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l - transposition of the great arteries ( l - tga ) is a rare congenital anomaly representing approximately 0.5% of all congenital heart disease . in l - tga , deoxygenated systemic blood flow from correctly located right atrium to discordant left ventricle [ lv , functional right ventricle ( rv ) ] through mitral valve ( mv ) and pumped to the discordant pulmonary artery ( pulmonary circulation ) . oxygenated blood from pulmonary veins flow from correctly located left atrium to discordant rv ( functional lv ) through tricuspid valve and pumped to discordant aorta ( systemic circulation).1 ) it has various terms including congenitally or physiologically corrected transposition of the great arteries , l - transposition , double discordance [ atrioventricular ( av ) , ventriculoarterial ] , ventricular inversion.2 ) in patients with l - tga , av node and his bundle have an unusual position and course .
therefore l - tga patients frequently have complete av block , approximately 2% rate per year and recurrent reentry tachycardia.3)4 ) here , we report the typical case of l - tga which was initially presented as complete av block in adult .
a 43-year - old male was transferred to our hospital with complaints of dizziness , dyspnea - on - exertion , and mild chest pain for 2 weeks
. he had been diagnosed hypertension two years ago , but he did not take antihypertensives for two months .
he denied any previous history of syncope , palpitation and peripheral edema except dyspnea - on - exertion for 2 weeks .
he also complained intermittent dizziness which was not related with specific situation or position . on admission ,
his blood pressure was 156/80 mm hg and grade 2 systolic murmur was audible in pulmonic area .
thyroid function test was normal ( thyroid stimulating hormone 1.24 uiu / ml and free t4 1.21 ng / dl ) and coronary angiography was followed to rule out coronary artery disease .
3 ) . complete av block at relatively younger age , engagement failure of right coronary artery , right - sided aortic arch in coronary angiography could suggest congenital heart disease .
transthoracic echocardiography revealed coarse trabeculations of functional lv and fine trabeculations and smooth surfaced functional rv , which correspond with l - tga .
left - sided systemic av valve was displaced inferiorly closer to the cardiac apex than right - sided av valve , which is consistent with tricuspid and mitral valve respectively .
in color doppler study , there was no significant valvular dysfunction in right - sided mitral valve , aortic valve , and pulmonary valve except mild left - sided tricuspid regurgitation .
systolic murmur in pulmonic area could be explained by left - sided grade 2 tricuspid regurgitation ( fig .
4 ) . following cardiac computed tomography showed congenitally corrected transposition of great arteries with av , ventriculoarterial discordance .
the patient 's symptom was resolved and he was discharged with prescription of angiotensin converting enzyme ( ace ) inhibitor without any complication .
most cases of l - tga are associated with other cardiac anomalies such as large ventricular septal defect , pulmonary stenosis , ebstein - like malformation , mv abnormalities , and these associated anomalies determine the signs and symptoms at presentation.5 ) however , less than 20% of l - tga patients without any other cardiac anomalies are usually asymptomatic and present later in life with signs and symptoms of arrhythmia and heart failure.6)7 ) in such cases , heart failure may occur because morphological rv as a systemic pump becomes progressively dysfunctional , and concomitant tricuspid valve ( systemic av valve ) regurgitation causes volume overload of the morphological rv .
complete av block also frequently occurs because bundle branch are vulnerable to fibrosis in l - tga.8 ) in our case , the patient was incidentally diagnosed with l - tga when implanting permanent pacemaker due to complete av block at a relatively earlier age . with ventricular inversion , bundles are also inverted and this makes septal activation from right to left .
this makes his electrocardiogram of q - waves in lead ii , iii and absent q waves in lead v5 , 6 besides complete av block .
therefore , electrocardiogram from l - tga could be misinterpreted as inferior myocardial infarction . during the coronary angiography
in congenital heart disease , invasive coronary angiography could be replaced with advanced imaging technique such as computed tomography , magnetic resonance imaging , and nuclear imagings due to associated coronary anomaly.9 ) we thought that the chest pain and dyspnea on exertion was developed due to complete av block , because both symptoms were resolved after pacemaker insertion , although it also could be explained as myocardial ischemia due to reduced coronary flow reserve in l - tga.10 ) in case of permanent pacemaker insertion , ventricular lead was positioned at morphologic lv .
it was reported that cardiac resynchronization therapy could help severe systemic ventricular dysfunction in l - tga cases.2 ) there are two treatment options for l - tga patients .
one is periodic follow - up with 2 dimensional - echocardiography for worsening ventricular function or tricuspid regurgitation , and the other is corrective surgery.11)12)13 ) our patient had relatively normal ejection fraction ( 57% ) , mild tricuspid regurgitation ( grade 2 ) and his sign and symptom was improved after implanting permanent pacemaker . therefore the patient was followed up with medical treatment rather than surgical repair . in case of medical follow - up , there is a paucity of evidence on proper medication .
ace inhibitor or beta blocker has not been studied in the l - tga population .
therefore most of patients received conventional systemic lv protection strategies.2)5 ) ace inhibitor was prescribed for his hypertension and ventricular dysfunction protection . when considering treatment options including periodic follow - up and corrective surgery , morphologic rv dysfunction is important . in l - tga
, ejection fraction measurement could be inaccurate by 2 dimensional - echocardiography because morphologic rv has multiple coarse trabeculations.9 ) therefore cardiac magnetic resonance imaging is considered as an additional tool for measurement of ejection fraction in patients with l - tga . in conclusion , as adult congenital cardiac diseases grow exponentially , congenital anomalies such as l - tga should be considered when complete av block is developed at a relatively younger age .
l - transposition of the great arteries ( l - tga ) is a rare congenital anomaly and could cause complete atrioventricular ( av ) block at relatively younger age . 
 we present a case of 43-year - old male who complained of dizziness due to complete av block . 
 we confirmed l - tga using transthoracic echocardiography and cardiac computed tomography . 
 permanent pacemaker was inserted without complications . 
 no invasive treatment including corrective surgery was performed because patient 's cardiac function was almost normal and the symptom was completely resolved after pacemaker insertion .