13% due to chromosomal defects: trisomy 21, trisomy 18, trisomy 13, or Turner syndrome (XO)
Trisomy 21 (Down syndrome): ECD, VSD, ASD, TOF; model for heart development, 40% have heart disease, 5 different heart defects; Turner syndrome: AS, COA, HLHS
8% due to single gene defects: Noonan syndrome (PS); Holt-Oram syndrome: ASD
recurrence risk for congenital heart defects is 3%; additional factors include maternal diabetes and alcoholism
Changing circulation: Fetus to Adult
A fetus has high PVR and low SVR due to the highly vascular placenta. Two sites of normal shunting: foramen ovale and ductus arteriosus. Oxygenated blood from placenta
Þ foramen ovale Þ aorta. Deoxygenated blood from head and SVC Þ right atrium Þ right ventricle Þ pulmonary artery Þ ductus arteriosus (due to high PVR) Þ aorta.
Transitional circulation: onset of respiration
Þ ß PVR; removal of placenta Þ Ý SVR. Ductus arteriosus closes (if not, blood flows from aorta to pulmonary artery) and foramen ovale closes due to higher pressures on left side of the heart.
Cardiovascular Changes from Infancy to Adulthood
: HR decreases (due to impedance, it’s more efficient to pump slower in longer tubes); BP (both systolic and diastolic) steadily increases; Cardiac output increases; PVR and pulmonary pressure decrease; Atria, ventricles, vessels, and valves all grow to keep pace with somatic growth.
Most congenital heart defects are well tolerated in utero. This is largely due to the presence of the ductus arteriosus, foramen ovale, and the normal fetal tolerance of hypoxia. Mitral or tricuspid regurg. are exceptions, however. For example, the increased PVR in the fetus limits the pulmonary blood flow in children with VSD; after birth, flow across the defect will increase and a murmur will develop. The ductus arteriosus is absolutely essential for babies with markedly restricted pulmonary flow (TOF, tricuspid atresia) and severe left heart obstruction (critical aortic stenosis, HPHS, critical COA). It is also important for babies with a transposition of the great arteries.
CHD classification
Classify by anatomic defect (VSD) and/or pathophysiologic impact – large ventricular septal defect, large shunt across defect, dilated LA, LV; elevated PA pressure.
Anatomic size or severity
µ pathophysiologic impact.
Left
Þ Right (Acyanotic) shunts: communication between systemic and pulmonary circulations; high systemic pressure Þ low pulmonary pressure
Right
Þ Left (Cyanotic) shunts: Children have 1) separate (parallel) systemic and pulmonic circulations (TGA); 2) restricted pulmonary blood flow and intercardiac communications (TOF, tricuspid atresia); 3) complete mixing of the systemic and pulmonary venous return with restricted pulmonary flow (truncus arteriosus, single ventricle without pulmonary stenosis)
Obstructions: can be at any valve or anywhere along systemic or pulmonary circulation.
Types of defect: VSD 28%, Obstructive 22%, Cyanotic 20%, PDA 10%, ASD 8%, Complex 8%, Other L-R shunt 0.8%
CHD Assessment
History – non-invasive, inexpensive; look for 1st degree relative, viral or drug exposure, maternal diabetes.
ß venous return; look at lung field and heart size.
Echo – non-invasive, expensive; defines anatomic size, relationships and motion; can see a scarred hyperplastic heart
Doppler – Measures blood flow velocity, detects abnormal direction or velocity, estimates pressure gradients.
MRI – non-invasive imaging of structure and blood flow.
Catheterization – invasive, expensive, therapeutic, can measure pressure and oxygen saturations directly.
Pathophysiologic Principles
Pressure in a chamber or vessel : P=Q*R
Blood flow may be estimated using the Fick principle: Qs = VO2/ ((Ao sat – SVC sat) * 13.6 * gHgb/dl); Qp=VO2/ ((Pv sat – PA sat) * 13.6 g Hgb/dL) ; Qp/Qs = (Ao sat – SVC sat)/ (PV sat – PA sat).
Shunts detected by oxygen saturation change
Flow across defect ~ size of defect, relative resistance
Change in pressure ~ obstruction and blood flow
Chamber and vessel size ~ blood flow
Wall thickness ~ wall stress (size and pressure)
Congestive Heart Failure has special meaning in children – inability to meet body’s demands for growth and exercise. Foremost signs and symptoms: exercise intolerance and failure to thrive. Acute weight gain, tachypnea, and tachycardia.
