- Email: [email protected]
The conduction system and arrhythmias in common atrioventricular canal
Progress in Pediatric Cardiology 10 Ž1999. 153᎐159
The conduction system and arrhythmias in common atrioventricular canal Naomi J. KerteszU Lillie Frank Abercrombie Section of Pediatric Cardiology, Texas Children’s Hospital, Baylor College of Medicine, 6621 Fannin MC 2-2280, Houston, TX 77030, USA
Abstract Atrioventricular ŽAV. canal defects are characterized by deficiencies in the atrial and ventricular septum. These defects result in posterior displacement of the conduction system with hypoplasia of the left anterior fascicle. The abnormal development of the conduction system results in a characteristic electrocardiogram consisting of a prolonged PR interval, left axis deviation, an initial counterclockwise frontal plane loop, and right ventricular hypertrophy. Arrhythmias are found in unrepaired patients as they reach the second and third decades of life. As surgical repair is usually performed during the first decade of life, these are now uncommonly seen. Postoperatively these patients are susceptible to complete AV block as well as other arrhythmias that are encountered following atrial or ventricular septal defect repair. 䊚 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Conduction system; Electrocardiogram; Atrioventricular canal defect; Arrhythmias
1. Introduction The electrocardiogram ŽECG. in patients with atrioventricular ŽAV. canal defects is distinctive and felt to be almost diagnostic w1,2x. This distinctive ECG pattern sparked renewed interest in the relationship between the displacement of the conduction system and its effect on the ECG w1,3,4x. This paper reviews the position of the conduction system, the ECG abnormalities, and the arrhythmias found in patients with AV canal defects.
2. The conduction system and the electrocardiogram Prior to reviewing the abnormalities of the conducU
tion system found in patients with AV canal defects, it is prudent to review the position of the conduction system in the normal heart. The AV node is situated in the floor of the right atrium in the apex of the triangle of Koch. The triangle is formed by the tendon of Todaro, the membranous septum, and the septal attachment of the tricuspid valve ŽFig. 1.. The AV bundle then extends anteriorly and inferiorly from the node through the fibrous valvular ring, becomes the penetrating ŽHis. bundle, and runs along the inferior part of the membranous septum onto the crest of the inlet part of the ventricular septum ŽFig. 1.. The left bundle branches are usually given off as discrete muscular fascicles over a broad extent of the common bundle and fan out over the left ventricular side of the ventricular septum ŽFig. 1b.. The right bundle branch, however, usually forms a continuation of the common bundle and passes obliquely, anteriorly, and
Tel.: q1-713-770-5600; fax: q1-713-770-5630.
1058-9813r99r$ - see front matter 䊚 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 1 0 5 8 - 9 8 1 3 Ž 9 9 . 0 0 0 2 8 - 4
154
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
inferiorly through the upper part of the ventricular septum toward the septal band w5,6x. AV canal defects are characterized by a deficiency in the inlet ventricular septum as well as a deficiency of the lower atrial septum. Because of these septal defects, the AV node is displaced posteriorly, lying in the posterodistal aspect of the atrial septum at its junction with the right atrial floor and is closely related to the coronary sinus and the attachments of the posterior bridging leaflet. It then penetrates the posterior part of the central fibrous body to become the penetrating portion of the His bundle. The bundle thus lies in the posterior rim of the defect on the crest of the inlet ventricular septum in the base of the connective tissue to which the posterior bridging
leaflet is attached ŽFig. 2. w7x. There is then a long non-penetrating non-branching bundle which courses along the inferior margin of the defect that is quite superficial as demonstrated in Fig. 2. The right bundle branch often arises from several separate fasciculi and its site of origin is near the crest of the septum w7,8x. The left bundle branch is displaced postero-inferiorly and has fewer anterior left bundle branches than in normal hearts w3,9x. The displacement of the left bundle branch and the hypoplasia of the anterior fascicle play an important role in the characteristic ECG pattern in these patients. AV canal defects are also commonly found in patients with heterotaxy syndrome, either with polysplenia or asplenia. When associated with L-
Fig. 1. The atrioventricular ŽAV. node and bundle branches as viewed from the right side of the heart Ža. and left side of the heart Žb.. RBB, right bundle branch.
