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Congenitally corrected L-transposition of the great arteries: abnormalities of atrioventricular conduction
Progress in Pediatric Cardiology 10 Ž1999. 37]43
Congenitally corrected L-transposition of the great arteries: abnormalities of atrioventricular conduction Peter S. FischbachU , Ian H. Law, Gerald S. Serwer Di¨ ision of Pediatric Cardiology, Uni¨ ersity of Michigan Health Systems, 1500 East Medical Center Dri¨ e, Box 0204, F 1310, Ann Arbor, MI 48109-0204, USA
Abstract L-transposition of the great arteries is a complex cardiac malformation with ventricular inversion and discordance of both atrioventricular and ventriculoarterial connections. Several electrophysiologic abnormalities can be associated with this entity including varying degrees of heart block, supraventricular arrhythmias such as sick sinus syndrome and supraventricular tachycardias Žatrial flutter, atrioventricular reentrant tachycardia., as well as ventricular tachycardias. A review of the anatomic and functional abnormalities of the conduction system in L-transposition is provided along with a summary of the unique problems associated with the use of pacemakers in this patient population. Q 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: L-Transposition of the great arteries ŽL-TGA.; Ventricular inversion; Heart block; Supraventricular arrhythmia; Pacemaker
1. Introduction Congenitally corrected L-transposition of the great vessels ŽL-TGA. is a complex cardiac malformation consisting of situs solitus of the atria with ventricular inversion and discordance of both atrioventricular ŽAV. and ventriculoarterial connections. The combined defects result in a physiologically correct circulation where the systemic venous return is routed to the pulmonary artery and pulmonary venous return is directed to the aorta. The morbidity and mortality associated with this malformation is the result of one or more frequently associated defects such as ventricular septal defect, pulmonary stenosis, systemic AV valve Žtricuspid. regurgitation, ventricular hypoplasia and electrophysiologic abnormalities w1,2x. The most common electrophysiologic abnormality associated with L-TGA is a delay or complete interruption of
U
Corresponding author. Tel.: q1-734-936-8994; fax: q1-734936-9470. E-mail address: [email protected] ŽP.S. Fischbach.
normal AV conduction w3,4x. In addition to the various degrees of heart block observed, several forms of supraventricular arrhythmia are relatively common, such as sick sinus syndrome, atrial flutter and reentrant AV tachycardia utilizing an accessory pathway along the tricuspid valve annulus w3]5x. Ventricular tachycardia has also been reported in L-TGA w6,7x. Conduction through the atrioventricular node ŽAVN. can be normal or abnormal. Abnormalities include various degrees of heart block, up to and including complete congenital heart block. AV conduction may be normal initially and thereafter demonstrate progressive degrees of block with aging w3x. The normal conduction through the AVN can be disrupted during invasive procedures such as cardiac catheterization and surgery w2x. In this review a brief discussion of the abnormal gross and histologic anatomy of the conduction system in L-TGA will be presented and compared to conduction in the normal heart. The implications that these abnormalities present for the cardiologist and cardiovascular surgeon will be discussed. Published
1058-9813r99r$ - see front matter Q 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 1 0 5 8 - 9 8 1 3 Ž 9 9 . 0 0 0 1 3 - 2
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P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
reports of heart block associated with L-TGA will be reviewed and the special concerns and indications for pacemaker therapy will be presented.
2. Anatomy Descriptions of the atypical anatomy of the conduction system in L-TGA with ventricular inversion were first published nearly 75 years ago. They described inversion of the bundle branches with the fan-like branch, normally associated with the left-sided systemic ventricle, passing to the anatomic right side of the ventricular septum, and the cord-like bundle branch, typically found on the right side of the septum, passing leftward into the morphologic right ventricle w8x. More recently the abnormal gross and histological anatomy of the conduction system in L-TGA has been fully delineated. This information has explained the high risk of injury to the system during invasive procedures and has led to changes in procedure that have significantly reduced the incidence of iatrogenicly induced block w1,9x. Using serial histopathological sections, Anderson and colleagues identified dual AVNs in patients with L-TGA w10,11x. In agreement with previous work by Lev et al. w12x, Anderson found that a histologically normal appearing AVN was located in the usual posterior location at the apex of the triangle of Koch. Although it appeared histologically normal, this AVN had no connections with the penetrating bundle and, hence, it was electrically isolated from the ventricle. Initially Lev thought that this discontinuity between the normally located posterior AVN and the penetrating bundle was the cause of the complete heart block associated with L-TGA w12x. However, Anderson’s group identified a second anterior AVN located in the right atrium at the junction of the right AV valve Žmitral valve. and the left border of the right atrial appendage. This second ‘accessory’ AVN was histologically identical to the posteriorly located node but connected directly with an aberrantly located penetrating bundle w10,11x. In his studies, Anderson was able to trace the course of the penetrating bundle. After leaving the AVN the conduction tissue passes laterally onto the roof of the pulmonary outflow tract just below the level of the pulmonary valve and then descends to reach the anterior margin of the interventricular septum. In hearts with intact ventricular septum the His bundle then descends along the anterior superior rim of the membranous septum remaining on the anatomic right side ŽFig. 1.. In hearts with L-TGA with an associated ventricular septal defect the His bundle passes abnormally along the anterior and superior margin of the defect remaining on the right side of
Fig. 1. Endomyocardial electrograms recorded from a patient with L-TGA at the time of surgical repair of a ventricular septal defect demonstrate His potential signals recorded along the superior anterior margin of the defect w15x.
the rim of ventricular tissue. This is quite different from its anatomic course in hearts with normally related ventricles and a ventricular septal defect where the conduction tissue descends on the posterior inferior rim of the defect remaining on the anatomic left side w12,13x. These histologic abnormalities of conduction in L-TGA with ventricular septal defect have been confirmed in several studies by direct intraoperative mapping of the system at the time of intracardiac surgical procedures w14]17x. Identification of the characteristic abnormal course of the conduction system is crucial during surgical closure of a ventricular septal defect or relief of pulmonary and subpulmonary obstruction associated with L-TGA, and its predictable location has led to a marked reduction in the incidence of surgically induced heart block w1,18x.