Left to Right Shunts (Acyanotic)
Definition: Blood flows from systemic (left) to pulmonary (right) circulation through an intra- or extracardiac communication, bypassing the capillary bed. Can occur at three sites: VSD, ASD, and PDA.
Pathophysiology
:
Size of L-R shunt (or amount of blood flow) is determined by anatomic size of defect, resistance ratio of pulmonary to systemic circulation, and relative compliance of the two ventricles.
Pulmonary blood flow exceeds systemic blood flow
Þ Ý total cardiac output (to both pulmonary and systemic vasculature) Þ Ý metabolic demands.
Ý
Pulmonary arterial pressure may Þ vasoconstriction and hypertrophy of the media of the pulmonary arteriolesÞ vessel obliteration Þ Pulmonary Occlusive Vascular Disease.
Ý
Pulmonary resistance Þ Changes (scarring) to pulmonary vasculature Þ ß left-right shunting; however, if pulmonary resistance > systemic resistance Þ right-left shunting Þ Eisenmenger Physiology.
(1) Ventricular Septal Defect
Can occur in one of four regions: I – supracristal VSD (outflow tract of RV), II – intracristal VSD (most common), III – atrioventricular canal region, IV – muscular VSD (anterior trabeculae of septum)
Small VSD
Asymptomatic, murmur is holosystolic caused by turbulence of blood flow across the VSD throughout systole.
Characteristics
: Qp>Qs (2:1); PVR normal; normal ECG, normal echo, normal x-ray, Doppler: high velocity turbulent flow from left to right, consistent with restrictive defect and preservation of the gradient between ventricles.
Excellent prognosis without surgery; Long term risks (LTR) include bacterial endocarditis and aortic leaflet prolapse.
Moderate or Large ("non-restrictive") VSD
Presents with tachypnea, tachycardia, feeding difficulties and growth retardation.
Holosystolic murmur, mid-diastolic murmur is caused across a normal mitral valve and is due to "relative mitral stenosis." P2 becomes louder with a larger defect.
Characteristics
: Qp>>Qs (>3:1); PVR normal; ECG: moderate shows LVH, large shows LVH/RVH; Echo shows VSD, dilated left atrium and ventricle; Doppler: moderate: turbulent flow across VSD, large: laminar flow across VSD; X-ray: cardiomegaly,
Ý pulmonary vascularity
Defect could
ß in size, stay same size, be accompanied with infundibular stenosis, be accompanied with aortic prolapse. Long-term risks include poor growth, arrhythmia, LV failure, subendocardial bacterial endocarditis (SBE), Eisenmenger syndrome. Surgical repair is necessary to avoid Eisenmenger and CHF in infancy.
Eisenmenger’s
PVR>SVR
Þ right-left shunting Þ arterial oxygen desaturation and become hypoxic with exertion. Ý risk of stroke and brain abcess.
Characteristics
: Qp<Qs; Ý PVR, ECG: RVH, Echo: large VSD, RVH, normal LV and LA; Doppler: low velocity, non-turbulent flow from right to left across VSD.
Death occurs in 30’s or 40’s; exercise intolerance from hypoxia, ventricular dysfunction, and arrhythmias. Endocarditis and brain abcess are complications.
(2) Patent Ductus Arteriosus
Shunt is dependent on relative resistances and size of ductus.
Classic murmur is a continuous "machinery" murmur which is present through systole and diastole because of a pressure gradient between the aorta and pulmonary artery throughout the cardiac cycle. Mid–diastolic rumble is caused by increased flow across the mitral valve.
Characteristics
: Qp>Qs (<2:1 small, >4:1 large); normal PVR; ECG: small shows normal, moderate shows LVH, large with pulmonary HTN shows RVH/LVH; Echo: shows ductus, dilated LV and LA; Doppler: continuous flow with turbulence in MPA; X-ray: moderate – large shows cardiomegaly and increased vascularity.
Surgical closure is indicated for management of congestive heart failure in infancy, or for persistent patency beyond 2 years of age even if small. The risk of surgery is less than the risk of bacterial endocarditis if the ductus remains patent.
