SPECIFIC FORMS OF CYANOTIC CONGENITAL HEART DISEASE

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Cyanotic Heart Disease

SPECIFIC FORMS OF CYANOTIC CONGENITAL HEART DISEASE

Table 3-5 lists the prevalence of selected subtypes of cyan-otic CHD identified during the first year of life in two different studies. The practitioner is most likely to encounter dextrotransposition of the great arteries (D -TGA), tetralogy of Fallot (TOF), and hypoplastic left heart syndrome. Specific anatomic lesions are addressed below in order of decreasing prevalence, with special attention to their neonatal presentations.

Transposition of the Great Arteries

Transposition of the great arteries (TGA) is defined anatomically as a malformation in which the aorta arises from the right ventricle and the pulmonary artery arises

from the left ventricle. In the most common form of TGA,D-TGA, the atria and ventricles are otherwise nor-mal. The aortic valve is positioned anterior and to the right of the pulmonary valve. When blood returns from the systemic veins, it passes into the right atrium, the right ventricle, and then into the aorta without being oxygenated in the lungs. When blood returns from the pulmonary veins, it passes into the left atrium, the left ventricle, and then into the pulmonary artery, to be returned again to the lungs (see Fig. 3-1). This parallel, rather than series, circulation of blood through the heart is termed transposition physiology, and is obviously incompatible with life without mixing of blood from the two circuits. The medical and surgical management of

D-TGA is described in Chapters 2 and 14, respectively.

Other forms of anatomic TGA exist, although they are much less common than D-TGA. In levotransposition of the great arteries (L-TGA),also called congenitally corrected Table 3-3 Classification of Cyanotic Congenital Heart Disease by the Amount of Pulmonary Blood Flow Seen on

Chest X-Ray

Increased Pulmonary Blood Flow Normal or Decreased Pulmonary Blood Flow

Tricuspid atresia with large VSD Tricuspid atresia with restrictive VSD

Total anomalous pulmonary venous return Pulmonary atresia with intact ventricular septum

Truncus arteriosus Ebstein’s anomaly

D-transposition of the great arteries D-transposition of the great arteries with pulmonary stenosis

Taussig-Bing anomaly Double outlet right ventricle with pulmonary stenosis

Tetralogy of Fallot with minimal right ventricular outflow tract obstruction Tetralogy of Fallot

Tetralogy of Fallot with pulmonary atresia and increased collateral flow Tetralogy of Fallot with pulmonary atresia Single ventricle without pulmonary stenosis Single ventricle with pulmonary stenosis

Interrupted aortic arch with PDA Vena cava to left atrium communication

Hypoplastic left heart syndrome ASD with Eisenmenger’s syndrome

VSD with Eisenmenger’s syndrome PDA with Eisenmenger’s syndrome VSD,Ventricular septal defect; PDA, patent ductus arteriosus; ASD, atrial septal defect.

Table 3-2 The Cost of a High Systemic Saturation in Single Ventricle Physiology *

Systemic Venous Pulmonary Venous Work Imposed on the Single Systemic Arterial Saturation Saturation Saturation Qp:Qs Ventricle (Qp + Qs)

65% 40% 98% 0.75:1 1.75 cardiac outputs

73% 48% 98% 1:1 2 cardiac outputs

86% 61% 98% 2:1 3 cardiac outputs

90% 65% 98% 3:1 4 cardiac outputs

92% 67% 98% 4:1 5 cardiac outputs

Qp,Pulmonary blood flow; Qs, systemic blood flow; Qp:Qs, the ratio of pulmonary to systemic blood flow.

*The systemic venous saturation is usually approximately 25 percentage points lower than the systemic arterial saturation if the cardiac output and hemoglobin are normal.

TGA, the right atrium drains to a right-sided morphologic left ventricle, which ejects to the pulmonary artery, whereas the left atrium drains to a left-sided morphologic rightventricle, which ejects to the aorta. Thus, the patient has anatomic TGA, but not transposition physiology and, in the absence of additional complicating intracardiac defects, may not be cyanotic. More complex anomalies may also exhibit TGA,for example,tricuspid atresia with TGA. These forms of TGA will not be further discussed here.