3. Conduction abnormalities Impaired AV conduction, including first, second and third degree block, is frequently associated with L-TGA w19x. Complete heart block may be congenital, surgically induced or caused by progressive deterioration of AV conduction. The risk of developing complete heart block persists throughout life, increasing almost linearly with age w3x. Among patients with L-TGA, complete heart block is more frequent in those with an intact ventricular septum than in others with an associated ventricular septal defect w3x. The incidence of heart block in patients with L-TGA
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
has been reported in five large studies published in English ŽTable 1.. The largest study from the Hospital for Sick Children in London found complete heart block in 35 of 111 L-TGA patients Ž32%. w20x. Complete block was induced during surgery in 14 of them. Among the other 21 patients, congenital heart block occurred in four and developed spontaneously in 17. It occurred before 10 years of age in 16 of the 17. Huhta et al. reviewed the experience at the Mayo Clinic with 107 patients with L-TGA, situs solitus and discordant functioning ventricles w3x. Complete heart block occurred in 23 patients Ž22%. and was congenital in four Ž4%. of them. The mean age for the development of spontaneously occurring complete heart block was 18.1 years, and in the oldest patient who developed block, it occurred at 53 years of age. An important finding in this review was that the risk for developing complete heart block persisted throughout life and its incidence increased almost
39
linearly at a rate of approximately 2% per year. Complete block occurred in eight of 101 patients Ž8%. studied at the Sick Children’s Hospital in Toronto w5x. In 90 patients with L-TGA and two functional ventricles who were studied at the Children’s Hospital in Boston w21x, 29 had complete heart block Ž33%., induced at surgery in six of them. In studies of 17 patients with isolated L-TGA, Daliento et al. found five patients with complete heart block, none of whom had any rhythm abnormalities as newborns w7x. At the Michigan Congenital Heart Center at the University of Michigan in Ann Arbor, 126 patients with L-TGA, 7 months to 48 years of age, were identified by searching echocardiography and pacemaker databases ŽTable 1.. A hypoplastic ventricle was found in 56 of them Ž45%.. Heart block was present in 40 of the 126 patients Ž32%.. The block was first degree in 11 of the 126 Ž9%., second degree
Table 1 Incidence of conduction abnormalities associated with L-TGAa Source
Patient population
Heart block incidence
Atrial arrhythmias
Bjarke et al. w5x
n s 101 43% single ventricles
n s 17 Ž17%. 1st: 7 Ž7%. 2nd: 2 Ž2%. 3rd: 8 Ž8%.
n s 12 Ž12%. Žpre-surgical.
Daliento et al. w7x
n s 17 All two ventricles
n s 5 Ž29%.
Friedberg et al. w4x
n s 60 42% SV 52% VSD 6% IVS
n s 19 Ž32%. 1st: 10 Ž17%. 2nd: 2 Ž3%. 3rd: 7 Ž12%.
Huhta et al. w3x
n s 107 All two ventricle 77% VSD
n s 23 Ž22%. CCHB: 4 Ž4%.
Lundstrom et al. w20x
n s 111 All two ventricle
n s 35 Ž32%. CCHB: 4 Ž4%. Spont: 17 Ž15%. SxHB: 14 Ž13%.
Fyler w21x Žincludes subset of Friedberg et al. population.
n s 90 All two ventricle
n s 29 Ž32%.
Michigan Congenital Heart, 1998
n s 126 SVs 57 Ž45%.
n s 40 Ž32%. 1st: 11 Ž9%. 2nd: 4 Ž3%. 3rd: 19 Ž15%. yCCHB 6 SxHB: 6 Ž5%.
a
n s 4 Ž4%. WPW: 2 AFL: 2
Pacemakers
n s 9 Ž39%.
n s 9 Ž8%. All for CHB
n s 19 Ž15%. WPW: 5 AFL: 6 AF: 1 PSVT: 2 SSS: 5
n s 27 Ž21%. SSS: 5 Ž4%. 2nd HB: 1 Ž1%. CHB: 10 Ž8%. SxHB: 9 Ž7%.
Notes. Incidence of heart block, atrial arrhythmias and pacemaker implants in patients with L-TGA. Abbre¨ iations. 1st, 2nd and 3rd s first, second and third degree heart block; SB, single ventricle; VSD, ventricular septal defect; IVS, intact ventricular septum; CCHB, complete congenital heart block; WPW, Wolff]Parkinson]White syndrome; AFL, atrial flutter; AF, atrial fibrillation; spont., spontaneous heart block; SxHB, surgical heart block; PSVT, paroxysmal supraventricular heart block not otherwise specified; and SSS, sick sinus syndrome.
40
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
in four Ž3%., complete and spontaneous in 19 Ž15%. and complete and congenital in 6 Ž5%. of them. Six other patients Ž5%. had surgically induced complete block. Atrial arrhythmias were found in 19 of the 126 patients Ž15%.. Pacemaker implantation was needed in 27 patients Ž21%. who had heart block or sick sinus syndrome. In many of the patients in these five series who had complete heart block, normal AV conduction was documented at one time or another by a surface ECG recording of a normal PR interval. A few of the patients in the series had progressive AV conduction abnormalities as demonstrated by first degree heart block leading to second degree and then to complete block, suggesting that progressive fibrosis of the AV conduction system is a risk factor in some patients with this defect w11x. In L-TGA patients with heart block the exact location of the slowing or interruption of the electrical signal within the AV conduction tissue has been investigated using catheter electrodes w22]24x. In His bundle recordings of 40 patients with L-TGA, Gillette et al. identified 15 patients Ž38%. with normal AV conduction who had normal AH and HV intervals w22x. Fourteen of the 15 patients had first degree AV block with conduction delay occurring variably above, within or below the bundle of His. The conduction delay was at a single site in several patients, but it was recorded at several locations in many. These varying levels of AV block were also found in studies of 11 patients with complete heart block. Two of the patients with complete heart block had intact retrograde AV conduction at the time of electrophysiologic study, demonstrating that in a subset of patients with L-TGA, complete AV block is not the result of anatomic interruption of the conduction tissue, a finding of particular importance when single chamber pacing is being considered.
