Fetal cardiac development occurs rapidly from day 18 to the 12th week of fetal life (Sedmera, 2011).

A. Cardiac tube.

1. Heart development is first identified at 18 to 19 days of fetal life with formation of a heart tube (Table 28-1; Fig. 28-1, A).

2. The heart tube elongates and develops dilatations and contractions that will later form the ventricles, bulbus cordis, and outflow tracts (Fig. 28-1, B). Molecular studies are beginning to identify that the heart tube actually becomes the left ventricle, but more studies are needed (van de Berg and Moorman, 2009).

3. The pairs of aortic arches develop from the cephalic, extracardial portion of the heart tube. The caudal end will form the early ventricle (Fig. 28-1, C).

4. Abnormal development during this time will include corrected transposition and dextrocardia (Collins-Nakai and McLaughlin, 2002).

B. Cardiac septation: begins in the middle of the fourth week and is complete by the end of the fifth week of fetal life (Fig. 28-1, D).

1. Atrial septum and foramen ovale are formed from two septa and endocardial cushions.

a. Atrial septum primum is formed by unidirectional growth from the top of the atrium toward the endocardial cushions, resulting in formation of the septum.

b. A second septum (septum secundum) appears to the right of the septum primum and grows to overlap the ostium secundum. Thus the flapped opening, the foramen ovale, is created (Fig. 28-2).

2. Ventricular septation results from fusion of the endocardial cushions and dilation and fusion of the ventricles (Fig. 28-3).

3. Tissue of endocardial cushion forms the atrioventricular valves (Fig. 28-4).

a. Tricuspid valve: between right atrium and ventricle.

b. Mitral valve: between left atrium and ventricle.

4. Abnormal development during cardiac septation can lead to the following:

a. VSD, ASD, and endocardial cushion defect (atrioventricular canal).

Great Vessel Development

A. Single vessel (truncus arteriosus) extends from the ventricles until the fourth week of fetal life. It will then separate into the aorta and the pulmonary artery (Fig. 28-5).

1. The semilunar valves (aortic and pulmonic valves) develop from three ridges of tissue at the opening to the aorta and pulmonary trunk.

B. Development of aorta and aortic branches (Table 28-2). The truncus arteriosus connects with the aortic sac, which in turn connects with the paired aortic branches. A series of six paired aortic arches then form in succession (Fig. 28-6).

1. The third arches become part of the common carotid arteries.

C. Developmental abnormalities of truncal septation include (Collins-Nakai and McLaughlin, 2002):

1. Truncus arteriosus.

Circulatory Development

A. Heart contractions begin around 21 days; the atrium and ventricle muscle layers are continuous. Contractions result in a rhythmic peristalsis.

B. Electrical conduction system is functional around 10 weeks, with normal sinus rhythm seen by 16 weeks (Blackburn, 2013).

C. Establishment of fetal circulation: With completion of atrial and ventricular septation, development of valves between chambers and outflow tracks, and separation of the truncus arteriosus into the great vessels, fetal circulation is established.

D. Fetal circulation is anatomically and physiologically different from adult circulation, and adaptation after birth is necessary (Blackburn, 2013). For a full discussion of fetal circulation and cardiopulmonary adaptation at birth, see Chapter 4.

Cardiovascular Physiology

A. Normal circulation (see Fig. 4-2).

1. Oxygen-poor blood enters the right atrium and passes through the tricuspid valve into the right ventricle, where it is pumped through the pulmonary artery to the lungs.

1. Results from the electrical discharge across the myocardial cell (total net movement of ions across the cell wall) and is measured by the electrocardiograph.

a. Congenital defects or surgical injury to the conduction system may result in arrhythmias or heart block.

(1) Hypokalemia and hyperkalemia.

1. Cardiac output is the volume of blood ejected by the heart in 1 minute. Approximations vary from 120 to 200 mL/kg/min.

a. As heart rate fluctuates, so will cardiac output.

(1) Normal term newborn heart rate is 110 to 166 beats per minute (bpm), although it may range from 70 to 180 bpm on an individual basis (Dawson et al., 2010).

b. Tachycardia seems to be an effective mechanism for improving cardiac output as long as the tachycardia does not compromise diastolic filling time and decrease coronary artery perfusion.

3. Stroke volume is relatively fixed at 1.5 mL/kg and is affected by three factors: preload, contractility, and afterload.

a. Preload: the volume of blood in the ventricles before contraction.

(1) Clinically, preload is a measurement of pressure, rather than volume, in the ventricles before contraction.

