Martin L. Bocks

Metallic zinc exhibits optimal biocompatibility for bioabsorbable endovascular stents

Although corrosion resistant bare metal stents are considered generally effective, their permanent presence in a diseased artery is an increasingly recognized limitation due to the potential for long-term complications. We previously reported that metallic zinc exhibited an ideal biocorrosion rate within murine aortas, thus raising the possibility of zinc as a candidate base material for endovascular stenting applications. This study was undertaken to further assess the arterial biocompatibility of metallic zinc. Metallic zinc wires were punctured and advanced into the rat abdominal aorta lumen for up to 6.5months. This study demonstrated that metallic zinc did not provoke responses that often contribute to restenosis. Low cell densities and neointimal tissue thickness, along with tissue regeneration within the corroding implant, point to optimal biocompatibility of corroding zinc. Furthermore, the lack of progression in neointimal tissue thickness over 6.5months or the presence of smooth muscle cells near the zinc implant suggest that the products of zinc corrosion may suppress the activities of inflammatory and smooth muscle cells.

Transcatheter Tricuspid Valve-in-Valve Implantation for the Treatment of Dysfunctional Surgical Bioprosthetic Valves: An International, Multicenter Registry Study.

Background— Off-label use of transcatheter aortic and pulmonary valve prostheses for tricuspid valve-in-valve implantation (TVIV) within dysfunctional surgical tricuspid valve (TV) bioprostheses has been described in small reports. Methods and Results— An international, multicenter registry was developed to collect data on TVIV cases. Patient-related factors, procedural details and outcomes, and follow-up data were analyzed. Valve-in-ring or heterotopic TV implantation procedures were not included. Data were collected on 156 patients with bioprosthetic TV dysfunction who underwent catheterization with planned TVIV. The median age was 40 years, and 71% of patients were in New York Heart Association class III or IV. Among 152 patients in whom TVIV was attempted with a Melody (n=94) or Sapien (n=58) valve, implantation was successful in 150, with few serious complications. After TVIV, both the TV inflow gradient and tricuspid regurgitation grade improved significantly. During follow-up (median, 13.3 months), 22 patients died, 5 within 30 days; all 22 patients were in New York Heart Association class III or IV, and 9 were hospitalized before TVIV. There were 10 TV reinterventions, and 3 other patients had significant recurrent TV dysfunction. At follow-up, 77% of patients were in New York Heart Association class I or II (P<0.001 versus before TVIV). Outcomes did not differ according to surgical valve size or TVIV valve type. Conclusions— TVIV with commercially available transcatheter prostheses is technically and clinically successful in patients of various ages across a wide range of valve size. Although preimplantation clinical status was associated with outcome, many patients in New York Heart Association class III or IV at baseline improved. TVIV should be considered a viable option for treatment of failing TV bioprostheses.

An extracorporeal artificial placenta supports extremely premature lambs for 1 week

PURPOSE The treatment of extreme prematurity remains an unsolved problem. We developed an artificial placenta (AP) based on extracorporeal life support (ECLS) that simulates the intrauterine environment and provides gas exchange without mechanical ventilation (MV) and compared it to the current standard of neonatal care. METHODS Extremely premature lambs (110-120 days; term=145d) were used. AP lambs (n=9) were cannulated (jugular drainage, umbilical vein reinfusion) for ECLS. Control lambs (n=7) were intubated, ventilated, given surfactant, and transitioned to high-frequency oscillatory ventilation. All lambs received parenteral nutrition, antibiotics, and steroids. Hemodynamics, blood gases, hemoglobin, and circuit flows were measured. RESULTS Four premature lambs survived for 1 week on the AP, with one surviving 6 days. Adequate oxygenation and ventilation were provided by the AP. The MV lambs survived 2-8 hours. Each of these lambs experienced a transient improvement with surfactant, but developed progressive hypercapnea and hypoxia despite high airway pressures and HFOV. CONCLUSIONS Extremely premature lambs were supported for 1 week with the AP with hemodynamic stability and adequate gas exchange. Mechanically ventilated lambs succumbed within 8 hours. Further studies will assess control of fetal circulation and organ maturation on the AP.

