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Ann Thorac Surg 2005;80:665-672
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Specific Issues After Extracardiac Fontan Operation: Ventricular Function, Growth Potential, Arrhythmia, and Thromboembolism

^a Department of Cardiothoracic and Vascular Surgery, Cardiothoracic Centre, All India Institute of Medical Sciences, New Delhi, India
^b Department of Cardiology, Cardiothoracic Centre, All India Institute of Medical Sciences, New Delhi, India
^c Department of Biostatistics, Cardiothoracic Centre, All India Institute of Medical Sciences, New Delhi, India
^d Department of Cardiac-Nuclear Medicine, Cardiothoracic Centre, All India Institute of Medical Sciences, New Delhi, India

Accepted for publication February 1, 2005.

^_* Address reprint requests to Dr Chowdhury, Department of Cardiothoracic and Vascular Surgery, All India Institute of Medical Sciences, Ansari Nagar, New Delhi-110029, India (Email: ujjwalchow{at}rediffmail.com).

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
BACKGROUND: The purpose of this study was to define the prevalence of specific sequelae after extracardiac Fontan operation.

METHODS: Sixty-five consecutive patients undergoing extracardiac Fontan operation were studied for mortality, Fontan failure, systemic ventricular function, supraventricular arrhythmias, thromboembolism, and growth potential. Age was 3 to 31 years (mean ± standard deviation, 9.4 ± 1.8; median, 7 years). The conduits were constructed of polytetrafluoroethylene (n = 50), and "viable" in situ pericardium (n = 15). The patients underwent serial echocardiogram, dynamic radionuclide studies, and cardiac catheterization.

RESULTS: Operative mortality was 3%, and the incidence of conduit thrombosis was 4.6%. There was paradoxic filling of the right lung after femoral injection of the radiotracer in all cases of conduit obstruction. Perioperative and late postoperative supraventricular arrhythmias were observed in 9.2% and 4.7% of patients, respectively. Risk factors for supraventricular arrhythmias included systemic ventricular dysfunction (p = 0.000), heterotaxy syndrome (p = 0.008), systemic venous anomalies (p = 0.015), and previous bidirectional Glenn operation (p = 0.017). At a mean follow-up of 77 ± 2 months (range, 8 to 79 months), there were no late deaths (actuarial survival at 79 months, 96.9% ± 0.02%). Serial echocardiograms demonstrated evidence of growth of the viable tunnels. Postoperatively, there was transient depression of ejection fraction in all patients (p = 0.000).

CONCLUSIONS: Supraventricular arrhythmias after extracardiac Fontan are more common in patients with heterotaxy syndrome, bilateral superior venae cavae, systemic ventricular dysfunction, and those undergoing completion Fontan operation. The viable tunnel may emerge as an optimal alternative by virtue of reduction of supraventricular arrhythmias, elimination of the need for anticoagulation, and addressing the issue of growth potential in selected patients.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Late morbidity and mortality after the Fontan operation are largely caused by systemic venous hypertension, systemic and pulmonary venous obstruction, systemic ventricular dysfunction, supraventricular arrhythmias, and thrombus formation [1–3]. These problems have been demonstrated for the atriopulmonary connections but remain to be defined for the lateral tunnel and extracardiac Fontan operation [1–3]. The presence of long intraatrial suture lines is thought to facilitate the development of slow reentry circuits and hence atrial flutter after the lateral tunnel Fontan operation [4]. The objectives of this retrospective study were (1) to determine the frequency of early and late supraventricular arrhythmias, (2) to identify the risk factors for the same, (3) to evaluate the effect on systemic ventricular performance, and (4) to determine the prevalence of thromboembolism and thrombotic obstruction after the extracardiac Fontan operation.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Selection Criteria for One-Stage Univentricular Repair
Patients with a functionally univentricular heart and satisfying the standard prescribed criteria underwent one-stage univentricular repair [1, 3, 5].

Preoperatively, these patients were grouped according to Texas Heart Institute Fontan risk score [6]. Those with 0 to 3 risk points were considered to be at low risk for Fontan operation (n = 56). Patients with 4 to 5 points were at moderate risk (n = 9). Patients with 6 or more risk points, or 3 points in any single category, were subjected to bidirectional Glenn operation (BDG) as an interim palliation.

Selection Criteria for Extracardiac Fontan
On the basis of our early experience, extracardiac total cavopulmonary connection was performed in patients with (1) age older than 3 years, (2) body weight greater than 10 kg, (3) anomalies of systemic and pulmonary venous return, (4) auricular juxtaposition, (5) completion Fontan circuit after a previous BDG, and (6) no requirement of additional intracardiac procedures [3, 7].