(3) Atrial Septal Defect
Secundum type is common, 2:1 female predominance. Sinus venosus defect lies in the upper atrial septum and is associated with 1 or 2 right pulmonary veins draining into the right SVC-RA junction. An ostium primum lies low in the septum is usually associated with a cleft in the mitral valve and is an incomplete atrioventricular septal defect.
Patients are usually asymptomatic, murmur first heard at school age. Physical findings are related to
Ý flow through right side of heart and include: active RV impulse, systolic ejection murmur (flow through the pulmonary valve), a mid-diastolic rumble (flow through tricuspid valve), and a widely split, fixed second heart sound.
Characteristics
: Qp>Qs (small <2:1, large 4:1); normal PVR; ECG: RVH in anterior precordial leads; Echo: defect in atrial septum, dilated right ventricle and pulmonary artery, paradoxical motion of interventricular septum; Doppler: Left to right, turbulent low velocity flow at ASD; X-ray: enlarged heart and Ý pulmonary vascularity.
Without surgery, most children with ASD live normal lives. Pulmonary vascular obstructive disease may occur in adulthood, but is rare in children.
Right to Left Shunt: Cyanotic
Cyanosis and Hypoxia
Cyanosis is bluish skin or mucous membrane coloration resulting from an abnormal level of Hbg. Central cyanosis would be recognized when there is a 3 gm/dL of unsaturated hemoglobin. This type of cyanosis must be differentiated from peripheral which is due to vasomotor tone and not true hypoxemia.
Defects in this group are associated with decreased arterial oxygen saturation and normal pulmonary venous oxygen saturation. Supplemental O2 will only have a modest impact on a right to left shunt.
Chronic hypoxemia is better tolerated than acute hypoxemia due to several adaptive mechanisms. Polycythemia
Þ increased hemoglobin Þ increased oxygen content at the same level of saturation. Increased oxygen extraction may be seen as a mechanism for improving tissue oxygen delivery. Can lead to high viscosity flow Þ ß blood flow.
Chronic hypoxemia
Þ low O2, polycythemia, and direct access of the systemic venous blood to the aorta. Cerebral vascular accidents, cerebral abcesses, bacterial endocarditis, changes in bone, kidneys, and lungs are common complications.
Cyanotic spells are sudden drops in the arterial oxygen. TOF
Þ Ý myocardial contractility and dynamic muscular obstruction Þ Ý sub-pulmonary obstruction Þ ß SVR with Ý PVR Þ cyanotic spells. Usually resolve spontaneously; however, coma, seizures, stroke and death can occur.
Management Principles
Infants with parallel circulations (transposition of the great arteries) or restricted pulmonary blood flow (tetralogy of Fallot, tricuspid atresia) usually become acutely cyanotic following closure of the ductus arteriosus. Restoring or maintaining ductal patency by infusing prostaglandin E1 may be life saving. Specific surgical management varies with each individual defect.
(1) Transposition of the Great Arteries
Most common congenital heart defect, presenting with cyanosis in first week. The defect connects the aorta to the right ventricle and the pulmonary artery to the left ventricle. Right ventricular pressure is high due to SVR and left ventricular pressure is low due to the low PVR. Pulmonary and systemic circulations are in parallel
Þ poor oxygenated blood Þ right atrium Þ right ventricle Þ aorta, while the fully oxygenated blood Þ left atrium Þ left ventricle Þ pulmonary artery. Profound and lethal systemic hypoxia results if ductus and foramen ovale are not patent. Bi-directional shunting at the atrial level is essential for survival. If not corrected, child will die by 1 year old.
Characteristics
: Qp>>Qs; normal PVR; ECG:RVH; Echo: demonstrates abnormal arterial connections and associated defects; X-ray: narrow mediastinum, Ý vascularity.
Establishing ductal patency with prostaglandin E1 in newborns with transposition of the great arteries frequently improves arterial oxygenation by
Ý shunting from aorta into the pulmonary artery. Ý pulmonary venous return Þ distended left atrium Þ Ý left atrial to right atrial shunting of fully saturated blood across the foramen ovale. If inadequate systemic oxygenation or long term patency of the atrial defect is required, a balloon atrial septostomy is performed. This procedure results in a tear in the atrial septum enlarging the foramen ovale into an atrial septal defect and allowing improved mixing of the systemic and pulmonary venous return at the atrial level.
