what happens to the blood in left ventricles in transposition of great arteries

Continuing Pedagogy Activity

Transposition of the neat arteries (TGA) is a congenital pediatric cardiac defect arising from an embryological discordance between the aorta and pulmonary trunk. Consequently, the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle thus creating 2 parallel circuits incompatible with life. Early diagnosis and handling of TGA is paramount to the prognosis of the patient. This activity illustrates the pathophysiology, clinical presentation, and management of patients with transposition of the great arteries. In addition, information technology highlights the role of the interprofessional team in managing and treating these patients.

Objectives:

Identify the etiology and of transposition of the bully arteries.
Describe the pathophysiology of transposition of the great arteries.
Summarize the treatment options for transposition of the dandy arteries.
Explain why careful planning and word amongst interprofessional squad members involved in the management of patients with transposition of the great arteries will ameliorate outcomes.

Access free multiple choice questions on this topic.

Introduction

Transposition of the cracking arteries (TGA) is a pediatric cardiac congenital defect arising from an embryological discordance between the aorta and pulmonary torso. During cardiac development, the conotruncal septum spirals toward the aortic sac thus dividing the truncus arteriosus into the pulmonary and aortic channels. These channels and so get the pulmonary arteries and aorta, respectively. TGA occurs when the conotruncal septum fails to follow its spiral course and instead forms in a linear orientation. Consequently, the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle. The most common grade of TGA is referred to as dextro-TGA (D-TGA) which is characterized past the right ventricle beingness positioned to the right of the left ventricle and the aorta arising inductive and rightward to the pulmonary artery thus forming two parallel circuits. In the systemic circuit, deoxygenated claret returns to the right atrium pass through the tricuspid valve and is so forced dorsum into systemic circulation past contraction of the right ventricle and passage into the aberrantly developed aorta. The 2d circuit is a pulmonary circuit in which oxygenated claret from the pulmonary veins drains into the left atrium, passes through the mitral valve, and is and then forced back into the lungs via contraction of the left ventricle and through the pulmonary arteries. Patients typically present with cyanosis during the first thirty days of life. Complete parallel circuits are incompatible with life and thus require a patent ductus arteriosus and ventriculoseptal defect that allows mixing of oxygen-rich and oxygen-poor claret. [1]

Etiology

The etiology for transposition of the great arteries is unknown; still, information technology is presumed to exist multifactorial. Currently, in that location are two principal theories regarding the embryological mechanisms of TGA development:

De la Cruz proposed the theory that the aortopulmonary septum fails to screw at the level of the infundibulum thus causing a linear development of the septum and TGA. [2]
The second theory, proposed by Goor and Edwards, suggests that TGA is acquired past abnormal resorption or underdevelopment of the subpulmonary conus, with persistence of the subaortic conus. [iii]

Epidemiology

The prevalence of TGA is 4.seven per 10,000 alive births. TGA accounts for iii percent of all congenital heart illness and xx percent of cyanotic heart disease.[4]

Pathophysiology

Knowledge of normal conotruncal septum formation facilitates understanding of D-TGA evolution. In the fifth week of gestation, opposing pairs of ridges form in the truncus arteriosus. These ridges are termed the right superior truncus swelling and the left junior truncus swelling. The correct superior truncus swelling grows distally and to the left while the left junior truncus swelling grows distally and to the right. The result is twisting of the swellings around each other and the foreshadowing of the anatomically normal screw septum.

Simultaneously, swellings in the dorsal and ventral walls of the conus cordis appear and abound toward each other and distally. Eventually, these swellings fuse with each other, also every bit the truncus septum, thus dividing the conus cordis into anterolateral (right ventricular outflow tract) and posteromedial (left ventricular outflow tract) portions.

Equally important to septal formation, is the migration of neural crest cells through pharyngeal arches three, four, and six, and to the center. There, they contribute to endocardial cushion formation in the truncus arteriosus and conus cordis, as well as lengthening of the outflow tracts. Any insult to the migration of neural crest cells tin cause tetralogy of Fallot, truncus arteriosus, and TGA. It is not uncommon to see cardiac and craniofacial defects in the same individual since neural crest cells also contribute to craniofacial development.

Transposition of the corking arteries occurs when the aorticopulmonary septum fails to spiral. This can be due to defects in the maturation of the correct superior truncus swelling and the left inferior truncus swelling, fusion of the conus swellings with the aorticopulmonary septum, or adversities in neural crest development or migration.