Patient Characteristics
A total of 215 patients underwent various modifications of univentricular repair between January 1998 and December 2003 at All India Institute of Medical Sciences, New Delhi, India, and 65 patients met the selection criteria for extracardiac Fontan. In addition, 182 children underwent BDG during this study period. The records of these patients were reviewed for demographic, operative, and perioperative features, follow-up echocardiographic, Holter electrocardiographic, radionuclide angiographic, catheterization, and clinical data. Descriptive characteristics, underlying cardiac diagnoses, and the relevant cardiac catheterization data are summarized in Table 1.

Hemoglobin ranged from 15 to 22 g/dL, and systemic arterial oxygen saturation was 65% to 88%. Mean pulmonary artery pressure or pulmonary capillary wedge pressure ranged between 9 and 20 mm Hg (median, 16 mm Hg), and mean systemic ventricular end-diastolic pressure ranged between 8 and 16 mm Hg (median, 14 mm Hg).

Surgical Technique
Two modifications of the extracardiac Fontan operation were used on surgeon preference: (1) extracardiac lateral conduit (n = 50) made of polytetrafluoroethylene (PTFE) graft (W.L. Gore and Associates, Flagstaff, AZ), and (2) "viable" in situ pericardial lateral tunnel (n = 15). All operations were performed without clamping the aorta at normothermia on a perfused beating heart. The ligamentum arteriosum or patent ductus arteriosus was divided in all cases, the Blalock-Taussig’s shunt was ligated (n = 20). A unilateral (n = 37) or bilateral (n = 28) BDG was performed. Total extracardiac right heart bypass was accomplished using either a PTFE conduit or a viable in situ pedicled pericardium as described by us earlier [7]. The conduit size ranged between 18 and 22 mm (mean, 20.4 ± 1.3 mm; median, 20 mm). Size of the conduit and weight distribution of the patients were as follows: (PTFE 18 mm: 7 patients, 10.5 to 14 kg; 20 mm: 27 patients, 12 to 20 kg; 22 mm: 16 patients, 21 to 34 kg). Fenestration was made using a 4-mm coronary punch in the PTFE conduit and on the thicker portion of the atrial wall close to the interatrial groove. Fenestration was used only in the setting of suboptimal anatomy or hemodynamics. Special precaution was taken to avoid injury to the coronary sinus, sinus node, and sinoatrial nodal artery, and to avoid mechanical compression of nearby structures (right superior pulmonary vein and right atrium).

In situ pericardial lateral tunnel was the preferred option in patients with levocardia, L-malposition or L-transposition of the aorta and dextrocardia, D-transposition, D-malposition of the aorta, or posteriorly placed main pulmonary artery.

To retain the maximal amount of atriopulmonary tissue as part of the viable tunnel and to avoid injury to the sinoatrial nodal artery the technique of Gundry and associates [8] was further modified by transecting the main pulmonary artery (MPA) at the sinotubular junction, and the posterior wall was sutured to the anterior right atrial wall as low as possible [7, 8].

Assessment of Operative Outcome
Cohort of survivors
Of the 65 original patients, there were 2 perioperative and no late deaths. Risk factors for in-hospital deaths were analyzed. All survivors (n = 63) were examined and studied between December 2003 and August 2004, which was the closing interval for the study.

Outcome variables
Outcome variables were Fontan failure and postoperative pleural effusion. Fontan failure included all deaths within 30 days of operation and those who required Fontan takedown. Postoperative pleural effusion of more than 14 days duration or recurrent pleural effusion after removal of chest tubes was considered significant. The patients’ clinical course (survival, need for cardiac medications, New York Heart Association class, occurrence of late complications) after hospital discharge was monitored.

Echocardiograms
Echocardiographic variables compared before and after the operation were atrioventricular valve regurgitation, presence or absence of flow through the fenestration, and systemic ventricular function. Transesophageal echocardiogram was performed to confirm a thrombus in case of doubt.

Analysis of rhythm changes
All 63 survivors underwent Holter monitoring in the closing interval of the study using a Mortara H-12 Holter unit (Mortara Instruments Inc, Milwaukee, WI). However, Holter studies were performed earlier if patients had symptoms with electrocardiographic evidence of dysrhythmias. The diagnosis of sinus nodal dysfunction and arrhythmias was made using the electrocardiographic criteria as defined by Kugler [9] and Balaji and colleagues [10].