Surgical correction for D-TGA by arterial switch opera-tion (see Chapter 14) is undertaken in the first few days of life unless complicating anatomic factors dictate another approach. Several older series reported approximately 15% mortality for this procedure; most major centers now expect a surgical mortality under 5%.19,20Center volume

has been shown to be inversely related to surgical mortal-ity.20General physical and psychosocial health status is not different from the general population at 8 years of age in patients with D-TGA after an arterial switch opera-tion.21Reintervention is required in 10–15% of patients within 2 years of the initial operation for development of supravalvar pulmonary stenosis (PS). Coronary occlu-sion occurs in a few percent of patients and usually is asymptomatic, but several large series report sudden death ( presumably secondary to coronary complications) in less than 1% of patients.19Consequently, many cardiol-ogists will perform an exercise stress test with myocardial perfusion imaging in patients with repaired D-TGA prior to competitive interscholastic sports participation. Prior to the 1980s, the surgical approach to D-TGA was an Table 3-4 Forms of cyanotic congenital heart disease organized by level of shunting

Site of Shunting Lesion Reason for Shunting Atrial level Connection of SVC or IVC to Obligatory connection

left atrium

ASD Tricuspid atresia Atretic tricuspid valve with no other outflow from RA

ASD Critical pulmonic stenosis Severe RV hypertrophy results in poor RV compliance and elevated RV filling pressures

ASD Pulmonary atresia with intact No RV outlet ventricular septum

ASD Ebstein’s anomaly Poor RV compliance

ASD ASD with Eisenmenger’s syndrome RV hypertrophy secondary to pulmonary hypertension results in poor RV compliance

ASD Total anomalous pulmonary Elevated RA pressure with low LA pressure venous return

Ventricular level Single ventricle (with common All blood mixes in ventricle, and both systemic and pulmonary vascular beds are inlet or double inlet) supplied from one ventricle

VSD Tetralogy of Fallot VSD with obstruction to flow to the pulmonary artery VSD VSD with Eisenmenger’s syndrome VSD with elevated PVR

Conotruncus* Truncus arteriosus One great vessel comes off both ventricles and therefore receives both ventricular outputs

Conotruncus* D-transposition of the great arteries The aorta arises from the RV, so venous blood passes from RA to RV to aorta Conotruncus* Double outlet right ventricle with Both great vessels come off the RV, but the pulmonary artery is closer to the LV

transposition of the great arteries while the aorta is very rightward and therefore gets blue blood (i.e.,Taussig-Bing anomaly)

Conotruncus* Double outlet right ventricle with Aorta comes off RV and there is obstruction to pulmonary blood flow subaortic VSD and pulmonic

stenosis

PDA Hypoplastic left heart syndrome Obstruction to aortic flow proximal to PDA favors right-to-left PDA flow and variants

PDA Interrupted aortic arch Interruption of the aorta favors right-to-left PDA flow to the aorta distal to the interruption, while LV supplies the aorta proximal to the interruption.

PDA Coarctation of the aorta Obstruction within aorta proximal to PDA favors right-to-left PDA flow to descending aorta

PDA Critical aortic stenosis Obstruction to flow across aortic valve favors right-to-left PDA flow, supplying both ascending and descending aorta

PDA Persistent pulmonary hypertension Elevated pulmonary vascular resistance favors right-to-left PDA flow, with or of the newborn without RV dysfunction, resulting in abnormal RV compliance and right-to-left

atrial-level shunting

* The conotruncus refers to the junction between the ventricles and the great arteries.

Not a form of congenital heart disease, but frequently in the differential diagnosis of the cyanotic newborn

SVC,Superior vena cava; IVC, inferior vena cava; ASD, atrial septal defect; VSD, ventricular septal defect; PDA, patent ductus arteriosus; RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle.

intra-atrial baffle or an atrial level switch, the Mustard or Senning procedures, respectively. These procedures achieved physiologic correction with low mortality but have been associated with sudden death, high rates of late postoperative atrial arrhythmias, and right ventricular fail-ure in a minority of patients.