(2) Increasing the volume in the ventricles, consequently lengthening the myocardial fibers before contraction, should result in improved stroke volume (Frank–Starling law). The newborn infant is capable of increasing stroke volume provided there is no increase in systemic vascular resistance (SVR) or rapid rise in aortic pressure. Given the neonate’s smaller contractile mass, less compliant myocardium, and normal maximization of myocardial fiber length, volume infusions are likely to increase aortic pressure and afterload, resulting in a decline in stroke volume (Wernovsky and Gruber, 2005).

b. Contractility: speed of ventricular contraction.

(1) Cardiac cycle consists of ventricular contraction (systole), followed by ventricular relaxation (diastole). As contraction time decreases, relaxation time (diastole) increases, with an increase in ventricular filling volume (preload) before contraction.

(a) Exogenous catecholamine (dopamine/dobutamine) use, which increases blood pressure and cardiac output.

(i) Acidosis, which impairs myocardial response to catecholamines.

(1) Dependent on SVR and pulmonary vascular resistance (PVR); if SVR or PVR increases, afterload increases.

(3) Afterload can be reduced by intravenous (IV) infusion of vasodilators (e.g., nitroglycerin, amrinone, and nitroprusside). Dobutamine can be used to decrease PVR (Young and Mangum, 2008).

4. Concepts of blood flow.

a. Flow is directly proportional to pressure/resistance.

d. PVR starts to fall by almost 80% after delivery, resulting in a dramatic increase in pulmonary blood flow and subsequent increase in systolic blood pressure (Blackburn, 2013). This normal decline is influenced by prematurity, low birth weight, and hypoxia episodes.

Occurrence

A. Incidence: 3 to 9 per 1000 live births (Miller et al., 2011); the incidence in premature infants is 2 to 3 times that of term infants (Altman, 2013).

1. 85% of cases are due to multifactorial causes.

4. 1% to 2% are due to exposure to maternal or environmental teratogens (Lott, 2014).

5. 14.5% to 66% are in conjunction with other structural anomalies.

B. Genetic factors: Chromosomal abnormalities: overall incidence of CHD in patients with a chromosome aberration is 30%. Isolated cardiac defects result from multiple genes and their interaction with factors in the environment. Advances in technology have identified genetic factors for many of these defects.

1. Incidence of CHD varies with chromosomal abnormality. Syndromes with an entire extra chromosome or syndromes with a missing chromosome are detected with normal chromosomal studies (van der Born et al., 2011):

a. Trisomy 21: approximately 45%.

a. Chromosome deletion syndromes 18, 13, 5, and 4: 25% to 50%.

b. Mosaic Turner’s syndrome: X and Y chromosome. FISH probe needed to rule out Y chromosome (Bishara and Clericuzio, 2008).

3. Microdeletions that are detected through FISH:

a. 22q11 deletion syndrome: 80% to 85%.

e. DiGeorge deletion: greater than 50% (22q11.2) (Hartman and Medoff-Cooper, 2012).

4. Single-mutant-gene syndromes: 1% to 2% of all cardiovascular abnormalities in newborn infants. Both autosomal dominant and recessive syndromes have been associated with CHD. According to Bishara and Clericuzio (2008), the tests for these syndromes include gene mutation analysis via array comparative genomic hybridization (aCGH). This type of testing can detect smaller imbalances in the genome, allowing for detection of mutations, insertions, deletions, and imprinting abnormalities.

a. Holt–Oram syndrome: greater than 85% to 95% (TBX5 gene found at 12q24.1).

c. Kartagener’s syndrome (Fleiner, 2006): 100% (DNAI1 on 9p21-p13, DNAH5 on 5p15-p14).

d. Beckwith–Wiedemann syndrome: 10% to 35%, imprinting defects of KIP2/LIT1 and paternal IGF2 genes at 11p15.5 (Jonas and Demmer, 2007).

5. Multifactorial: approximately 90% due to genetic predisposition coupled with a causative factor.

a. Cornelia de Lange’s syndrome: approximately 30%.

b. VACTERL (vertebral anomalies, anal atresia/stenosis, cardiac defects [50%], tracheoesophageal fistula, radial defects, limb anomalies) (Wechsler and Wernovsky, 2004).

c. CHARGE (coloboma, heart defects [50% to 70%], choanal atresia, restriction of growth and development, genital anomalies, ear anomalies) (Wechsler and Wernovsky, 2004).

6. Genetic counseling is done to evaluate cause and recurrence risk. The risk of having another child with a cardiac lesion is 3% to 4% if the cause is unknown (Beck and Hudgins, 2003). However, this risk may be as much as 13% higher in specific syndromes.

a. DiGeorge syndrome: Chromosomal microarray analysis should be recommended as first-line test if the infant has developmental disabilities (Hartman, et al., 2011).

