A. CYANOSIS
I. Pathophysiology of Cyanosis
Before discussing individual cyanotic CHD, a brief review of pathophysiology of cyanosis is in order.
II. Causes of Cyanosis
Cyanosis is a bluish discoloration of the skin and mucous membranes resulting from an increased concentration of reduced hemoglobin to about 5 g/100 mL in the cutaneous veins. This level of reduced hemoglobin in the cutaneous vein may result from either desaturation of arterial blood (central cyanosis) or increased extraction of oxygen by peripheral tissue in the presence of normal arterial saturation (peripheral cyanosis). Cyanosis is more difficult to detect in children with dark pigmentation.
- 1.
Peripheral cyanosis is due to excessive extraction of oxygen in the venules. Examples of peripheral cyanosis are:
- 2.
Central cyanosis is seen in children with cyanotic CHD, lung disease, or central nervous system (CNS) depression. Rarely cyanosis is caused by methemoglobinema (seen when methemoglobin level is greater than 15% of normal hemoglobin)
- a.
Acrocyanosis, a bluish color of the fingers seen in neonates and infants and reflects sluggish blood flow in the fingers.
- b.
Circumoral cyanosis refers to a bluish skin color around the mouth, seen in a healthy child with fair skin due to a sluggish capillary blood flow in association with vasoconstriction.
- a.
III. Influence of Hemoglobin Level on Cyanosis
The level of hemoglobin greatly influences the occurrence of cyanosis. Normally, about 2▒g/100▒mL of reduced hemoglobin is present in the venules so that an additional 3▒g/100▒mL of reduced hemoglobin in arterial blood is needed to reach 5▒g/100▒mL of reduced hemoglobin to produce clinical cyanosis.
- 1.
For a normal person with hemoglobin of 15▒g/100▒mL, 3▒g of reduced hemoglobin results from 20% desaturation (because 3 is 20% of 15). Thus cyanosis appears when the oxygen saturation is reduced to about 80%.
- 2.
In a person with polycythemia, cyanosis is recognized at a higher level of oxygen saturation. For example, in a person with hemoglobin of 20▒g/100▒mL, 3▒g of reduced hemoglobin result from only 15% desaturation (or at 85% arterial saturation).
- 3.
In patients with anemia, cyanosis is recognized at a lower level of oxygen saturation. For example, if a patient has a marked anemia (hemoglobin of 6▒g/100▒mL), 3▒g of reduced hemoglobin does not result until the patient’s arterial oxygen saturated goes down to 50% desaturation.
IV. Cyanosis of Cardiac Versus Pulmonary Origin
Differentiation of cardiac cyanosis from cyanosis caused by pulmonary diseases is crucially important for proper management of cyanotic infants. Traditionally, one tests the response of arterial P o 2 to 100% oxygen inhalation (hyperoxia test). With pulmonary disease, arterial P o 2 usually rises to a level greater than 100▒mm Hg. When there is a significant intracardiac R-L shunt, the arterial P o 2 does not exceed 100▒mm Hg, and the rise is usually not more than 10 to 30▒mm Hg.
V. Consequences and Complications of cyanosis
- 1.
Polycythemia . Low arterial oxygen content stimulates bone marrow through erythropoietin release from the kidneys and produces increased number of red blood cells (RBCs). Polycythemia, with a resulting increase in oxygen-carrying capacity, benefits cyanotic children. However, when the hematocrit reaches 65% or higher, a sharp increase in the viscosity of blood occurs, and the polycythemic response becomes disadvantageous.
- 2.
Clubbing . Clubbing is caused by soft tissue growth under the nail bed as a consequence of chronic central cyanosis. Clubbing usually does not occur until a child is 6 months or older, and it is seen first and is most pronounced in the thumb. In the early stage, it appears as shininess and redness of the fingertips. When fully developed, the fingers and toes become thick and wide and have convex nail beds. Clubbing may also be seen in patients with liver disease or infective endocarditis and on a hereditary basis without cyanosis.
- 3.
Central nervous system (CNS) complications . Very high hematocrit levels place individuals with cyanotic CHD at risk for disorders of the CNS, such as brain abscess and vascular stroke. In the past, cyanotic CHDs accounted for 5% to 10% of all cases of brain abscesses. Vascular stroke caused by embolization arising from thrombus in the cardiac chamber or in the systemic veins may be associated with surgery or cardiac catheterization.
- 4.
Bleeding disorders . Disturbances of hemostasis are frequently present in children with severe cyanosis and polycythemia. Most frequently noted are thrombocytopenia and defective platelet aggregation. Other abnormalities include prolonged prothrombin time and partial thromboplastin time and lower levels of fibrinogen and factors V and VIII. Clinical manifestations may include easy bruising, petechiae of the skin and mucous membranes, epistaxis, and gingival bleeding. RBC withdrawal from polycythemic patients and replacement with an equal volume of plasma tend to correct the hemorrhagic tendency and lower blood viscosity.
- 5.
Hypoxic spells and squatting . Although most frequently seen in infants with unrepaired TOF, hypoxic spells may occur in infants with other CHDs (see a later section on TOF for further discussion).
B. CRITICAL CONGENITAL HEART DISEASE (CCHD) SCREENING
I. Role of Pulse Oximetry Screen in Detection of Hypoxemia
Many neonates with hypoxemia from significant CHDs may not show cyanosis on routine neonatal examination in the first days of life. About one-third of neonates with critical CHD were estimated to be undetected on routine neonatal examination. Pulse oximetry can detect mild degree of arterial hypoxemia without recognizable cyanosis in the newborn.
