Liam P. Ryan

Allogeneic Mesenchymal Precursor Cell Therapy to Limit Remodeling After Myocardial Infarction : The Effect of Cell Dosage

BACKGROUND This experiment assessed the dose-dependent effect of a unique allogeneic STRO-3-positive mesenchymal precursor cell (MPC) on postinfarction left ventricular (LV) remodeling. The MPCs were administered in a manner that would simulate an off-the-self, early postinfarction, preventative approach to cardiac cell therapy in a sheep transmural myocardial infarct (MI) model. METHODS Allogeneic MPCs were isolated from male crossbred sheep. Forty-six female sheep underwent coronary ligation to produce a transmural LV anteroapical infarction. One hour after infarction, the borderzone myocardium received an injection of 25, 75, 225, or 450 x 10(6) MPCs, or cell medium. Echocardiography was performed at 4 and 8 weeks after MI to quantify LV end-diastolic (LVEDV) and end-systolic volumes (LVESV), ejection fraction (EF), and infarct expansion. CD31 and smooth muscle actin (SMA) immunohistochemical staining was performed on infarct and borderzone specimens to quantify vascular density. RESULTS Compared with controls, low-dose (25 and 75 x 10(6) cells) MPC treatment significantly attenuated infarct expansion and increases in LVEDV and LVESV. EF was improved at all cell doses. CD31 and SMA immunohistochemical staining demonstrated increased vascular density in the borderzone only at the lower cell doses. There was no evidence of myocardial regeneration within the infarct. CONCLUSION Allogeneic STRO-3 positive MPCs attenuate the remodeling response to transmural MI in a clinically relevant large-animal model. This effect is associated with vasculogenesis and arteriogenesis within the borderzone and infarct and is most pronounced at lower cell doses.

The Influence of Annuloplasty Ring Geometry on Mitral Leaflet Curvature

BACKGROUND The effect of mitral leaflet curvature on stress reduction is an important mechanism in optimizing valve function. We hypothesize that annuloplasty ring shape could directly influence leaflet curvature and, potentially, repair durability. We describe an echocardiographically based methodology for quantifying mitral valve geometry and its application to the characterization of ovine mitral valve geometry before and after implantation of an annuloplasty ring. METHODS Multiple mitral annular and leaflet geometric variables were calculated for 8 naïve adult male sheep using real-time three-dimensional echocardiographic images. These indexes were recalculated after annuloplasty using a 30-mm Carpentier-Edward Physio ring (n = 4; Edwards Lifesciences, Irvine, CA) or a 30-mm saddle ring (n = 4). RESULTS After implantation of the Physio ring, the annular height to commissural width ratio (AHCWR) decreased from 19.4% +/- 2.3% to 11.1% +/- 2.5% (p = 0.06). After implantation of the saddle ring, AHCWR increased from 19.6% +/- 1.3% to 24.3% +/- 1.3% (p < 0.05). Statistically significant increases in three-dimensional Gaussian curvature occurred after implantation within six defined leaflet regions (A1 to A3, P1 to P3) of the saddle ring but only within the P1 and P3 leaflet regions with the Physio ring. CONCLUSIONS Annuloplasty ring shape affects leaflet curvature. Implantation of a saddle ring reflecting normal human annular geometry augmented ovine annular nonplanarity and increased three-dimensional leaflet curvature across the entire mitral valve surface. The Physio ring decreased annular nonplanarity and increased leaflet curvature only across limited regions of the posterior leaflet. These findings confirm the hypothesis that ring design influences leaflet curvature.

