Intra-Atrial Reentrant Tachycardia in the Fontan Population

Ian H Law^a, David J Bradley^b, Peter S. Fischbach^c, Elizabeth V. Saarel^c, Caren Goldberg^c,
Edward L. Bove^c, and Dick Macdonald II^c

^aChildren’s Hospital of Iowa, University of Iowa of Hospial and Clincs, Iowa City, IA, USA
^bPrimary Children’s Medical Center, University of Utah School of Medicine, Salt Lake City, UT, USA
^cMichigan Congenital Heart Center, University of Michigan, Ann Arbor, MI, USA

Correspondence: IH Law, Children’s Hopsital of Iowa, University of Iowa Hospital and Clinics, 200 Hawkins Drive, Iowa City,
IA 52242-1083, USA. E-mail: ian-law@uiowa.edu, phone (319) 356-4697, fax (319) 356-4693

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Methods. This randomized, blinded, controlled, prospective study investigated whether a strategic incision (between the lateral tunnel baffle and tricuspid valve annulus) placed during the Fontan operation (test group, T) would reduce the incidence of post-operative IART. Diagnoses, patient demographics, echocardiographic, catheterization, electrophysiologic and follow-up data were recorded. Electrophysiology studies (EPS) were performed pre- and post-Fontan (when possible). IART induction protocol included programed extrastimulation and rapid atrial pacing, with and without isoproterenol.

Results. 105 patients (T = 53) have enrolled and completed Fontan palliation (median age = 1.8 yrs, range: 1.2-5.2). No significant difference in hemodynamic status (echocardiogram, heart cathetrization) existed between T and control group (C) pre- or post-Fontan palliation. 24 of 73 patients (33%) had inducible sustained (> 1 minute) IART (S-IART) pre-Fontan. 15 of 100 patients (15%) had S-IART post-Fontan. 50 patients underwent both pre- and post-Fontan EPS, there was no significant difference between T and C in electrophysiology parameters, pre-Fontan S-IART (T 24% v C 42%, p = 0.11) or post-Fontan S-IART (T 16% v C 14%, p = 0.78). To date only 3 patients have developed clinical IART, T = 1, C = 2.

Conclusion. A strategic incision at the time of Fontan does not affect conduction properties but does not appear to reduce inducibilty of inducible S-IART. Longer follow-up will be required to determine if clinical IART can be reduced with a strategic incision.

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1.  Introduction

Intra-atrial reentrant tachycardia is a well-recognized sequelae of the Fontan operation. The incidence of both early and late intra-atrial reentrant tachycardia is 10-40%, and can significantly compromise the univentricular repair [Garson et al., 1985; Gewillig et al., 1992; Balaji et al., 1994] In spite of several modifications of the Fontan operation [Balaji et al., 1991], intra-atrial reentrant tachycardia has persisted [Cecchin et al., 1995; Kurer et al., 1991; Gelatt et al., 1994; Pearl et al., 1991]. Data from canine models suggest that the suture line of the lateral cavopulmonary connection and the natural anatomical right atrial boundaries (vena cava orifices, coronary sinus orifice, and possibly the crista terminalis) can serve as barriers creating a pathway which, along with changes in intra-atrial conduction, provide the substrate for an intra-atrial reentrant tachycardia. [Rodefeld et al., 1996]. Recent studies in humans using new atrial mapping techniques have verified these reentrant circuits around surgical incisions [Gelatt et al., 1994; Triedman et al., 1997]. Clinical studies have demonstrated that ablative lesions delivered by the transcatheter technique and generated by radiofrequency can abolish reentrant pathways supporting human atrial flutter, a common form of intra-atrial reentry tachycardia [Baker et al., 1996].

The purpose of this study is to investigate if a strategically placed linear incision, incorporated at the completion of the lateral Fontan, will prevent the postoperative intra-atrial reentrant tachycardia.