4. Pacing Permanent pacemaker treatment must be considered in every patient with L-TGA and complete heart block ŽFig. 2.. Guidelines for pacemaker treatment in general have recently been published jointly by the American College of Cardiology and the American Heart Association w25x. The first group of patients with L-TGA to be considered for pacing is composed of those with congenital complete heart block. The ACCrAHA guidelines identify a Class I indication for permanent pacing in patients with any type of congenital heart disease and congenital complete heart block with a ventricular rate less than 70 b.p.m. In many centers, the criteria for pacemaker therapy has been based on symptoms of inadequate cardiac
Fig. 2. Clinical algorithm for selecting patients with L-TGA and complete heart block who require permanent pacing.
output rather than on a specific minimal heart rate. In all newborns with functionally significant congenital heart disease, we believe that pacemaker therapy is necessary before hospital discharge. Those infants with L-TGA without associated lesions Ži.e. ventricular septal defect, pulmonic stenosis, and systemic AV valve regurgitation. who have no symptoms of heart failure have been managed conservatively with close follow-up without pacemaker insertion. In infants with L-TGA who have associated defects, pacemakers have been implanted without regard to the heart rate or symptoms of heart failure. Patients with L-TGA who have developed complete heart block spontaneously form a second group. In these patients complete block can appear at any time from infancy to late adulthood. We believe that the need for pacemaker therapy in this group of patients should be based, not simply on a selected low heart rate, but on symptoms of heart failure such as fatigue, exercise intolerance, syncope or near-syncope and on signs of cardiomegaly on chest X-ray or ventricular dysfunction on echocardiogram. A third group of patients with L-TGA is made up of those with surgically acquired complete heart block. Because unstable ventricular escape rhythms are common after surgical interruption of the AV conduction system w26x, all patients with L-TGA who have complete block after cardiac surgery should have pacemaker implantation before hospital discharge, regardless of the ventricular rate or the presence of symptoms. After a need for permanent pacing is identified, a choice between epicardial or endocardial pacing leads
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
must be made. In the past epicardial lead systems were preferred in patients with L-TGA because of unreliable active fixation of leads to the smooth-walled endocardium of the inverted right-sided morphologic left ventricle w27x. However, currently available endocardial leads for active fixation are considered to be as reliable as passive fixation leads. Immediately after implantation, the electrical capture threshold tends to be slightly higher in active fixation leads, but with time it approaches those of passive fixation leads. Moreover, recently developed steroid eluting active fixation leads are now available which should allow for lower pacing thresholds for much longer periods of time. Consequently, with currently available leads, the choice of endocardial or epicardial pacing is no longer based on differences in lead fixation, but on criteria such as the size of the patient, venous access to the right-sided ventricle, intracardiac right to left shunting, the presence of increased pulmonary vascular resistance and the consideration that epicardial
41
placement requires a surgical thoracotomy w28x. When permanent pacemaker therapy is indicated at the time of cardiac surgery, placement of an epicardial system may be prudent. In patents requiring a pacemaker who are not undergoing cardiac surgery, our current practice is to use a dual chamber endocardial lead system in patients weighing more than 15 kg and a single endocardial ventricular lead in infants and children weighing 8]15 kg. Passage and fixation of endocardial leads can be complicated by obstruction from aberrant intracardiac anatomy. In patients with L-TGA, the inverted ventricle and unusual position of the right-sided mitral valve can present problems in passing the lead into the right-sided ventricle along the misleadingly smooth appearing arcing course seen on fluoroscopy. As shown in Fig. 3, the superior and anterior deflection of the ventricular lead within the atrium can create uncertainty as to the anatomic location of the lead tip as it is passed into the right ventricle. In a few
Fig. 3. Chest radiographs showing the unusual course taken by the ventricular pacing lead in patients with L-TGA compared to the normal heart. The anteroposterior Ža. and lateral Žb. radiographs of a patient with L-TGA demonstrate the more superior and anterior course of the ventricular lead passing across the mitral valve into the apex of the right-sided left ventricle. In a patient with normal cardiac anatomy Žc., a dual chamber pacing system is shown with the normal smooth course of the ventricular electrode lead.
42
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
instances we have used transesophageal echocardiography to identify and confirm the correct location of the lead tip. There are several options for the type of pulse generator to be used. A single ventricular chamber pacing unit ŽVVI or VVIR. is probably not the ideal choice for most patients with L-TGA for several reasons: Ž1. dysfunction of the systemic Žleft-sided. right ventricular is relatively common in these patients with ventricular inversion and, as with all ventricles operating at the peak of the Frank-Starling curve, the atrial systole provided by synchronous dual chamber AV pacing can be quite helpful; Ž2. many of these patients are at risk for pacemaker syndrome because retrograde VA conduction remains intact w22x; Ž3. the option of atrial pacing can become useful because of the high incidence of atrial and sinus node arrhythmias; and Ž4. many of the new pulse generators allow for termination of atrial flutter by rapid atrial overdrive pacing. Dual chamber pacing is preferred for almost all children, and certainly in those with L-TGA. We have used single chamber pacing only when there is a contraindication to dual chamber pacing. The major contraindications include persistent tachyarrhythmias, unstable AV node conduction requiring numerous pacer programming changes, and the inability to reliably fix atrial and ventricular leads. In small children the placement of both atrial and ventricular endocardial leads through a relatively small superior vena cava can present a risk of thrombosis and obstruction. Another reason for single chamber pacing is in a child requiring epicardial ventricular lead placement who would need a more involved surgical procedure to also implant an atrial epicardial electrode. In D-TGA patients with intermittent atrial tachyarrhythmia, choosing a generator that allows for the use of mode switching can decrease the risk of a rapid increase in ventricular response rate or an abrupt decrease in heart rate that can occur at the onset of the tachyarrhythmia.
