By using an orderly approach, the physician is able to correlate bedside obervations and laboratory findings with pathophysiology and the basic elements of cardiac pathology.
Tetralogy of Fallot - Pathologic Complex
Tetralogy of Fallot is a pathologic complex based upon anterior displacement of the truncoconal septum of the developing embryo heart. As a result of this error, the conus septum, which forms the crista supraventricularis, cannot fuse with the ventricular septum. This results in a large ventricular septal defect located below the crista. Anterior displacement of the conus septum also narrows the right ventricular outflow tract, creating obstruction. Anterior displacement of the truncal septum narrows the pulmonary valve annulus and pulmonary artery, adding to the obstruction.
Four components
The ventricular septal defect and right ventricular outflow tract obstruction are the most significant of the four components of tetralogy of Fallot. Right ventricular hypertrophy occurs because right ventricular systolic pressure equals that of the left ventricle. Overriding of the aorta refers to the anatomic relationship of the aortic annulus stride the ventricular septal defect. This comes about because both the VSD and the ascending aorta are large. It is, therefore, more an apparent than a real abnormality. In typical tetralogy of Fallot the posterior wall of the aorta does not lose its relatioship to the anterior leaflet of the mitral valve, as they remain in fibrous continuity.