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
ventricular looping, two AV nodes may be found. The two nodes are located anterior and posterior to the defect and are related to the anterior and posterior components of the central fibrous body. Many times the distal components of the anterior and posterior bundles can join to form a sling w10,11x. It was initially thought that the distinctive ECG pattern in patients with AV canal defects was due to hemodynamic abnormalities. However, further research demonstrated that the ECG was caused by displacement of the conduction system andror underdevelopment of the anterior left bundle branches, though this remained controversial for a number of years w1᎐4,12,13x. The characteristic features of the ECG in patients with partial or complete forms of AV
155
canal defects include a prolonged PR interval, left axis deviation, an initial counterclockwise frontal plane loop, and criteria for right ventricular hypertrophy w1,2,4,14᎐16x ŽFig. 3.. The prolonged PR interval is caused by prolonged internodal conduction time and not due to an abnormality in the AV node or His᎐Purkinje system w15,16x. Left axis deviation with an initial counterclockwise frontal plane loop beyond y60⬚ is diagnostic for left anterior hemiblock ŽLAH.. The mechanism by which LAH is generated in AV canal defects is not agreed upon and may be caused by one or a combination of the following: Ž1. mechanical elongation and stretching of the anterior division of the left bundle branch ŽLBB. caused by the posterior displacement of the conduction system which
Fig. 2. The AV node and bundle branches in AV canal defect as viewed from the right side of the heart Ža. and the left side of the heart Žb.. Part of the AV valves have been removed. RBB, right bundle branch.
156
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
would affect the anterior division more than the posterior division because of the more distal takeoff of the former; Ž2. anomalous development of the anterior division of the LBB; and Ž3. interruption of the anterior division by anomalous insertion of mitral chordae tendinae w1,3,13,17,18x. In the normal heart, the anterior᎐superior and the posterior᎐inferior portions of the left ventricle are depolarized simultaneously by their respective fascicles. Block in the anterior division, either caused by abnormal development or position, changes the sequence of depolarization. The inferior regions are activated normally, but the depolarization wavefront must then spread superiorly producing a superiorly directed vector in the frontal plane w18x. Further investigation of the endocardial and epicardial activation in patients with AV canal defects confirmed that the ECG abnormalities were caused by the abnormal conduction system and not by altered hemodynamics w12x. In patients with partial AV canal defects, the initial QRS vector forces are usually directed inferiorly and to the right and the QRS loop moves counterclockwise superiorly and to the left. The mean QRS axis ranges from y30⬚ to y120⬚ with most lying between y30⬚ and ᎐90⬚. Evidence of right ventricular volume overload manifest by an rsR’ or RSR’ in the right precordial leads is seen in 84% of patients w1x. Slightly more than half of the patients Ž54%. will have some evidence of atrial enlargement w14,19x. Approximately 70% have a q wave in V6 in contrast to only 35% of patients with a secundum atrial septal defect w1x. In patients with complete AV canal defects,
the QRS vector is initially directed inferiorly and moves in a counterclockwise direction with the main loop lying superiorly and to the right in 70% and to the left in 23%. The QRS axis ranges from y60⬚ to y135⬚ but is usually between y90⬚ and y120⬚, which is more leftward than that found in partial AV canals w19x. Again, greater than 50% of patients have evidence of atrial enlargement and two-thirds have an rsR’, RSR’, or rR’ in V1 with the remainder a qR or R wave consistent with right ventricular hypertrophy w14x. Additional factors believed to influence the appearance of the ECG include: the size of the atrial and the ventricular septal defects, mitral and tricuspid regurgitation, pulmonary vascular resistance, and associated defects w1,16x. These factors can affect the degree of axis deviation, atrial enlargement, and ventricular hypertrophy. While the above electrocardiographic abnormalities can occasionally be found in isolated ventricular septal defects, the combination of left axis deviation and a counterclockwise frontal plane loop are believed to be almost diagnostic of an AV canal defect w1,2x.
3. Arrhythmias in patients with AV canal defects The arrhythmias found in patients with AV canal defects have little to do with the displaced conduction system other than its susceptibility to surgically acquired injury when the ventricular component is repaired. As these patients usually undergo surgery in the first decade of life, arrhythmias are not common
Fig. 3. A 15-lead electrocardiogram in a 1-month-old infant with a complete AV canal. Note the left axis deviation, counterclockwise frontal plane loop and right atrial enlargement.
