Fig. 11.4 ). Clinical consequences of severe, systemic cyanosis include clubbing of the tips of the fingers and toes (hypertrophic osteoarthropathy), polycythemia, and paradoxical embolization.
Tetralogy of Fallot
Tetralogy of Fallot is the most common cause of cyanotic congenital heart disease. It accounts for about 5% of all
Fig.11.4 Commoncongenitalright-to-leftshunts(cyanoticcongenitalheartdisease).(A)TetralogyofFallot(arrow indicatesdirectionofbloodflow).
(B)TranspositionofthegreatvesselswithandwithoutVSD.Ao, Aorta;LA, leftatrium;LV, leftventricle;PT, pulmonarytrunk;RA, rightatrium;RV, rightventricle.
Table 11.1 ). The four cardinal features are (
Fig. 11.4A
Overriding of the VSD by the aorta
All of the features of tetralogy of Fallot result from anterosuperior displacement of the infundibular septum leading to abnormal septation between the pulmonary trunk and the aortic root.
MORPHOLOGYTheheartisenlargedand“boot-shaped”asaconsequenceofright ventricular hypertrophy; theproximalaortaisdilated,whilethepulmonarytrunkishypoplastic.Theleft-sidedcardiacchambersareofnormalsize,whiletherightventricularwallismarkedlyhypertrophied,sometimesevenexceedingthethicknessoftheleftventricle.TheVSD usuallyislargeandliesinthevicinityofthemembranousportionoftheinterventricularseptum;theaorticvalveliesimmediatelyovertheVSD(overriding aorta) andisthemajorsiteofegressforbloodflowfrombothventricles.Theobstructionoftherightventricularoutflowmostoftenisduetonarrowingoftheinfundibulum(subpulmonic stenosis) butalsocanbecausedbypulmonaryvalvestenosisorcompleteatresiaofthevalveandtheproximalpulmonaryarteries.Insuchcases,apersistentPDAordilatedbronchialarteriesaretheonlyrouteforbloodtoreachthelungs.
http://ebooksmedicine.net
The hemodynamic consequences of tetralogy of Fallot are right-to-left shunting, decreased pulmonary blood flow, and increased aortic volumes. The clinical severity largely depends on the degree of the pulmonary outflow obstruction; even untreated, some patients can survive into adult life. Thus, if the pulmonic obstruction is mild, the condition resembles an isolated VSD because the high left-sided pressure causes only a left-to-right shunt with no cyanosis. More commonly, more severe degrees of pulmonic stenosis cause early cyanosis. Moreover, as the child grows and the heart increases in size, the pulmonic orifice does not expand proportionately, leading to progressive worsening of the stenosis. Fortuitously, the pulmonic outflow stenosis protects the pulmonary vasculature from pressure and volume overloads, so that pulmonary hypertension does not develop, and right ventricular failure is rare. Nevertheless, patients develop the typical sequelae of cyanotic heart disease, such as hypertrophic osteoarthropathy and polycythemia (due to hypoxia) with attendant hyperviscosity; right-to-left shunting also increases the risk for infective endocarditis and systemic embolization. Complete surgical repair is possible with classic tetralogy of Fallot but is more complicated in the setting of pulmonary atresia.
Transposition of the Great Arteries
Transposition of the great arteries is a discordant connection of the ventricles to their vascular outflow. The embryologic defect is an abnormal formation of the truncal and aortopulmonary septa so that the aorta arises from the right ventricle and the pulmonary artery emanates from the left ventricle (