Mustard Operation: In this operation, the great arteries remain in the same position and the superior and inferior vena caval blood was tunneled across the atrium to the mitral valve and the pulmonary veins directed to the tricuspid valve. This physiologic repair resulted in fully oxygenated blood
Þ right ventricle and aorta, and poorly oxygenated blood Þ left ventricle and pulmonary artery; however, anatomic relationships of the heart remained abnormal. Long term post-operative problems include atrial arrhythmias, pulmonary and systemic venous obstruction, and right ventricular enlargement and dysfunction.
Jatene (Arterial Switch) Operation: This operation requires transection of the aorta and pulmonary artery to move the pulmonary artery anteriorly to the right ventricle and the aorta posteriorly to the left ventricle. The coronary arteries are moved from their original position on the aorta to the newly created aorta and atrial and ventricular septal defects are repaired. The arterial switch operation in infants with TGA with an intact ventricular septum is optimally performed in the first two weeks of life. At two weeks, the left ventricle can support the systemic blood pressure; if longer than two weeks, the left ventricle will be weaker like the right ventricle of a normal baby, and may not be able to adapt to the large systemic blood pressure. Surgery results in excellent ventricular function, normal rhythm and a low incidence of obstruction at the pulmonary, aortic and coronary suture lines.
(2) Tetralogy of Fallot
Most common cyanotic congenital heart defect presenting after 2 weeks of age. Tetralogy: association of infundibular (subvalve) and valvular pulmonary stenosis, large ventricular septal defect, large aorta overriding ventricular septum, and right ventricular hypertrophy. A variable degree of pulmonary artery hypoplasia, an atrial septal defect or foramen ovale, patent ductus arteriosus, or systemic-to-pulmonary collaterals are frequently present.
The obstruction of the right ventricular outflow
Þ ß pulmonary blood flow and produces systemic arterial desaturation by diverting poorly oxygenated right ventricular blood across the VSD Þ ascending aorta. Ý systemic resistance (for example, by squatting) at any given pulmonary resistance will diminish shunting. In contrast, acutely Ý the pulmonary infundibular obstruction, for example with endogenous catecholamine, will exacerbate the shunting. Additional pulmonary blood flow coming through a patent ductus arteriosus or collateral vessels will tend to modulate acute fluctuations due to infundibular contractility and the chronic status produced by pulmonary obstruction.
Characteristics
: Qp<Qs; normal PVR; ECG:RVH; Echo/Doppler: VSD, pulmonary stenosis, high velocity, turbulent pulmonary flow
Clinical Features: palpable right ventricular impulse (due to RV HTN), and a single second heart sound without a pulmonary component due to the marked abnormality of the pulmonary outflow tract. The systolic ejection murmur heard in children with TOF is produced by turbulent blood flow across the pulmonary stenosis; the intensity of the murmur
µ pulmonary blood flow; murmur µ 1/size of pulmonary obstruction. No systolic ejection murmur in children with TOF implies atresia of the right ventricular outflow tract Þ a continuous murmur indicates blood flow through a PDA or collaterals as the sole source of pulmonary blood flow. Episodic cyanotic spells are frequently seen in the first months to year of life and are characterized by intense cyanosis, hyperpnea and change in mental status.
Newborns with severe cyanosis are stabilized by an infusion of prostaglandin E1 to dilate the ductus arteriosus and
Ý pulmonary blood flow. These newborns often have severely hypoplastic pulmonary arteries and must have a palliative procedure to establish a source of pulmonary blood flow. Surgeries include a systemic-to-pulmonary shunt, a direct connection of the subclavian artery to the pulmonary artery (Blalock-Taussig shunt) or a synthetic tubular graft (Gore-tex) between the aorta or one of its branches and the pulmonary artery. Alternatively the right ventricular outflow tract is surgically opened without closing the ventricular septal defect.