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
157
Fig. 4. A rhythm strip in an infant following an ASD and VSD repair with atrial tachycardia with variable AV conduction. Leads I, II and III are displayed in both Ža. and Žb.. In Žb., however, the right arm and left arm electrocardiogram leads are attached to the temporary atrial wires. One can now clearly see the atrial activity in lead I and both atrial and ventricular activity in leads II and III.
preoperatively. A natural history study of patients with the partial form of AV canal defects found that there was a distinct increase in the incidence of arrhythmias in unoperated patients after age 30 w20x. Arrhythmias, most commonly atrial fibrillation, occurred in 20% of patients and were frequently associated with clinical deterioration. Acquired complete AV block was common in those patients who deteriorated and occurred as early as 18 years w20x. Acquired complete AV block has also been reported in an 11-year-old with a complete AV canal defect w21x. There is very little documentation of early and late postoperative arrhythmias in this patient population. These patients are susceptible to any arrhythmia that is encountered following either atrial or ventricular surgery. Among the most common postoperative arrhythmias are atrial tachycardia and surgical AV block. A ventriculotomy is not required to repair the ventricular component and therefore ventricular tachycardia is uncommon in the author’s experience.
Atrial tachycardia can be found following any type of atrial surgery. It can be caused by either microreentry in the atrium or to an ectopic focus. Atrial rates range from 160 to 260 b.p.m. with variable AV conduction and, in many instances, the tachycardia is non-sustained. It is usually characterized by a ‘warm up,’ or a progressive shortening of the PP interval, and a ‘cool down,’ or lengthening of the PP interval prior to termination of the tachycardia. This arrhythmia is typically found in the first 1 or 2 days postoperatively and, initially, may be well-tolerated w22x. Use of direct ECG recording using temporary atrial pacing wires can be very useful in diagnosing this arrhythmia ŽFig. 4.. First-line therapy consists of intravenous procainamide and if the arrhythmia persists beyond the early postoperative period, D,L-sotalol or amiodarone may be used for 6 months to 1 year postoperatively. AV canal repair has been identified as one of four types of surgery commonly associated with postopera-
158
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
tive surgical AV block w23,24x. Postoperative complete AV block has been reported to occur in 0᎐3.5% of patients w24᎐27x. There have been no instances of permanent surgical complete AV block in the last 64 AV canal repairs at our institution. Smaller patient size has also been shown to be an independent predictor of the incidence of AV block following surgery w28x. Both Weindling et al. and Kertesz et al. found that approximately 50% of surgical AV block resolves within the first 8 postoperative days w28,29x. Because of the high mortality reported in patients with surgical complete AV block w24,30x, it is categorized as a Class I indication in the AHArACC guidelines for implantation of permanent pacemakers w31x. Thus in the presence of complete surgical AV block 8 days postoperatively, a pacemaker is indicated. If there is any evidence of AV conduction prior to the 8th postoperative day it is prudent to wait up to 2 weeks for sinus rhythm to return. We believe that patients must return to sinus rhythm in order to avoid pacemaker placement.
4. Conclusion Defects in the AV canal result in displacement of the conduction system and abnormal development of the left bundle branch w8x. This displacement and abnormal development result in a characteristic ECG that is very useful as a diagnostic modality. Arrhythmias in this patient population are not common and are similar to those found following repair of atrial and ventricular septal defects. References w1x Burchell HB, DuShane JW, Brandenburg RO. The electrocardiogram of patients with atrioventricular cushion defects Ždefects of the atrioventricular canal.. Am J Cardiol 1960;6: 575᎐588. w2x Toscano-Barbosa E, Brandenberg HO, Burchell HB. Electrocardiographic studies of cases with intracardiac malformations of atrioventricular canal. Proc Staff Meet Mayo Clin 1956;31:513᎐523. w3x Feldt RH, DuShane JW, Titus JL. The atrioventricular conduction system in persistent common atrioventricular canal defect: correlations with electrocardiogram. Circulation 1970; 42:437᎐444. w4x Durrer D, Roos JP, van Dam RTh. The genesis of the electrocardiogram of patients with ostium primum defects Žventral atrial septal defects.. Am Heart J 1966;71:642᎐650. w5x Titus JL, Daugherty GW, Edwards JE. Anatomy of the atrioventricular conduction system in ventricular septal defect. Circulation 1963;28:72᎐81. w6x Kurosawa H, Becker AE. Atrioventricular conduction in congenital heart disease. Tokyo: Springer-Verlag, 1987:1᎐14. w7x Kurosawa H, Becker AE. Atrioventricular conduction in congenital heart disease. Tokyo: Springer-Verlag, 1987:87᎐96.