Ischemic Mitral Regurgitation: A Quantitative Three-Dimensional Echocardiographic Analysis

BACKGROUND A comprehensive three-dimensional echocardiography based approach is applied to preoperative mitral valve (MV) analysis in patients with ischemic mitral regurgitation (IMR). This method is used to characterize the heterogeneous nature of the pathologic anatomy associated with IMR. METHODS Intraoperative real-time three-dimensional transesophageal echocardiograms of 18 patients with IMR (10 with anterior, 8 with inferior infarcts) and 17 patients with normal MV were analyzed. A customized image analysis protocol was used to assess global and regional determinants of annular size and shape, leaflet tethering and curvature, relative papillary muscle anatomy, and anatomic regurgitant orifice area. RESULTS Both mitral annular area and MV tenting volume were increased in the IMR group as compared with patients with normal MV (mitral annular area=1,065±59 mm2 versus 779±44 mm2, p=0.001; and MV tenting volume=3,413±403 mm3 versus 1,696±200 mm3, p=0.001, respectively). Within the IMR group, patients with anterior infarct had larger annuli (1,168±99 mm2) and greater tenting volumes (4,260±779 mm3 versus 2,735±245 mm3, p=0.06) than the inferior infarct subgroup. Papillary-annular distance was increased in the IMR group relative to normal; these distances were largest in patients with anterior infarcts. Whereas patients with normal MV had very consistent anatomic determinants, annular shape and leaflet tenting distribution in the IMR group were exceedingly variable. Mean anatomic regurgitant orifice area was 25.8±3.0 mm2, and the number of discrete regurgitant orifices varied from 1 to 4. CONCLUSIONS Application of custom analysis techniques to three-dimensional echocardiography images allows a quantitative and systematic analysis of the MV, and demonstrates the extreme variability in pathologic anatomy that occurs in patients with severe IMR.

Dermal Filler Injection: A Novel Approach for Limiting Infarct Expansion

BACKGROUND Early infarct expansion after coronary occlusion compromises contractile function in perfused myocardial regions and promotes adverse long-term left ventricular (LV) remodeling. We hypothesized that injection of a tissue-expanding dermal filler material into a myocardial infarction (MI) would attenuate infarct expansion and limit LV remodeling. METHODS Fifteen sheep were subjected to an anteroapical MI involving approximately 20% of the LV followed by the injection of 1.3 mL of a calcium hydroxyapatite-based dermal filler into the infarct. Real-time three-dimensional echocardiography was performed at baseline, 30 minutes after MI, and 15 minutes after injection to assess infarct expansion. Sixteen additional sheep were subjected to the same infarction and followed echocardiographically and hemodynamically for 4 weeks after MI to assess chronic remodeling. Eight animals had injection with dermal filler as described above immediately after MI, and 8 animals were injected with an equal amount of saline solution. RESULTS All animals exhibited infarct expansion soon after coronary occlusion. The regional ejection fraction of the apex became negative after infarction, consistent with systolic dyskinesia. Injection of the dermal filler converted the apical wall motion from dyskinetic to akinetic and resulted immediately in significant decreases in global, regional, and segmental LV volumes. Chronically, relative to saline control, dermal filler injection significantly reduced LV end-systolic volume (62.2 +/- 3.6 mL versus 44.5 +/- 3.9 mL; p < 0.05) and improved global ejection fraction (0.295 +/- 0.016 versus 0.373 +/- 0.017; p < 0.05) at 4 weeks after infarction. CONCLUSIONS Injection of an acellular dermal filler into an MI immediately after coronary occlusion reduces early infarct expansion and limits chronic LV remodeling.

Modification of infarct material properties limits adverse ventricular remodeling.

BACKGROUND Infarct expansion after myocardial infarction (MI) is an important phenomenon that initiates and sustains adverse left ventricular (LV) remodeling. We tested the hypothesis that infarct modification by material-induced infarct stiffening and thickening limits infarct expansion and LV remodeling. METHODS Anteroapical infarction was induced in 21 sheep. Sheep were randomized to injection of saline (2.6 mL) or tissue filler material (2.6 mL) into the infarct within 3 hours of MI. Animals were monitored for 8 weeks with echocardiography to assess infarct expansion and global LV remodeling. Morphometric measurements were performed of excised hearts to quantify infarct thickness. Regional blood flow was assessed with colored microspheres. Infarct material properties were measured using biaxial tensile testing. RESULTS Compared with controls at 8 weeks, treatment animals had less infarct expansion, reduced LV dilatation (LV systolic volumes: 60.8±4.3 vs 80.3±6.9 mL; p<0.05), greater ejection fraction (0.310±0.026 vs 0.276±0.013; p<0.05), thicker infarcts (5.5±0.2 vs 2.2±0.3 mm; p<0.05), and greater infarct blood flow (0.22±0.04 vs 0.11±0.03 mL/min/g; p<0.05). The longitudinal peak strain in the treatment group was less (0.05014±0.0141) than the control group (0.1024±0.0101), indicating increased stiffness of the treated infarcts. CONCLUSIONS Durable infarct thickening and stiffening can be achieved by infarct biomaterial injection, resulting in the amelioration of infarct expansion and global LV remodeling. Further material optimization will allow for clinical translation of this novel treatment paradigm.