5. Conclusion L-TGA is an uncommon congenital heart malformation that is almost uniformly associated with other structural lesions and electrophysiological abnormalities. Over the last 25 years, identification of the predictable abnormal anatomic location and course of the ventricular conduction system in L-TGA has resulted in a significant reduction in the risk of heart block during surgical closure of associated ventricular septal defects or relief of pulmonary outflow tract obstruction. The increased incidence of conduction abnormali-
ties and atrial arrhythmias in L-TGA patients, with and without associated structural lesions, requires diligent lifelong patient follow-up because heart block may appear at anytime from infancy to late adulthood. Congenital and spontaneous Žnon-surgical. heart block does not always require permanent pacemaker treatment, depending on the patient’s symptoms and associated heart defects, whereas surgically induced complete heart block always requires pacing. In most children with L-TGA the treatment of choice is dual chamber pacing through right atrial and rightsided ventricular endocardial active fixation leads. References w1x Doty D, Truesdell S, Marvin W. Techniques to avoid injury of the conduction tissue during the surgical treatment of corrected transposition circulation. 1983;68ŽSuppl II.:II-3]II-9. w2x Kirklin J, Barratt-Boyes B. Congenitally corrected transposition of the great arteries. In: Barratt-Boyes B, Kirklin J, editors. Cardiac surgery. New York: Churchill Livingston, 1993:1511]1533. w3x Huhta J, JD M, Ritter D, Ilstrup D, Feldt R. Complete atrioventricular block in patients with atrioventricular discordance. Circulation 1983;67Ž6.:1374]1377. w4x Friedberg D, Nadas A. Clinical profile of patients with congenital corrected transposition of the great arteries: a study of 60 cases. N Engl J Med 1970;282:1053]1059. w5x Bjarke B, Kidd B. Congenitally corrected transposition of the great arteries: a clinical study of 101 cases. Acta Paediatr Scand 1976;65:153]160. w6x Levy A, Camm A, Keane J. Multiple arrhythmias detected during nocturnal monitoring in patients with congenital complete heart block. Circulation 1977;55:247]253. w7x Daliento L, Corrado D, Buja G et al. Rhythm and conduction disturbances in isolated, congenitally corrected transposition of the great arteries. Am J Cardiol 1986;58:314]318. w8x Sato S. Uber die entwicklung der atrioventrikularklappne und der pars membranacea unter berucksichtigung zugehoriger herzmissbildungen. Anat Heft 1914;50:1195. w9x Hwang B, Bowman F, Malm J, Krongrad E. Surgical repair of congenitally corrected transposition of the great arteries: results and follow-up. Am J Cardiol 1982;50:781]785. w10x Anderson R, Arnold R, Wilkinson J. The conducting system in congenitally corrected transposition. Lancet 1973;1: 1286]1288. w11x Anderson R, Becker A, Arnold R, Wilkinson J. The conducting tissues in congenitally corrected transposition. Circulation 1974;50:911]923. w12x Lev M, Licata R, May R. The conduction system in mixed levocardia with ventricular inversion Žcorrected transposition.. Circulation 1063;28:232. w13x Truex R, Bishof J. Conducting system in human hearts with ventricular septal defects. Ann Arbor Thorac Surg 1958; 35:421. w14x Maloney J, Ritter D, McGoon D, Danielson G. Identification of the conduction system in corrected transposition and common ventricle at operation. Mayo Clin Proc 1975;50:387]394. w15x Dick M, Norwood W, Chipman C, Castaneda A. Intraoperative recording of specialized atrioventricular conduction tissue electrograms in 47 patients. Circulation 1979;59:150]160. w16x Kupersmith J, Krongrad E, Gersony W, Bowman F. Electrophysiologic identification of the specialized conduction system
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w17x
w18x
w19x w20x w21x w22x w23x
in corrected transposition of the great arteries. Circulation 1974;50:795]800. Waldo A, Pacifico A, Bargeron L, James T, Kirklin J. Electrophysiological delineation of the specialized AV conduction system in patients with corrected transposition of the great vessels and ventricular septal defect. Circulation 1975; 52:435]441. deLeval M, Bastos P, Stak J et al. Surgical technique to reduce the risks of heart block following closure of ventricular septal defect in atrioventricular discordance. J Thorac Cardiovasc Surg 1979;78:515. Cardell B. Corrected transposition of the great vessels. Br Heart J 1956;18:186]192. Lundstrom U, Bull C, Wyse R, Somerville J. The natural and ‘unnatural’ history of congenitally corrected transposition. Am J Cardiol 1990;65:1222]1229. Fyler D. Corrected transposition of the great arteries. In: Fyler D, editor. Nadas’ pediatric cardiology. Philadelphia: Hanley and Belfus Inc, 1992:701]706. Gillette P, Busch U, Mullins C, McNamara D. Electrophysiologic studies in patients with ventricular inversion and ‘corrected transposition’. Circulation 1979;60:939]945. Friedman H, Lipski J, Pantazopoulos J, Genkins G, Donoso E. Bundle of his electrograms in congenital corrected
w24x
w25x
w26x
w27x
w28x
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transposition of the great arteries: a study of two cases. Br Heart J 1973;35:1207]1214. Foster J, Damato A, Kline L, Akhtar M, Ruskin J. Congenitally corrected transposition of the great vessels: localization of the site of complete atrioventricular block using his bundle electrograms. Am J Cardiol 1976;38:383]387. Gregoratos G, Cheitlin M, Conill A et al. ACCrAHA guidelines for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of CardiologyrAmerican Heart Association Task Force on Practice Guidelines ŽCommittee on Pacemaker Implantation.. J Am Coll Cardiol 1998;31Ž5.:1175]1209. Lillehei C, Sellers R, Bonnanbeau R, Eliot R. Chronic postsurgical complete heart block with particular reference to prognosis, management and a new P-wave pacemaker. J Thorac Cardiovasc Surg 1963;46:436]456. Estes N, Salem D, Isner J, Gamble W. Permanent pacemaker therapy in corrected transposition of the great arteries: analysis of site of lead placement in 40 patients. Am J Cardiol 1983;52:1091]1097. Serwer G, Dorostkar P, LeRoy S. Pediatric pacing and defibrillator usage. In: Clinical cardiac pacing. Philadelphia: WB Saunders, in press.