w8x Lev M. The architecture of the conduction system in congenital heart disease: I. Common atrioventricular orifice. Arch Pathol 1958;65:174᎐190. w9x Vick GW. Defects of the atrial septum including atrioventricular septal defects. In: Garson Jnr A, Bricker JT, Fisher DJ, Neish SR, editors. The science and practice of pediatric cardiology. Baltimore: Williams and Wilkins, 1998:1141᎐1179. w10x Ih S, Fukuda K, Okada R, Saitoh S. The location and course of the atrioventricular conduction system in common atrioventricular orifice and in its related anomalies with transposition of the great arteries: a histopathological study of six cases. Jpn Circ J 1983;47:1262᎐1273. w11x Bharati S, Lev M. The course of the conduction system in dextrocardia. Circulation 1978;57:163᎐171. w12x Campbell RM, Dick II M, Hess P, Behrendt DM. Epicardial and endocardial activation in patients with endocardial cushion defect. Am J Cardiol 1983;51:277᎐281. w13x Rosenbaum MB, Elizari MV, Lazzari JO. The hemiblocks: new concepts of intraventricular conduction based on human anatomical, physiological and clinical studies. Florida: Tampa Tracings, 1970:134. w14x Feldt RH, Porter CJ, Edwards WD, Puga FJ, Seward JB. Atrioventricular septal defects. In: Emmanouilides GC, Riemenschneider TA, Allen HD, Gutgesell HP, editors. Moss and Adams’ heart disease in infants, children, and adolescents: including the fetus and young adult. 5th ed. Baltimore: Williams and Wilkins, 1995:704᎐723. w15x Waldo AL, Kaiser GA, Bowman FO, Malm JR. Etiology of prolongation of the P-R interval in patients with an endocardial cushion defect: further observations on internodal conduction and the polarity of the retrograde P wave. Circulation 1973;43:19᎐26. w16x Perloff JK. The clinical recognition of congenital heart disease. Philadelphia, PA: W.B. Saunders Company, 1978: 357᎐360. w17x Boineau JP, Moore EN, Patterson DF. Relationship between the ECG, ventricular activation, and the ventricular conduction system in ostium primum ASD. Circulation 1973; 48:556᎐564. w18x Walsh EP. Electrocardiography and introduction to electrophysiologic techniques. In: Fyler DC, editor. Nadas’ pediatric cardiology. Philadelphia: Hanley and Belfus, 1992:117᎐158. w19x Ongley PA, Pongpanich B, Spangler JG, Feldt RH. The electrocardiogram in atrioventricular canal. In: Feldt RH, McGoon DC, Ongley PA, Rastelli GC, Titus JL, Van Mierop LHS, editors. Atrioventricular canal defects. Philadelphia: W.B. Saunders, 1976:51᎐75. w20x Somerville J. Ostium primum defect: factors causing deterioration in the natural history. Br Heart J 1965;27:413᎐419. w21x Mehta AV, O’Riordan AC, Sanchez GR, Black IFS. Acquired nonsurgical complete atrioventricular block in a child with endocardial cushion defect. Clin Cardiol 1982;5:603᎐605. w22x Perry JC, Garson Jr. A. Arrhythmias following surgery for congenital heart disease. In: Zipes DP, Jalife J, editors. Cardiac electrophysiology: from cell to bedside. 2nd ed. Philadelphia: W.B. Saunders, 1995:838᎐847. w23x Kertesz NJ, McQuinn T, Collins E, Friedman R. Surgical atrioventricular block in 888 congenital heart operations: new implications for early implantation of a permanent pacemaker. PACE 1996;19:613. w24x Fryda RJ, Kaplan S, Helmsworth JA. Postoperative complete heart block in children. Br Heart J 1971;33:456᎐462. w25x Uretzky G, Puga FJ, Danielson GK et al. Complete atrioventricular canal associated with tetrology of fallot: morphologic and surgical considerations. J Thorac Cardiovasc Surg 1984; 87:756᎐766.
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159 w26x Backer CL, Mavroudis C, Alboliras ET, Zales VR. Repair of complete atrioventricular canal defects: results with the twopatch technique. Ann Thorac Surg 1995;60:530᎐537. w27x Studer M, Blackstone EH, Kirklin JW. Determinants of early and late results of repair of atrioventricular septal Žcanal. defects. J Thorac Cardiovasc Surg 1982;84:523᎐542. w28x Kertesz NJ, McQuinn T, Collins E, Friedman RA. Neonatal congenital heart surgery increases the risk of acquired atrioventricular block: implications for early elective repair. J Am Coll Cardiol 1997;29:357A. w29x Weindling SN, Saul JP, Gamble WJ, Mayer Jr. JE, Walsh EP.
159
Duration of complete heart block after congenital heart disease surgery. J Am Coll Cardiol 1994;23:104A. w30x Lillihei CW, Sellers RD, Bonnaneau RC et al. Chronic postsurgical complete heart block. J Thorac Cardiovasc Surg 1973;46:436᎐456. w31x Gregoratos G, Cheitlin MD, Conill A et al. The 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;31:1175᎐1209.
