Maladaptive aortic properties after the Norwood procedure: An angiographic analysis of the Pediatric Heart Network Single Ventricle Reconstruction Trial

Ascending aortic extension to enlarge the retroaortic space in children after the Norwood procedure

Left pulmonary artery stenosis is a well-recognized complication following the Norwood procedure. We herein report two cases in which ascending aortic extension was performed to enlarge the retroaortic space in children with left pulmonary artery stenosis after the Norwood procedure. We used graft interposition in the ascending aorta to increase the retroaortic apace and concomitantly performed extended left pulmonary artery reconstruction. This procedure obtains a more balanced distribution of the pulmonary blood flow, which is crucial to achieve good Fontan circulation.

Chimney reconstruction provides a wider subaortic space and reduces the risk of pulmonary artery compression in the Norwood-type aortic arch reconstruction without patch supplementation

OBJECTIVES

Pulmonary artery (PA) compression by the neoaorta is a serious complication after the Norwood-type palliation (NP) for hypoplastic left heart syndrome. Either excess patch tailoring or limited use of autologous tissue may cause narrowing of the subaortic space. The chimney technique could theoretically provide a wide subaortic space.

METHODS

Twenty-nine patients with both pre- and post-NP computed tomography data available of the 37 consecutive patients who underwent NP in our institution were reviewed. Arch height, arch width, sinus of Valsalva diameter, area under the neoaortic arch and arch angle were measured. These patients were divided according to the neo-arch reconstruction technique, chimney reconstruction technique (CR) or conventional direct reconstruction technique (DR).

RESULTS

Median age and weight at NP were 2.1 months and 3.5 kg, respectively. Twenty-two patients underwent previous bilateral PA banding. During NP, 17 CR and 12 DR were performed. Four patients in the DR group developed PA compression. No neoaortic arch dilatation was found in either group. Post-NP arch width, area under the neo-arch and the arch angle were significantly larger in the CR group. Pre-NP arch height was significantly smaller in DR patients with PA compression than in those without.

CONCLUSIONS

The chimney technique decreased the risk of PA compression and provided a wider subaortic space and a less acute arch angle. This technique had no short-term effect on the neoaortic root. Small preoperative arch height is a potential risk factor for PA compression in DR, and the chimney technique could be an effective solution.

High-degree Norwood neoaortic tapering is associated with abnormal flow conduction and elevated flow-mediated energy loss

OBJECTIVE

The Norwood neoaortic arch biomechanical properties are abnormal due to reduced vessel wall compliance and abnormal geometry. Others have previously described neoaortic geometric distortion by the degree of diameter reduction (tapering) and associated this with mismatched ventricular-neoaortic coupling, abnormal flow hemodynamic parameters, and worse patient outcome. Our purposes were to investigate the influence of neoaortic tapering (ie, diameter reduction) on flow-mediated viscous energy loss (E_L') in post-Norwood palliated hypoplastic left heart syndrome patients, and correlate flow-geometry with single ventricle power generation.

METHODS

Twenty-six palliated hypoplastic left heart syndrome patients underwent comprehensive cardiac evaluation with 4-dimensional-flow magnetic resonance imaging. Patients were grouped into high- (group H, n = 13) and low- (group L, n = 13) degree neoaortic tapering using the median cutoff value of neoaortic diameter variance. E_L' was calculated along standardized segments using 4-dimensional-flow magnetic resonance imaging. Flow-mediated power loss as a percentage of total power generated by the single ventricle was determined.

RESULTS

Group H had a higher prevalence of abnormal recirculating flow in the neoaorta and elevated neoaortic E_L' in the ascending aorta (1.0 vs 0.6 mW; P = .004). Group H E_L' was increased across the entire thoracic aorta (2.6 vs 1.3 mW; P = .002) and accounted for 0.7% of generated ventricular power versus 0.3% in group L (P = .024). E_L' directly correlated with the degree of ascending aortic dilation (R = 0.49; P = .012).

CONCLUSIONS

Patients with high degree neoaortic tapering have more perturbed flow through the neoaorta and increased E_L'. Flow-mediated energy loss due to abnormal flow represents irreversibly wasted power generated by the single right ventricle. In patients with high-degree neoaortic tapering, E_L' was more than 2-fold greater than low-degree tapering patients. These data suggest that oversizing the Norwood neoaortic reconstruction should be avoided and that patients with distorted neoaortic geometry may warrant increased surveillance for single-ventricle deterioration.