First developed in 1972 by Takuo Aoyagi and Michio Kishi of Japan, pulse oximetry monitors a person’s arterial oxygen saturation noninvasively. The principle of the pulse oximeter is based on the difference in absorption of red light (wavelength of 660▒nm) and infrared light (at 940-nm wavelength) by oxygenated hemoglobin and deoxygenaed hemoglobin. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through. A pair of small light-emitting diodes (LEDs) in the probe emit red and infrared lights, which go through a translucent part of the body (such as fingertip or earlobe). Red and infrared lights that passed through are detected by a photodiode on the opposite side of the probe. The pulse oximetery detects oxygen saturation of only arterial blood, not the venous or capillary blood. This ability is based on the principle that the amount of red and infrared light absorbed fluctuates with the cardiac cycle as the arterial blood volume increases during systole and decreases during diastole; in contrast, the blood volume in the veins and capillaries remains relatively constant. The processor of pulse oximeters calculates the ratio of the red light detected (transmitted light) to the infrared light detected by the photodiode. This ratio represents the ratio of oxygenated hemoglobin to deoxygenated hemoglobin, and the ratio is then converted to oxygen saturation by the processor.
In 2011, the pulse oximetry screen was made the standard of care in newborn screening and has been endorsed by the American Academy of Pediatrics (AAP), American Heart Association, and American College of Cardiology. The neonatal pulse oximetry screen (POS) can detect cyanotic CHD and other life-threatening noncaardiac neonatal conditions prior to the discharge from the birth hospital. Examples of noncardiac conditions include hypothermia, infection (including sepsis), lung disease, persistent pulmonary hypertension of the newborn, hemoglobinopathy, and others.
II. Neonatal Pulse Oximetry Screen Algorithm
The U.S. pulse oximetry (PO) algorithm, which is approved by the AAP, is presented in Fig. 9.1 .
- 1.
The screen should be done after 24▒hours of life or just prior to early discharge from the hospital. The POS done earlier than 24▒hours of age increases false-positive results. Interestingly, however, the false-positive tests detect noncardiac conditions that require prompt attention and treatment.
- 2.
Oxygen saturation should be measured in the right hand (RH) (for preductal arterial saturation) and either foot (for postductal arterial saturation) to detect cyanotic CHDs and ductal-dependent lesions.
Description of the Algorithm
- 1.
First screening
- a.
Normal neonates should have oxygen (O 2 ) saturation in the RH and foot higher than 95% and the difference in oxygen saturation between the RH and the foot should be 3% or less (PASS). These infants may be given normal newborn care.
- b.
The following are abnormal test results.
- (1)
O 2 saturation 89% or less in either the RH or a foot (FAIL). These infants are referred for immediate assessment.
- (2)
O 2 saturation between 90% and 94% in the RH and the foot, or difference in the saturation 4% or more between the two sites (RETEST). These infants should be screened again after 1▒hour.
- (1)
- a.
- 2.
Second screening
- a.
Neonates with normal results (PASS) are given routine newborn care.
- b.
Neonates with abnormal test results are handled the same way as stated earlier for the first screen. They should be screened again after 1▒hour.
- a.
- 3.
Third screening
- a.
Neonates with normal results (PASS) are given routine newborn care.
- b.
Neonates with abnormal test results (both RETEST and FAIL categories) are referred for immediate assessment.
- a.
What to Do With Infants Who Failed the CCHD Screening
Infants who failed the screen should not be discharged from the hospital without excluding potentially life-threatening conditions; they should undergo evaluation to identify the cause of hypoxemia.
- 1.
An echocardiography and/or cardiology consultation is the next step.
- 2.
However, evaluation of the baby using other means (e.g., chest radiograph, blood work) should not be delayed while awaiting an echocardiogram.
- 3.
If infants with ductal-dependent lesions are found, prostaglandin E 1 (PGE 1 ) infusion should be initiated to maintain patency of the ductus arteriosus. Cardiology consultation should be requested on an urgent basis. The starting dose of dinoprostone (Prostin) is 0.05 to 0.1 μg/kg/min administered in a continuous intravenous (IV) drip. When the desired effects (increased P o 2 , increased systemic blood pressure, improved pH) are achieved, the dose should be reduced step-by-step to 0.01 μg/kg/min. When the initial starting dose has no effect, the dose may be increased up to 0.4 μg/kg/min. Three common side effects of IV infusion of PGE 1 are apnea (12%), fever (14%), and flushing (10%). Less common side effects include tachycardia or bradycardia, hypotension, and cardiac arrest.
C. CYANOTIC CARDIAC DEFECTS
I. Complete Transposition of the Great Arteries
Prevalence
TGA occurs in about 5% to 7% of all CHDs. It is more common in boys (3:1).
Pathology and Pathophysiology
- 1.
The aorta (AO) and the PA are transposed, with the AO arising anteriorly from the RV, and the PA arising posteriorly from the LV. The end result is complete separation of the two circuits, with hypoxemic blood circulating in the body and hyperoxemic blood circulating in the pulmonary circuit ( Fig. 9.2 ) The classic complete TGA is also called d -transposition (D-TGA), denoting d -looping of the cardiac tube during embryogenesis.
- 2.
Defects that permit mixing of the two circulations, such as ASD, VSD, and PDA, are necessary for survival. A VSD is present in 40% of cases. In about 50% of the patients no associated defects are present other than PFO, small ASD, or small PDA.
- 3.
LVOT obstruction (subpulmonary stenosis), either dynamic or fixed obstruction, occurs in about 5% of patients without VSDs. PS occurs in 30% to 35% of patients with VSD.