Congenitally corrected L-transposition of the great arteries: abnormalities of atrioventricular conduction Peter S. FischbachU , Ian H. Law, Gerald S. Serwer Di¨ ision of Pediatric Cardiology, Uni¨ ersity of Michigan Health Systems, 1500 East Medical Center Dri¨ e, Box 0204, F 1310, Ann Arbor, MI 48109-0204, USA
Abstract L-transposition of the great arteries is a complex cardiac malformation with ventricular inversion and discordance of both atrioventricular and ventriculoarterial connections. Several electrophysiologic abnormalities can be associated with this entity including varying degrees of heart block, supraventricular arrhythmias such as sick sinus syndrome and supraventricular tachycardias Žatrial flutter, atrioventricular reentrant tachycardia., as well as ventricular tachycardias. A review of the anatomic and functional abnormalities of the conduction system in L-transposition is provided along with a summary of the unique problems associated with the use of pacemakers in this patient population. Q 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: L-Transposition of the great arteries ŽL-TGA.; Ventricular inversion; Heart block; Supraventricular arrhythmia; Pacemaker
1. Introduction Congenitally corrected L-transposition of the great vessels ŽL-TGA. is a complex cardiac malformation consisting of situs solitus of the atria with ventricular inversion and discordance of both atrioventricular ŽAV. and ventriculoarterial connections. The combined defects result in a physiologically correct circulation where the systemic venous return is routed to the pulmonary artery and pulmonary venous return is directed to the aorta. The morbidity and mortality associated with this malformation is the result of one or more frequently associated defects such as ventricular septal defect, pulmonary stenosis, systemic AV valve Žtricuspid. regurgitation, ventricular hypoplasia and electrophysiologic abnormalities w1,2x. The most common electrophysiologic abnormality associated with L-TGA is a delay or complete interruption of
U
Corresponding author. Tel.: q1-734-936-8994; fax: q1-734936-9470. E-mail address: [email protected] ŽP.S. Fischbach.
normal AV conduction w3,4x. In addition to the various degrees of heart block observed, several forms of supraventricular arrhythmia are relatively common, such as sick sinus syndrome, atrial flutter and reentrant AV tachycardia utilizing an accessory pathway along the tricuspid valve annulus w3]5x. Ventricular tachycardia has also been reported in L-TGA w6,7x. Conduction through the atrioventricular node ŽAVN. can be normal or abnormal. Abnormalities include various degrees of heart block, up to and including complete congenital heart block. AV conduction may be normal initially and thereafter demonstrate progressive degrees of block with aging w3x. The normal conduction through the AVN can be disrupted during invasive procedures such as cardiac catheterization and surgery w2x. In this review a brief discussion of the abnormal gross and histologic anatomy of the conduction system in L-TGA will be presented and compared to conduction in the normal heart. The implications that these abnormalities present for the cardiologist and cardiovascular surgeon will be discussed. Published
1058-9813r99r$ - see front matter Q 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 1 0 5 8 - 9 8 1 3 Ž 9 9 . 0 0 0 1 3 - 2
38
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
reports of heart block associated with L-TGA will be reviewed and the special concerns and indications for pacemaker therapy will be presented.
2. Anatomy Descriptions of the atypical anatomy of the conduction system in L-TGA with ventricular inversion were first published nearly 75 years ago. They described inversion of the bundle branches with the fan-like branch, normally associated with the left-sided systemic ventricle, passing to the anatomic right side of the ventricular septum, and the cord-like bundle branch, typically found on the right side of the septum, passing leftward into the morphologic right ventricle w8x. More recently the abnormal gross and histological anatomy of the conduction system in L-TGA has been fully delineated. This information has explained the high risk of injury to the system during invasive procedures and has led to changes in procedure that have significantly reduced the incidence of iatrogenicly induced block w1,9x. Using serial histopathological sections, Anderson and colleagues identified dual AVNs in patients with L-TGA w10,11x. In agreement with previous work by Lev et al. w12x, Anderson found that a histologically normal appearing AVN was located in the usual posterior location at the apex of the triangle of Koch. Although it appeared histologically normal, this AVN had no connections with the penetrating bundle and, hence, it was electrically isolated from the ventricle. Initially Lev thought that this discontinuity between the normally located posterior AVN and the penetrating bundle was the cause of the complete heart block associated with L-TGA w12x. However, Anderson’s group identified a second anterior AVN located in the right atrium at the junction of the right AV valve Žmitral valve. and the left border of the right atrial appendage. This second ‘accessory’ AVN was histologically identical to the posteriorly located node but connected directly with an aberrantly located penetrating bundle w10,11x. In his studies, Anderson was able to trace the course of the penetrating bundle. After leaving the AVN the conduction tissue passes laterally onto the roof of the pulmonary outflow tract just below the level of the pulmonary valve and then descends to reach the anterior margin of the interventricular septum. In hearts with intact ventricular septum the His bundle then descends along the anterior superior rim of the membranous septum remaining on the anatomic right side ŽFig. 1.. In hearts with L-TGA with an associated ventricular septal defect the His bundle passes abnormally along the anterior and superior margin of the defect remaining on the right side of
Fig. 1. Endomyocardial electrograms recorded from a patient with L-TGA at the time of surgical repair of a ventricular septal defect demonstrate His potential signals recorded along the superior anterior margin of the defect w15x.
the rim of ventricular tissue. This is quite different from its anatomic course in hearts with normally related ventricles and a ventricular septal defect where the conduction tissue descends on the posterior inferior rim of the defect remaining on the anatomic left side w12,13x. These histologic abnormalities of conduction in L-TGA with ventricular septal defect have been confirmed in several studies by direct intraoperative mapping of the system at the time of intracardiac surgical procedures w14]17x. Identification of the characteristic abnormal course of the conduction system is crucial during surgical closure of a ventricular septal defect or relief of pulmonary and subpulmonary obstruction associated with L-TGA, and its predictable location has led to a marked reduction in the incidence of surgically induced heart block w1,18x.