2.  Methods

This study used a controlled, randomized, blinded, prospective design in which candidate patients received either the conventional lateral tunnel atriopulmonary (LT-APC) connection Fontan operation (control group, C), or a LT-APC Fontan operation with a strategic surgical incision (test group, T) placed between the lateral tunnel baffle and the tricuspid valve annulus. The endpoints are: 1) a lower incidence of inducible intra-atrial reentrant tachycardia in T compared to the C during the immediate post operative period (prior to hospital discharge), 2) a lower incidence of inducible intra-atrial reentrant tachycardia in T compared to C at time of fenestration closure (6-12 months after surgery), and 3) a lower incidence of clinical IART in T compared to C during a five year follow-up period.

2.1. Patient Population

Patients with univentricular who were scheduled for the LT-APC Fontan operation were approached for participation. An IRB approved informed consent was obtained. The patients were randomized during the surgery. Patients were excluded if they were deemed “high risk” (elevated pulmonary artery pressure, elevated pulmonary arteriolar resistance) as determined by pre-Fontan heart catheterization or if during the surgery the surgeon felt placing the strategic incision would jeopardize the patient.

2.2. Operative Procedure

Figure 1. Illustration of the strategic incision LT/APC Fontan with atriopulmonary connection showing strategic incision connecting combined atriotomy incision/baffle structure line to the tricuspid valve annulus. SVC = superior vena cava.

The incision adjoined the lateral tunnel suture line and the tricuspid valve annulus, incorporating the caudal tip of the atriotomy incision (see figure 1). The lesion avoided the triangle of Koch. The patients in both the T and C groups had temporary transthoracic epicardial pacing wires placed on the “right atrium” at the conclusion of the repair.

2.3. Data Collection

The patients received standard post-operative monitoring and care. Arrhythmias in the post-operative course were treated in a standard manner as determined by the attending physicians/surgeons. The medical records were abstracted each day to capture pertinent outcome data regarding postoperative arrhythmias.

2.4. Electrophysiology Study Protocol

A quadrapolar 5 or 6 French electrode catheter was used during pre-Fontan EPS. Transthoracic atrial and ventricular epicardial leads were used for the postoperative electrophysiologic studies. Sinus node function was examined using extrastimulation coupled to sinus rhythm. Attempts at induction of IART were carried out by both atrial burst pacing (10-20 sec) at decreasing cycle lengths of 600 to 200 ms in 10-50 ms decrement and programmed extrastimulation with up to two extrastimuli given coupled to sinus rhythm or paced eight beat drive (600, 500 or 400 msec). If IART was not inducible, an intravenous isoproterenol infusion was given up to a maximum of 0.1 mcg/kg/min to increase the resting heart rate to 120-130 bpm, or 20-25% above the resting rate. If IART was induced it was interrupted by overdrive pacing, or if hemodynamically unstable (>20 mmHg decrease in blood pressure), by DC cardioversion.

2.5. Long Term Follow-Up

Long-term follow-up included an every 6 - 12 month history of signs/symptoms of arrhythmia along with pertinent demographic and clinical data, including but not restricted to, cardiac active medications, and annual 24-hour Holter recordings during five-year follow-up.

2.6. Statistical Analysis

A Students t-test was used to examine the continuous data (age, weight, height, anatomic type, electrophysiology data). A Wilcoxon Rank sum test was used to analyze non-normally distributed data. A chi-squared test was used to examine the categorical data (inducibility and incidence of IART). A multivariate analysis of the variables was performed to assess relative weight of these variables. A p- value of 0.05 was taken to denote statistical significance.

