Author + information
- Received January 7, 1998
- Revision received April 1, 1998
- Accepted May 13, 1998
- Published online September 1, 1998.
- Mei-Hwan Wu, MD, PhD∗,* (, )
- Jou-Kou Wang, MD, PhD∗,
- Jiunn-Lee Lin, MD, PhD†,
- Ling-Ping Lai, MD†,
- Hung-Chi Lue, MD, FACC∗,
- Ming-Lon Young, MD, FACC∗ and
- Fon-Jou Hsieh, MD‡
- ↵*Address for correspondence: Dr. Mei-Hwan Wu, Department of Pediatrics, National Taiwan University Hospital, No. 7 Chung-Shan South Road, Taipei, Taiwan, 100
Objectives. To clarify the prevalence and mechanism of supraventricular tachycardia in patients with right atrial isomerism.
Background. Paired SA and dual atrioventricular (AV) nodes have been described in patients with right atrial isomerism. However, the clinical significance remains unclear.
Methods. From 1987 to 1996, a total of 101 patients (61 male, 40 female) and four fetuses were identified with right atrial isomerism. The diagnosis of supraventricular tachycardia exclude the tachycardia with prolonged QRS duration or AV dissociation, and primary atrial tachycardia.
Results. The median follow-up duration was 38 months (range 0.2–270 months). Supraventricular tachycardia was documented in 25 patients (24.8%) and one fetus (25%) (onset age ranged from prenatal to 14 years old; median 4 years old). Actuarial Kaplan-Meier analysis revealed that the probability of being free from tachycardia was 67% and 50% at 6 and 10 years of age, respectively. These tachycardias could be converted by vagal maneuvers in one, verapamil in seven, propranolol in four, digoxin in two, procainamide in one, and rapid pacing in five. Spontaneous conversion was noted in six (including the fetus). Seven cases had received electrophysiological studies. Reciprocating AV tachycardia could be induced in five and echo beats in one. The tachycardia in three patients was documented as incorporating a posterior AV node (antegrade) and an anterior or a lateral AV node (retrograde). Two of them received radiofrequency ablation. Successful ablation in both was obtained by delivering energy during tachycardia, aimed at the earliest retrograde atrial activity and accompanied by junctional ectopic rhythm. The patient with echo beats developed tachycardia soon after operation.
Conclusions. Supraventricular tachycardia is common in patients with right atrial isomerism and can occur during the prenatal stage. Drugs to slow conduction through the AV node may help to terminate the tachycardia. Radiofrequency ablation is a safe and effective treatment alternative to eliminate tachycardia.
Heterotaxy is a rare congenital disorder characterized by abnormal visceroatrial situs with either right atrial isomerism (RAI) or left atrial isomerism (LAI). It is usually associated with complex cyanotic congenital heart disease (1). The conduction system is characterized by paired sinus node and paired atrioventricular (AV) nodes. The AV nodes are connected by a sling of conduction tissue (2,3). Such paired AV nodes, as shown in our previous study, can cause AV reentrant tachycardia (4). However, prior studies on rhythm disturbances of the patients with atrial isomerism have only emphasized the prevalence of AV conduction block in LAI patients (5,6). The major rhythm disturbances of RAI patients and the clinical significance of paired AV nodal system remain undefined (4,7). This can be related to a relatively lower incidence of RAI as compared with that of LAI (8–10). Furthermore, the severity of cardiac defects as well as the compromised splenic function of RAI patients may predispose them to an early death (6). Patient lifespan may be too short to observe the development of arrhythmias. Recently, advances in surgical palliations for such complex lesions have improved such patients’ long-term prognosis (10,11). Therefore, it is imperative and feasible to define the clinical significance of such unique conduction system in RAI patients. This longitudinal study on 101 RAI patients and four fetuses has demonstrated a high incidence of supraventricular tachycardia (SVT), which is caused most likely by a reentry between the paired AV nodes.