Global Leadership in Paediatric and Congenital Cardiac Care: "Using data to improve outcomes - an interview with Jennifer S. Li, MD, MHS"

Dr. Jennifer Li is the focus of our second in a planned series of interviews in Cardiology in the Young entitled, "Global Leadership in Paediatric and Congenital Cardiac Care". Dr. Li was born in Boston, Massachusetts, United States of America, and moved to Indianapolis, Indiana where she completed her secondary education. She then attended Stanford University, majoring in Chemistry and English and graduating with distinction in 1983. Dr. Li then attended Duke University School of Medicine, graduating in 1987. She then completed her internship at Children's Hospital of Philadelphia in 1987-1989, returning to Duke University Medical Center to complete both her residency in general paediatrics in 1989-1990 followed by her fellowship in paediatric cardiology in 1990-1993. She would later complete her Master's Degree in Health Sciences at Duke University in 2005.Dr. Li has spent her entire career as a paediatric cardiologist at Duke University Medical Center, where she was appointed a Professor of Pediatrics and Professor of Medicine in 2008 and has held the position as Beverly C. Morgan Endowed Professor of Pediatrics since 2012. She has served as the Chief of Paediatric Cardiology at Duke University Medical Center since 2006. She also was the Director of Paediatric Research at Duke Clinical Research Institute from 2001-2015. Dr. Li has played an instrumental role in evaluating the safety and efficacy of drugs in children, as well as in analysing and linking large multicentric databases to evaluate the outcomes, quality, and cost of paediatric and congenital cardiac care. Dr. Li has received funding from the National Institute of Health of the United States of America, as well as from industry and foundation grants. This article presents our interview with Dr. Li, an interview that covers her experience collaborating with governmental organizations and industry in the pursuit of common interests to design clinical drug trials, link and analyse large, multicentric databases, and improve paediatric health care.

Mechano-biological adaptation of the pulmonary artery exposed to systemic conditions

Cardiac surgeries may expose pulmonary arterial tissue to systemic conditions, potentially resulting in failure of that tissue. Our goal was to quantitatively assess pulmonary artery adaptation due to changes in mechanical environment. In 17 sheep, we placed a pulmonary autograft in aortic position, with or without macroporous mesh reinforcement. It was exposed to systemic conditions for 6 months. All sheep underwent 3 ECG-gated MRI’s. Explanted tissue was subjected to mechanical and histological analysis. Results showed progressive dilatation of the unreinforced autograft, while reinforced autografts stabilized after two months. Some unreinforced pulmonary autograft samples displayed more aorta-like mechanical behavior with increased collagen deposition. The mechanical behavior of reinforced autografts was dominated by the mesh. The decrease in media thickness and loss of vascular smooth muscle cells was more pronounced in reinforced than in unreinforced autografts. In conclusion, altering the mechanical environment of a pulmonary artery causes changes in its mechano-biological properties.

Early outcomes and computational fluid dynamic analyses of chimney reconstruction in the Norwood procedure†

OBJECTIVES

The ideal configuration of a reconstructed aortic arch in the Norwood procedure for hypoplastic left heart syndrome is still a matter of debate. Chimney reconstruction was developed to avoid postoperative complications and turbulent flow in the aortic arch. This study sought to clarify early outcomes of the procedure and verify its haemodynamic advantages using computational fluid dynamics (CFD).

METHODS

Fourteen consecutive patients with hypoplastic left heart syndrome or a variant who underwent chimney reconstruction in the Norwood procedure between January 2013 and March 2018 were enrolled. Median age and body weight at the time of operation were 2.5 months and 4.1 kg, respectively. Thirteen patients (93.9%) had been palliated with previous bilateral pulmonary artery (PA) banding. In addition, patient-specific CFD models of neoarches based on postoperative computed tomograms from 6 patients were created and the flow profiles analysed.

RESULTS

Survival rates at 1, 3 and 5 years were 76.6%, 67.3% and 67.3%, respectively. No patient developed left PA compression by neoaorta, neoaortic dilation or neoaortic insufficiency. Only 2 patients (14.3%) required surgical intervention for recoarctation. Fontan completion was performed on 5 patients. On CFD analysis, all reconstructed aortic arches showed low energy loss (9.16-14.4 mW/m2) and low wall shear stresses.

CONCLUSIONS

Chimney reconstruction was a feasible technique when homografts were not readily available. CFD analyses underscored the fact that this technique produced excellent flow profiles. Larger studies should be conducted to clarify long-term outcomes.

Relationship of Aortic Stiffness to Exercise and Ventricular Volumes in Single Ventricles

BACKGROUND

Patients with single ventricle (SV) may often undergo aortic reconstruction that creates a stiff large vessel, increasing afterload and affecting exercise performance. The objective of this study was to determine the relationship of pulse wave velocity (PWV) and distensibility in reconstructed and normal aortic arches after Fontan with exercise variables.