Development of an artificial placenta V: 70 h veno-venous extracorporeal life support after ventilatory failure in premature lambs

PURPOSE An artificial placenta would change the paradigm of treating extremely premature infants. We hypothesized that using a veno-venous extracorporeal life support (VV-ECLS) artificial placenta after ventilatory failure would stabilize premature lambs and maintain normal fetal physiologic parameters for 70 h. METHODS A near-term neonatal lamb model (130 days; term=145) was used. The right jugular vein (drainage) and umbilical vein (reinfusion) were cannulated with 10-12 Fr cannulas. Lambs were then transitioned to an infant ventilator. After respiratory failure, the endotracheal tube was filled with amniotic fluid, and VV-ECLS total artificial placenta support (TAPS) was initiated. Lambs were maintained on TAPS for 70 h. RESULTS Six of seven lambs survived for 70 h. Mean ventilation time was 57 ± 22 min. During ventilation, mean MAP was 51 ± 14 mmHg, compared to 44 ± 14 mmHg during TAPS (p=0.001). Mean pH and lactate during ventilation were 7.06 ± 0.15 and 5.7 ± 2.3 mmol/L, compared to 7.33 ± 0.07 and 2.0 ± 1.8 mmol/L during TAPS (p<0.001 for both). pO(2) and pCO(2) remained within normal fetal parameters during TAPS, and mean carotid blood flow was 25 ± 7.5 mL/kg/min. Necropsy showed a patent ductus arteriosus and no intracranial hemorrhage in all animals. CONCLUSIONS The artificial placenta stabilized premature lambs after ventilatory failure and maintained fetal circulation, hemodynamic stability, gas exchange, and cerebral perfusion for 70 h.

Multicenter Experience Evaluating Transcatheter Pulmonary Valve Replacement in Bovine Jugular Vein (Contegra) Right Ventricle to Pulmonary Artery Conduits

Background— Follow-up of transcatheter pulmonary valve replacement (TPVR) with the Melody valve has demonstrated good short-term and long-term outcomes, but there are no published studies focused on valve performance in the Contegra bovine jugular vein conduit. Methods and Results— This is a retrospective, multicenter study of the short- and intermediate-term outcomes of Melody TPVR within the Contegra conduit in the right ventricle to pulmonary artery position. Data from 13 centers were included in the analysis. During the study period, 136 patients underwent 139 catheterizations for attempted Melody TPVR with a median follow-up of 3 years (1 day to 9.1 years). Of the 136 patients, 117 underwent successful Melody TPVR. Two patients underwent a second Melody TPVR. The majority of patients underwent placement of ≥1 stents before transcatheter pulmonary valve implantation. There was a significant reduction in peak conduit pressure gradient acutely after transcatheter pulmonary valve implantation (39 versus 10 mm Hg; P<0.001). At most recent follow-up, the maximum pulmonary valve gradient by echocardiogram remained significantly reduced relative to prevalve implant measurements (65.9 versus 27.3 mm Hg; P<0.001). The incidence of Melody transcatheter pulmonary valve stent fracture (3.4%) and infectious endocarditis (4.3%) were both low. Serious adverse events occurred in 3 patients. Conclusions— Melody TPVR in Contegra conduits is safe and effective and can be performed in a wide range of conduit sizes with preserved valve function and low incidence of stent fracture and endocarditis.

Transcatheter Tricuspid Valve-in-Valve Implantation for the Treatment of Dysfunctional Surgical Bioprosthetic Valves

Background— Off-label use of transcatheter aortic and pulmonary valve prostheses for tricuspid valve-in-valve implantation (TVIV) within dysfunctional surgical tricuspid valve (TV) bioprostheses has been described in small reports. Methods and Results— An international, multicenter registry was developed to collect data on TVIV cases. Patient-related factors, procedural details and outcomes, and follow-up data were analyzed. Valve-in-ring or heterotopic TV implantation procedures were not included. Data were collected on 156 patients with bioprosthetic TV dysfunction who underwent catheterization with planned TVIV. The median age was 40 years, and 71% of patients were in New York Heart Association class III or IV. Among 152 patients in whom TVIV was attempted with a Melody (n=94) or Sapien (n=58) valve, implantation was successful in 150, with few serious complications. After TVIV, both the TV inflow gradient and tricuspid regurgitation grade improved significantly. During follow-up (median, 13.3 months), 22 patients died, 5 within 30 days; all 22 patients were in New York Heart Association class III or IV, and 9 were hospitalized before TVIV. There were 10 TV reinterventions, and 3 other patients had significant recurrent TV dysfunction. At follow-up, 77% of patients were in New York Heart Association class I or II (P<0.001 versus before TVIV). Outcomes did not differ according to surgical valve size or TVIV valve type. Conclusions— TVIV with commercially available transcatheter prostheses is technically and clinically successful in patients of various ages across a wide range of valve size. Although preimplantation clinical status was associated with outcome, many patients in New York Heart Association class III or IV at baseline improved. TVIV should be considered a viable option for treatment of failing TV bioprostheses.