Radionuclide studies
In a prior publication, we have detailed the standard protocol for this study [5]. A combination of both first-pass and equilibrium radionuclide angiocardiography were used to assess systemic or pulmonary venous pathway obstruction and ventricular function. Patients with supraventricular arrhythmias (n = 9) were digitalized, and the method of online postbeat filtration was used.

Postoperative cardiac catheterization
Only 19 of 65 patients consented for cardiac catheterization. This includes 4 patients with Fontan failure and 15 patients with in situ pericardial lateral tunnel. Correlation between the systemic venous pressures and arrhythmias was possible only in the early postoperative phase when the pressure data were available by invasive catheters and in patients undergoing cardiac catheterization.

Statistical Analysis
Data were analyzed with Biomedical Data Processing Statistical Software (University of California Press, Berkeley, CA) and SPSS 7.5 statistical package (SPSS Inc, Chicago, IL). Interval-related data were expressed as mean ± standard deviation. Categorical variables were assessed individually for their relationship to Fontan failure and supraventricular arrhythmias by determining the odds ratio, and ² analysis was attained to assess their association to each other. Interval data were analyzed using unpaired Student’s t test. Analysis of time-related survival was performed using the Kaplan-Meier method.

Logistic regression was used to represent Fontan failure and supraventricular arrhythmias in extracardiac Fontan operation using 17 risk factors through the "Enter" method. There were few events regarding Fontan failure and supraventricular arrhythmias, and data analyses did not reveal any variable with statistical significance. Hence, the multivariate data for the above factors are not presented. Two-tailed probability was used for all the statistical tests. A probability value of less than 0.05 was considered statistically significant.

	Results

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Short-Term Results
Operative mortality was 3% (n = 2), Fontan failure rate was 6.1% (n = 4), and the incidence of conduit thrombosis was 4.6% (n = 3). Systemic ventricular dysfunction, mean pulmonary artery pressure greater than 15 mm Hg, and nonuse of fenestration were the risk factors for Fontan failure (Table 1).

One patient who underwent rechanneling of the supracardiac total anomalous pulmonary venous connection along with extracardiac cavopulmonary connection died early postoperatively. He had persistent chylous drainage from the chest tubes and underwent thoracic duct ligation on the 15th postoperative day. He died of intractable ventricular arrhythmia 24 hours later.

The second patient underwent extracardiac Fontan using a fenestrated 22-mm PTFE conduit in the setting of right atrial isomerism and a complex double-inlet left ventricle. Preoperatively, he had a mean pulmonary artery pressure of 20 mm Hg, systemic ventricular end-diastolic pressure of 18 mm Hg, and an ejection fraction of 0.40. Postoperatively, he exhibited low cardiac output, prolonged junctional atrial tachycardia, and massive fluid losses. Echocardiography and radionuclide angiography revealed partial obstruction of the PTFE conduit. On the second postoperative day, a Fontan takedown and BDG conversion was performed. The anastomoses were technically unrestricted, and there was no evidence of kinking or mechanical compression of the conduit. On the fifth postoperative day, he died of low cardiac output.

The third patient exhibited persistent hypoxemia (arterial oxygen saturation < 60%) and progressive hepatomegaly on the fourth postoperative day without evidence of low cardiac output. The lungs were adequately expanded, and there was no evidence of superior vena caval obstruction. Echocardiography revealed sluggish blood flow through the conduit. Reoperation on the fifth postoperative day revealed graft thrombosis with technically unrestricted anastomoses. There was extensive thrombosis of the inferior vena cava and hepatic veins. The pulmonary arteries were free from any blood clots. Under cardiopulmonary bypass on a beating heart, the entire graft was removed with thrombectomy of the pulmonary arteries, inferior vena cava, and hepatic veins. A 20-mm aortic homograft was interposed between the pulmonary artery and the inferior vena cava without fenestration. He made an uneventful recovery.

The fourth patient exhibited thrombosis of the PTFE tube on the fourth postoperative day diagnosed echocardiographically and by radionuclide angiography. There was no technical error and no evidence of low cardiac output early postoperatively. Fontan revision was performed using viable in situ pericardium with a 5-mm fenestration. Subsequent recovery was uneventful.

The remaining patients were extubated on the first postoperative day. Mean duration of chest tube drainage was 7 days. Prolonged chest tube drainage (>14 days) occurred in 2 patients with pericardial lateral tunnel.