- 4.
In neonates with poor mixing of the two circulations, progressive hypoxia and acidosis result in early death, requiring an early intervention.
Clinical Manifestations
- 1.
Cyanosis and signs of CHF in the newborn period. Severe arterial hypoxemia unresponsive to oxygen inhalation and acidosis are present in neonates with poor mixing (of systemic and pulmonary circulation). Hypoglycemia and hypocalcemia are occasionally present.
- 2.
Moderate to severe cyanosis is present. Auscultatory findings are nonspecific. The S2 is single and loud. No heart murmur is audible in infants with intact ventricular septum. When TGA is associated with VSD or PS, a systolic murmur of these defects may be audible.
- 3.
The electrocardiogram (ECG) shows RAD and RVH. An upright T wave in V1 after 3 days of age may be the only abnormality suggestive of RVH. BVH may be present in infants with large VSDs, PDA, or PS.
- 4.
Chest radiographs show cardiomegaly with increased PVMs. An egg-shaped cardiac silhouette with a narrow superior mediastinum is characteristic.
- 5.
Two-dimensional echo study is diagnostic.
- a.
It fails to show a “circle-and-sausage” pattern of the normal great arteries in the parasternal short-axis view. Instead, it shows two circular structures.
- b.
Other views show the PA arising from the LV and the aorta arising from the RV.
- c.
Associated defects (VSD, LVOT obstruction, PS, ASD, and PDA) can be imaged.
- d.
The status of atrial communication, both before and after balloon septostomy, is best evaluated in the subcostal view.
- e.
The coronary arteries can be imaged in most patients in the parasternal and apical views.
- a.
- 6.
Natural history and prognosis depend on anatomy.
- a.
Infants with intact ventricular septum are the sickest group, but they demonstrate the most dramatic improvement following PGE 1 infusion or the Rashkind balloon atrial septostomy.
- b.
Infants with VSD or large PDA are the least cyanotic group but are most likely to develop CHF and PVOD (beginning as early as 3 or 4 months of age).
- c.
Combination of VSD and PS allows considerably longer survival without surgery, but repair surgery carries a high risk.
- d.
Cerebrovascular accident and progressive PVOD, particularly in infants with large VSD or PDA, are rare late complications.
- a.
Management
Medical and Nonsurgical
- 1.
Metabolic acidosis, hypoglycemia, and hypocalcemia should be treated if present.
- 2.
PGE 1 infusion is started to raise arterial oxygen saturation by reopening the ductus.
- 3.
Administration of oxygen may help raise systemic arterial oxygen saturation by lowering PVR and increasing PBF, with resulting increase in mixing.
- 4.
A therapeutic balloon atrial septostomy (Rashkind procedure) may be performed. The balloon procedure is needed when (a) there is inadequate atrial mixing through the PFO (evidenced by a high Doppler flow velocity of >1▒m/sec) and/or (b) immediate surgical intervention is not ready or planned. Occasionally, blade atrial septostomy may be performed for older infants and those for whom the initial balloon atrial septostomy is not successful.
- 5.
Treatment of CHF may be indicated.
Surgical
Definite treatment is surgical. In the past, prior to the area of arterial switch operation, intracardiac flow pattern was switched at the atrial level (Senning operation) or at the ventricular level (Rastelli operation). At this time, arterial switch operation (Jatene procedure) is clearly the procedure of choice, and intraatrial repair surgeries are very rarely performed only under unusual situations. The indication, timing, and type of surgical treatment vary from institution to institution. For completeness, all of the surgical procedures done in patients with TGA are briefly described with schematic illustrations.
- 1.
Intraatrial repair surgeries (e.g., Senning operation) are no longer performed, except in rare cases, because of undesirable late complications (such as obstruction to the pulmonary or systemic venous return, TR, arrhythmias, and depressed systemic ventricular [i.e., RV] function).
- 2.
Rastelli operation, which redirects the pulmonary and systemic venous blood, is carried out at the ventricular level. It may be carried out in patients with VSD and severe PS. The LV blood is directed to the aorta by creating an intraventricular tunnel between the VSD and the aortic valve. A valved conduit or a homograft is placed between the RV and the PA ( Fig. 9.3 ). This procedure is less popular because of late complications and higher surgical mortality rate. Two alternative procedures are now available: réparation à l’étage ventriculaire (REV) procedure and Nikaidoh procedure (see the following for discussion of these procedures).
- 3.
Arterial switch operation (ASO) is the procedure of choice ( Fig. 9.4 ). This procedure provides anatomic correction with infrequent complications. The proximal portions of the aorta and PA are transected, the coronary arteries are transplanted to the PA, and the proximal great arteries are connected to the distal end of the other great arteries. For this procedure to be successful, the LV pressure should be near systemic levels at the time of surgery, and therefore should be performed before 3 weeks of age. Surgical mortality is down to 2% to 3%. Possible complications include coronary artery occlusion, supravalvar PS, supravalvar neoaortic stenosis, and AR.
Fig. 9.4
Arterial switch operation. (A) The aorta is transected slightly above the coronary ostia, and the main PA is transected at about the same level. The ascending aorta is lifted, and both coronary arteries are removed from the aorta with triangular buttons. (B) Triangular buttons of similar size are made at the proper position in the PA trunk. (C) The coronary arteries are transplanted to the PA. The ascending aorta is brought behind the PA (Lecompte maneuver) and is connected to the proximal PA to form a neoaorta. (D) The triangular defects in the proximal aorta are repaired, and the proximal aorta is connected to the PA. Note that the neopulmonary artery is in front of the neoaorta. AO , aorta; PA, pulmonary artery.