A methodology for assessing human mitral leaflet curvature using real-time 3-dimensional echocardiography.

OBJECTIVES Using 3-dimensional echocardiography in conjunction with novel geometric modeling and rendering techniques, we have developed a high-resolution, quantitative, 3-dimensional methodology for imaging the human mitral valve. Leaflet and annular geometry are important determinants of mitral valve stress. Repair techniques that optimize valvular geometry will reduce stress and potentially increase repair durability. The development of such procedures will require image-processing methodologies that provide a quantitative description of 3-dimensional valvular geometry. METHODS Ten healthy adult subjects underwent mitral valve imaging with real-time 3-dimensional echocardiography. By using specially designed image analysis software, multiple valvular geometric parameters, including 2- and 3-dimensional leaflet curvature, leaflet surface area, annular height, intercommissural width, septolateral annular diameter, and annular area were determined for each subject. Image-rendering techniques that allow for the clear and concise presentation of this detailed information are also presented. RESULTS Although 3-dimensional annular and leaflet geometry were found to be highly conserved between healthy human subjects in general, substantial intrasubject and intersubject regional geometric heterogeneity was observed in the midposterior leaflet, the region most commonly involved in leaflet flail in subjects with myxomatous disease. CONCLUSIONS The image-processing and graphic-rendering techniques that we have developed can be used to provide a complete description of 3-dimensional mitral valve geometry in human subjects. Widespread application of these techniques to healthy subjects and patients with mitral valve disease will provide insight into the geometric basis of both valvular pathology and repair durability.

Targeted Regional Injection of Biocomposite Microspheres Alters Post–Myocardial Infarction Remodeling and Matrix Proteolytic Pathways

Background— Although localized delivery of biocomposite materials, such as calcium hydroxyapatite (CHAM), have been demonstrated to potentially attenuate adverse left ventricular (LV) remodeling after myocardial infarction (MI), the underlying biological mechanisms for this effect remain unclear. This study tested the hypothesis that targeted CHAM injections would alter proteolytic pathways (matrix metalloproteinases [MMPs] and tissue inhibitors of MMPs [TIMPs]) and would be associated with parameters of post-MI LV remodeling. Methods and Results— MI was induced in adult sheep followed by 20 targeted injections of a total volume of 1.3 mL (n=6) or 2.6 mL of CHAM (n=5) or saline (n=13) and LV end-diastolic volume (EDV) and MMP/TIMP profiles in the MI region were measured at 8 weeks after MI. LV EDV decreased with 2.6 mL CHAM versus MI only (105.4±7.5 versus 80.6±4.2 respectively, P<0.05) but not with 1.3 mL CHAM (94.5±5.0, P=0.32). However, MI thickness increased by 2-fold in both CHAM groups compared with MI only (P<0.05). MMP-13 increased 40-fold in the MI only group (P<0.05) but fell by >6-fold in both CHAM groups (P<0.05). MMP-7 increased approximately 1.5-fold in the MI only group (P<0.05) but decreased to referent control values in both CHAM groups in the MI region (P<0.05). Collagen content was reduced by approximately 30% in the CHAM groups compared with MI only (P<0.05). Conclusions— Differential effects on LV remodeling and MMP/TIMP profiles occurred with CHAM. Thus, targeted injection of a biocomposite material can favorably affect the post-MI remodeling process and therefore holds promise as a treatment strategy in and of itself, or as a matrix with potentially synergistic effects with localized pharmacological or cellular therapies.