The pathological defects in D-TGA cause a detrimental modify in cardiac physiology. Due to the beingness of two parallel circuits, deoxygenated blood continues to circulate systemically, and oxygenated blood continually flows through the pulmonary circuit. Parallel channels are incompatible with life unless mixing between deoxygenated and oxygenated blood occurs. Mixing can occur via an atrial or ventricular septal defect, patent ductus arteriosus, or through collateral bronchopulmonary circulation. Interventional cardiologists may also perform a balloon atrial septostomy (BAS) to facilitate mixing between the atria. [i]

Several common cardiac anomalies that can occur in patients with D-TGA can include:

Ventriculoseptal defects
Left ventricular outflow tract obstruction
Mitral and tricuspid valve abnormalities
Coronary artery variations

A bottom known course of TGA is levo-TGA (L-TGA). In this case, the left ventricle is positioned to the right of the correct ventricle. Mainly, the ventricles are on contrary sides of the heart. The pulmonary trunk and aorta ascend in their anatomically correct orientations, nonetheless, since the ventricles are reversed, the aorta is fused with the correct ventricle, and the pulmonary torso is combined with the left ventricle. The resultant menstruation of blood in a patient with L-TGA is every bit follows: Deoxygenated blood enters the anatomically right right atrium, passes through the mitral valve into the left ventricle, and is pumped into the pulmonary trunk to the lungs. From the lungs, the oxygenated blood enters the left atrium, passes through the tricuspid valve, and into the right ventricle where blood is and so pumped into the aorta. Since the flow of blood in patients with L-TGA passes through the normal systemic and pulmonary circuits, L-TGA is sometimes termed anatomically correct TGA. [5]

History and Concrete

Antenatally, TGA is challenging to diagnose. Screening ultrasounds do not routinely reveal TGA in-utero.

Postnatal:

The clinical features of D-TGA are solely dependent on the degree of mixing between the parallel circuits. Most patients present with signs and symptoms during the neonatal catamenia (get-go 30 days of life). The following are the typical clinical manifestations of TGA:

Cyanosis: The degree of cyanosis is dependent on the amount of mixing betwixt the two parallel circuits. Factors affecting intracardiac mixing include the size and presence of an ASD or VSD. Cyanosis is non affected past exertion or supplemental oxygen. [6]
Tachypnea: Patients unremarkably have a respiratory rate higher than 60 breaths per minute but without retractions, grunting, or flaring and appear comfortable.
Murmurs: murmurs are not typically nowadays unless a modest VSD or pulmonic stenosis exists. A murmur resulting from a VSD volition be pansystolic and prominent at the lower left sternal edge. Pulmonic stenosis causes a systolic ejection murmur at the upper left sternal edge. [7]

Patients with Fifty-TGA are typically unaffected until later in life when the right ventricle can no longer recoup for the increased afterload of the systemic circulation. These patients nowadays with signs and symptoms of middle failure. [7]

Evaluation

As previously stated, D-TGA is difficult to detect on fetal ultrasound due to the absenteeism of differences in ventricle size. [8] Postnatally, when a cardiac disease is suspected based on clinical exam, echocardiography is performed. Echocardiography will reveal the aberrant origins of the aorta and pulmonary trunk as well equally whatsoever associated intracardiac defects. Other studies often performed include:

Electrocardiography: Often normal merely may show right axis difference and right ventricular hypertrophy
Chest radiography: The classic radiographic features of TGA is an "egg on a string" appearance.
Cardiac catheterization: Angiography is rarely used to diagnose TGA; notwithstanding, information technology is the gilded standard for elucidating the origins of the coronary arteries. Cardiac catheterization is routinely used in D-TGA to perform a balloon septostomy in patients with severe cyanosis.[nine]

Handling / Management

Initial direction of patients with D-TGA centers on ensuring adequate oxygenation. Prostaglandin E1 administration stabilizes patients by attempting to keep the ductus arteriosus patent and performing a balloon atrial septostomy (BAS). Once the patient is hemodynamically stable, corrective surgery can be performed. [10] [11]

Surgical repair of D-TGA is usually undertaken within the first week of life. There are currently two usually used surgical procedures for D-TGA:

Arterial switch functioning (ASO): The arterial switch performance is the standard procedure for patients with D-TGA without major pulmonic stenosis. During the ASO, the surgeon will transect both the pulmonary trunk and aorta then translocate them to their anatomically correct positions. The coronary arteries are mobilized and reimplanted into the aortic trunk. If a VSD is nowadays., it is likewise repaired during this time. [12]
Rastelli procedure: The Rastelli procedure is indicated in patients presenting with D-TGA, a large VSD, and pulmonary stenosis. During this process, the VSD is closed using a baffle. By doing so, oxygenated claret from the left ventricle is directed into the aorta. A conduit is then placed from the right ventricle to the pulmonary artery thus shunting deoxygenated blood into the pulmonary avenue. [13]

Other cosmetic procedures exist including the Mustard and Senning procedure, Nakaidoh process, Réparation à l'Etage ventriculaire (REV) procedure, and Yasui procedure even so these are less normally performed. [14]

Differential Diagnosis

Double-Outlet Right Ventricle
Tricuspid Atresia
Pulmonary Atresia
Tetralogy of Fallot
Full anomalous pulmonary venous return
Truncus arteriosus

Prognosis

The prognosis for patients with D-TGA is more often than not excellent following surgical correction. Current survival rates are greater than ninety%. The ASO has the best long-term survival and functional outcome. Some studies report a >95% rate survival at fifteen to twenty-v years post-obit discharge. [xv][xvi]

Complications

Several complications can result following corrective operations. These include:

Arrhythmias [17]
Obstacle or leakage of the baffle (Rastelli Procedure)
Pulmonary artery stenosis
Coronary artery stenosis
Aortic root dilation
Aortic regurgitation [18]

Deterrence and Patient Education

Patients with corrected D-TGA have slightly reduced exercise capacity. Some predictors of poor practice performance include VSD repair, decreased left ventricular function, and repair before the evolution of the ASO. Reduced exercise chapters has not been shown to affect activities of daily living. [19]

Studies take as well shown that patients who underwent ASO are more probable to have a neurodevelopmental damage. One center reports that 65% of adolescents who experienced ASO every bit infants required special pedagogy services. The same center also reports that patients with surgically corrected ASO were more than likely to take attention-deficit/hyperactivity disorder (ADHD). The American Heart Association (AHA) recommends that children who underwent corrective surgery for D-TGA undergo continued screening and referral for neurodevelopmental harm. [20]

Enhancing Healthcare Team Outcomes

The management of dextro-transposition of the great arteries can be challenging. While the correction of D-TGA is mostly the responsibility of a pediatric cardiothoracic surgeon, other specialists demand to be involved in the care of the patient. Interventional pediatric cardiology needs to be consulted immediately for evaluation of cyanosis in a newborn which may facilitate the assistants of prostaglandin E1 and balloon atrial septostomy. Interventional cardiology volition also be able to concomitantly perform angiography to determine which anomalies of the coronary arteries are present. During handling and post-obit discharge, general pediatrics should exist involved in the care of the baby for routine preventative care and neurodevelopmental screening. If deficiencies in neurodevelopment are found on annual testing, pediatric neurology and psychiatry will need to be consulted as well. The pharmacist pre-operatively should help with medication reconciliation and hurting management.

In order to obtain the best outcomes the nurse caring for a patient with corrected TGA will monitor for:

Cardiac dysrhythmias or heart palpitations
New centre murmurs, bruits, or extra heart sounds
Fatigue, shortness of breath, or chest pain
An increasing or decreasing claret pressure
A subtract in oxygen saturation or development of cyanosis
Swelling in the lower extremities

These symptoms may bespeak a serious complication, and should be addressed promptly with the clinical team.

Additionally, the nurse should wait to perform frequent concrete, cardiac, respiratory, and neurological assessments, monitor vital signs and hemodynamics, and check fluid and electrolyte condition. Patient and family education will exist important during the pre-op, post-op, and discharge period. The best outcomes are achieved when the nurse, pharmacist, and surgeons piece of work together to evaluate and monitor the patient and provide patient and family education in a coordinated fashion. [Level V]

Review Questions

Figure

dextro-Transposition of the Great Arteries (d-TGA). Contributed by The Centers for Affliction Command and Prevention (Public Domain)

References

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Source: https://www.ncbi.nlm.nih.gov/books/NBK538434/