From Park, M. K., & Salamat, M. (2020). Park’s pediatric cardiology for practitioners (7th ed.). Philadelphia: Mosby.
- 4.
REV procedure may be performed for patients with associated VSD and severe PS ( Fig. 9.5 ). The procedure consists of the following: (1) infundibular resection to enlarge the VSD, (2) intraventricular baffle to direct LV output to the aorta, (3) aortic transection in order to perform the Lecompte maneuver (by which the RPA is brought anterior to the ascending aorta), and (4) direct RV-to-PA reconstruction by using an anterior patch (see Fig. 9.5 ). Lecompte reported surgical mortality of 18%.
Fig. 9.5
Réparation à l’étage ventriculaire procedure for patients with D-TGA + VSD + severe PS. (A) The broken lines indicate the planned aortic and RV incision sites. The broken circle indicates a VSD. (B) The aorta and PA have been transected and the RPA is brought anterior to the aorta (Lecompte maneuver). The proximal PA has been oversewn. The VSD is exposed through the right ventriculotomy. Dotted lines indicate the portion of the infundibular septum to be excised to enlarge the VSD. (C) The aortic valve is well shown by retractors. The broken line indicates the planned site of a patch placement for the LV-AO connection. The transected aorta has been reconnected behind the RPA. (D) The completed LV-to-AO tunnel is shown. The superior portion of the right ventriculotomy is sutured directly to the posterior portion of the main PA. (E) A pericardial or synthetic patch is used to complete the RV-to-PA reconstruction. AO , aorta; LV , left ventricle; LVOT , left ventricular outflow tract; PA , pulmonary artery ; RA , right atrium; RV, right ventricle; RVOT , right ventricular outflow tract; VSD , ventricular septal defect.
From Park, M. K., & Salamat, M. (2020). Park’s pediatric cardiology for practitioners (7th ed.). Philadelphia: Mosby.
- 5.
The Nikaidoh procedure can be performed for patients with associated VSD and severe PS ( Fig. 9.6 ). The repair consists of the following: (1) harvesting the aortic root from the RV (with attached coronary arteries), (2) relieving the LVOT obstruction (by dividing the outlet septum and excising the pulmonary valve), (3) reconstructing the LVOT (with a patch between the aortic root and the VSD), and (4) reconstructing the RVOT with a pericardial patch or a homograft. In the modified Nikaidoh procedure, one or both coronary arteries are moved to a more favorable position as necessary (not shown) and the Lecompte maneuver is also performed (see Fig. 9.6 ). The hospital mortality is less than 10%.
Fig. 9.6
Nikaidoh procedure (for patients with D-TGA, VSD, and severe PS). (A) The circular broken line around the aorta is the planned incision site for aortic root mobilization. The smaller broken circle indicates a VSD. (B) The aortic root has been mobilized by a circular incision around the aortic root, which leaves an opening in the RV free wall. The main PA is also transected. Through the opening, part of the VSD, ventricular septum, and hypoplastic PA stump are seen. The dotted vertical line in the ventricular septum (in the smaller inset in (B)) is the planned incision through the infundibular septum. (C) The incision in the infundibular septum has created a large opening, which includes the PA annulus and stump and the VSD. (D) The posterior portion of the aorta is directly sutured to the PA stump, which results in a large VSD. This completes translocation of the aorta to the original PA position. The thick oval-shaped broken line through the front of the transected aortic root is the planned site for placement of the LV outflow tract patch, which will direct the LV flow to the aorta. (E) The completed tunnel is shown (LVOT patch, which directs the LV flow to the aorta). The distal segment of the main PA is fixed to the aorta. Some surgeons use the Lecompte maneuver to bring the RPA in front of the ascending aorta (as shown here). (F) A pericardial patch is oversewn to complete the RV-to-PA connection (RVOT patch).
From Park, M. K., & Salamat, M. (2020). Park’s pediatric cardiology for practitioners (7th ed.). Philadelphia: Mosby.
The Damus-Kaye-Stansel operation may be performed at 1 to 2 years of age in infants with a large VSD and significant subaortic stenosis. In this procedure, the subaortic stenosis is bypassed by connecting the proximal PA trunk to the ascending aorta. The VSD is closed, and a conduit is placed between the RV and the distal PA ( Fig. 9.7 ). Fig. 9.8 shows a partial listing of surgical approaches used for infants with TGA, including the timing.
Follow-Up
- 1.
Patients who receive an arterial switch operation need to be followed for stenosis of the anastomosis sites in the PA and AO, signs of AR, and possible coronary obstruction (such as myocardial ischemia, LV dysfunction, arrhythmias).
- 2.
Limitation of activity may be indicated if arrhythmias or coronary insufficiency is present.
Fig. 9.8
Surgical approaches for TGA. ASO , arterial switch operation; BT , Blalock-Taussig; PDA, patent ductus arteriosus; PS, pulmonary stenosis; REV, réparation à l’étage ventriculare; TGA , transposition of the great arteries; VSD , ventricular septal defect.
From Park, M. K., & Salamat, M. (2020). Park’s pediatric cardiology for practitioners (7th ed.). Philadelphia: Mosby.
II. Congenitally Corrected Transposition of the Great Arteries (L-TGA)
Prevalence
Much less than 1% of all CHDs.
Pathology and Pathophysiology
- 1.
