Pediatric cardiac surgery in the 1990s

Insight into pathologic abnormalities in congenital semilunar valve disease based on advances in understanding normal valve microstructure and extracellular matrix

Congenitally diseased valves are relatively frequent causes of significant morbidity and mortality. Pathology descriptions of such valves have primarily focused on gross structural features including the number of leaflets or commissures (bicuspid/bicommissural valve) and alterations in the contour, thickness, and consistency of the leaflets (dysplastic valve). Functional correlates of these pathologic alterations are valvar stenosis, insufficiency, or both. Further characterization of the microstructural abnormalities seen in these malformed valves may not only provide insight into the correlation of distinct pathologies with their respective pathogenesis and clinical sequelae but also prove pivotal in uncovering new avenues for therapeutic interventions and prevention regimens. This review summarizes microstructural findings in congenital semilunar valve disease (CSVD) and discusses their relevance in light of recent advances in knowledge of normal valve microstructure, biology, and function. Specifically, the biological and mechanical roles of various matrix components and their interactions are discussed in the context of CSVD. Indeed, recent research in normal valves adds significant insight into CSVD and raises many hypotheses that will need to be addressed by future studies.

Extracellular matrix remodeling and cell phenotypic changes in dysplastic and hemodynamically altered semilunar human cardiac valves

INTRODUCTION

Congenital cardiac valve disease is common, affecting ∼1% of the population, with substantial morbidity and mortality, but suboptimal treatment options. Characterization of the specific matrix and valve cell phenotypic abnormalities in these valves could lend insight into disease pathogenesis and potentially pave the way for novel therapies.

METHODS

Thirty-five human aortic and pulmonic valves were categorized based on gross and microscopic assessment into control valves (n=21); dysplastic valves, all except one also displaying hemodynamic changes (HEMO/DYSP, n=6); and hemodynamically altered valves (HEMO, n=8). Immunohistochemistry was performed on valve sections and flow cytometry on valvular interstitial cells.

RESULTS

While both hemodynamically altered aortic and pulmonic valves demonstrated increased collagen turnover and cell activation, prolyl 4-hydroxylase and hyaluronan increased in hemodynamically altered aortic valves but decreased in hemodynamically altered pulmonic valves relative to control valves (P<.001). HEMO/DYSP aortic valves demonstrated decreased collagen and elastic fiber synthesis and turnover compared to both hemodynamically altered aortic valves and control aortic valves (each P<.006). Valvular interstitial cells from both hemodynamically altered and HEMO/DYSP pulmonic valves showed altered cell phenotype compared to control valves (each P<.032), especially increased non-muscle myosin. Furthermore, valvular interstitial cells from hemodynamically altered pulmonic valves and HEMO/DYSP aortic and pulmonic valves each demonstrated greater size and complexity compared to control valves (each P<.05).

CONCLUSIONS

Dysplastic semilunar valves displayed alterations in collagen and elastic fiber turnover that were distinct from valves similarly exposed to altered hemodynamics as well as to control valves. These results demonstrate that dysplastic valves are not simply valves with gross changes or loss of leaflet layers, but contain complex matrix and cell phenotype changes that, with future study, could potentially be targets for novel nonsurgical treatments.

The development of tissue-engineered grafts for reconstructive cardiothoracic surgical applications

Surgical correction of congenital heart defects often requires the use of valves, patches, or conduits to establish anatomic continuity. Homografts, xenografts, or mechanical prosthetic devices are frequently implanted during these surgical procedures. These grafts however lack growth potential, are associated with increased risk of thrombosis and infection and have limited durability, thus increasing the morbidity and mortality of their application in pediatric cardiac surgery. These limitations are being addressed through the development of living, biologic tissue-engineered valves, patches, and conduits. Pilot studies and phase 1 clinical trials are currently underway to evaluate their feasibility, safety, and efficacy. The optimal scaffold, cell source, and conditioning parameters, however, still remain to be determined and are areas of active research.

Structural cardiac anomalies

Although it is unrealistic to expect that all major structural cardiac anomalies will be detected at the time of routine prenatal ultrasound, an increase in prenatal diagnosis is anticipated as accreditation of ultrasound practices takes place nationwide. Following the diagnosis of congenital heart disease, evaluation for extracardiac anomalies and chromosomal abnormalities is important because these are found in up to 62% and 38% of prenatally identified cases, respectively. Although the literature is limited, counseling parents based on the prenatal experience gives them realistic information about frequency, diagnosis, associated findings, and prognosis of the heart defect found in their fetus. A multidisciplinary team of perinatologists, pediatric cardiologists, geneticists, pediatric cardiac surgeons, and neonatologists should be assembled to assist patients in making informed decisions about their pregnancies and to establish a reasonable management plan for ongoing pregnancies with congenital heart disease.