From January 1987 to December 1996, a total of 9,230 pediatric patients were diagnosed to have congenital heart disease at this institution. Among them, 114 patients were identified to have heterotaxy syndrome. From January 1995 to December 1996, fetal echocardiography had been performed in 326 fetuses, and disclosed heterotaxy syndrome in seven cases. Among them, 101 pediatric patients (61 male and 40 female) and four fetuses were RAI and constituted the study population. The diagnosis of RAI was based on a combination of echocardiography, cardiac catheterization/angiography, and available magnetic resonance imaging or computerized tomography (12–15). Open heart surgery or autopsy in 34 patients confirmed the diagnosis. Patients with RAI have: 1) bilateral pyramidal atrial appendages, 2) ipsilateral descending aorta and inferior vena cava at the level of T10, or 3) bilateral hypobronchial pulmonary arteries. The diagnosis of SVT was based on the electrocardiogram findings of narrow QRS tachycardia, and excluded: 1) the tachycardia with prolonged QRS duration 2) the tachycardia with AV dissociation, and 3) primary atrial tachycardia (including ectopic atrial tachycardia, atrial flutter, and chaotic atrial rhythm). The diagnosis of SVT in fetus was based on fetal echocardiography.
Data were expressed as mean ± SD. Actuarial event-free curves were drawn according to the nonparametric estimation by Kaplan and Meier (16). Chi-square test was used to examine the significance when appropriate.
Three of the four fetuses were ended with termination before the gestational age of 24 wk. Excluding the three fetuses, age of the patients at the last follow-up ranged from 0.2 to 270 months (44 ± 56 months; median 38 months). The associated cardiac anomalies were summarized in Table 1. Palliative interventions had been performed in 65 patients (Table 2). The actuarial analysis of survival in patients without palliative interventions (which of course may be not justified for the patients or may have been refused by the family) revealed a 2-year survival of 59% (Fig. 1A). Postoperative follow-up revealed a 2-year survival for patients after palliation or total correction (total cavopulmonary connection or Rastelli operation) is 62% and 31%, respectively (Fig. 1B and 1C).
Sinus rhythm was noted in all at initial presentation. None of the patients had AV block. The normal sinus rhythm of three patients was found to have two types of QRS morphology. Supraventricular tachycardia was documented in one fetus (25%) and 25 patients (24.8%, 15 male, 10 female): clinical SVT in 20 and induced by programmed pacing in five. The relation between ventricular morphological features and SVT occurrence was analyzed. Patients with two ventricles were more likely to develop SVT than those with univentricular heart (0.01 < p < 0.05), whereas the type of ventricular loop, the position of cardiac apex, and the type of univentricular heart were not significant predictors for the SVT occurrence.
Precipitating factors for SVT included: cardiac catheterization in four cases, blue spells in three, and surgery in seven. Five of these seven patients had SVT attacks within 3 days after the total cavopulmonary connection operation or AV valve replacement: four were the first SVT attacks and one has preoperative SVT. Two of the seven patients had SVT the day after shunt operation. The incidence of SVT after open heart surgery (total cavopulmonary connection or AV valve replacement) and shunt operation was five of 20 (25%) and two of 30 (7%), respectively.
The ages at initial SVT attack in each patient are summarized in Figure 2A. Median age of initial SVT episodes was 4 years (onset age ranged from prenatal to 14 years old). Since the survival of RAI patients decreased with age, actuarial Kaplan-Meier analysis was obtained to predict the probability of being SVT-free at different ages. The probability of being free from tachycardia decreased with age and reached 67% and 50% at 6 and 10 years of age, respectively (Fig. 2B). Electrocardiograms during the attacks showed narrow QRS tachycardia with a heart rate varying from 150 to 240/min (186 ± 27/min). The QRS morphology was similar to that of sinus rhythm. In three patients with retrograde P wave documented during SVT, the PR interval was longer than the RP interval (Fig. 3). These tachycardias could be converted by vagal maneuvers in one, verapamil in seven, propranolol in four (two of them also responded to verapamil), digoxin in two, procainamide in one, ATP in one, and programmed pacing in five. Spontaneous conversion was noted in six (including the fetus). None of the patients died directly from SVT. The relationship between postoperative SVT and early surgical mortality is summarized in Table 3. Although patients with postoperative SVT after total cavopulmonary connection tended to have a higher mortality than those without, the difference was not significant.
