Overview

Definition

Transposition of the great vessels (TGV) is the switching of the origins of the great vessels whereby the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle.

Epidemiology

• 3% of all cases of congenital heart disease and 20% of cyanotic congenital heart disease
• Prevalence: approximately 4 in 10,000 live births
• Associated cardiac anomalies:
  • Ventricular septal defect (VSD): in 50% of cases
  • Left ventricle outflow tract obstruction: 
    • Noted in 25% of cases
    • Pulmonary stenosis Pulmonary stenosis Valvular disorders can arise from the pulmonary valve, located between the right ventricle (RV) and the pulmonary artery (PA). Valvular disorders are diagnosed by echocardiography. Pulmonary stenosis (PS) is valvular narrowing causing RV outflow tract obstruction. Pulmonary Stenosis, especially if a VSD is present
  • Coronary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables origins and short course
  • Mitral or tricuspid valve abnormalities

Etiology

• Not completely delineated
• Attributed to:
  •  Failed growth of the subpulmonary conus 
  •  Failure of absorption at the subaortic conus
• Increased risk in diabetic mothers
• No strong genetic component, may be seen in some cases of DiGeorge syndrome DiGeorge syndrome DiGeorge syndrome (DGS) is a condition caused by a microdeletion at location q11.2 of chromosome 22 (thus also called 22q11.2 syndrome). There is a defective development of the third and fourth pharyngeal pouches, leading to thymic and parathyroid hypoplasia (causing T-cell immunodeficiency and hypocalcemia, respectively). DiGeorge Syndrome

Pathophysiology and Clinical Presentation

Pathophysiology

• 2 parallel circuits:
  • Deoxygenated blood returns to the right ventricle and is pumped back into the systemic circulation by the misplaced aorta.
  • Oxygenated blood returns to the left ventricle and is pumped into the pulmonary circulation by the misplaced pulmonary vein.
• Tolerated well in utero:
  • Oxygenated blood from umbilical vein → right atrium
  • Right atrium → fossa ovalis → left atrium → left ventricle→ pulmonary artery→ ductus arteriosus→ aorta
• After birth, complete separation of the circuits is not compatible with life.
• Viability depends on the intercirculatory mixing of blood:
  • Intracardiac: 
    • Patent foramen ovale Patent Foramen Ovale A patent foramen ovale (PFO) is an abnormal communication between the atria that persists after birth. The condition results from incomplete closure of the foramen ovale. Small, isolated, and asymptomatic PFOs are a common incidental finding on echocardiography and require no treatment. Patent Foramen Ovale (PFO)
    • Atrial septal defect Atrial Septal Defect Atrial septal defects (ASDs) are benign acyanotic congenital heart defects characterized by an opening in the interatrial septum that causes blood to flow from the left atrium (LA) to the right atrium (RA) (left-to-right shunt). Atrial Septal Defect (ASD)
    • VSD
  • Extracardiac: patent ductus arteriosus Patent ductus arteriosus The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) ( PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA))
• Mixing of blood: 
  • Reduced concentration of oxygen in the systemic circulation causing cyanosis
  • Effective: between atria because of low-pressure gradient
  • Less effective: VSD or PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA)—blood is preferentially shunted in 1 direction because of pressure gradient
• Preferential shunting in 1 direction → clinical deterioration:
  • Worsening hypoxemia/cyanosis
  • Heart failure

Clinical presentation

• Apparent in the neonatal phase (1st 30 days of life)
• Cyanosis:
  • Severe, with intact ventricular septum
  • Mild, with ASD, PFO, or large VSD
  • Not responsive to supplemental oxygen
  • Not affected by feeding/crying
  • Reverse differential cyanosis:
    • Higher post-ductal than pre-ductal saturations
    • If aortic coarctation, interrupted aortic arch Aortic arch The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Branchial Apparatus and Aortic Arches, or pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension are also present with TGV
• Tachypnea
• Heart failure:
  • Usually if there is a concomitant large VSD
  • Respiratory distress by 3–4 weeks of life

Diagnosis

Physical examination

• Visible cyanosis 
• Respiratory rate > 60/min
• Failed pulse oximetry screening test
• Murmurs:
  • Pansystolic murmur of VSD 
  • Systolic ejection murmur if left ventricular outlet obstruction is present
• Diminished femoral pulses: if there is also aortic coarctation or arch interruption