3.  Results

Enrollment started in March, 1998. To date 105 patients (F = 35) have undergone LT/APC Fontan and were randomized to T (n = 53) or C group (n = 52). Diagnoses included: hypoplastic left heart syndrome (n = 73), pulmonary atresia with intact ventricular septum (n = 7), tricuspid atresia (n= 6), double inlet left ventricle (n = 7), unbalanced atrioventricular septal defect (n = 6), double outlet right ventricle (n = 5), Ebstein’s anomaly (n = 1). The T and C groups were not statistically different with regard to hemodynamic data (echocardiographic and heart catheterization) prior to or following Fontan operation. Similarly, the two groups did not differ statistically in operative and post-operative course except for a statistically longer circulatory arrest time in the study group ( 22.1 v 18.4 min, p = 0.04). 73 patients underwent a pre-Fontan EPS. 100 patients underwent post-Fontan EPS prior to post-surgical discharge home. 68 patients (SG, n = 37) underwent both a pre- and post-Fontan EPS. No significant difference was seen between the pre- or post-Fontan electrophysiology parameters between the two study groups. A summary of selected demographic, operative, hemodynamic and electrophysiology data is shown in Table 1.

Table 1.    Comparison table of test and control groups.

Parametric data expressed as mean ± st dev, non-parametric data expressed as median (min – max). PVR = pulmonary vascular resistance, PAP = pulmonary artery pressure, MCSNRT = maximum corrected sinus node recovery time, AERP = atrial effective refractory period, AVCERP = atrioventricular effective refractory period, TSACT = total sinoatrial conduction time, AV WB = atrioventricular Wenckebach cycle length, S-IART = sustained (> 1 minute) intra-atrial reentrant tachycardia

4.  Discussion

IART following the Fontan operation continues to compromise the palliated single ventricle population. Numerous treatment strategies have been attempted to address this problematic arrhythmia including antiarrhythmic medication (often requiring multiple mediations), radiofrequency ablation, and the surgical Maze procedure. While some success has been achieved, recurrence is not uncommon, and each therapy has associated risks. Given the prevalence of this arrhythmia and suboptimal treatment options, a strategy to prevent IART has obvious advantages.

Previous work in a canine model has verified the creation of an IART isthmus during the lateral tunnel Fontan, the anatomical boundaries being the lateral tunnel baffles suture line and the tricuspid valve annulus [Rodefeld et al., 1996]. Subsequent canine studies have shown that transection of this isthmus can prevent the inducibility of IART [Gandhi et al., 1996]. Mavroudis and colleagues have shown that surgical and cryothermal lesions incorporated into the conversion of a classic atriopulmonary connection Fontan to a lateral tunnel or external conduit Fontan can greatly reduce the recurrence of IART [Mavroudis et al., 2001]. In contrast to the Mavroudis experience, this study prospectively investigates the efficacy of incorporating a strategic incision (transversing a proposed critical isthmus) at the time of Fontan to prevent the development of IART.

This study confirms that the proposed surgical lesion does not adversely alter the post-operative course and does not have detrimental affects on the heart’s conduction system.

It is interesting to note that this study has shown that induciblity of IART prior to Fontan operation is similar to post-Fontan IART inducibility, previously reported by Kurer and colleagues [Kurer et al., 1991]. This would suggest that the substrate for inducible IART, and possible clinical IART, exists prior to Fontan completion. In this study the incidence of post-Fontan inducible S-IART was less in both the treatment and study groups, but this reduction, while less than that reported by Kurer, did not reach statistical significance.

Contrary to the canine studies, this study’s proposed strategic lesion does not significantly reduce the inducibility of S-IART following the Fontan operation. In addition, no other demographic, hemodynamic, or electrophysiologic parameters were found to be associated with post-Fontan inducible S-IART. While this finding is surprising, no previous studies have investigated the inducibility of IART in the post-operative, pre-discharge home Fontan population. Post-operative inflammatory changes resulting in alteration in the electrophysiologic properties of the atrial tissue may affect post-operative inducibility to a similar extent in both study groups. Inducible S-IART during subsequent EP studies, as planned in this investigation during fenestration closure, may be more predictive of clinical IART.

The more important question is whether the strategic incision will prevent clinical IART in these patients at high risk for IART. To address this question, longer follow-up will be necessary.

Acknowledgements

We would like to acknowledge our great appreciation of Karen King for managing the data.

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