Tetralogy of Fallot

The four components tetralogy of Fallot ( TOF ) are a VSD, an over-riding aorta, pulmonary stenosis, and right ven-tricular hypertrophy (Fig. 3-2). However, TOF can be reduced to a single unifying anatomic malformation:

underdevelopment of the right ventricular infundibu-lum (i.e., the outflow portion of the right ventricle).22 Underdevelopment of the infundibulum results in hypoplasia of the pulmonary outflow tract and, conse-quently, PS. Pulmonary stenosis can be at the subvalvar, valvar, and supravalvar levels (Fig. 3-3A). The infundibu-lum also contributes to the development of the ventricu-lar septum; the infundibuventricu-lar portion of the septum lies between the right and left ventricular outflow tracts.

When the infundibulum is hypoplastic, the infundibular septum is displaced anteriorly (toward the right ventricu-lar outflow tract) and a ventricu-large VSD results, which is accom-panied by a large aorta over-riding the VSD (Fig. 3-3B).

The right and left ventricular pressures are equalized by the large VSD, and secondary right ventricular hypertro-phy results. Right aortic arch is present in about 25% of cases of TOF.23

There are additional notable variants of TOF. The vari-ant of TOF with pulmonary atresia often has tiny central (i.e., true) pulmonary arteries, with arterial supply to seg-ments of lung arising from a variable number of major collateral vessels off the aorta. These collateral vessels do not have the histologic characteristics of normal pul-monary arteries, and pulpul-monary vascular disease or severe stenosis frequently develops. Thus,TOF with pul-monary atresia and major aortopulpul-monary collaterals is a difficult disease to treat and has a considerably worse prognosis than uncomplicated TOF. Another variant, TOF with absent pulmonary valve, is associated with markedly dilated central pulmonary arteries in utero;

however, the intraparenchymal pulmonary arteries may be small. Severe bronchomalacia can result from com-pression of the bronchi by the large central pulmonary arteries, and the prognosis of these patients may be lim-ited by their ventilatory difficulties. Finally, particularly in trisomy 21, complete atrioventricular canal (CAVC) and TOF can coexist.

The etiology of TOF is heterogeneous and in many cases idiopathic, although specific genetic causes are increasingly recognized. Approximately 16% of patients with TOF in a hospital-based series had a microdeletion of chromosome 22q11.24 In the population-based Baltimore–Washington Infant Study, 7% of cases of TOF had trisomy 21.18 TOF occurs in patients with Alagille syn-drome, VACTERL association (vertebral abnormalities, tracheoesophageal fistula and/or esophageal atresia, renal agenesis and dysplasia, and limb defects) syndrome, and many other rarer genetic syndromes associated with Table 3-5 Prevalence of Subtypes of Cyanotic CHD Identified in the First Year of Life in the New England Regional

Infant Cardiac Program Study, 1968–197417and The Baltimore-Washington Infant Study, 1981–1989.18

Lesion NERICP # per 100,000 Live Births BWIS # per 100,000 Live Births

D-transposition of the great arteries 21.8 20.1

Tetralogy of Fallot 19.6 26.0

Hypoplastic left heart syndrome 16.3 17.8

Heterotaxy syndrome 8.8 9.2*

Severevalvar pulmonic stenosis 7.3 7.1

Pulmonary atresia with intact ventricular septum 6.9 5.8

Total anomalous pulmonary venous return 5.8 6.6

Tricuspid atresia 5.6 3.6

Single ventricle 5.4

Severevalvar aortic stenosis 4.1 4.3

Double outlet right ventricle 3.2 6.7

Truncus arteriosus 3.0 4.9

SevereEbstein’s anomaly § 2.8

*Patients classified in BWIS as having defects of laterality and looping, excluding those with L-transposition of the great arteries or dextrocardia with situs inversus.

Patients who died or required catheterization or surgery in the first year of life; not all patients in this group will be cyanotic.

‡Category not specified separately in BWIS.

§Category not specified separately in NERICP.

NERICP, New England Regional Infant Cardiac Program; BWIS, Baltimore-Washington Infant Study.

CHD. Still, most patients with TOF have no other identi-fied anomalies.