Hydrogel Expandable Coils for Vascular Occlusion in Congenital Cardiovascular Disease: A Single Center Experience

OBJECTIVE   The objective of this study is to evaluate the safety and feasibility of the AZUR hydrogel-polymer coated platinum coil (hydrocoil) for vascular occlusion in patients with congenital cardiovascular disease (CCVD). DESIGN   Retrospective case review. PATIENTS   Eight patients with CCVD who underwent attempted vascular occlusion procedure with the hydrocoil at the University of Michigan between January 1, 2008 and March 1, 2011. Median patient age was 1.6 years (range 0.6-27.5 years) and median weight was 10.6 kg (3.9-74.8 kg). OUTCOME MEASURES   Complete vascular occlusion of the target vessel was assessed at procedural completion with angiography and noninvasive imaging at follow-up. Key procedural variables and adverse events were also evaluated. RESULTS   A total of 21 hydrocoils were successfully placed in seven vessels, in six patients. Vessels included four (57%) veno-venous collaterals, two (29%) aortopulmonary collaterals, and one (14%) main pulmonary artery. Hydrocoils could not be placed successfully in two patients, including one baffle leak and one veno-venous collateral. Pretreatment of the hydrocoil with steam to soften the coil, prior to vascular introduction, increased the likelihood of successful implant (100% vs. 60%). Complete occlusion was observed in 100% of vessels either at the time of catheterization or at follow-up. There were no complications attributable to the hydrocoil. CONCLUSIONS   Hydrocoils are safe and effective devices that can be utilized for vascular occlusion in a variety of blood vessels in patients with CCVD. Coil pretreatment may increase the likelihood of procedural success.

Factors associated with the internal jugular venous approach for Melody™ Transcatheter Pulmonary Valve implantation.

BACKGROUND Transcatheter pulmonary valve implantation is usually performed from a femoral venous - transfemoral - approach, but this may not be the optimal vascular access option in some patients. This study aimed to determine which group of patients might benefit from an internal jugular - transjugular - approach for transcatheter pulmonary valve implantation. METHODS This multicentre retrospective study included all patients who underwent attempted transcatheter pulmonary valve placement in the right ventricular outflow tract between April 2010 and June 2012 at two large congenital heart centres. Patients were divided into two groups based on venous access site - transfemoral or transjugular. Patient characteristics, procedural outcomes, and complications were compared between groups. RESULTS Of 81 patients meeting the inclusion criteria (median age 16.4 years), the transjugular approach was used in 14 patients (17%). The transjugular group was younger (median age 11.9 versus 17.3 years), had lower body surface area (mean 1.33 versus 1.61 m2), more often had moderate or greater tricuspid regurgitation (29% versus 7%), and had a higher ratio of right ventricle-to-systemic systolic pressure (mean 82.4 versus 64.7). Patients requiring a transjugular approach after an unsuccessful transfemoral approach had longer fluoroscopic times and procedure duration. CONCLUSIONS The transjugular approach for transcatheter pulmonary valve implantation is used infrequently but is more often used in younger and smaller patients. Technical limitations from a transfemoral approach may be anticipated if there is moderate or greater tricuspid regurgitation or higher right ventricular pressures. In these patients, a transjugular approach should be considered early.

Tailoring the physicochemical and shape memory properties of the biodegradable polymer poly(Glycerol dodecanoate) via curing conditions

A major challenge in the repair and regeneration of soft tissue damage occurring as a result of aging, injury, or disease is recapitulating the biomechanical properties of the native tissue. Ideally, a candidate biomaterial for soft tissue engineering applications should be biocompatible, nonlinearly elastic to match soft tissue mechanical behavior, biodegradable to enable tissue remodeling, and tailorable to achieve a range of nonlinear elastic mechanical properties to match specific soft tissues. In addition, for cardiac and other applications, the biomaterial should have shape memory characteristics to facilitate minimally invasive and/or catheter-based delivery. Poly(glycerol dodecanoate) (PGD) is a shape memory material that has nonlinear elastic properties at body temperature and elastic-plastic behavior at room temperature. In this study, we investigated the effects of curing conditions on the nonlinear elastic, shape memory, and biocompatibility properties of PGD. Increased curing and crosslinking resulted in an increase in both the initial stiffness and the nonlinear strain stiffening behavior of PGD. After shape fixation at 60% strain, 100% shape recovery was achieved within 1 min at body temperature for all conditions tested. Polymer curing had no adverse effects on the cellular biocompatibility or non-hemolytic characteristics of PGD, indicating the potential suitability of these formulations for blood-contacting device applications.

Severely regurgitant left ventricle to ascending aorta conduit in a failing fontan patient treated with a vascular endograft and melody transcatheter pulmonary valve via hybrid approach

A 28‐year‐old male with single ventricular heart disease status post Fontan palliation and subsequent placement of left ventricle to ascending aorta (LV‐AAo) valved conduit developed ascites and edema. Diagnostic catheterization revealed elevated ventricular end diastolic pressures (EDP) secondary to severe LV‐AAo conduit regurgitation. Given the unique anatomy, surgical access via the right axillary artery provided optimal route for transcatheter valve implantation within the conduit. The procedure resulted in significant hemodynamic improvement with no complications.