Abstract 15120: Mechanistic Determinants of Atrial Functional Mitral Regurgitation

Introduction: Atrial functional mitral regurgitation (AFMR) is an increasingly recognized entity that is defined as MR in the absence of primary leaflet pathology and left ventricular dysfunction. Objectives: Identify the mechanistic determinants of AFMR by cardiac computed tomography (CT). Methods: We reviewed all consecutive CTs performed in atrial fibrillation (Afib) patients pre/post-ablation and appendage occlusion procedures starting in February 2017. We identified the first 50 patients with significant MR (≥2+) then 50 controls without MR that were age and gender-matched. Clinical and echo data were collected. A dedicated CT software (Aquarius, TeraRecon) was used to perform detailed annular measurements Results; The median age was 70.7 years, and 39% were females. There were no significant differences in baseline clinical comorbidities, including type and duration of Afib, and medication use, including rate control agents and antiarrhythmics (Table 1). On echo, patients with significant MR had larger LA volumes (mean +/- SD, 47.63 ml/m2 +/- 17.21 vs. 35.53 +/- 14.22, p<0.001) higher estimated RVSP (40.77 +/- 13.88 mmHg vs. 33.54 +/-6.92, p 0.004), and more frequent concomitant significant TR (32% vs 8%, p=0.006). On CT analysis, there were significant differences (all p<0.001) in the mitral annular measurements, including larger area, perimeter, and septo-lateral and inter-commissural distances in the MR group (Figure 1). Conclusion: Patients with Afib who develop significant AFMR have significantly larger annular and atrial sizes, higher RVSP, and more concomitant significant TR. The type and duration of Afib do not appear to be significant predictors.

Collagen fibre-mediated mechanical damage increases calcification of bovine pericardium for use in bioprosthetic heart valves

In cases of aortic stenosis, bioprosthetic heart valves (BHVs), with leaflets made from glutaraldehyde fixed bovine pericardium (GLBP), are often implanted to replace the native diseased valve. Widespread use of these devices, however, is restricted due to inadequate long-term durability owing specifically to premature leaflet failure. Mechanical fatigue damage and calcification remain the primary leaflet failure modes, where glutaraldehyde treatment is known to accelerate calcification. The literature in this area is limited, with some studies suggesting mechanical damage increases calcification and others that they are independent degenerative mechanisms. In this study, specimens which were non-destructively pre-sorted according to collagen fibre architecture and then uniaxially cyclically loaded until failure or 1 million cycles, were placed in an in-vitro calcification solution. Measurements of percentage volume calcification demonstrated that the weakest specimen group (those with fibres aligned perpendicular to the load) had statistically significantly higher volumes of calcification when compared to those with a high fatigue life. Moreover, SEM imaging revealed that ruptured and damaged fibres presented binding sites for calcium to attach; resulting in more than 4 times the volume of calcification in fractured samples when compared to those which did not fail by fatigue. To the authors’ knowledge, this study quantifies for the first time, that mechanical damage drives calcification in commercial-grade GLBP and that this calcification varies spatially according to localised levels of damage. These findings illustrate that not only is calcification potential in GLBP exacerbated by fatigue damage, but that both failure phenomena are underpinned by the unloaded collagen fibre organisation. Consequently, controlling for GLBP collagen fibre architecture in leaflets could minimise the progression of these prevalent primary failure modes in patient BHVs.

High-Risk Repair of Traumatic Mitral Valve Rupture in the Setting of Polytrauma

Background The rare complication of mitral valve rupture from blunt trauma is certainly not at the top of the differential of shock. Case Description We report the case of a 56-year-old woman who sustained numerous injuries after a 30-m fall with cardiogenic shock secondary to mitral valve rupture causing severe mitral valve regurgitation. Management included successful primary leaflet repair, annuloplasty, and single vessel coronary artery bypass. Conclusion Valvular repair in the setting of polytrauma is a complex decision that requires careful balance of risks and benefits relative to patient stability.

Leaflet initiation is temporally and spatially separated in simple and complex tomato (Solanum lycopersicum) leaf mutants: a developmental analysis

Formation of a compound leaf requires the involvement of multiple factors, including KNOX1 gene expression. To further characterize simple and complex tomato leaf mutants, we analyzed their morphology and development by assessing: leaf phenotypes, primary leaf morphogenesis, expression of the class I KNOX gene LeT6, and meristematic activity of the marginal blastozone. Mutants with alterations in lobing and (or) pinnation (decrease/increase) were analyzed. Primary leaflet initiation is delayed in mutants with decreased lobing. In contrast, leaflet initiation is advanced or similar to the wild type in mutants with deep lobes. Leaves with increased pinnation along the rachis require a protracted developmental program to form their final leaf morphology. Using a morphometric analysis, we show that leaf complexity can be quantified. The expression pattern of LeT6 correlates with histological analysis of meristematic activity of the marginal blastozone, suggesting that LeT6 may play a role, through some unknown mechanism, to regulate meristematic competence, not only in the marginal blastozone to regulate leaflet lobing, but along the entire length of the leaf to regulate pinnation in compound leaves.