Late pulmonary valve replacement in congenital heart disease patients without original congenital pulmonary valve pathology

Insights into regional adaptations in the growing pulmonary artery using a meso-scale structural model: effects of ascending aorta impingement

As the next step in our investigations into the structural adaptations of the main pulmonary artery (PA) during postnatal growth, we utilized the extensive experimental measurements of the growing ovine PA from our previous study (Fata et al., 2013, "Estimated in vivo Postnatal Surface Growth Patterns of the Ovine Main Pulmonary Artery and Ascending Aorta," J. Biomech. Eng., 135(7), pp. 71010-71012). to develop a structural constitutive model for the PA wall tissue. Novel to the present approach was the treatment of the elastin network as a distributed fiber network rather than a continuum phase. We then utilized this model to delineate structure-function differences in the PA wall at the juvenile and adult stages. Overall, the predicted elastin moduli exhibited minor differences remained largely unchanged with age and region (in the range of 150 to 200 kPa). Similarly, the predicted collagen moduli ranged from ∼1,600 to 2700 kPa in the four regions studied in the juvenile state. Interestingly, we found for the medial region that the elastin and collagen fiber splay underwent opposite changes (collagen standard deviation juvenile = 17 deg to adult = 28 deg, elastin standard deviation juvenile = 35 deg to adult = 27 deg), along with a trend towards more rapid collagen fiber strain recruitment with age, along with a drop in collagen fiber moduli, which went from 2700 kPa for the juvenile stage to 746 kPa in the adult. These changes were likely due to the previously observed impingement of the relatively stiff ascending aorta on the growing PA medial region. Intuitively, the effects of the local impingement would be to lower the local wall stress, consistent with the observed parallel decrease in collagen modulus. These results suggest that during the postnatal somatic growth period local stresses can substantially modulate regional tissue microstructure and mechanical behaviors in the PA. We further underscore that our previous studies indicated an increase in effective PA wall stress with postnatal maturation. When taken together with the fact that the observed changes in mechanical behavior and structure in the growing PA wall were modest in the other three regions studied, our collective results suggest that the majority of the growing PA wall is subjected to increasing stress levels with age without undergoing major structural adaptations. This observation is contrary to the accepted theory of maintenance of homeostatic stress levels in the regulation of vascular function, and suggests alternative mechanisms might regulate postnatal somatic growth. Understanding the underlying mechanisms will help to improve our understanding of congenital defects of the PA and lay the basis for functional duplication in their repair and replacement.

Estimated in vivo postnatal surface growth patterns of the ovine main pulmonary artery and ascending aorta

Delineating the normal postnatal development of the pulmonary artery (PA) and ascending aorta (AA) can inform our understanding of congenital abnormalities, as well as pulmonary and systolic hypertension. We thus conducted the following study to delineate the PA and AA postnatal growth deformation characteristics in an ovine model. MR images were obtained from endoluminal surfaces of 11 animals whose ages ranged from 1.5 months/15.3 kg mass (very young) to 12 months/56.6 kg mass (adult). A bicubic Hermite finite element surface representation was developed for the each artery from each animal. Under the assumption that the relative locations of surface points were retained during growth, the individual animal surface fits were subsequently used to develop a method to estimate the time-evolving local effective surface growth (relative to the youngest measured animal) in the end-diastolic state. Results indicated that the spatial and temporal surface growth deformation patterns of both arteries, especially in the circumferential direction, were heterogeneous, leading to an increase in taper and increase in cross-sectional ellipticity of the PA. The longitudinal PA growth stretch of a large segment on the posterior wall reached 2.57 ± 0.078 (mean ± SD) at the adult stage. In contrast, the longitudinal growth of the AA was smaller and more uniform (1.80 ± 0.047). Interestingly, a region of the medial wall of both arteries where both arteries are in contact showed smaller circumferential growth stretches-specifically 1.12 ± 0.012 in the PA and 1.43 ± 0.071 in the AA at the adult stage. Overall, our results indicated that contact between the PA and AA resulted in increasing spatial heterogeneity in postnatal growth, with the PA demonstrating the greatest changes. Parametric studies using simplified geometric models of curved arteries during growth suggest that heterogeneous effective surface growth deformations must occur to account for the changes in measured arterial shapes during the postnatal growth period. This result suggests that these first results are a reasonable first-approximation to the actual effective growth patterns. Moreover, this study clearly underscores how functional growth of the PA and AA during postnatal maturation involves complex, local adaptations in tissue formation. Moreover, the present results will help to lay the basis for functional replacement by defining critical geometric metrics.

Performance of bovine pericardial valves in the pulmonary position

BACKGROUND

The purpose of this study is to determine the outcome and performance of bovine pericardial valves in the pulmonary position.

METHODS

This is a retrospective review of all patients with congenital heart disease who had pulmonary valve replacement using a bovine pericardial valve from 2002 to 2009 at a single institution.

RESULTS

There were 73 consecutive patients, with a median age of 17.3 years (range, 2.1 to 64.4). Their diagnosis was tetralogy of Fallot (n = 47), pulmonary stenosis (n = 11), or other (n = 15). Sixty-nine patients had 91 previous surgical procedures. The mean time from last surgery was 19.9 ± 11.6 years. Forty-three patients had concomitant surgical procedures. There were no perioperative deaths. Clinical follow-up was available in 68 patients (93%). There were no late deaths, and all patients were in New York Heart Association functional class I during a median follow-up period of 2.6 years (range, 0.2 to 8.0). One patient had endocarditis necessitating valve removal 2 years after surgery. Freedom from pulmonary valve reoperation was 100%, 97.7%, and 97.7% at 1, 3, and 5 years, respectively (95% confidence interval: 93.2% to 100%). Mean pulmonary valve gradient at follow-up was 19 ± 14 mm Hg. Degree of pulmonary insufficiency was less than moderate in 62 patients, moderate in 4, and more than moderate in 2. Freedom from moderate-severe or severe pulmonary insufficiency was 97.7%, 89.1%, and 89.1% at 1, 3, and 5 years, respectively (5-year 95% confidence interval: 77.0% to 100%).

CONCLUSIONS

Pulmonary valve replacement using a bovine pericardial valve can be accomplished with low perioperative morbidity and favorable midterm outcomes. Further follow-up is necessary to evaluate the long-term performance of bovine pericardial valves in the pulmonary position.