3. Conduction abnormalities Impaired AV conduction, including first, second and third degree block, is frequently associated with L-TGA w19x. Complete heart block may be congenital, surgically induced or caused by progressive deterioration of AV conduction. The risk of developing complete heart block persists throughout life, increasing almost linearly with age w3x. Among patients with L-TGA, complete heart block is more frequent in those with an intact ventricular septum than in others with an associated ventricular septal defect w3x. The incidence of heart block in patients with L-TGA
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
has been reported in five large studies published in English ŽTable 1.. The largest study from the Hospital for Sick Children in London found complete heart block in 35 of 111 L-TGA patients Ž32%. w20x. Complete block was induced during surgery in 14 of them. Among the other 21 patients, congenital heart block occurred in four and developed spontaneously in 17. It occurred before 10 years of age in 16 of the 17. Huhta et al. reviewed the experience at the Mayo Clinic with 107 patients with L-TGA, situs solitus and discordant functioning ventricles w3x. Complete heart block occurred in 23 patients Ž22%. and was congenital in four Ž4%. of them. The mean age for the development of spontaneously occurring complete heart block was 18.1 years, and in the oldest patient who developed block, it occurred at 53 years of age. An important finding in this review was that the risk for developing complete heart block persisted throughout life and its incidence increased almost
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linearly at a rate of approximately 2% per year. Complete block occurred in eight of 101 patients Ž8%. studied at the Sick Children’s Hospital in Toronto w5x. In 90 patients with L-TGA and two functional ventricles who were studied at the Children’s Hospital in Boston w21x, 29 had complete heart block Ž33%., induced at surgery in six of them. In studies of 17 patients with isolated L-TGA, Daliento et al. found five patients with complete heart block, none of whom had any rhythm abnormalities as newborns w7x. At the Michigan Congenital Heart Center at the University of Michigan in Ann Arbor, 126 patients with L-TGA, 7 months to 48 years of age, were identified by searching echocardiography and pacemaker databases ŽTable 1.. A hypoplastic ventricle was found in 56 of them Ž45%.. Heart block was present in 40 of the 126 patients Ž32%.. The block was first degree in 11 of the 126 Ž9%., second degree
Table 1 Incidence of conduction abnormalities associated with L-TGAa Source
Patient population
Heart block incidence
Atrial arrhythmias
Bjarke et al. w5x
n s 101 43% single ventricles
n s 17 Ž17%. 1st: 7 Ž7%. 2nd: 2 Ž2%. 3rd: 8 Ž8%.
n s 12 Ž12%. Žpre-surgical.
Daliento et al. w7x
n s 17 All two ventricles
n s 5 Ž29%.
Friedberg et al. w4x
n s 60 42% SV 52% VSD 6% IVS
n s 19 Ž32%. 1st: 10 Ž17%. 2nd: 2 Ž3%. 3rd: 7 Ž12%.
Huhta et al. w3x
n s 107 All two ventricle 77% VSD
n s 23 Ž22%. CCHB: 4 Ž4%.
Lundstrom et al. w20x
n s 111 All two ventricle
n s 35 Ž32%. CCHB: 4 Ž4%. Spont: 17 Ž15%. SxHB: 14 Ž13%.
Fyler w21x Žincludes subset of Friedberg et al. population.
n s 90 All two ventricle
n s 29 Ž32%.
Michigan Congenital Heart, 1998
n s 126 SVs 57 Ž45%.
n s 40 Ž32%. 1st: 11 Ž9%. 2nd: 4 Ž3%. 3rd: 19 Ž15%. yCCHB 6 SxHB: 6 Ž5%.
a
n s 4 Ž4%. WPW: 2 AFL: 2
Pacemakers
n s 9 Ž39%.
n s 9 Ž8%. All for CHB
n s 19 Ž15%. WPW: 5 AFL: 6 AF: 1 PSVT: 2 SSS: 5
n s 27 Ž21%. SSS: 5 Ž4%. 2nd HB: 1 Ž1%. CHB: 10 Ž8%. SxHB: 9 Ž7%.
Notes. Incidence of heart block, atrial arrhythmias and pacemaker implants in patients with L-TGA. Abbre¨ iations. 1st, 2nd and 3rd s first, second and third degree heart block; SB, single ventricle; VSD, ventricular septal defect; IVS, intact ventricular septum; CCHB, complete congenital heart block; WPW, Wolff]Parkinson]White syndrome; AFL, atrial flutter; AF, atrial fibrillation; spont., spontaneous heart block; SxHB, surgical heart block; PSVT, paroxysmal supraventricular heart block not otherwise specified; and SSS, sick sinus syndrome.