Visceroatrial relationship is normal (the RA on the right of the LA). The RA empties into the anatomic LV through the mitral valve, and the LA empties into the RV through the tricuspid valve. For this to occur, the LV lies to the right of the RV (i.e., ventricular inversion). The great arteries are transposed, with the aorta arising from the RV and the PA arising from the LV. The final result is a functional correction in that oxygenated blood coming into the LA goes out the aorta ( Fig. 9.9 ). This anomaly is also called l -transposition (L-TGA), indicating levo looping of the cardiac tube during embryogenesis.
Fig. 9.9
Diagram of congenitally corrected TGA (L-TGA). AO , aorta; LA , left atrium; LV , left ventricle; PA , pulmonary artery; RA , right atrium; R V , right ventricle.
- 2.
Theoretically, no functional abnormalities exist, but unfortunately most cases are complicated by associated defects. VSD (occurring in 80%) and PS (in 50%) with or without VSD are common, resulting in cyanosis. Regurgitation of the systemic AV valve (tricuspid) occurs in 30% of the patients. Varying degrees of AV block, which are sometimes progressive, and supraventricular tachycardia (SVT) are also frequent.
- 3.
The cardiac apex is in the right chest (dextrocardia) in about 50% of patients.
- 4.
The coronary arteries show a mirror-image distribution. The right-sided coronary artery supplies the anterior descending branch and gives rise to a circumflex; the left-sided coronary artery resembles a right coronary artery.
Clinical Manifestations
- 1.
Patients with associated defects are symptomatic during the first few months of life with cyanosis (VSD + PS) or CHF (large VSD). Patients without associated defects asymptomatic.
- 2.
The S2 is single and loud. A grade 2 to 4/6 harsh holosystolic murmur along the LLSB may indicate a VSD or the systemic AV valve (tricuspid) regurgitation. A grade 2 to 3/6 systolic ejection murmur at the ULSB or URSB may indicate PS.
- 3.
Characteristic ECG findings are the absence of Q waves in V5 and V6 and/or the presence of Q waves in V4R or V1. Varying degrees of AV block (first degree and second degree AV blocks, sometimes progressing to complete heart block) may be present. Atrial and/or ventricular hypertrophy may be present in complicated cases.
- 4.
Chest radiographs may show a characteristic straight left upper cardiac border (formed by the ascending aorta). Cardiomegaly and increased PVMs suggest associated VSD. Dextrocardia is frequent (50%).
- 5.
Two-dimensional echo is diagnostic of the condition and associated defects.
- a.
A “double circle” of the semilunar valves is imaged in the parasternal short-axis view. The posterior circle with no demonstrable coronary arteries is the PA. The aorta is usually anterior to and left of the PA.
- b.
The LV, which has two well-defined papillary muscles, is seen anteriorly and on the right and is connected to the characteristic “fish mouth” appearance of the mitral valve.
- c.
In the apical and subcostal four-chamber views, the LA is seen to connect to the tricuspid valve (which has a more apical attachment to the ventricular septum than the other).
- d.
The anterior artery (aorta) arises from the left-sided morphologic RV, and the posterior artery with bifurcation (PA) arises from the right-sided morphologic LV.
- e.
The situs solitus of the atria is confirmed.
- f.
Associated anomalies such as PS (type and severity), VSD (size and location), and straddling of the AV valve should be checked.
- a.
- 6.
Natural history: TR develops in about 30% of patients. Progressive AV conduction disturbances, including complete heart block (up to 30%), may occur.
Management
Medical
- 1.
Treatment of CHF and arrhythmias is indicated, if present.
- 2.
Antiarrhythmic agents are used to treat arrhythmias.
Surgical
- 1.
Palliative procedures: PA banding for uncontrollable CHF due to a large VSD or a B-T shunt for patients with severe PS.
- 2.
Corrective procedures: The presence or absence of TR determines the type of corrective surgery that can be performed, either anatomic repair or classic repair (see Fig. 9.10 , surgical summary of L-TGA).
- a.
When there is no TR, a classic repair is done, which leaves the anatomic RV as the systemic ventricle.
- b.
When there is TR or RV dysfunction, attempts are made to make the LV the systemic ventricle (anatomic repair).
- c.
For complex intracardiac anatomy, a staged Fontan-type operation is performed.
- a.
- 3.
Other procedures may be necessary:
- a.
Valve replacement for significant TR.
- b.
Pacemaker implantation for either spontaneous or postoperative complete heart block.
- a.
Follow-Up
- 1.
Follow-up every 6 to 12 months for a possible progression of AV conduction disturbances, arrhythmias, or worsening TR.
- 2.
Routine pacemaker care is needed if a pacemaker is implanted.
- 3.
Varying degrees of activity restriction may be indicated depending on hemodynamic abnormalities or pacemaker status.
III. Tetralogy of Fallot
Prevalence
Five percent to 10% of all CHD.
Pathology and Pathophysiology
- 1.
The original description of TOF included four abnormalities: a large VSD, RVOT obstruction, RVH, and an overriding of the aorta. However, only two abnormalities are important: a VSD large enough to equalize pressures in both ventricles and an RVOT obstruction ( Fig. 9.11 ). The RVH is secondary to the RVOT obstruction and VSD, and the overriding of the aorta varies in degree.
- 2.
The VSD is a perimembranous defect with extension into the infundibular septum and anterior malalignment of the conus. The RVOT may be in the form of infundibular stenosis (50%), pulmonary valve stenosis (10%), or both (30%). The pulmonary annulus and the PA are usually hypoplastic. The pulmonary valve is atretic in 10% of the patients. Abnormal coronary arteries are present in about 5% of the patients, with the most common one being the anterior descending branch arising from the right coronary artery and passing over the RV outflow tract (which prohibits a surgical incision in the region). Right aortic arch is present in 25% of the cases.
