Aart Mookhoek

Biomechanical Properties of Human Ascending Thoracic Aortic Aneurysms

BACKGROUNDnSurgical management of ascending thoracic aortic aneurysms (aTAAs) relies on maximum diameter, growth rate, and presence of connective tissue disorders. However, dissection and rupture do occur in patients who do not meet criteria for surgical repair. This study investigated the mechanical properties of aTAAs compared with normal human ascending aortas for eventual development of biomechanical aTAA risk models.nnnMETHODSnaTAA specimens (n = 18) were obtained from patients undergoing surgical aneurysm repair, and fresh, healthy ascending aortas (n = 19) as controls were obtained from the transplant donor network. Biaxial stretch testing was performed to obtain tissue mechanical properties. Patient-specific aTAA physiologic stress was calculated based on preoperative computed tomography diameter. aTAA and ascending aorta tissue stiffness at respective physiologic stress were determined.nnnRESULTSnPhysiologic stress of aTAA was significantly greater (241.6 ± 59.4 kPa) than the 74 kPa for normal controls. Tissue stiffness of aTAAs was significantly greater than that of the ascending aortas at their respective physiologic stresses in the circumferential (3041.4 ± 1673.7 vs 905.1 ± 358.9 kPa, respectively; p < 0.001) and longitudinal (3498.2 ± 2456.8 vs 915.3 ± 368.9 kPa, respectively; p < 0.001) directions. Tissue stiffness of aTAAs positively correlated with aTAA diameter but did not correlate with patient age. No correlation was found between aTAA physiologic stress level and maximum aTAA diameter.nnnCONCLUSIONSnaTAAs are much stiffer than normal ascending aortas at their respective physiologic stress, which was also significantly greater in ATAAs than ascending aortas. Patient-specific physiologic stress did not correlate with maximum aTAA diameter, and patient-specific aTAA wall stress may be a useful variable to predict adverse aTAA events.

Reported Outcome After Valve-Sparing Aortic Root Replacement for Aortic Root Aneurysm: A Systematic Review and Meta-Analysis

Valve-sparing aortic root techniques have progressively gained ground in the treatment of aortic root aneurysm and aortic insufficiency. By avoiding anticoagulation therapy they offer a good alternative to composite graft replacement. This systematic review describes the reported outcome of valve-sparing aortic root replacement, focusing on the remodeling and reimplantation technique. A systematic literature search on the characteristics of and outcomes after valve-sparing aortic root replacement revealed 1,659 articles. The inclusion criteria were a focus on valve-sparing aortic root replacement in adults with aortic root aneurysm, presentation of survival data, and inclusion of at least 30 patients. Data were pooled by inverse variance weighting and analyzed by linear regression. Of 1,659 articles published between January 1, 2000, and January 1, 2014, 31 were included (n = 4,777 patients). The mean age at operation was 51 ± 14.7 years, and 14% of patients had a bicuspid aortic valve. The reimplantation technique was used in 72% and remodeling in 27% (1% other). No clinical advantage in terms of survival and reoperation of one technique over the other was found. Cusp repair was performed in 33%. Pooled early mortality was 2% (n = 103). During follow-up (21,716 patient-years), 262 patients died (survival 92%), and 228 (5%) underwent reoperation, mainly valve replacement. Major adverse valve-related events were low (1.66% patient-years). Preoperative severe aortic valve regurgitation showed a trend toward higher reoperation rate. Remodeling and reimplantation techniques show comparable survival and valve durability results, providing a valid alternative to composite valve replacement. The heterogeneity in the data underlines the need for a collaborative effort to standardize outcome reporting.

Bentall Procedure: A Systematic Review and Meta-Analysis

BACKGROUNDnThe Bentall procedure is considered the gold standard in the treatment of patients requiring aortic root replacement. An up-to-date overview of outcomes after the Bentall procedure is lacking.nnnMETHODSnWe conducted a systematic review and meta-analysis of characteristics of and long-term outcome after the Bentall procedure with a mechanical valve prosthesis. Pooling was performed using the inverse variance method within a random-effects model. Outcome events are reported as linearized occurrence rates (percentage per patient year) with 95% confidence intervals.nnnRESULTSnIn total, 46 studies with 7,629 patients (mean age, 50 years; 76% men) were selected. Pooled early mortality was 6% (422 patients). During a mean follow-up of 6 years (49,175 patient-years), the annual linearized occurrence rate for late mortality was 2.02% (1.77%- 2.31%; 892 patients), for aortic root reoperation it was 0.46% (0.36%-0.59%), for hemorrhage it was 0.64% (0.47%-0.87%), for thromboemboli it was 0.77% (0.60%-1.00%), for endocarditis it was 0.39% (0.33%-0.46%), and for major adverse valve-related events it was 2.66% (2.17%-3.24%). Operations performed in more recent years were associated with lower rates of aortic root reoperation (betaxa0= -0.452; pxa0= 0.015).nnnCONCLUSIONSnThis systematic review illustrates that rates of aortic root reoperation after the Bentall procedure have decreased over the years. However, late mortality, major bleeding, and thromboembolic complications remain a concern. This report may be used to benchmark the potential therapeutic benefit of novel surgical approaches, such as valve-sparing aortic root replacement.