The conduction system and arrhythmias in common atrioventricular canal Naomi J. KerteszU Lillie Frank Abercrombie Section of Pediatric Cardiology, Texas Children’s Hospital, Baylor College of Medicine, 6621 Fannin MC 2-2280, Houston, TX 77030, USA
Abstract Atrioventricular ŽAV. canal defects are characterized by deficiencies in the atrial and ventricular septum. These defects result in posterior displacement of the conduction system with hypoplasia of the left anterior fascicle. The abnormal development of the conduction system results in a characteristic electrocardiogram consisting of a prolonged PR interval, left axis deviation, an initial counterclockwise frontal plane loop, and right ventricular hypertrophy. Arrhythmias are found in unrepaired patients as they reach the second and third decades of life. As surgical repair is usually performed during the first decade of life, these are now uncommonly seen. Postoperatively these patients are susceptible to complete AV block as well as other arrhythmias that are encountered following atrial or ventricular septal defect repair. 䊚 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Conduction system; Electrocardiogram; Atrioventricular canal defect; Arrhythmias
1. Introduction The electrocardiogram ŽECG. in patients with atrioventricular ŽAV. canal defects is distinctive and felt to be almost diagnostic w1,2x. This distinctive ECG pattern sparked renewed interest in the relationship between the displacement of the conduction system and its effect on the ECG w1,3,4x. This paper reviews the position of the conduction system, the ECG abnormalities, and the arrhythmias found in patients with AV canal defects.
2. The conduction system and the electrocardiogram Prior to reviewing the abnormalities of the conducU
tion system found in patients with AV canal defects, it is prudent to review the position of the conduction system in the normal heart. The AV node is situated in the floor of the right atrium in the apex of the triangle of Koch. The triangle is formed by the tendon of Todaro, the membranous septum, and the septal attachment of the tricuspid valve ŽFig. 1.. The AV bundle then extends anteriorly and inferiorly from the node through the fibrous valvular ring, becomes the penetrating ŽHis. bundle, and runs along the inferior part of the membranous septum onto the crest of the inlet part of the ventricular septum ŽFig. 1.. The left bundle branches are usually given off as discrete muscular fascicles over a broad extent of the common bundle and fan out over the left ventricular side of the ventricular septum ŽFig. 1b.. The right bundle branch, however, usually forms a continuation of the common bundle and passes obliquely, anteriorly, and
Tel.: q1-713-770-5600; fax: q1-713-770-5630.
1058-9813r99r$ - see front matter 䊚 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 1 0 5 8 - 9 8 1 3 Ž 9 9 . 0 0 0 2 8 - 4
154
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
inferiorly through the upper part of the ventricular septum toward the septal band w5,6x. AV canal defects are characterized by a deficiency in the inlet ventricular septum as well as a deficiency of the lower atrial septum. Because of these septal defects, the AV node is displaced posteriorly, lying in the posterodistal aspect of the atrial septum at its junction with the right atrial floor and is closely related to the coronary sinus and the attachments of the posterior bridging leaflet. It then penetrates the posterior part of the central fibrous body to become the penetrating portion of the His bundle. The bundle thus lies in the posterior rim of the defect on the crest of the inlet ventricular septum in the base of the connective tissue to which the posterior bridging
leaflet is attached ŽFig. 2. w7x. There is then a long non-penetrating non-branching bundle which courses along the inferior margin of the defect that is quite superficial as demonstrated in Fig. 2. The right bundle branch often arises from several separate fasciculi and its site of origin is near the crest of the septum w7,8x. The left bundle branch is displaced postero-inferiorly and has fewer anterior left bundle branches than in normal hearts w3,9x. The displacement of the left bundle branch and the hypoplasia of the anterior fascicle play an important role in the characteristic ECG pattern in these patients. AV canal defects are also commonly found in patients with heterotaxy syndrome, either with polysplenia or asplenia. When associated with L-
Fig. 1. The atrioventricular ŽAV. node and bundle branches as viewed from the right side of the heart Ža. and left side of the heart Žb.. RBB, right bundle branch.