TOF exists along a continuum of severity of PS, which in turn determines the patient’s physiology. Patients with little PS display the physiology of a large VSD and are prone to heart failure. Patients with severe PS may be ductal-dependent for pulmonary blood flow; that is, they may have insufficient pulmonary blood flow once the ductus arteriosus closes, resulting in profound cyanosis. The latter patients are described in Chapter 2, and require surgical intervention in the neonatal period.

Patients with an intermediate degree of PS will have acceptable oxygen saturations in the absence of heart failure and may be repaired electively. The degree of PS can progress with time, causing the patient to become more cyanotic and to experience hypercyanotic spells.

TOF can be diagnosed prenatally by fetal echocardiog-raphy; outflow tract views increase the sensitivity of ultrasound over a simple four-chamber view. Most patients with TOF present clinically with a systolic mur-mur attributable to pulmonic or subpulmonic stenosis.

The VSD is large, has no pressure gradient across it, and does not generate a murmur. On physical examination, if there is little PS and a large left-to-right shunt through the VSD (the so-called pink tetralogy), the patient will become tachypneic as the pulmonary vascular resistance falls. There may be no visible cyanosis, and desaturation by pulse oximetry is minimal. These patients will

develop hepatomegaly if they have symptomatic heart failure. Most commonly,TOF is accompanied by a signifi-cant degree of PS, a normal respiratory rate, and cyanosis.

As pulmonary blood flow decreases, oxygen saturation, measured by pulse oximetry, decreases.

Figure 3-3 Angiograms from a patient with tetralogy of Fallot.

A, Right ventricular injection shows multiple levels of right ventricular outflow tract obstruction. There is narrowing below the valve because of infundibular muscle (i.e., subpulmonic stenosis).

The pulmonary valve annulus is small and the valve leaflets are thickened and doming, consistent with valvar PS. There are stenoses of the proximal right (RPA) and left pulmonary arteries (LPA).B, Left ventricular injection seen from a long axial oblique projection demonstrates contrast passing through a large malalignment-type VSD under the aortic valve and an overriding aorta. This patient also had additional defects in the muscular ventricular septum.

Ao

RA

RV

LV LA PA

Figure 3-2 Schematic drawing of tetralogy of Fallot with subpulmonic stenosis and valvar PS.The arrows indicate the direction of blood flow. A substantial right-to-left shunt exists across the VSD. RA, right atrium; LA, left atrium; RV, right ventricle;

LV,left ventricle; Ao, aorta; PA, pulmonary artery. ( From Friedman WF, Silverman N: Congenital heart disease in infancy and

childhood. In Braunwald E, Zipes DP, Libby P [eds]: Heart Disease:

A textbook of cardiovascular medicine, 6th ed. Philadelphia:

WB Saunders, 2001.)

Across the spectrum of patients with TOF, the right ventricular impulse is increased and the second heart sound is usually single. A harsh systolic murmur is pres-ent along the left upper sternal border radiating across the precordium and to the back. An ejection click may be generated by a dilated aortic root or by an abnormal pulmonary valve. In TOF with an absent pulmonary valve, a “to-and-fro” murmur is heard from systolic ejec-tion of blood across the right ventricular outflow tract and from diastolic regurgitation of the same. In contrast, patients with TOF with pulmonary atresia and multiple collaterals have no flow across the right ventricular out-flow tract and thus no systolic ejection murmur. There may be continuous murmurs over the back, correspon-ding to flow through collaterals, but these are often sub-tle in the newborn period. If the degree of cyanosis is mild,TOF with pulmonary atresia and major collaterals may go undiagnosed for a prolonged period of time.

The electrocardiogram ( ECG) in TOF characteristi-cally demonstrates right ventricular hypertrophy, includ-ing right axis deviation. If left axis deviation with counterclockwise looping is present preoperatively, one should consider the diagnosis of TOF with CAVC. On chest x-ray, the classic finding of the “boot-shaped heart”

is attributed to a combination of right ventricular promi-nence and hypoplasia of the main pulmonary artery seg-ment. This finding usually is evident in older children but may not be apparent in newborns, especially if a thy-mus is present. The degree of pulmonary blood flow is reflected in the prominence of the pulmonary vascular markings, which usually are decreased in TOF but may be increased in “pink”TOF. A right aortic arch may be appar-ent. Echocardiography provides a definitive anatomic diagnosis.