- 3.
Because of the nonrestrictive VSD, systolic pressures in the RV and the LV are identical. Depending on the degree of the RVOT obstruction, an L-R, bidirectional, or R-L shunt is present. With a mild PS, an L-R shunt is present (“acyanotic” TOF). With a more severe degree of PS, a predominant R-L shunt occurs (cyanotic TOF). The heart murmur audible in cyanotic TOF originates from the RVOT obstruction, not from the VSD.
Clinical Manifestations
- 1.
Neonates with TOF with pulmonary atresia are deeply cyanotic (see the later separate heading). Most infants with TOF are symptomatic, with cyanosis, clubbing, dyspnea on exertion, squatting, or hypoxic spells. Patients with acyanotic TOF may be asymptomatic.
- 2.
A right ventricular tap and a systolic thrill at the MLSB are usually found. An ejection click of aortic origin, a loud and single S2, and a loud (grade 3 to 5/6) systolic ejection murmur at the middle and upper LSB are present. In the acyanotic form, a long systolic murmur resulting from VSD and infundibular stenosis is audible along the entire LSB, and cyanosis is absent.
- 3.
The ECG shows RAD and RVH. BVH may be seen in the acyanotic form.
- 4.
In cyanotic TOF, chest radiographs show normal heart size, decreased PVMs, and a boot-shaped heart with a concave MPA segment. Right aortic arch is present in 25% of the cases. Chest radiographs of acyanotic TOF are indistinguishable from those of a small to moderate VSD.
- 5.
Two-dimensional echo shows a large subaortic VSD and an overriding of the aorta in the parasternal long-axis view. The anatomy of the RVOT, pulmonary valve, pulmonary annulus, and main PA and its branches is imaged in the parasternal short-axis view. Anomalous coronary artery distribution can be imaged accurately. The major concern is to rule out any branch of the coronary artery crossing the RV outflow tract. Computed tomography (CT) and magnetic resonance imaging (MRI) angiography may clarify questions on the anomalous coronary arteries. Two-dimensional echo and Doppler studies are the primary method of evaluation before surgery. Cardiac catheterization is reserved only for those patients with specific unanswered questions after the noninvasive studies.
- 6.
Natural history: Children with the acyanotic form of TOF gradually change to the cyanotic form by 1 to 3 years of age. Hypoxic spells may develop in infants (see next section). Brain abscess, cerebrovascular accident, and IE are rare complications. Polycythemia is common, but relative iron deficiency state (hypochromic) with normal hematocrit may be present. Coagulopathies are late complications of a long-standing severe cyanosis.
Hypoxic Spell
Hypoxic spell requires timely recognition and prompt appropriate treatment. The following describes key points of the spell.
- 1.
General description: Hypoxic spell (also called cyanotic spell or “tet” spell) is characterized by (a) a paroxysm of hyperpnea (rapid and deep respiration), (b) irritability and prolonged crying, (c) increasing cyanosis, and (d) decreased intensity of the heart murmur. A severe spell may lead to limpness, convulsion, cerebrovascular accident, or even death. It occurs in young infants, with peak incidence between 2 and 4 months of age.
- 2.
Pathophysiology of hypoxic spell: In TOF, the RV and LV can be viewed as a single pumping chamber, as there are large VSD equalizing pressures in both ventricles ( Fig. 9.12 ). Lowering the SVR or increasing resistance at the RVOT will increase the R-L shunting, and this in turn stimulates the respiratory center to produce hyperpnea. Hyperpnea results in an increase in systemic venous return, which in turn increases the R-L shunt through the VSD, as there is an obstruction at the RVOT. A vicious circle becomes established ( Fig. 9.13 ). Spasm of the RVOT is unlikely cause of the initiation of hypoxic spell; lowering of the SVR probably initiates the spell.
Fig. 9.12
Simplified concept of TOF that demonstrates how a change in the systemic vascular resistance ( SVR ) or right ventricular outflow tract obstruction (pulmonary resistance [ PR ]) affects the direction and the magnitude of the ventricular shunt. AO , aorta; LV , left ventricle; PA , pulmonary artery; RV , right ventricle.
From Park, M. K., & Salamat, M. (2020). Park’s pediatric cardiology for practitioners (7th ed.). Philadelphia: Mosby.
Fig. 9.13
Mechanism of hypoxic spell. R-L shunt , right-to-left shunt; RVOT , right ventricular outflow tract; SVR , systemic vascular resistance.
From Park, M. K., & Salamat, M. (2020). Park’s pediatric cardiology for practitioners (7th ed.). Philadelphia: Mosby.
- 3.
Treatment of hypoxic spell: The aim of the treatment is to break the vicious circle of hypoxic spell (as shown in Fig. 9.13 ). One or more of the following may be used in decreasing order of preference:
- a.
Pick up the infant and hold in a knee-chest position.
- b.
Morphine sulfate, 0.1 to 0.2▒mg/kg subcutaneously or intramuscular, suppresses the respiratory center and abolishes hyperpnea.
- c.
Treat acidosis with sodium bicarbonate, 1 mEq/kg IV. This reduces the respiratory center–stimulating effect of acidosis.
- d.
Oxygen inhalation has only limited value, because the problem is a reduced PBF, not the ability to oxygenate.
- e.
With these treatments the infant usually becomes less cyanotic and the heart murmur becomes louder, indicating improved PBF.
- f.
If the spell is not fully under control with the above measures, the following may be tried.
- (1)
Ketamine, 1 to 3▒mg/kg (average of 2▒mg/kg) in a slow IV push, works well (by increasing the SVR and sedating the infant).