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
ventricular looping, two AV nodes may be found. The two nodes are located anterior and posterior to the defect and are related to the anterior and posterior components of the central fibrous body. Many times the distal components of the anterior and posterior bundles can join to form a sling w10,11x. It was initially thought that the distinctive ECG pattern in patients with AV canal defects was due to hemodynamic abnormalities. However, further research demonstrated that the ECG was caused by displacement of the conduction system andror underdevelopment of the anterior left bundle branches, though this remained controversial for a number of years w1᎐4,12,13x. The characteristic features of the ECG in patients with partial or complete forms of AV
155
canal defects include a prolonged PR interval, left axis deviation, an initial counterclockwise frontal plane loop, and criteria for right ventricular hypertrophy w1,2,4,14᎐16x ŽFig. 3.. The prolonged PR interval is caused by prolonged internodal conduction time and not due to an abnormality in the AV node or His᎐Purkinje system w15,16x. Left axis deviation with an initial counterclockwise frontal plane loop beyond y60⬚ is diagnostic for left anterior hemiblock ŽLAH.. The mechanism by which LAH is generated in AV canal defects is not agreed upon and may be caused by one or a combination of the following: Ž1. mechanical elongation and stretching of the anterior division of the left bundle branch ŽLBB. caused by the posterior displacement of the conduction system which
Fig. 2. The AV node and bundle branches in AV canal defect as viewed from the right side of the heart Ža. and the left side of the heart Žb.. Part of the AV valves have been removed. RBB, right bundle branch.
156
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
would affect the anterior division more than the posterior division because of the more distal takeoff of the former; Ž2. anomalous development of the anterior division of the LBB; and Ž3. interruption of the anterior division by anomalous insertion of mitral chordae tendinae w1,3,13,17,18x. In the normal heart, the anterior᎐superior and the posterior᎐inferior portions of the left ventricle are depolarized simultaneously by their respective fascicles. Block in the anterior division, either caused by abnormal development or position, changes the sequence of depolarization. The inferior regions are activated normally, but the depolarization wavefront must then spread superiorly producing a superiorly directed vector in the frontal plane w18x. Further investigation of the endocardial and epicardial activation in patients with AV canal defects confirmed that the ECG abnormalities were caused by the abnormal conduction system and not by altered hemodynamics w12x. In patients with partial AV canal defects, the initial QRS vector forces are usually directed inferiorly and to the right and the QRS loop moves counterclockwise superiorly and to the left. The mean QRS axis ranges from y30⬚ to y120⬚ with most lying between y30⬚ and ᎐90⬚. Evidence of right ventricular volume overload manifest by an rsR’ or RSR’ in the right precordial leads is seen in 84% of patients w1x. Slightly more than half of the patients Ž54%. will have some evidence of atrial enlargement w14,19x. Approximately 70% have a q wave in V6 in contrast to only 35% of patients with a secundum atrial septal defect w1x. In patients with complete AV canal defects,
the QRS vector is initially directed inferiorly and moves in a counterclockwise direction with the main loop lying superiorly and to the right in 70% and to the left in 23%. The QRS axis ranges from y60⬚ to y135⬚ but is usually between y90⬚ and y120⬚, which is more leftward than that found in partial AV canals w19x. Again, greater than 50% of patients have evidence of atrial enlargement and two-thirds have an rsR’, RSR’, or rR’ in V1 with the remainder a qR or R wave consistent with right ventricular hypertrophy w14x. Additional factors believed to influence the appearance of the ECG include: the size of the atrial and the ventricular septal defects, mitral and tricuspid regurgitation, pulmonary vascular resistance, and associated defects w1,16x. These factors can affect the degree of axis deviation, atrial enlargement, and ventricular hypertrophy. While the above electrocardiographic abnormalities can occasionally be found in isolated ventricular septal defects, the combination of left axis deviation and a counterclockwise frontal plane loop are believed to be almost diagnostic of an AV canal defect w1,2x.
3. Arrhythmias in patients with AV canal defects The arrhythmias found in patients with AV canal defects have little to do with the displaced conduction system other than its susceptibility to surgically acquired injury when the ventricular component is repaired. As these patients usually undergo surgery in the first decade of life, arrhythmias are not common
Fig. 3. A 15-lead electrocardiogram in a 1-month-old infant with a complete AV canal. Note the left axis deviation, counterclockwise frontal plane loop and right atrial enlargement.
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
157
Fig. 4. A rhythm strip in an infant following an ASD and VSD repair with atrial tachycardia with variable AV conduction. Leads I, II and III are displayed in both Ža. and Žb.. In Žb., however, the right arm and left arm electrocardiogram leads are attached to the temporary atrial wires. One can now clearly see the atrial activity in lead I and both atrial and ventricular activity in leads II and III.
preoperatively. A natural history study of patients with the partial form of AV canal defects found that there was a distinct increase in the incidence of arrhythmias in unoperated patients after age 30 w20x. Arrhythmias, most commonly atrial fibrillation, occurred in 20% of patients and were frequently associated with clinical deterioration. Acquired complete AV block was common in those patients who deteriorated and occurred as early as 18 years w20x. Acquired complete AV block has also been reported in an 11-year-old with a complete AV canal defect w21x. There is very little documentation of early and late postoperative arrhythmias in this patient population. These patients are susceptible to any arrhythmia that is encountered following either atrial or ventricular surgery. Among the most common postoperative arrhythmias are atrial tachycardia and surgical AV block. A ventriculotomy is not required to repair the ventricular component and therefore ventricular tachycardia is uncommon in the author’s experience.