(1) 7% of parents carry the deletion.

(2) Recurrence risk is up to 50% (Bishara and Clericuzio, 2008).

(3) Prenatal diagnosis in future pregnancies via chorionic villus sampling (CVS) or amniocentesis, with FISH requested specifically.

b. Trisomies 13, 18, and 21 all carry recurrence risk of 1%, and prenatal diagnosis in future pregnancies is done using CVS or amniocentesis. The recurrence risk for trisomy 21 increases after maternal age 40.

C. Environmental factors and teratogens can include fetal exposure to drug, chemical, infectious, or physical agents; maternal disease or altered metabolic state with the period of greatest risk at 14 to 50 days of fetal life (Lott, 2014).

1. Cardiac teratogenesis is associated with maternal ingestion of the following:

a. Thalidomide: dramatically illustrated the extraordinarily deleterious effects of prescribed drug on a developing fetus; included PDA, ASD, VSD, and pulmonary stenosis (Smithells and Newman, 1992).

b. Anticonvulsants: 2% to 3% of infants exposed to anticonvulsants will have associated congenital cardiac defects such as pulmonary stenosis, coarctation of the aorta, and PDA. Glickstein (2007) reported the following defects with use of specific anticonvulsants in pregnancy:

(1) Phenytoin (fetal hydantoin syndrome): VSD, D-transposition of the great vessels (D-TGV), TOF, HLHS, pulmonary atresia, ASD, aortic stenosis, and pulmonic stenosis.

(1) Warfarin (Coumadin): abortion or fetal embryopathic development in weeks 6 to 9 of gestation. Cardiac malformations have been identified, but no consistent cardiac defect has been noted.

(1) Aminopterin: cardiac manifestations include dextroposition but are not as prominent as other defects resulting from drug ingestion.

(2) In general, the disorders for which antineoplastic agents are used are serious enough to preclude pregnancy (Glickstein, 2007).

e. Lithium: approximately 10% of infants exposed will have defects such as Ebstein’s anomaly, ASD, and tricuspid atresia.

f. Retinoic acid: aortic arch abnormalities, other congenital heart malformations.

g. Isotretinoin.

h. Alcohol: fetal alcohol syndrome (FAS) is accompanied by a variety of cardiac lesions (e.g., VSD with or without subpulmonic and subaortic stenosis, ASD, coarctation of the aorta, TOF).

i. Amphetamine: 5% to 10% will have congenital cardiac defects such as VSD, PDA, ASD, and TGV (Kensey et al, 2011).

j. Selective serotonin reuptake inhibitors: increased risk of VSD if used in first trimester (Koren and Nordeng, 2012).

k. Tobacco and smoking: correlation between first-trimester smoking and defects such as pulmonary valve stenosis, TGV, ASD, right ventricular outflow tract defects, and PDA in term newborns (Alverson et al., 2011).

2. Exposure to environmental hazards such as radiation, heat, and gases may produce teratogenic effects, but there are no specific associated cardiac malformations.

3. Assisted reproductive technology highly linked to cardiac defects such as outflow tract abnormalities, VSD, TGV, and ASD (Tararbit et al., 2011).

D. Maternal disease and viral infections (Box 28-1).

1. Women with diabetes mellitus, especially insulin-dependent, have a 5 times greater risk of their children being born with cardiac anomalies than the general population of pregnant women have. Disorders include hypertrophy of the septum and myocardium, VSD, double-outlet right ventricle, TGV, truncus arteriosus, and coarctation of the aorta.

3. Rubella and cytomegalovirus produce clinically significant heart disease (Kensey et al, 2011). Disorders seen are PDA, pulmonary stenosis and branch pulmonary artery stenosis, VSD, and ASD.

4. Maternal obesity has been linked to congenital heart disease (Glickstein, 2007).

5. Maternal fever and influenza are linked to right ventricular outflow tract and atrioventricular defects (Oster et al., 2011).

A. Males.

1. Coarctation of the aorta.

1. ASD.

History (Kensey et al, 2011)

A. Gestational age.

1. Preterm. Infants born prematurely are much more likely to have pulmonary problems resulting in cyanosis than to have congestive heart failure (CHF), but they do have a higher incidence of:

a. PDA.

B. Maternal history (see Box 28-1).

1. Infants of mothers with uncontrolled diabetes have an increased risk of:

a. TGV.

1. Incidence of CHDs increases by 3- to 4-fold when a first-order relative (parent or sibling) has CHD (Oyen et al., 2009; Park, 2008). Risk increases by 10-fold if two first-order relatives have congenital heart disease (Table 28-4).

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