Congenital Heart DiseasesIncidence: Most common type heart disease among children. Incidence is 1% of live births. The incidence is higher in premature infants andin stillborns.Etiology and Pathogenesis: Chromosomal abnormalities ( trisomies 13, 15, 18,and 21, and Turner syndrome). Trisomy 21 ( Down syndrome) is most commongenetic cause of CHD.
Environmental factors: congenital rubella orteratogens. Multifactorial : genetic, environmental, andmaternal factors account for remaining of cases.Clinical Features:CHD fall into three major categories: Malformations causing left-to-right shunt. Malformations causing right-to-left shunt . Malformations causing obstruction.
LEFT-TO-RIGHT SHUNTS: Cause cyanosis several months or yearsafter birth. Include:o Atrial Septal Defects( ASD)o Ventricular Septal Defects( VSD )o Patent (or persistent) Ductus Arteriosus( PDA)o AV Septal Defects (AVSD ).Atrial Septal Defect ( ASD ): Abnormal opening in atrial septum. Usually asymptomatic until adulthood.
Usually isolated ( not associated with otheranomalies). Irreversible pulmonary hypertension developsin fewer than 10% of cases. Mortality is low, and postoperative survival iscomparable to that of normal population.
Morphology: Three major types classified according to theirlocation in septum : secundum, primum, andsinus venosus.o Secundum ASD ( 90% of ASDs ) located at andresulting from a deficient oval fossa.o Primum ASD (5% of ASDs) occur adjacent to AVvalves .o Sinus venosus defects (5%) located near entranceof superior vena cava.
Ventricular Septal Defect (VSD ): Incomplete closure of ventricular septum. Associated with other defects, such as tetralogyof Fallot ( 70% ). 30% occur as isolated anomalies.Morphology: 90% involve region of membranous septum(membranous VSD). The remainder ( 10% ) lie below pulmonary valve(infundibular VSD) , or within muscular septum. 50% of small muscular VSDs close spontaneously.
Large defects:o Membranous or infundibular.o Remain patent and permit significantleft-to-right flow.o Right ventricular hypertrophy and pulmonaryhypertension are present from birth.o Over time, irreversible pulmonary vascular diseasedevelops leading to shunt reversal ( right to left ),cyanosis, and death.o Correction is indicated at age 1 year beforebecomes irreversible.
Patent Ductus Arteriosus ( PDA ): Ductus arteriosus remains open after birth. 90% occur as an isolated anomaly. The remainder ( 10% ) are associated with VSD,coarctation of aorta, or pulmonary or aortic stenosis. Continuous harsh murmur "machinery-like" The shunt first is left-to-right, so no cyanosis. Obstructive pulmonary vascular diseaseeventually ensues.
Conversely, preservation of ductal patency(by administering prostaglandin E) assumes greatimportance in survival of infants with various CHDsuch as aortic valve atresia. Therefore PDA may be either life-threatening, orlife-saving.
Atrioventricular Septal Defect (AVSD): Abnormal development of AV canal. Superior and inferior endocardial cushions failto fuse adequately. Resulting in incomplete closure of AV septum andinadequate formation of tricuspid and mitral valves .
RIGHT-TO-LEFT SHUNTS:Cause cyanosis early in postnatal life:Tetralogy of Fallot: Four features of tetralogy of Fallot are:(1) VSD.(2) obstruction to right ventricular outflow( subpulmonary stenosis).(3) aorta that overrides VSD.(4) right ventricular hypertrophy.
The clinical consequences depend on severityof subpulmonary stenosis:o If mild, the abnormality resembles an isolated VSDand the shunt may be left-to-right without cyanosis(pink tetralogy).o If sever, there is greater resistance to rightventricular outflow , right-to-left shunting withcyanosis (classic tetralogy of Fallot).
Morphology: The heart is often enlarged and may be"boot-shaped“ owing to marked right ventricularhypertrophy, particularly of apical region. The VSD is usually large.
Transposition of Great Arteries (TGA): Aorta arises from right ventricle andpulmonary artery emanates from left ventricle. The AV connections are normal ( with right atriumjoining right ventricle and left atrium emptyinginto left ventricle). The result is separation of systemic and pulmonarycirculations, a condition incompatible with postnatallife unless a shunt exists for adequate mixing ofblood.
Patients with TGA and VSD ( 35%) have a stableshunt. Those with only patent foramen ovale or PDA ( 65%)have unstable shunts that tend to close , thereforerequire immediate intervention to create a shunt(such as balloon atrial septostomy) within first fewdays of life.
Truncus Arteriosus : Developmental failure of separation of embryologictruncus arteriosus into aorta and pulmonary artery. This results in a single great artery that receivesblood from both ventricles. Because blood from right and left ventricles mixes,there is early systemic cyanosis.
Tricuspid Atresia : Complete occlusion of tricuspid valve orifice . Associated with underdevelopment (hypoplasia)of right ventricle. The circulation is maintained by a right-to-left shuntthrough inter-atrial communication (ASD or patentforamen ovale). Cyanosis is present from birth, and there is highmortality in first weeks or months of life.
OBSTRUCTIVE CONGENITAL ANOMALIES:Coarctation of Aorta: Two classic forms :(A) Infantile form : proximal to PDA.(B) Adult form : just opposite the closed ductusarteriosus (ligamentum arteriosum).
(A) Infantile form: leads to manifestations early in life. do not survive without surgical intervention. Unoxygenated blood through PDA produces cyanosisin lower half of body.
(B) Adult form: most of children are asymptomatic. may go unrecognized until adult life. hypertension in upper extremities, but weak pulsesand lower blood pressure in lower extremities. manifestations of arterial insufficiency(claudication and coldness).
Pulmonary Stenosis and Atresia: Obstruction at pulmonary valve, may bemild to severe. May occur as an isolated defect, or as part oftetralogy of Fallot . Right ventricular hypertrophy often develops. Mild stenosis may be asymptomatic and compatiblewith long life. Sever stenosis is associated with cyanosis andearlier appearance.
Aortic Stenosis and Atresia: Three major types : valvular, subvalvular, andsupravalvular. Prominent systolic murmur and sometimes a thrill. Hypertrophy of left ventricle. Well tolerated unless very severe. Mild stenoses can be managed conservatively withantibiotic prophylaxis and avoidance of strenuousactivity. Sudden death with exertion always expected.