Atrial tachycardia can be found following any type of atrial surgery. It can be caused by either microreentry in the atrium or to an ectopic focus. Atrial rates range from 160 to 260 b.p.m. with variable AV conduction and, in many instances, the tachycardia is non-sustained. It is usually characterized by a ‘warm up,’ or a progressive shortening of the PP interval, and a ‘cool down,’ or lengthening of the PP interval prior to termination of the tachycardia. This arrhythmia is typically found in the first 1 or 2 days postoperatively and, initially, may be well-tolerated w22x. Use of direct ECG recording using temporary atrial pacing wires can be very useful in diagnosing this arrhythmia ŽFig. 4.. First-line therapy consists of intravenous procainamide and if the arrhythmia persists beyond the early postoperative period, D,L-sotalol or amiodarone may be used for 6 months to 1 year postoperatively. AV canal repair has been identified as one of four types of surgery commonly associated with postopera-
158
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159
tive surgical AV block w23,24x. Postoperative complete AV block has been reported to occur in 0᎐3.5% of patients w24᎐27x. There have been no instances of permanent surgical complete AV block in the last 64 AV canal repairs at our institution. Smaller patient size has also been shown to be an independent predictor of the incidence of AV block following surgery w28x. Both Weindling et al. and Kertesz et al. found that approximately 50% of surgical AV block resolves within the first 8 postoperative days w28,29x. Because of the high mortality reported in patients with surgical complete AV block w24,30x, it is categorized as a Class I indication in the AHArACC guidelines for implantation of permanent pacemakers w31x. Thus in the presence of complete surgical AV block 8 days postoperatively, a pacemaker is indicated. If there is any evidence of AV conduction prior to the 8th postoperative day it is prudent to wait up to 2 weeks for sinus rhythm to return. We believe that patients must return to sinus rhythm in order to avoid pacemaker placement.
4. Conclusion Defects in the AV canal result in displacement of the conduction system and abnormal development of the left bundle branch w8x. This displacement and abnormal development result in a characteristic ECG that is very useful as a diagnostic modality. Arrhythmias in this patient population are not common and are similar to those found following repair of atrial and ventricular septal defects. References w1x Burchell HB, DuShane JW, Brandenburg RO. The electrocardiogram of patients with atrioventricular cushion defects Ždefects of the atrioventricular canal.. Am J Cardiol 1960;6: 575᎐588. w2x Toscano-Barbosa E, Brandenberg HO, Burchell HB. Electrocardiographic studies of cases with intracardiac malformations of atrioventricular canal. Proc Staff Meet Mayo Clin 1956;31:513᎐523. w3x Feldt RH, DuShane JW, Titus JL. The atrioventricular conduction system in persistent common atrioventricular canal defect: correlations with electrocardiogram. Circulation 1970; 42:437᎐444. w4x Durrer D, Roos JP, van Dam RTh. The genesis of the electrocardiogram of patients with ostium primum defects Žventral atrial septal defects.. Am Heart J 1966;71:642᎐650. w5x Titus JL, Daugherty GW, Edwards JE. Anatomy of the atrioventricular conduction system in ventricular septal defect. Circulation 1963;28:72᎐81. w6x Kurosawa H, Becker AE. Atrioventricular conduction in congenital heart disease. Tokyo: Springer-Verlag, 1987:1᎐14. w7x Kurosawa H, Becker AE. Atrioventricular conduction in congenital heart disease. Tokyo: Springer-Verlag, 1987:87᎐96.