Special attention is paid to the coronary artery anatomy because the anterior descending coronary artery arises from the right coronary and crosses the right ventricular outflow tract in about 4% of patients.23 This anatomic feature complicates the surgical repair.

Typically, an incision is made across the right ventricular outflow tract to relieve obstruction, but if the anterior descending coronary crosses the outflow tract, a conduit must be placed from the right ventricle to the pulmonary artery instead.

Cardiac catheterization is not indicated preoperatively in most patients with uncomplicated TOF and can confer a significant risk of precipitating a hypercyanotic spell.

Hypercyanotic spells (“Tet spells”) result in an acute increase in right-to-left shunting. Although the precise precipitating cause has been debated over the years, likely any stimulus which either increases right ventricu-lar outflow tract obstruction or decreases systemic vas-cular resistance will tip the balance of blood flow towards more right-to-left shunting, less pulmonary blood flow, and increased cyanosis. Such stimuli can

include increased catecholamines, dehydration, exercise, and sedatives with systemic vasodilatory properties.

Clinically, increased cyanosis, hyperpnea, and agitation are observed. Although most spells are self-limited, there is the potential for a vicious cycle to be set up as hypox-emia leads to increased agitation, metabolic acidosis, and worsening hypoxemia. Spells should be managed ini-tially with the knee-chest position (to increase systemic vascular resistance), removal of noxious stimuli, and allowing a familiar caregiver to comfort the child. For spells that do not resolve promptly, oxygen, morphine ( given subcutaneously, intramuscularly, or intra-venously), intravenous volume, intravenous phenyle-phrine, and intravenous β-blockers can be used. In the extreme, management is escalated to intubation, heavy sedation, and paralysis. Occurrence of a hypercyanotic spell is an indication for prompt surgical repair.

Surgical repair of TOF is reviewed in Chapter 14. In the current era, primary repair is undertaken on infants at most major centers, rather than initial palliation with a shunt. In brief, repair involves closure of the VSD and relief of right ventricular outflow tract obstruction.

Frequently, the annulus of the pulmonary valve is signifi-cantly hypoplastic and is enlarged with a patch (i.e., the

“transannular patch” technique), which results in free pulmonic insufficiency. Even if all obstruction to right ventricular outflow is relieved, the physical examination of a patient after repair of TOF usually reveals a “to-and-fro” murmur due to increased systolic ejection volume through the right ventricular outflow tract and diastolic pulmonary insufficiency. The postoperative ECG usually displays a right bundle branch block pattern.

In uncomplicated TOF, repair is a low-mortality proce-dure with excellent short- and long-term term results.

Surgical mortality is approximately 2%. In a cohort of patients with TOF operated on at the Mayo Clinic between 1955 and 1960, the 32-year actuarial survival was 86%, whereas that in a control population without CHD was 96%.25In contrast,less than 5% of patients with unrepaired TOF survive to adulthood. In the Mayo Clinic study,77% of survivors were in New York Heart Association functional class I (i.e., asymptomatic), 17% in class II (i.e., symptoms with ordinary levels of physical activity), and 6% in class III (i.e.,symptoms with minimal exertion). Pulmonary insuffi-ciency is usually well-tolerated for many years, although decades of pulmonary insufficiency may result in right ven-tricular dilation and dysfunction. Indications for pul-monary valve replacement in this patient population are controversial; ideal prostheses are currently not available.

Surgical mortality is approximately 2%. In a cohort of patients with TOF operated on at the Mayo Clinic between 1955 and 1960, the 32-year actuarial survival was 86%, whereas that in a control population without CHD was 96%.25In contrast,less than 5% of patients with unrepaired TOF survive to adulthood. In the Mayo Clinic study,77% of survivors were in New York Heart Association functional class I (i.e., asymptomatic), 17% in class II (i.e., symptoms with ordinary levels of physical activity), and 6% in class III (i.e.,symptoms with minimal exertion). Pulmonary insuffi-ciency is usually well-tolerated for many years, although decades of pulmonary insufficiency may result in right ven-tricular dilation and dysfunction. Indications for pul-monary valve replacement in this patient population are controversial; ideal prostheses are currently not available.

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