Electrophysiological study and ablation
Electrophysiological study was performed in seven under propofol anesthesia, but the study was limited by severe cyanosis and hypotension during SVT in two. The sinus node function, assessed by the maximal sinus recovery time, and the atrial and ventricular refractory periods, were all within normal limits. The AV conduction is summarized in Table 4. Two types of narrow QRS morphology during normal sinus rhythm and normal PR interval could be demonstrated in four patients (Fig. 4). The Wenchebach cycle length and the refractory period of the antegrade AV conduction were normal for the patients’ age. Two patterns of retrograde atrial activation sequence during RV pacing or SVT, both with a decremental conduction pattern, were found in one case. Retrograde VA conduction was not documented in one patient, in whom no SVT could be induced. By atrial or ventricular programmed pacing, narrow QRS tachycardia could be induced in five patients and echo beats only (after atropine) in one. RV extrastimulation during the His refractory period could not advance the atrial activity of SVT, but more premature RV pacing or RA pacing could reset the tachycardia. In three patients, the SVT was mapped antegradely through a posterior AV node and retrogradely through an anterior (two cases) or left lateral VA pathways (one case) with decremental conduction property. Radiofrequency ablation was applied during SVT in two patients to the AV groove where the earliest retrograde atrial activity was recorded. At the successful site, the SVT stopped and was followed by transient junctional ectopic tachycardia (Fig. 5). At the end of study, no tachycardia could be induced by programmed pacing. Because of the risk of aggravating preexisting severe infundibular stenosis, isoproterenol was not used during the study in five patients.
Of the seven patients who had received electrophysiological study, five received subsequent total cavopulmonary connection and one was given a systemic-to-pulmonary shunt. No SVT recurrences were noted in the two patients with ablation. However, one died of severe right heart failure 4 days postoperatively. One patient with SVT who did not receive ablation experienced SVT recurrences soon after the operation. He died of sepsis 2 weeks after surgery. The patient who had echo beats only during the study developed SVT attacks on the first postoperative day, and the SVT was controlled by digoxin. One patient with SVT received a shunt operation and had no further SVT attacks. One patient with SVT refused operation and was lost to follow-up. The patient who had only unidirectional antegrade AV conduction underwent a total cavopulmonary connection with an uneventful course.
Right atrial isomerism is commonly associated with complex congenital heart disease and a paired conduction system (1–3). This present study demonstrated a high incidence (24.8%) of SVT in RAI patients, even during fetal life. The SVT may be attributed to a reentrant tachycardia between the paired AV nodes. A term, AV nodal–to–AV nodal tachycardia is proposed as characteristic of the electrophysiological mechanism.
Clinical significance of paired conduction system
The conduction system in RAI patients as described by Dickinson et al (2,3)has two AV nodes; the posterior node was constant in position and related to tendon of Tordaro. A sling of conducting tissue, commonly connected to both nodes, could be identified either on the inferior rim of the ventricular septal defect or on a prominent trabeculation within the ventricular chamber of the univentricular hearts. The paired AV nodes, possibly along with the conduction sling, might consequently constitute a potential anatomical substrate for reentrant tachycardia. However, previous reports that describe the AV block in LAI patients have rarely mentioned the occurrence of SVT in RAI patients (4–7). This may be related to a relatively more severe heart disease and a lower incidence of RAI as compared with those of LAI (17). However, we have observed a much higher incidence of RAI than LAI patients in the postnatal stage. During the study period, the ratio of RAI to LAI patients was 4 to 3 for the fetus and 101 to 13 for the children, respectively. Racial differences have been clearly shown in the prevalence of various types of congenital heart disease (18,19). Therefore, the different distribution of the heterotaxy syndrome between RAI and LAI patients of this series can be explained, at least in part, by racial differences.
The paired AV nodal system in RAI patients, as shown in this study, may be closely associated with SVT occurrence. The incidence of SVT in RAI, in both fetus and pediatric patients, is about one-fourth, only next to that of Ebstein’s anomaly among various types of congenital heart disease (20,21). By Kaplan-Meier analysis, the probability of being SVT-free decreased with age. By the age of 10 years, about half of the patients might have experienced SVT attacks. Therefore, if more and more of the RAI patients can be rescued by palliative interventions, diagnosis and treatment of the SVT will be one of the major medical issues for RAI patients.
As to the morphological features of RAI patients, we found that only the two-ventricle morphology was associated with the SVT occurrence. It has been shown that the location of the second AV node in RAI patient with two ventricles was different from that in patients with a univentricular heart (1,2). However, the location of the second AV node identified in our cases with two ventricles varied. Therefore, the location of the second AV nodes itself may not be an important determinant for SVT occurrence.