w8x Lev M. The architecture of the conduction system in congenital heart disease: I. Common atrioventricular orifice. Arch Pathol 1958;65:174᎐190. w9x Vick GW. Defects of the atrial septum including atrioventricular septal defects. In: Garson Jnr A, Bricker JT, Fisher DJ, Neish SR, editors. The science and practice of pediatric cardiology. Baltimore: Williams and Wilkins, 1998:1141᎐1179. w10x Ih S, Fukuda K, Okada R, Saitoh S. The location and course of the atrioventricular conduction system in common atrioventricular orifice and in its related anomalies with transposition of the great arteries: a histopathological study of six cases. Jpn Circ J 1983;47:1262᎐1273. w11x Bharati S, Lev M. The course of the conduction system in dextrocardia. Circulation 1978;57:163᎐171. w12x Campbell RM, Dick II M, Hess P, Behrendt DM. Epicardial and endocardial activation in patients with endocardial cushion defect. Am J Cardiol 1983;51:277᎐281. w13x Rosenbaum MB, Elizari MV, Lazzari JO. The hemiblocks: new concepts of intraventricular conduction based on human anatomical, physiological and clinical studies. Florida: Tampa Tracings, 1970:134. w14x Feldt RH, Porter CJ, Edwards WD, Puga FJ, Seward JB. Atrioventricular septal defects. In: Emmanouilides GC, Riemenschneider TA, Allen HD, Gutgesell HP, editors. Moss and Adams’ heart disease in infants, children, and adolescents: including the fetus and young adult. 5th ed. Baltimore: Williams and Wilkins, 1995:704᎐723. w15x Waldo AL, Kaiser GA, Bowman FO, Malm JR. Etiology of prolongation of the P-R interval in patients with an endocardial cushion defect: further observations on internodal conduction and the polarity of the retrograde P wave. Circulation 1973;43:19᎐26. w16x Perloff JK. The clinical recognition of congenital heart disease. Philadelphia, PA: W.B. Saunders Company, 1978: 357᎐360. w17x Boineau JP, Moore EN, Patterson DF. Relationship between the ECG, ventricular activation, and the ventricular conduction system in ostium primum ASD. Circulation 1973; 48:556᎐564. w18x Walsh EP. Electrocardiography and introduction to electrophysiologic techniques. In: Fyler DC, editor. Nadas’ pediatric cardiology. Philadelphia: Hanley and Belfus, 1992:117᎐158. w19x Ongley PA, Pongpanich B, Spangler JG, Feldt RH. The electrocardiogram in atrioventricular canal. In: Feldt RH, McGoon DC, Ongley PA, Rastelli GC, Titus JL, Van Mierop LHS, editors. Atrioventricular canal defects. Philadelphia: W.B. Saunders, 1976:51᎐75. w20x Somerville J. Ostium primum defect: factors causing deterioration in the natural history. Br Heart J 1965;27:413᎐419. w21x Mehta AV, O’Riordan AC, Sanchez GR, Black IFS. Acquired nonsurgical complete atrioventricular block in a child with endocardial cushion defect. Clin Cardiol 1982;5:603᎐605. w22x Perry JC, Garson Jr. A. Arrhythmias following surgery for congenital heart disease. In: Zipes DP, Jalife J, editors. Cardiac electrophysiology: from cell to bedside. 2nd ed. Philadelphia: W.B. Saunders, 1995:838᎐847. w23x Kertesz NJ, McQuinn T, Collins E, Friedman R. Surgical atrioventricular block in 888 congenital heart operations: new implications for early implantation of a permanent pacemaker. PACE 1996;19:613. w24x Fryda RJ, Kaplan S, Helmsworth JA. Postoperative complete heart block in children. Br Heart J 1971;33:456᎐462. w25x Uretzky G, Puga FJ, Danielson GK et al. Complete atrioventricular canal associated with tetrology of fallot: morphologic and surgical considerations. J Thorac Cardiovasc Surg 1984; 87:756᎐766.
N.J. Kertesz r Progress in Pediatric Cardiology 10 (1999) 153᎐159 w26x Backer CL, Mavroudis C, Alboliras ET, Zales VR. Repair of complete atrioventricular canal defects: results with the twopatch technique. Ann Thorac Surg 1995;60:530᎐537. w27x Studer M, Blackstone EH, Kirklin JW. Determinants of early and late results of repair of atrioventricular septal Žcanal. defects. J Thorac Cardiovasc Surg 1982;84:523᎐542. w28x Kertesz NJ, McQuinn T, Collins E, Friedman RA. Neonatal congenital heart surgery increases the risk of acquired atrioventricular block: implications for early elective repair. J Am Coll Cardiol 1997;29:357A. w29x Weindling SN, Saul JP, Gamble WJ, Mayer Jr. JE, Walsh EP.
159
Duration of complete heart block after congenital heart disease surgery. J Am Coll Cardiol 1994;23:104A. w30x Lillihei CW, Sellers RD, Bonnaneau RC et al. Chronic postsurgical complete heart block. J Thorac Cardiovasc Surg 1973;46:436᎐456. w31x Gregoratos G, Cheitlin MD, Conill A et al. The 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;31:1175᎐1209.