of mechanical and bioprosthetic valves. However, clinical data have raised concern with respect to patch failure. The aim of our study was to evaluate the impact of extracellular matrix mitral tube graft implantation on mitral annular and subvalvular regional dynamics in pigs.

METHODS

A modified tube graft design made of 2-ply extracellular matrix was used (CorMatrix®; Cardiovascular Inc., Alpharetta, GA, USA). The reconstructions were performed in an acute 80-kg porcine model (N = 8), where each pig acted as its own control. Haemodynamics were assessed with Mikro-Tip pressure catheters and mitral annular and subvalvular geometry and dynamics with sonomicrometry.

RESULTS

Catheter-based peak left atrial pressure and pressure difference across the mitral and aortic valves in the reconstructions were comparable to the values seen in the native mitral valves. Also comparable were maximum mitral annular area (755 ± 100 mm2), maximum septal-lateral distance (29.7 ± 1.7 mm), maximum commissure-commissure distance (35.0 ± 3.4 mm), end-systolic annular height-to-commissural width ratio (10.2 ± 1.0%) and end-diastolic interpapillary muscle distance (27.7 ± 3.3 mm). Systolic expansion of the mitral annulus was, however, observed after reconstruction.

CONCLUSIONS

The reconstructed mitral valves were fully functional without regurgitation, obstruction or stenosis. The reconstructed mitral annular and subvalvular geometry and subvalvular dynamics were found in the same range to those in the native mitral valve. A regional annular ballooning effect occurred that might predispose to patch failure. However, the greatest risk was found at the papillary muscle attachments.

Annular Dynamics and Leaflet Geometry in Patch Reconstruction of the Posterior Mitral Leaflet After Adding a Flexible Annuloplasty Ring

PURPOSE

Patch reconstruction of the posterior mitral leaflet using small intestinal submucosa extracellular matrix has been successfully performed in a porcine study. The patch reconstruction, however, resulted in non-physiological systolic widening of the mitral annulus, suggesting the need for an annuloplasty ring. The objective was to characterize the impact on annular dynamics and leaflet geometry of adding a flexible annuloplasty ring to the posterior mitral leaflet patch reconstruction.

METHODS

Measurements were performed in an acute 80-kg porcine model, with seven pigs acting as their own controls. The posterior mitral leaflet was reconstructed with a 2-ply small intestinal submucosa extracellular matrix patch (CorMatrix®). Additionally, a Simulus® Flexible Annuloplasty Ring (Medtronic Inc., Minneapolis, MN, USA) was inserted. Mitral annular dynamics were evaluated using sonomicrometry, and leaflet geometry was described using echocardiography.

RESULTS

The annuloplasty ring reduced mitral annular dimensions and restricted cyclic changes in mitral annular area (126 ± 19 vs. 30 ± 13 mm², p < 0.001), septal-lateral and commisure-commisure distances. Ring annuloplasty prevented systolic widening in the mitral annulus after posterior mitral leaflet reconstruction. The annular saddle shape and leaflet coaptation length (8.7 ± 2.3 vs. 9.7 ± 1.3 mm, p = 0.221) were comparable before and after ring insertion.

CONCLUSIONS

The flexible annuloplasty ring resulted in a downsized annulus with restriction of cyclic annular changes in the reconstructed mitral valve. Ring insertion preserved the annular saddle shape and coaptation length. The ring annuloplasty counteracted the non-physiological annular dynamics, and this may improve durability of the posterior mitral leaflet patch reconstruction.

The importance of collagen composition and biomechanics for the porcine aortic root

A thorough understanding of the aortic root structure and biomechanics is necessary when performing aortic valve-sparing procedures in patients with aortic root aneurysms. This study aimed to evaluate the amount of collagen and biomechanics at different levels and segments of the aortic root. Ten aortic roots from healthy pigs were excised including the aortic annulus, the sinuses of Valsalva, and the sinotubular junction (STJ). Specimens were further divided into three circumferential segments; left coronary (LC)-, right coronary (RC)-, and non-coronary (NC) sinus. Collagen was determined using hydroxyproline analysis and specimens were tested biomechanically for stress-strain relations. The annulus showed significantly larger average maximum stiffness (9.6 ± 4.5 N/mm) compared with the sinus (4.5 ± 2.0 N/mm) and STJ (4.8 ± 1.8 N/mm). The average collagen content was likewise higher in the annulus (4.0 ± 1.0 mg/ml) compared with the sinus (2.4 ± 0.6 mg/ml) and STJ (2.2 ± 0.5 mg/ml) for all three segments. The NC sinus segment exhibited a significantly larger maximum stiffness and stress under static conditions compared with the RC. These results suggest that the aortic root is heterogeneous in both structure and biomechanical properties and that it varies both in levels and segments of the aortic root. Future surgical approaches should consider enhanced strength parameters for specific areas of the aortic root to achieve the best results when performing aortic valve-sparing techniques. From this study, we conclude that the aortic annulus needs special attention to imitate normal physiologic properties during aortic valve-sparing surgery due to its higher maximum stiffness, stress, and load. Modified future surgical procedures could potentially prevent recurrent aneurysmal formation.

Comparison of the Dacron ring and suture annuloplasty for aortic root repair: an in vitro evaluation

OBJECTIVES

Increasing evidence shows that annular stabilization is essential in most aortic valve repair procedures. However, a standardized comparison of the 2 commonly used annuloplasty procedures is lacking. We hypothesized that the Dacron ring is more rigid than the polytetrafluoroethylene suture, whereas both procedures decrease annular dimensions. The aim of this study was to compare the biomechanical properties of the ring and suture techniques with native aortic roots in vitro.

METHODS

Eighteen aortic roots explanted from 80-kg pigs were randomized into a Dacron ring group, a suture annuloplasty group and a native control group. Each sample was tested in a pulsatile in vitro model with a force transducer attached to the aortic annulus to obtain radial force measurements, and annular dynamics was evaluated using 2-dimensional echography.

RESULTS

Among the 2 annuloplasty procedures, only the Dacron ring group provided a significant reduction in the annular diameter compared with the native group (P < 0.006). Both annuloplasty procedures significantly reduced the geometric orifice area, tenting area and sinus diameter while increasing the coaptation length compared with the native group. Systolic annular distension was retained between groups, although the total radial forces were significantly reduced in the procedure groups compared with the native group (ring 1.07 ± 0.45 N, suture 1.13 ± 0.39 N and native 3.55 ± 1.34 N, P < 0.001).

CONCLUSIONS

Although both annuloplasty procedures increase coaptation length and decrease geometric orifice area, a significant downsizing of the annulus was achieved using the Dacron ring only. The systolic annular distension was similar to the native aortic root, whereas the radial annular forces were evenly decreased by both annuloplasty procedures. Long-term studies are needed to disclose any difference in long-term effect of the annuloplasty procedures.