European multicenter experience with valve-sparing reoperations after the Ross procedure

BACKGROUNDnAutograft valve preservation at reoperation may conserve some of the advantages of the Ross procedure. However, results of long-term follow-up are lacking. In this retrospective multicenter study, we present our experience with valve-sparing reoperations after the Ross procedure, with a focus on long-term outcome.nnnMETHODSnA total of 86 patients from 6 European centers, who underwent valve-sparing reoperation after the Ross procedure between 1997 and 2013, were included in the study.nnnRESULTSnReoperation was performed a median of 9.1xa0years after the Ross procedure in patients with a median age of 38.4xa0years (interquartile range: 27.1-51.6xa0years). Preoperative severe autograft regurgitation (grade ≥3) was present in 46% of patients. In-hospital mortality was 1%. During a median follow-up of 4.3xa0years, 3 more patients died of noncardiac causes, resulting in a cumulative survival at 8xa0years of 89% (95% confidence interval: 65%-97%). Fifteen patients required a reintervention after valve-sparing reoperation, mostly owing to prolapse or retraction of autograft cusps. Freedom from reintervention was 76% (95% confidence interval: 57%-87%) at 8xa0years. The reintervention hazard was increased in patients who had isolated and/or severe aortic regurgitation at valve-sparing reoperation. In patients without reintervention after valve-sparing autograft reoperation (nxa0=xa063), severe aortic regurgitation was present in 3% at last follow-up.nnnCONCLUSIONSnValve-sparing autograft reoperations after the Ross procedure carry a low operative risk, with acceptable reintervention rates in the first postoperative decade. Patients with isolated and/or severe autograft regurgitation have an increased hazard of reintervention after valve-sparing reoperation; for these patients, careful preoperative weighing of surgical options is required.

Biomechanics of Failed Pulmonary Autografts Compared With Normal Pulmonary Roots

BACKGROUNDnProgressive dilatation of pulmonary autografts after the Ross operation may reflect inadequate remodeling of the native pulmonary root to adapt to systemic circulation. Understanding the biomechanics of autograft root dilatation may aid designing strategies to prevent dilatation. We have previously characterized normal human pulmonary root material properties; however, the mechanical properties of failed autografts are unknown. In this study, failed autograft roots explanted during reoperation were acquired, and their material properties were determined.nnnMETHODSnFailed pulmonary autograft specimens were obtained from patients undergoing reoperation after the Ross operation. Fresh human native pulmonary roots were obtained from the transplant donor network as controls. Biaxial stretch testing was performed to determine tissue mechanical properties. Tissue stiffness was determined at patient-specific physiologic stresses at pulmonary pressures.nnnRESULTSnNonlinear stress-strain response was present in both failed autografts and normal pulmonary roots. Explanted pulmonary autografts were less stiff than were their native pulmonary root counterparts at 8 mm Hg (134 ± 42 vs 175 ± 49 kPa, respectively) (pxa0= 0.086) and 25 mm Hg (369 ± 105 vs 919 ± 353 kPa, respectively) (pxa0= 0.006). Autograft wall stiffness at both 8 and 25 mm Hg was not correlated with age at the Ross procedure (pxa0= 0.898 and pxa0= 0.813, respectively) or with time in the systemic circulation (pxa0= 0.609 and pxa0= 0.702, respectively).nnnCONCLUSIONSnFailed pulmonary autografts retained nonlinear response to mechanical loading typical of healthy human arterial tissue. Remodeling increased wall thickness but decreased wall stiffness in failed autografts. Increased compliance may explain progressive autograft root dilatation in autograft failures.

Ross Procedure in Neonates and Infants: A European Multicenter Experience.