Imaging

• Echocardiogram:
  • Prenatal: not always diagnostic
  • Postnatal echocardiogram is a main confirmatory test:
    • Evaluate the degree of atrial mixing.
    • VSD
    • Valve abnormalities
    • PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA)
    • Coronary artery anatomy
• Chest X ray: classic “egg on a string” appearance

Other tests

• Electrocardiogram Electrocardiogram An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG):
  • Generally not diagnostic
  • May show right axis deviation and right ventricular hypertrophy
• Cardiac catheterization (angiogram):
  • Can help assess origins/anatomy of coronary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries prior to surgery
  • Can be therapeutic: balloon atrial septostomy to increase blood mixing

Management and Prognosis

Management

Medical:

• For initial stabilization and optimization prior to surgery
• Intravenous prostaglandin infusion to keep PDA PDA The ductus arteriosus (DA) allows blood to bypass pulmonary circulation. After birth, the DA remains open for up to 72 hours and then constricts and involutes, becoming the ligamentum arteriosum. Failure of this process to occur results in patent ductus arteriosus (PDA), a condition that causes up to 10% of congenital heart defects. Patent Ductus Arteriosus (PDA) open
• Balloon atrial septostomy (with cardiac catheterization)

Surgery:

• Definitive management
• Performed within 1st 2 weeks of life
• Most common: 
  • Arterial switch operation (ASO) + VSD repair if necessary
  • Rastelli procedure if left ventricular outflow obstruction is also present
• Post-surgical complications that require regular screening include:
  • Coronary artery stenosis, or insufficiency
  • Pulmonary artery stenosis
  • Aortic root dilation
  • Right ventricular failure
  • Arrhythmias (e.g., atrial flutter Atrial flutter Atrial flutter is a regular supraventricular tachycardia characterized by an atrial heart rate between 240/min and 340/min (typically 300/min), atrioventricular (AV) node conduction block, and a "sawtooth" pattern on an electrocardiogram (ECG). Atrial Flutter and fibrillation)

Prognosis

• If not treated: 
  • 90% of patients will die within the 1st year.
  • 30% of patients will die within the 1st week.
• If treated, high morbidity with continuous follow-up and decreased exercise capacity
• Higher chance of neurodevelopmental delay in infants

Differential Diagnosis

• Tetralogy of Fallot Tetralogy of Fallot Tetralogy of Fallot is the most common cyanotic congenital heart disease. The disease is the confluence of 4 pathologic cardiac features: overriding aorta, ventricular septal defect, right ventricular outflow obstruction, and right ventricular hypertrophy. Tetralogy of Fallot: a congenital heart disease characterized by the occurrence of 4 key cardinal  features: overriding aorta, VSD, RVOT obstruction, and right ventricular hypertrophy. Patients present with cyanosis and a history of tet spells. Diagnosis is confirmed by an echocardiogram and patients are surgically managed.
• Tricuspid atresia: congenital heart disease characterized by the lack of development of the tricuspid valve. Presents with cyanosis, labored breathing, and hypoxic spells. Holosystolic murmur and single S2 are present on exam. Diagnosis is made by echocardiogram and ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG).
• Truncus arteriosus Truncus arteriosus Truncus arteriosus (TA) is a congenital heart defect characterized by the persistence of a common cardiac arterial trunk tract that fails to divide into the pulmonary artery and aorta during embryonic development. Truncus arteriosus is a rare congenital malformation with a high mortality rate within the 1st 5 weeks of life if not managed promptly. Truncus Arteriosus: emergence of aorta and pulmonary artery from a common trunk overriding a VSD. Symptomatic from the 1st days of life, including cyanosis, respiratory distress, heart failure, poor feeding, and excessive sweating. Diagnosed by echocardiogram.
• Total anomalous pulmonary venous return: rare congenital cardiopathy in which pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins drain to sites other than the left atrium. Presents with cyanosis from birth, heart failure, and respiratory distress. Characterized by wide-split S2.
• Ebstein anomaly: congenital heart defect in which there is downward displacement of the tricuspid valve leaflets causing RVOT obstruction. Presents with cyanosis, arrhythmias, and failure to thrive Failure to Thrive Failure to thrive (FTT), or faltering growth, describes suboptimal weight gain and growth in children. The majority of cases are due to inadequate caloric intake; however, genetic, infectious, and oncological etiologies are also common. Failure to Thrive. Diagnosed by echocardiogram.