METHODS

PWV and distensibility of the descending aorta at the level of the diaphragm (DAo) were calculated with real-time exercise cardiac magnetic resonance in 48 patients with SV after Fontan (18 after aortic reconstruction; 30 without aortic reconstruction) and compared with metabolic exercise stress test variables.

RESULTS

PWV was greater in the reconstructed group than in the non-reconstructed group (median 4.4 m/s [range: 2.3 to 9.8 m/s] versus 3.6 [range: 2.6 to 6.3 m/s], respectively, p = 0.003). Statistically significant inverse correlations were found between PWV and end-diastolic, end-systolic, and stroke volumes at rest and at exercise in the reconstructed group. In addition, inverse correlations also existed in the reconstructed group between distensibility of the DAo and the exercise variables such as peak oxygen pulse (R = 0.56, p = 0.02), peak oxygen consumption (R = 0.63, p = 0.008), oxygen consumption at ventilatory anaerobic threshold (R = 0.48, p = 0.04), and peak work (R = 0.54, p = 0.02). Similar correlations were not seen in patients with non-reconstructed aortas.

CONCLUSIONS

Patients with SV with reconstructed aortas have increased aortic stiffness, increasing afterload on the ventricle. Native DAo stiffness distal to the reconstruction is inversely correlated with exercise performance, presumably to decrease impedance mismatch to maintain homogeneity of the aortic wall. This information suggests a possible mechanism for decreased exercise performance in patients with SV with aortic reconstructions.

Arch Augmentation via Median Sternotomy for Coarctation of Aorta With Proximal Arch Hypoplasia

BACKGROUND

Coarctation of the aorta can be associated with hypoplasia of the proximal transverse aortic arch. One approach to manage this condition is via left thoracotomy and extended end-to-end anastomosis with the expectation that the proximal arch will grow over time. Our preferred approach is to augment the aorta via midline sternotomy. We hypothesized that this approach is safe, durable, and allows reliable growth of the aorta.

METHODS

We identified the records of patients with biventricular anatomy who had coarctation of the aorta, hypoplasia of the proximal transverse arch, and no other cardiac lesion that would mandate cardiopulmonary bypass use and midline sternotomy. The records of 62 such patients operated on between 2005 and 2016 were retrospectively reviewed. Patient demographics, clinical variables and outcome data were collected and analyzed using SAS 9.4. Data are presented as median (interquartile range [IQR]).

RESULTS

Sixty-two patients (23 girls [37%]) underwent repair at 10 (IQR, 5 to 21) days of life. Forty-nine (79%) patients were on prostaglandin infusion to maintain ductal patency. Fifteen (24%) patients presented in shock with end organ dysfunction, 17 (27%) were on inotropes, and 26 (42%) were mechanically ventilated. The proximal transverse arch was 41% (IQR, 34% to 47%) of the size of ascending aorta as measured by echocardiography (z-score, -5 [IQR, -5.8 to -4.3]). Following median sternotomy, repair was carried out on cardiopulmonary bypass (41 [IQR, 37 to 47] minutes). The arch was reconstructed with (n = 26 [42%]) or without (n = 36 [58%]) coarctectomy usually using homograft patch aortoplasty (n = 58 [94%]). In all but 2 patients, repair was undertaken with circulatory arrest (27 [IQR, 22 to 31] minutes). Patients were extubated 4 (IQR, 3 to 5) days later and discharged home in 12 (IQR, 8 to 18) days. There was no mortality, and 8 morbidity events (3 recurrent nerve injury, 2 chylothorax, 1 phrenic nerve injury, 1 seizure, and 1 superficial wound infection) in 7 (11%) patients. All patients are alive at 41 (IQR, 11 to 64) months of follow-up. Reintervention was required in 6 (10%) patients (5 catheter based and 3 surgical) for recurrent distal coarctation. Reintervention-free survival at 1, 3, and 5 years was 87%. Only 1 child was currently on antihypertensive therapy, and all were in New York Heart Association functional class I symptoms. At last echocardiogram, the proximal transverse arch was 97% (IQR, 84% to 103%) of the diameter of the ascending aorta (z-score, 0.8 (IQR, 0.3 to 1.3]), ejection fraction was 70% (IQR, 60% to 76%), and only 2 patients had significant left ventricular hypertrophy.

CONCLUSIONS

Arch augmentation via median sternotomy is a safe and effective procedure that can be accomplished with low morbidity and mortality. The reconstructed arch retains excellent growth potential resulting in a very favorable physiologic outcome.