- (2)
Propranolol, 0.01 to 0.25▒mg/kg (average 0.05▒mg/kg) in a slow IV push, reduces the heart rate and may reverse the spell.
- (1)
- a.
Management
Medical
- 1.
Hypoxic spells should be recognized and treated appropriately (as described in the preceding section).
- 2.
Oral propranolol, 2 to 4▒mg/kg/day, may be used to prevent hypoxic spells while waiting for an optimal time for corrective surgery. The beneficial effect of propranolol may be related to its stabilizing action on peripheral vascular reactivity (and thus prevent sudden fall of the SVR), rather than by prevention of RV outflow tract spasm.
- 3.
Detection and treatment of relative iron deficiency state, if present. Anemic children are particularly prone to cerebrovascular accident.
Surgical
- 1.
Palliative procedures are indicated to increase PBF in infants with severe cyanosis or uncontrollable hypoxic spells on whom the corrective surgery cannot safely be performed, and in children with hypoplastic PA on whom the corrective surgery is technically difficult. Different types of systemic-to-pulmonary (S-P) shunts have been performed ( Fig. 9.14 ).
- a.
The B-T shunt (1945) (anastomosis between the subclavian artery and the ipsilateral PA) may be performed in older infants.
- b.
Potts operation (1946) (anastomosis between the descending aorta and the left PA) is no longer performed for TOF.
- c.
Waterston shunt (1962) (anastomosis between the ascending aorta and the right PA) is no longer performed because of many complications following the operation.
- d.
Gore-Tex interposition shunt (modified B-T shunt) between the subclavian artery and the ipsilateral PA is the most popular procedure for any age, especially for infants younger than 3 months of age.
- a.
- 2.
Complete repair surgery
- a.
Timing:
- (1)
Most centers prefer primary elective repair between 3 months and 12 months of age, even if they are asymptomatic, acyanotic (i.e., “pink tet”), or minimally cyanotic.
- (2)
The occurrence of hypoxic spell is generally considered an indication for operation, even in conservative centers.
- (3)
Mildly cyanotic infants who have had previous shunt surgery may have total repair 1 to 2 years after the shunt operation.
- (4)
Patients with coronary artery anomalies may have an early surgery at the same time as those without anomalous coronary arteries.
- (1)
- b.
Total repair of the defect is carried out under cardiopulmonary bypass. The procedure includes patch closure of the VSD, widening of the RVOT by resection of the infundibular muscle tissue, and pulmonary valvotomy, avoiding placement of a transannular fabric patch ( Fig. 9.15 ). At the present time, surgeons aim to avoid right ventriculotomy and transannular patch whenever possible. However, if the pulmonary annulus and main PA are hypoplastic, transannular patch placement is unavoidable. Some centers advocate placement of a monocusp valve at the time of initial repair, whereas other centers advocate pulmonary valve replacement at a later time if indicated.
- c.
Surgery for TOF with anomalous anterior descending coronary artery from the right coronary artery (which results in the LAD crossing the RV outflow tract) requires placement of a conduit between the RV and PA. The surgery is usually performed after 1 year of age. A B-T shunt may be necessary initially to palliate the patient. Alternatively, when a small conduit is necessary between the RV and the PA, the native outflow tract should be made as large as possible using transatrial and transpulmonary approach, so that a “double outlet” (the native outlet and the conduit) results from the RV.
- a.
Follow-Up
- 1.
Long-term follow-up every 6 to 12 months is recommended, especially for patients with residual VSD shunt, residual RVOT obstruction, residual PA stenosis, arrhythmias, or conduction disturbances.
- 2.
Significant, and usually progressive, pulmonary regurgitation may develop following repair of TOF. Although the PR is well tolerated for a decade or two, it may eventually lead to significant RV enlargement and RV dysfunction. A homograft pulmonary valve may need to be inserted (by either a transcatheter technique or surgery) while the RV function remains reversible. Although the indications for the valve replacement are evolving, the presence of moderate or severe PR (with RV regurgitation fraction 25% or greater), decreased RV function, and/or significant RV dilatation appears to be prerequisite. RV function and size and regurgitant fraction are best investigated by MRI (or CT).
- 3.
Some patients, particularly those who had Rastelli operation using valved conduit, develop valvular stenosis or regurgitation. Valvular stenosis may improve after balloon dilatation, but PR may worsen. Nonsurgical percutaneous pulmonary valve implantation technique developed by Bonhoeffer et al. has been used successfully.
- 4.
Some children develop late arrhythmias, particularly VT, which may result in sudden death. Arrhythmias are primarily related to persistent RVH as a result of unsatisfactory repair.
- 5.
Pacemaker therapy is indicated for surgically induced complete heart block or sinus node dysfunction.
- 6.
Varying levels of activity limitation may be necessary.
- 7.
For patients who have residual defects or have prosthetic material for repair, IE prophylaxis should be observed throughout life.
IV. Tetralogy of Fallot (TOF) with Pulmonary Atresia
Prevalence
About 30% of patients with TOF.
Pathology and Pathophysiology
- 1.
In this extreme form of TOF, the intracardiac pathology resembles that of TOF in all respects except for the presence of pulmonary atresia.
- 2.
The PBF is more commonly through a PDA (70%) and less commonly through multiple systemic collaterals (30%), which are called multiple aortopulmonary collateral arteries (or MAPCAs). Both PDA and collateral arteries may coexist as the source of PBF. The ductus is small and long and descends vertically from the transverse arch (“vertical” ductus) and connects to the Pas, which are usually confluent. The subgroup of patients with MAPCAs is associated with nonconfluent PAs, with the right upper lobe and the left lower lobe frequently supplied by systemic collateral arteries. This subgroup is designated as pulmonary atresia and VSD.