Surgical repair of TOF consists of closure of the ventricular septal defect, excision of the pulmonary stenosis, and enlargement of the right ventricular outflow tract with a patch. In the absence of marked pulmonary artery hypoplasia or unfavorable coronary artery anatomy, surgery is undertaken at virtually any age. Specific indications for surgery are increasing cyanosis or cyanotic spells by one or two years of age. The risk of total repair is low and the long-term results are excellent. Residual pulmonary stenosis and regurgitation are common but well tolerated. Post-operative ventricular arrhythmias may be symptomatic and require pharmacological suppression, but tend to be less frequent in patients repaired in the first decade of life.
Obstruction
General Characteristics: Narrowing or obstruction may be present at any site/s in the inflow or outflow portion of either the right or left side of the heart. Syncope, heart failure or sudden death can occur. Symptoms of heart failure are related to poor tissue perfusion, and
Ý preload needed to maintain CO. Right sided heart failure Þ systemic venous congestionÞ engorged veins, hepatomegaly and edema. Left sided HF Þ Ý LVDP, Ý LAP Þ tachypnea, rales and pulmonary edema. Multiple levels of obstruction. This is particularly true for left-sided defects where mitral stenosis, subaortic stenosis, aortic valve stenosis and coarctation of the aorta may be present in the same child.
(1) Pulmonary Stenosis
1/1000 live births. Severity varies from small obstruction with little pressure gradient and hypertrophy to critical obstruction with marginally adequate cardiac output and pressure gradients reaching 100 mm Hg.
Clinical features: accentuated precordial impulse over the right ventricle, an ejection click which decreases with inspiration, and a systolic ejection murmur at the upper sternal border with radiation to the lung fields. Intensity and harshness of the murmur is directly related to the severity of the obstruction.
Characteristics
: Qp=Qs; normal PVR; ECG: RVH in proportion to the obstruction. Also shows valve anatomy and the extent of post-stenotic dilatation of the pulmonary artery. Doppler: estimates pressure gradient across the obstruction.
Cardiac catheterization has a therapeutic goal in children with pulmonary valve stenosis. Balloon dilatation is an excellent means of decreasing the obstruction and is indicated for moderate (35-60 mm Hg) or severe (>60 mm Hg) obstruction. Good prognosis for mild PVS. Although rare, bacterial endocarditis prophylaxis is advised.
(2) Aortic Valve Stenosis
1/ 2000 live births. The severity varies from trivial obstruction with
ß pressure gradient and hypertrophy due to a bicuspid aortic valve to critical obstruction. Neonatal death due to left ventricular failure and shock may occur. A patent ductus arteriosus is required for life with left-to-right shunting at the atrial level and right-to-left shunting at the ductal level.
Clinical features
: accentuated precordial impulse over the left ventricle, an ejection click which does not vary with respiration, and a systolic ejection murmur at the upper sternal border with radiation to the neck. Intensity µ severity.
Characteristics
: ECG: LVH in proportion to the obstruction. Severe obstruction if associated T wave inversion in the inferior and lateral leads. Shows the valve anatomy and the extent of post-stenotic dilatation of the ascending aorta. Doppler: estimates the pressure gradient across the obstruction.
Cardiac catheterization and balloon dilatation has a therapeutic goal in children with aortic stenosis. In contrast to stenosis of pulmonary valve, immediate and long-term results of both techniques on aortic valve are not good. In addition,children with mild aortic stenosis
Þ Ý obstruction with timeÞ aortic regurgitation. Bacterial endocarditis prophylaxis is advised.
(3) Coarctation of the Aorta
1/1300 live births. Obstruction is typically "juxta-ductal" to the origin of the left subclavian artery. Closure of the ductus accentuates the obstruction. It can go undetected at birth. Collateral vessels develop and help supply the distal aorta.
Clinical findings
: ß pulse pressure in the lower extremities, upper extremity HTN, an ejection murmur heard in the mid back and markedly delayed and diminished pulse volume in the legs.
Characteristics
: ECG: LVH, although babies presenting in the neonatal period frequently maintain their RVH pattern throughout life. Also demonstrates the location and anatomic severity of the obstruction. Doppler: Ý velocity immediately at the coarctation and ß pulsatility in the descending aorta.
Balloon dilatation has a limited role in the management of primary coarctation. Neonates presenting with shock are surgically repaired at that time. Elective repair of coarctation is undertaken in early childhood to avoid the long-term sequelae of proximal hypertension and left ventricular pressure overload. There is a risk of poor growth of the repair site following surgery and in these children balloon dilatation has been effective.