BACKGROUNDnInfants and neonates with severe left ventricular outflow tract obstruction may require pulmonary autograft replacement of the aortic root. In this retrospective multicenter cohort study, we present our experience with the Ross procedure in neonates and infants with a focus on midterm survival and pulmonary autograft durability.nnnMETHODSnA retrospective observational study was performed in 76 infants (aged less than 1 year) operated on in six congenital cardiac centers in The Netherlands and Germany between 1990 and 2013.nnnRESULTSnPatients had a pulmonary autograft replacement of the aortic valve with (68%) or without (32%) septal myectomy. Median patient age was 85 days (range, 6 to 347). Early mortality (n = 13, 17%) was associated with neonatal age, preoperative use of intravenous inotropic drugs, and congenital aortic arch defects. Five patients (9%) died during follow-up. Freedom from autograft reintervention was 98% at 10 years. Echocardiography demonstrated good valve function, with no or trace regurgitation in 73% of patients. Freedom from right ventricular outflow tract reintervention was 51% at 10 years. Univariable analysis demonstrated superior freedom from reintervention of pulmonary homografts compared with aortic homografts or xenografts.nnnCONCLUSIONSnPulmonary autograft replacement of the aortic valve in neonates and infants is a high-risk operation but offers a durable neoaortic valve. Midterm durability reflects successful adaptation of the autograft to the systemic circulation. Late mortality associated with heart failure was an unexpected finding.

Biomechanics of Failed Pulmonary Autografts Compared to Native Aortic Roots

BACKGROUNDnProgressive autograft dilatation after a Ross operation suggests that remodeling does not effectively reproduce native aortic root biomechanics. In the first of this two-part series, we compared mechanical properties of explanted autografts to pulmonary roots at pulmonary pressures. The goal of this study was to compare mechanical properties of explanted autografts to native aortic roots at systemic pressures.nnnMETHODSnAutograft specimens were obtained from patients undergoing reoperation after Ross operation. Forxa0comparison, native aortic roots were obtained from unused donor hearts. Biaxial stretch testing was performed to determine tissue mechanical properties. Tissue stiffness was determined at patient-specific physiologic stresses corresponding to systemic pressures (80 and 120 mm Hg) and hypertensive state (200 mm Hg).nnnRESULTSnNonlinear stress-strain curves were present for both failed autografts and native aortic roots. Explanted autografts were significantly more compliant than native aortic roots at 80 mm Hg (1.53 ± 0.68 versus 2.99 ± 1.34 MPa; pxa0= 0.011), 120 mm Hg (2.54 ± 1.18 versus 4.93 ± 2.21 MPa; pxa0= 0.013), and 200 mm Hg (4.79 ± 2.30 versus 9.21 ± 4.16 MPa; pxa0= 0.015). Autograft tissue stiffness at 80, 120, and 200 mm Hg was not correlated with age at the time of Ross operation (pxa0= 0.666, pxa0=xa00.639, and pxa0= 0.616, respectively) or time in the systemic circulation (pxa0= 0.635, pxa0= 0.637, and pxa0= 0.647, respectively).nnnCONCLUSIONSnFailed pulmonary autografts retained a nonlinear response to mechanical loading typical of healthy arterial tissue. Despite similar wall thickness between autografts and aorta, autograft stiffness in this patient population was significantly reduced compared with native aortic roots. We demonstrated that biomechanical remodeling was inadequate in these specimens to achieve native aortic mechanical properties, which may have resulted in progressive autograft root dilatation.

Material properties of CorCap passive cardiac support device.

BACKGROUNDnMyocardial function deteriorates during ventricular remodeling in patients with congestive heart failure (HF). Ventricular restraint therapy using a cardiac support device (CSD) is designed to reduce the amount of stress inside the dilated ventricles, which in turn halts remodeling. However, as an open mesh surrounding the heart, it is unknown what the mechanical properties of the CSD are in different fiber orientations.nnnMETHODSnComposite specimens of CorCap (Acorn Cardiovascular, Inc, St. Paul, MN) CSD fabric and silicone were constructed in different fiber orientations and tested on a custom-built biaxial stretcher. Silicone controls were made and stretched to detect the parameters of the matrix. CSD coefficients were calculated using the composite and silicone matrix stress-strain data. Stiffness in different fiber orientations was determined.nnnRESULTSnSilicone specimens exerted a linear behavior, with stiffness of 2.57 MPa. For the composites with 1 fiber set aligned with respect to the stretch axes, stiffness in the direction of the aligned fiber set was higher than that in the cross-fiber direction (14.39 MPa versus 5.66 MPa), indicating greater compliance in the cross-fiber direction. When the orientation of the fiber sets in the composite were matched to the expected clinical orientation of the implanted CorCap, the stiffness in the circumferential axis (with respect to the heart) was greater than in the longitudinal axis (10.55 MPa versus 9.70 MPa).nnnCONCLUSIONSnThe mechanical properties of the CorCap demonstrate directionality with greater stiffness circumferentially than longitudinally. Implantation of the CorCap clinically should take into account the directionality of the biomechanics to optimize ventricular restraint.