Rapid Aortic Arch Debranching Using the Gore Hybrid Vascular Graft

A significant fraction of patients who survive repair of a DeBakey type I aortic dissection will require a secondary intervention to address ongoing aortic remodeling. Strategic treatment of this population mandates that the technical feasibility of secondary operations be considered at the index procedure. We evaluated a hybrid-based modification of a widely accepted surgical approach that obviates the need for advanced perfusion management techniques and facilitates secondary endografting. Hybrid technology allows for the physiologic equivalent of a total arch replacement without the operative complexity associated with a traditional approach while allowing for strategic planning if a secondary operation is warranted.

Successful support and separation from veno–venous extracorporeal membrane oxygenation support in a three-month-old patient following bidirectional Glenn procedure

While extracorporeal membrane oxygenation (ECMO) is a useful mechanism of providing support in pediatric patients with cardiopulmonary dysfunction following surgery for congenital heart disease, outcomes have varied dramatically between distinct cardiac diagnoses. Reported outcomes of ECMO support following a bidirectional Glenn procedure in patients with single ventricle physiology are uniformly poor due in part to physiological and anatomical challenges inherent to cannulation in this population. We describe a unique veno-venous cannulation that can be applied to this patient population and has allowed for successful decannulation in our practice.

Geometric orientation of the aortic neoroot in patients with raphed bicuspid aortic valve disease undergoing primary cusp repair and a root reimplantation procedure

OBJECTIVES Primary cusp repair + aortic root reimplantation in bicuspid aortic valve (BAV) disease presenting with root aneurysm with aortic insufficiency (AI) is an effective surgical treatment. We assessed whether the geometric orientation of the repaired BAV into its reimplanted neoroot affects outcomes-180°/180° orientation was compared with the 150°/210° orientation. METHODS From 2005 to 2012, 66 BAV repairs were performed. This is a retrospective review of all types of Ib/II BAV AI patients undergoing root reimplantation (n = 26) at two different geometric orientations: 180°/180° (n = 11) vs 150°/210° (n = 15). In the 180°/180° group, reimplantation into the neoroot was such that both conjoint and non-conjoint cusps occupied 180° of the annular circumference. In the 150°/210° group, the repaired valve was configured to the more typical native orientation of a type I BAV: the non-conjoint cusp occupied 150°, and the conjoint cusp occupied 210° of the annular circumference. RESULTS Preoperative characteristics were similar in both groups. In-hospital mortality, stroke, reoperation, renal failure and pacemaker rates were zero in both groups. No patient left the operating room with >1+ AI and one had a peak gradient >20 mmHg. Transvalvular gradients were higher in the 180°/180° group, but not significant (P > 0.05). M.ean follow-ups for the 180°/180° and 150°/210° group were 48 and 33 months, respectively. Actuarial freedom from AI >2+ at 5 years was 100% in both groups. Freedom from AI >1+ at 5 years was 90 ± 10% in the 150°/210° group and 86 ± 13% in the 180°/180° group (P = 0.71). Freedom from peak gradient >20 mmHg was 80% (n = 8) in the 180°/180° group and 100% in the 150°/210° group at 1-year follow-up. Transvalvular gradients were higher in the 180°/180° group (16 ± 8 vs 10 ± 4 mmHg, P = 0.02; 9 ± 3 vs 5 ± 3 mmHg, P = 0.01). Five-year actuarial survival and freedom from aortic reoperation have remained at 100% in the entire cohort. CONCLUSION Cusp repair + root reimplantation for BAV type Ib/II AI can be safely performed at either geometric orientation. Conceptually, 150°/210° orientation respects the natural type I BAV anatomy with regard to cusp surface area and leaflet insertion perimeter. The 180°/180° group may have higher transvalvular gradients and smaller coaptation zones than the 150°/210° group. Further follow-up may reveal the superiority of one geometric orientation over the other.