- 3.
The central and branch PAs are hypoplastic in most patients but more frequently in patients with MAPCAs than in those with PDA. Incomplete arborization (distribution) of one or both PAs is also more common in patients with nonconfluent PAs than those with confluent PAs.
Clinical Manifestations
- 1.
The patient is cyanotic at birth; the degree of cyanosis depends on whether the ductus is patent and how extensive the systemic collateral arteries are.
- 2.
Usually no heart murmur is audible, but a faint, continuous murmur of PDA may be audible. The S2 is loud and single.
- 3.
The ECG shows RAD and RVH.
- 4.
Chest radiographs show normal heart size, often with a boot-shaped silhouette and a markedly decreased PVM (“black” lung field).
- 5.
Echo studies are diagnostic of the condition, but an angiocardiogram is necessary for complete delineation of the pulmonary artery anatomy and the collaterals. Alternatively, MRI or CT angiography is used for complete anatomic delineation of the aortic collaterals and PA branches.
Management
Medical
- 1.
IV PGE 1 infusion is started to keep the ductus open for cardiac catheterization and in preparation for surgery (see Appendix E for the dosage).
- 2.
Emergency cardiac catheterization or MRI (or CT angiography) is performed to delineate anatomy of the pulmonary arteries and systemic arterial collaterals.
Surgical
- 1.
Primary surgical repair (closure of the VSD, conduit between the RV and the central PA) is possible only when a central PA of adequate size exists and the central PA connects without obstruction to sufficient regions of the lungs (at least equal to one whole lung).
- 2.
Staged repair consists of an initial procedure that increases PBF and induces the growth of the central PA (before 1 or 2 years of age) followed by additional surgical procedure(s) at a later time.
- a.
When there is a confluence of central PAs, either a B-T shunt or a PA homograft placement can be performed.
- (1)
A B-T shunt procedure often results in an iatrogenic stenosis of the PA branch. For a very small confluent central PA, a central end-to-side shunt (Mee procedure) can be performed.
- (2)
Initial RVOT reconstruction with a small homograft conduit may need to be replaced with a larger one later. Anastomosis of collateral arteries to the central artery is carried out later. In this case, the VSD may be left open, or closed with a fenestrated patch to maintain an increased PBF ( Fig. 9.16 , top row ).
- (1)
- b.
When the central PA is nonconfluent , with multiple collaterals supplying different segments of the lungs, a surgical connection between or among the isolated regions of the lungs may be made so they might be perfused from a single source (termed unifocalization of PBF ) (see Fig. 9.16 , bottom row ). Later, a conduit between the RV and a newly created central PA can be made.
- c.
Occlusion of systemic collateral arteries is done by coil embolization preoperatively or at the time of surgery.
- a.
- 3.
Fig. 9.17 summarizes surgical approaches for patients with TOF with pulmonary atresia.
Follow-Up
- 1.
Frequent follow-up is needed to assess the palliative surgery, to decide the appropriate time for further operations, and to determine an appropriate time for conduit replacement.
- 2.
IE prophylaxis is indicated for an indefinite period.
- 3.
A certain level of activity restriction is needed for most patients even after surgery.
V. Tetralogy of Fallot (TOF) with Absent Pulmonary Valve
Prevalence
Approximately 2% to 6% of patients with TOF.
Pathology and Pathophysiology
- 1.
The pulmonary valve leaflets are either absent or rudimentary, and the pulmonary annulus is stenotic, usually in association with TOF. A massive aneurysmal dilatation of the PAs develops during fetal life and compresses the lower end of the developing trachea and bronchi. Postnatally, this produces signs of airway obstruction and respiratory difficulties. Pulmonary complications (e.g., atelectasis, pneumonia), rather than the intracardiac defect, are the usual cause of death when managed medically.
- 2.
The ductus arteriosus is frequently absent, with a more severe aneurysmal dilatation of the PAs. A right aortic arch is frequently found (in about 50%)
- 3.
Since the annular stenosis is only moderate, a bidirectional shunt is initially present but it becomes predominantly an L-R shunt beyond the newborn period.
Clinical Manifestations
- 1.
Mild cyanosis may be present in the neonate, but cyanosis disappears and signs of CHF may develop when the PVR falls.
- 2.
A to-and-fro murmur (“sawing-wood sound”) at the upper and middle LSB (resulting from PS and PR) is characteristic of the condition. The S2 is loud and single, and RV hyperactivity is palpable.
- 3.
The ECG shows RAD and RVH.
- 4.
Chest radiographs reveal a markedly dilated MPA and hilar PAs. The heart size is either normal or mildly enlarged, and PVMs may be slightly increased. The lung fields may show hyperinflated and/or atelectatic areas.
- 5.
Echo studies reveal a large, subaortic VSD with overriding of the aorta (as seen in TOF), distally displaced pulmonary annulus (with thick ridges instead of fully developed pulmonary valve leaflets), and gigantic aneurysm of the PA and its branches. The RV is markedly dilated, often with paradoxical motion of the ventricular septum. Doppler studies reveal evidence of stenosis and regurgitation at the annulus.
- 6.
Natural history: Most infants with severe pulmonary complications (e.g., atelectasis, pneumonia) die during infancy if treated only medically. The surgical mortality of infants with pulmonary complications is as high as 40%. Therefore surgery should be performed in early infancy before pulmonary complications develop.
Management