The electrophysiological data of the seven RAI patients of this study revealed that in over half of the RAI patients the electrocardiograms during normal sinus rhythm had two types of QRS morphology without bundle branch block or preexcitation. Both antegrade AV conduction pathways revealed a decremental conduction pattern. In the normal heart, the AV node is characterized by decremental conduction behavior. Although such behavior can also be demonstrated in Mahaim fibers, the findings of normal PR interval and narrow QRS morphology support the diagnosis that either antegrade conduction was through one of the paired AV nodes.
Retrograde conduction through one or both AV pathways in a decremental manner was also shown in most of the cases. In all except two patients, SVT could be induced. A reentry mechanism is suggested by the findings of: 1) pacing induction/termination of SVT, and 2) resetting of the SVT by extrastimulation from RA or RV. RV pacing during His refractory period failed to advance the atrial activity of the SVT. By retrograde atrial activation sequence, the earliest atrial activation was away from the AV node with antegrade conduction. Furthermore, this retrograde VA pathway was found to have decremental conduction property. Radiofrequency ablation at this VA retrograde pathway terminated the SVT, and was accompanied by transient junctional ectopic tachycardia. The occurrence of junctional tachycardia is a well-known phenomenon for radiofrequency ablation of the slow or fast pathway of AV node. Therefore, based on these findings, we suggest that RAI patients who have paired AV nodes are prone to develop SVT. During SVT, the antegrade AV conduction was through one AV node (most likely the posterior one) and conducted probably via the conduction sling to the other AV node. The His potential may represent part of the activation of the conduction sling. Hence, RV extrastimulation during the His refractory period would fail to penetrate the conduction sling to alter the retrograde VA activation sequence.
Because the SVT in RAI patients is thought to be an “AV nodal–to–AV nodal reentrant tachycardia,” drugs to slow the AV conduction may help to terminate the SVT. Patients have responded to vagal maneuver, digoxin, propranolol, verapamil, or ATP. The effects of these treatment are mainly to slow the AV conduction and terminate the SVT. These clinical responses support proposed electrophysiological mechanism of SVT in RAI patients.
The natural history of RAI patients is death for more than one-third of the untreated patients within the first week of life. One-year survival was only 21% in the Rose series (6), and 2-year survival was 59% in the series of untreated patients here. Cardiac failure, anoxia, and infection were the predominant causes of death. Some patients, either with or without palliation, may have balanced hemodynamics and grow up to the age for further palliation. Total cavopulmonary connection with rerouting of the anomalous pulmonary veins is usually needed. Maintaining normal sinus rhythm is crucial for such RV bypass circulation. The incidence of SVT after total cavopulmonary connection was 25%. Preoperative radiofrequency ablation in the two patients prevented perioperative SVT. The patient who during electrophysiological study had only echo beats even after atropine had SVT soon after the operation. The relatively lower incidence of SVT in RAI patients after shunt operation, 7%, may be related to the youthful age at shunt operation and the nature of the operation. Patients who developed SVT after shunt operation could be successfully treated by intravenous propranolol or DC conversion and not have associated poor outcome. Therefore, the preoperative treatment of arrhythmia in RAI patients is indicated for those before total cavopulmonary connection or those who had clinical SVT.
In conclusion, RAI patients are prone to develop SVT, which is most likely a reentrant tachycardia between the paired AV nodes. The probability of being free from SVT decreases with age, and the SVT attacks may compromise the borderline hemodynamics of the underlying complex congenital heart disease. Therefore, electrophysiological study and radiofrequency ablation should be carried out in RAI patients before the total cavopulmonary connection or when they have clinical SVT. Because both of the AV nodes may have retrograde VA conduction, radiofrequency ablation should be applied during SVT attacks and aim for the earliest retrograde atrial activity. Successful ablation may be associated with the development of transient junctional ectopic tachycardia.
☆ This study has been supported by a grant from the Cardiac Children Foundation, R.O.C. (CCF 97-020).
- left atrial isomerism
- right atrial isomerism
- supraventricular tachycardia
- Received January 7, 1998.
- Revision received April 1, 1998.
- Accepted May 13, 1998.
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