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P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
in four Ž3%., complete and spontaneous in 19 Ž15%. and complete and congenital in 6 Ž5%. of them. Six other patients Ž5%. had surgically induced complete block. Atrial arrhythmias were found in 19 of the 126 patients Ž15%.. Pacemaker implantation was needed in 27 patients Ž21%. who had heart block or sick sinus syndrome. In many of the patients in these five series who had complete heart block, normal AV conduction was documented at one time or another by a surface ECG recording of a normal PR interval. A few of the patients in the series had progressive AV conduction abnormalities as demonstrated by first degree heart block leading to second degree and then to complete block, suggesting that progressive fibrosis of the AV conduction system is a risk factor in some patients with this defect w11x. In L-TGA patients with heart block the exact location of the slowing or interruption of the electrical signal within the AV conduction tissue has been investigated using catheter electrodes w22]24x. In His bundle recordings of 40 patients with L-TGA, Gillette et al. identified 15 patients Ž38%. with normal AV conduction who had normal AH and HV intervals w22x. Fourteen of the 15 patients had first degree AV block with conduction delay occurring variably above, within or below the bundle of His. The conduction delay was at a single site in several patients, but it was recorded at several locations in many. These varying levels of AV block were also found in studies of 11 patients with complete heart block. Two of the patients with complete heart block had intact retrograde AV conduction at the time of electrophysiologic study, demonstrating that in a subset of patients with L-TGA, complete AV block is not the result of anatomic interruption of the conduction tissue, a finding of particular importance when single chamber pacing is being considered.
4. Pacing Permanent pacemaker treatment must be considered in every patient with L-TGA and complete heart block ŽFig. 2.. Guidelines for pacemaker treatment in general have recently been published jointly by the American College of Cardiology and the American Heart Association w25x. The first group of patients with L-TGA to be considered for pacing is composed of those with congenital complete heart block. The ACCrAHA guidelines identify a Class I indication for permanent pacing in patients with any type of congenital heart disease and congenital complete heart block with a ventricular rate less than 70 b.p.m. In many centers, the criteria for pacemaker therapy has been based on symptoms of inadequate cardiac
Fig. 2. Clinical algorithm for selecting patients with L-TGA and complete heart block who require permanent pacing.
output rather than on a specific minimal heart rate. In all newborns with functionally significant congenital heart disease, we believe that pacemaker therapy is necessary before hospital discharge. Those infants with L-TGA without associated lesions Ži.e. ventricular septal defect, pulmonic stenosis, and systemic AV valve regurgitation. who have no symptoms of heart failure have been managed conservatively with close follow-up without pacemaker insertion. In infants with L-TGA who have associated defects, pacemakers have been implanted without regard to the heart rate or symptoms of heart failure. Patients with L-TGA who have developed complete heart block spontaneously form a second group. In these patients complete block can appear at any time from infancy to late adulthood. We believe that the need for pacemaker therapy in this group of patients should be based, not simply on a selected low heart rate, but on symptoms of heart failure such as fatigue, exercise intolerance, syncope or near-syncope and on signs of cardiomegaly on chest X-ray or ventricular dysfunction on echocardiogram. A third group of patients with L-TGA is made up of those with surgically acquired complete heart block. Because unstable ventricular escape rhythms are common after surgical interruption of the AV conduction system w26x, all patients with L-TGA who have complete block after cardiac surgery should have pacemaker implantation before hospital discharge, regardless of the ventricular rate or the presence of symptoms. After a need for permanent pacing is identified, a choice between epicardial or endocardial pacing leads
P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
must be made. In the past epicardial lead systems were preferred in patients with L-TGA because of unreliable active fixation of leads to the smooth-walled endocardium of the inverted right-sided morphologic left ventricle w27x. However, currently available endocardial leads for active fixation are considered to be as reliable as passive fixation leads. Immediately after implantation, the electrical capture threshold tends to be slightly higher in active fixation leads, but with time it approaches those of passive fixation leads. Moreover, recently developed steroid eluting active fixation leads are now available which should allow for lower pacing thresholds for much longer periods of time. Consequently, with currently available leads, the choice of endocardial or epicardial pacing is no longer based on differences in lead fixation, but on criteria such as the size of the patient, venous access to the right-sided ventricle, intracardiac right to left shunting, the presence of increased pulmonary vascular resistance and the consideration that epicardial
41
placement requires a surgical thoracotomy w28x. When permanent pacemaker therapy is indicated at the time of cardiac surgery, placement of an epicardial system may be prudent. In patents requiring a pacemaker who are not undergoing cardiac surgery, our current practice is to use a dual chamber endocardial lead system in patients weighing more than 15 kg and a single endocardial ventricular lead in infants and children weighing 8]15 kg. Passage and fixation of endocardial leads can be complicated by obstruction from aberrant intracardiac anatomy. In patients with L-TGA, the inverted ventricle and unusual position of the right-sided mitral valve can present problems in passing the lead into the right-sided ventricle along the misleadingly smooth appearing arcing course seen on fluoroscopy. As shown in Fig. 3, the superior and anterior deflection of the ventricular lead within the atrium can create uncertainty as to the anatomic location of the lead tip as it is passed into the right ventricle. In a few
Fig. 3. Chest radiographs showing the unusual course taken by the ventricular pacing lead in patients with L-TGA compared to the normal heart. The anteroposterior Ža. and lateral Žb. radiographs of a patient with L-TGA demonstrate the more superior and anterior course of the ventricular lead passing across the mitral valve into the apex of the right-sided left ventricle. In a patient with normal cardiac anatomy Žc., a dual chamber pacing system is shown with the normal smooth course of the ventricular electrode lead.
