The myocardium in tetralogy of Fallot: a histological and morphometric study.

BACKGROUND: Patients with Tetralogy of Fallot frequently develop ventricular dysfunction in the postoperative period. The histological basis of this functional alteration has been scarcely studied. OBJECTIVE: To evaluate myocardial remodeling in anatomical specimens, comparing the subepicardial and subendocardial regions, especially because the subendocardial region is easily approached by means of endomyocardial biopsy. METHODS: Transmural sections of myocardium from the right ventricular (RV) inflow tract, anterior wall and infundibulum, and from the left ventricular (LV) free wall were evaluated regarding the degree of cardiomyocyte hypertrophy, vascularization and interstitial fibrosis were analyzed. RESULTS: The mean diameter of subendocardial cardiomyocytes is similar to that of subepicardial cardiomyocytes in all regions, except for the RV infundibulum, in which subendocardial cardiomyocytes are significantly larger in relation to those of the subepicardium (p=0.007). The amount of interstitial collagen is in the upper limits of normal and was similar in the subendocardial layers in comparison with the subpericardial layer of each region; however, it was greater in the inflow tract and RV anterior wall than in the LV lateral wall. The numerical density of subendocardial capillaries was similar to that of the subepicardium and was lower than the mean minus two standard deviations of normal in all regions and layers, except for the infundibulum, in which the subepicardium showed normal values and the subendocardium showed values lower than the mean minus two standard deviations. CONCLUSION: The postnatal myocardial changes in Tetralogy of Fallot are homogeneously distributed in the subepicardial and subendocardial halves of the ventricular walls, except for the infundibulum, which has peculiar remodeling characteristics and, therefore, is not representative of the other ventricular regions and layers for morphometric studies.

O miocárdio na tetralogia de Fallot: estudo histológico e morfométrico / The myocardium in tetralogy of Fallot: a histological and morphometric study / El miocardio en la tetralogía de Fallot: estudio histológico y morfométrico

FUNDAMENTO: Pacientes com tetralogia de Fallot freqüentemente cursam com disfunção ventricular no período pós-operatório. A base histológica dessa alteração funcional tem sido pouco estudada. OBJETIVO: Avaliar, em espécimes anatômicos, o remodelamento miocárdico comparando as regiões subepicárdica e subendocárdica, especialmente por esta última ser facilmente abordável por meio de biópsias endomiocárdicas. MÉTODOS:Análises em cortes transmurais de miocárdio da via de entrada, parede anterior e infundíbulo do ventrículo direito (VD) e da parede livre do esquerdo (VE), foram avaliados quanto ao grau de hipertrofia de cardiomiócitos, de vascularização e fibrose intersticial. RESULTADOS:O diâmetro médio dos cardiomiócitos do subendocárdio é semelhante ao do subepicárdio em todas as regiões, com exceção do infundíbulo do VD, em que os subendocárdicos se mostraram significativamente maiores em relação aos do subepicárdio (p=0,007). A quantidade de colágeno intersticial encontra-se nos limites superiores do normal e foi similar nas camadas subendocárdicas, comparada à subpericárdica de cada região, sendo, todavia, maior na via de entrada e na parede anterior do VD, do que na parede lateral do VE. A densidade numérica de capilares do subendocárdio foi semelhante à do subepicárdio e esteve menor que a média menos dois desvios-padrão do normal em todas as regiões e camadas, com exceção do infundíbulo, em que o subepicárdio mostrava valores normais e o subendocárdio valores menores que a média menos dois desvios-padrão. CONCLUSÃO: As alterações do miocárdio pós-natal na tetralogia de Fallot estão distribuídas homogeneamente nas metades subepicárdica e subendocárdica das paredes ventriculares, com exceção do infundíbulo, que apresenta características peculiares de remodelamento e que, portanto, não é representativo das demais regiões e camadas ventriculares para estudos morfométricos.

BACKGROUND: Patients with Tetralogy of Fallot frequently develop ventricular dysfunction in the postoperative period. The histological basis of this functional alteration has been scarcely studied. OBJECTIVE: To evaluate myocardial remodeling in anatomical specimens, comparing the subepicardial and subendocardial regions, especially because the subendocardial region is easily approached by means of endomyocardial biopsy. METHODS: Transmural sections of myocardium from the right ventricular (RV) inflow tract, anterior wall and infundibulum, and from the left ventricular (LV) free wall were evaluated regarding the degree of cardiomyocyte hypertrophy, vascularization and interstitial fibrosis were analyzed. RESULTS: The mean diameter of subendocardial cardiomyocytes is similar to that of subepicardial cardiomyocytes in all regions, except for the RV infundibulum, in which subendocardial cardiomyocytes are significantly larger in relation to those of the subepicardium (p=0.007). The amount of interstitial collagen is in the upper limits of normal and was similar in the subendocardial layers in comparison with the subpericardial layer of each region; however, it was greater in the inflow tract and RV anterior wall than in the LV lateral wall. The numerical density of subendocardial capillaries was similar to that of the subepicardium and was lower than the mean minus two standard deviations of normal in all regions and layers, except for the infundibulum, in which the subepicardium showed normal values and the subendocardium showed values lower than the mean minus two standard deviations. CONCLUSION: The postnatal myocardial changes in Tetralogy of Fallot are homogeneously distributed in the subepicardial and subendocardial halves of the ventricular walls, except for the infundibulum, which has peculiar remodeling characteristics and, therefore, is not representative of the other ventricular regions and layers for morphometric studies.

FUNDAMENTO: Frecuentemente, pacientes con tetralogía de Fallot cursan con disfunción ventricular en el período postoperatorio. La base histológica de esa alteración funcional ha sido poco estudiada. OBJETIVO: Evaluar, en especímenes anatómicos, la remodelación miocárdica comparándose las regiones subepicárdica y subendocárdica, sobre todo por esta última ser fácilmente abordable por medio de biopsias endomiocárdicas. MÉTODOS: Se evaluaron análisis en cortes transmurales de miocardio de la vía de entrada, pared anterior e infundíbulo del ventrículo derecho (VD) y de la pared libre del izquierdo (VI), en cuanto al grado de hipertrofia de cardiomiocitos, de vascularización y fibrosis intersticial. RESULTADOS: El diámetro promedio de los cardiomiocitos del subendocardio se asemeja al del subepicardio en todas las regiones, con excepción del infundíbulo del VD, en que los subendocárdicos se mostraron significativamente mayores con relación a los del subepicardio (p=0,007). La cantidad de colágeno intersticial se encuentra en los límites superiores al normal y fue similar en las camadas subendocárdicas, comparada a la subpericárdica de cada región; pero se mostró mayor en la vía de entrada y en la pared anterior del VD, que en la pared lateral del VI. La densidad numérica de capilares del subendocardio se asemejó a la del subepicardio y se mostró menor que el promedio menos dos desviaciones estándar del normal, en todas las regiones y capas, con excepción del infundíbulo, en lo que el subepicardio revelaba valores normales y el subendocardio valores menores que el promedio menos dos desviaciones estándar. CONCLUSIÓN: Las alteraciones del miocardio postnatal en la tetralogía de Fallot están distribuidas de modo homogéneo en las mitades subepicárdica y subendocárdica de las paredes ventriculares, a excepción del infundíbulo, que presenta características peculiares de remodelación y que, por lo tanto, no es representativo de las otras regiones...