11.5: Congenitally Corrected Transposition of the Great Arteries
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- 42789
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Congenitally corrected transposition of the great arteries
Introduction
The congenitally corrected transposition of the great arteries (ccTGA) is characterized by a normal anatomical position of both atria, with an abnormal connection between the atria and the ventricles. The right atrium is connected with the left ventricle and the left atrium is connected with the right ventricle. (Figure 11.5.1) Furthermore the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. There are, in conclusion, abnormal atrioventricular connections and abnormal ventricular-arterial connections present in ccTGA. CcTGA is a very rare defect, accounting for about 1% of all congenital heart disease.
Pathophysiology
The blood flow in ccTGA is ‘corrected’ because oxygenated blood flows through the systemic circulation and deoxygenated blood is transported to the lungs. In this particular heart defect the right ventricle functions as a systemic ventricle. With the atrioventricular valves following the position of the ventricles, the tricuspid valve is now the systemice AV-valve.
Additionally the coronary arteries are a mirror image of the normal anatomic situation. The coronary artery on the right side of the heart runs like a morphological left coronary artery; starting with a main stem which divides into a left anterior descending and circumflex branch. The coronary artery on the left is the morphological right coronary artery, which now runs around the tricuspid valve on the left.
Even the conduction system is abnormal in this congenital heart defect. Normally the AV node is positioned at the base of the interatrial septum, from where the His bundle arises into the interventricular septum. Due to misalignment in ccTGA there is no bundle directly from the normal AV node into the interventricular septum. Usually there is an additional AV node located more anterior and laterally from where a long bundle arises which runs beneath the pulmonary valve leaflets into the interventricular septum. Due to the long route this bundle is rather vulnerable. Where in normal hearts the electrical activation of the ventricles in the septum runs from left to right, in ccTGA it is the exact opposite; the septum is activated from right to left, which is visible on the ECG as an abnormal initial activation.
There is a VSD present in 60% of all ccTGA patients, who will often become symptomatic at younger age. Pulmonary valve stenosis is seen in 30 – 50% of patients, usually in those who already have a VSD as well. Abnormal anatomy of the tricuspid valve (M. Ebstein like) is seen in 25-30% of patients, sometimes accompanied by VSD or pulmonary valve stenosis. More than 80 percent of patients have an abnormal function of the tricuspid valve, which often becomes insufficient.
Evaluation
When only ccTGA is present, without other cardiac defects, the diagnosis is often not recognized until adulthood. However, when there is a VSD and/or pulmonary valve stenosis present, it presents short after birth with cyanosis and heart failure or even a total AV-block.
Adult patients are usually recognized due to an abnormal ECG, abnormal chest radiograph, systolic murmur due to the regurgitation of the systemic AV-valve, occurrence of atrial tachycardia or an AV-block. Reduced exercise capacity might be present.
The ECG is the most typical for ccTGA; left heart axis deviation, septum activation in mirror image (no Q-wave in I, aVL and V6, no R-top in V1) and a rather deep Q-wave in III and aVF. Echocardiography is a good diagnostic tool to review the exact anatomy. The right ventricle positioned on the left side is identified by the typical morphology of the trabeculae. Furthermore the tricuspid valve has a lower insertion compared to the mitral valve.
Treatment and outcome
Patients with ccTGA require lifelong follow up due to the risk of arrhythmias and associated sudden death, increase of pulmonary valve stenosis, increase of tricuspid valve regurgitation, supraventricular tachycardia, heart failure or endocarditis. Due to the complex anatomy and the low incidence of this pathology, this is best acquired at a specialised centre of congenital heart disease.
Arrhythmias need treatment, preferably not with negative inotropic agents, but digoxin and possibly amiodaron are preferred. When presenting with atrial arrhythmias conversion to sinus rhythm is highly important in these patients, who are in need of their ‘atrial kick’.
Many patients with ccTGA require pacemaker placement, often already in childhood or early adulthood. Frequent followup in these patients is required due to the high complication rate; dislocation of the lead which is located in the smooth-walled left ventricle and risk of infection or endocarditis.
Determining the right time to replace the tricuspid valve is difficult in these patients. Preferably this is done just before the right systemic ventricle starts dilating and fails, but it remains an estimation which should be made for each individual patient.
To restore normal blood flow through the ventricles, with the left ventricle functioning as the systemic ventricle, there is an option to perform a double switch operation. During this procedure both atria and both great arteries are switched, meaning a combination of the arterial switch and the atrial switch procedure. From a physiologic point of view this operation is worth considering while the left ventricle will function as systemic ventricle, however it is associated with a high perioperative mortality due to the extent of surgery. Furthermore the left ventricle requires training prior to surgery, to be able to cope with the high arterial pressure after years of low pulmonary pressure. In conclusion the chance of success of this double switch operation is very low in patients above 16 years of age.