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P.S. Fischbach et al. r Progress in Pediatric Cardiology 10 (1999) 37]43
instances we have used transesophageal echocardiography to identify and confirm the correct location of the lead tip. There are several options for the type of pulse generator to be used. A single ventricular chamber pacing unit ŽVVI or VVIR. is probably not the ideal choice for most patients with L-TGA for several reasons: Ž1. dysfunction of the systemic Žleft-sided. right ventricular is relatively common in these patients with ventricular inversion and, as with all ventricles operating at the peak of the Frank-Starling curve, the atrial systole provided by synchronous dual chamber AV pacing can be quite helpful; Ž2. many of these patients are at risk for pacemaker syndrome because retrograde VA conduction remains intact w22x; Ž3. the option of atrial pacing can become useful because of the high incidence of atrial and sinus node arrhythmias; and Ž4. many of the new pulse generators allow for termination of atrial flutter by rapid atrial overdrive pacing. Dual chamber pacing is preferred for almost all children, and certainly in those with L-TGA. We have used single chamber pacing only when there is a contraindication to dual chamber pacing. The major contraindications include persistent tachyarrhythmias, unstable AV node conduction requiring numerous pacer programming changes, and the inability to reliably fix atrial and ventricular leads. In small children the placement of both atrial and ventricular endocardial leads through a relatively small superior vena cava can present a risk of thrombosis and obstruction. Another reason for single chamber pacing is in a child requiring epicardial ventricular lead placement who would need a more involved surgical procedure to also implant an atrial epicardial electrode. In D-TGA patients with intermittent atrial tachyarrhythmia, choosing a generator that allows for the use of mode switching can decrease the risk of a rapid increase in ventricular response rate or an abrupt decrease in heart rate that can occur at the onset of the tachyarrhythmia.
5. Conclusion L-TGA is an uncommon congenital heart malformation that is almost uniformly associated with other structural lesions and electrophysiological abnormalities. Over the last 25 years, identification of the predictable abnormal anatomic location and course of the ventricular conduction system in L-TGA has resulted in a significant reduction in the risk of heart block during surgical closure of associated ventricular septal defects or relief of pulmonary outflow tract obstruction. The increased incidence of conduction abnormali-
ties and atrial arrhythmias in L-TGA patients, with and without associated structural lesions, requires diligent lifelong patient follow-up because heart block may appear at anytime from infancy to late adulthood. Congenital and spontaneous Žnon-surgical. heart block does not always require permanent pacemaker treatment, depending on the patient’s symptoms and associated heart defects, whereas surgically induced complete heart block always requires pacing. In most children with L-TGA the treatment of choice is dual chamber pacing through right atrial and rightsided ventricular endocardial active fixation leads. References w1x Doty D, Truesdell S, Marvin W. Techniques to avoid injury of the conduction tissue during the surgical treatment of corrected transposition circulation. 1983;68ŽSuppl II.:II-3]II-9. w2x Kirklin J, Barratt-Boyes B. Congenitally corrected transposition of the great arteries. In: Barratt-Boyes B, Kirklin J, editors. Cardiac surgery. New York: Churchill Livingston, 1993:1511]1533. w3x Huhta J, JD M, Ritter D, Ilstrup D, Feldt R. Complete atrioventricular block in patients with atrioventricular discordance. Circulation 1983;67Ž6.:1374]1377. w4x Friedberg D, Nadas A. Clinical profile of patients with congenital corrected transposition of the great arteries: a study of 60 cases. N Engl J Med 1970;282:1053]1059. w5x Bjarke B, Kidd B. Congenitally corrected transposition of the great arteries: a clinical study of 101 cases. Acta Paediatr Scand 1976;65:153]160. w6x Levy A, Camm A, Keane J. Multiple arrhythmias detected during nocturnal monitoring in patients with congenital complete heart block. Circulation 1977;55:247]253. w7x Daliento L, Corrado D, Buja G et al. Rhythm and conduction disturbances in isolated, congenitally corrected transposition of the great arteries. Am J Cardiol 1986;58:314]318. w8x Sato S. Uber die entwicklung der atrioventrikularklappne und der pars membranacea unter berucksichtigung zugehoriger herzmissbildungen. Anat Heft 1914;50:1195. w9x Hwang B, Bowman F, Malm J, Krongrad E. Surgical repair of congenitally corrected transposition of the great arteries: results and follow-up. Am J Cardiol 1982;50:781]785. w10x Anderson R, Arnold R, Wilkinson J. The conducting system in congenitally corrected transposition. Lancet 1973;1: 1286]1288. w11x Anderson R, Becker A, Arnold R, Wilkinson J. The conducting tissues in congenitally corrected transposition. Circulation 1974;50:911]923. w12x Lev M, Licata R, May R. The conduction system in mixed levocardia with ventricular inversion Žcorrected transposition.. Circulation 1063;28:232. w13x Truex R, Bishof J. Conducting system in human hearts with ventricular septal defects. Ann Arbor Thorac Surg 1958; 35:421. w14x Maloney J, Ritter D, McGoon D, Danielson G. Identification of the conduction system in corrected transposition and common ventricle at operation. Mayo Clin Proc 1975;50:387]394. w15x Dick M, Norwood W, Chipman C, Castaneda A. Intraoperative recording of specialized atrioventricular conduction tissue electrograms in 47 patients. Circulation 1979;59:150]160. w16x Kupersmith J, Krongrad E, Gersony W, Bowman F. Electrophysiologic identification of the specialized conduction system
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transposition of the great arteries: a study of two cases. Br Heart J 1973;35:1207]1214. Foster J, Damato A, Kline L, Akhtar M, Ruskin J. Congenitally corrected transposition of the great vessels: localization of the site of complete atrioventricular block using his bundle electrograms. Am J Cardiol 1976;38:383]387. Gregoratos G, Cheitlin M, Conill A et al. ACCrAHA guidelines for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of CardiologyrAmerican Heart Association Task Force on Practice Guidelines ŽCommittee on Pacemaker Implantation.. J Am Coll Cardiol 1998;31Ž5.:1175]1209. Lillehei C, Sellers R, Bonnanbeau R, Eliot R. Chronic postsurgical complete heart block with particular reference to prognosis, management and a new P-wave pacemaker. J Thorac Cardiovasc Surg 1963;46:436]456. Estes N, Salem D, Isner J, Gamble W. Permanent pacemaker therapy in corrected transposition of the great arteries: analysis of site of lead placement in 40 patients. Am J Cardiol 1983;52:1091]1097. Serwer G, Dorostkar P, LeRoy S. Pediatric pacing and defibrillator usage. In: Clinical cardiac pacing. Philadelphia: WB Saunders, in press.