All patients were administered oral captopril on day one postoperatively (0.5 to 1.0 mg/kg, every 8 hours) before discontinuing inotropic support. Postoperatively, digoxin, diuretics, and angiotensin-converting enzyme inhibitors were discontinued from the third month onward. All patients with a PTFE conduit received warfarin for 6 months for anticoagulation to maintain an international normalized ratio between 2.5 and 3.0. In addition, they were administered aspirin (5 mg/kg per day), which was continued indefinitely.

Long-Term Results
Midterm mortality and morbidity
There were no late deaths. Actuarial survival at 79 months was 96.9% ± 0.02% (Fig 1). At a mean follow-up of 77 ± 2 months (range, 8 to 79 months), 56 patients (88.8%) were in New York Heart Association functional class I and II. Postoperative oxygen saturation ranged from 89% to 95% (mean, 92%). None had closure of the fenestration and cerebrovascular accidents.

View larger version (14K): [in this window] [in a new window]   Fig 1. Survival function.

Effect of supraventricular tachyarrhythmias on first-pass study and equilibrium radionuclide angiocardiography
The radiotracer remained visible in the intracardiac tunnel for 16 to 24 seconds (mean, 20.7 ± 2.5 seconds), and the systemic ventricular ejection fraction ranged between 0.35 and 0.38 (mean, 0.368 ± 0.026) in all patients with supraventricular arrhythmias (n = 9).

Systemic venous pathway evaluation
In patients with viable extracardiac tunnel, serial echocardiograms revealed wide unrestricted anastomoses and unobstructed venous flow to both pulmonary arteries with cardiac pulsations and respiratory variations in the pulmonary arteries owing to the compressible lateral tunnel. There was continued growth of the conduit in length and width.

The pressure data as assessed by invasive catheters were similar in all patients in the initial postoperative phase. Patients who underwent late postoperative catheterization in the lateral tunnel group (n = 4) or viable tunnel group (n = 15) exhibited similar data. The mean pressure of the extracardiac lateral tunnel and pulmonary arteries were 12.2 ± 1.6 mm Hg (range, 9 to 15 mm Hg) and 12.1 ± 1.6 mm Hg (range, 9 to 14 mm Hg), respectively. There were no gradients on any portion of the conduit. The Fontan failure group, however, had higher postoperative right-sided pressures (range, 16 to 19 mm Hg; mean, 17.2 ± 1.6 mm Hg). Cavopulmonary angiograms (n = 15) demonstrated a smooth, nonturbulent, somewhat pulsatile flow to both pulmonary arteries in patients with viable lateral tunnel.

The mean radiotracer transit time on first-pass angiography of the extracardiac conduit was 10.3 ± 3.2 seconds (range, 5 to 16 seconds) in patients with New York Heart Association functional class I and II. All patients with Fontan failure and conduit obstruction (n = 3) had hepatic vein reflux, and the radiotracer remained visible in the intracardiac tunnel for 16 to 25 seconds (mean, 18.8 ± 2.7 seconds). Patients with conduit obstruction (n = 3) demonstrated paradoxic filling of the right lung by the radiotracer after femoral venous injection.

Evaluation of systemic ventricular function by radionuclide angiocardiography
Postoperative systemic ventricular ejection fraction of patients with New York Heart Association class I and II (n = 56) ranged from 0.45 to 0.60 (mean, 0.517 ± 0.048). Preoperatively, this subset of patients had ejection fraction between 0.45 and 0.60 on echocardiography (mean, 0.547 ± 0.048; p = 0.000). All patients with Fontan failure (n = 2) had low ejection fraction ranging between 0.35 and 0.38 (mean, 0.368 ± 0.026). Preoperatively, this subgroup was at moderate risk, and their ejection fraction ranged from 0.40 to 0.45 (mean, 0.411 ± 0.049; p = 0.000). Serial evaluation of survivors did not demonstrate any deterioration of systemic ventricular ejection fraction.

	Comment

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Two currently favored approaches to the modified Fontan circuit include the extracardiac or lateral tunnel techniques [1–3, 6–8, 11]. The extracardiac technique separates the high-pressure conduit from the atrial wall and systemic venous atrial cavity, avoids intraatrial placement of prosthetic material, theoretically minimizes the risk of supraventricular arrhythmias, and possibly preserves ventricular and pulmonary function because it can be performed without aortic cross-clamp [1–4, 6–8]. Concerns include lack of growth potential of the synthetic conduit, late supraventricular dysrhythmias, conduit narrowing or obstruction, and thromboembolic complications [1–12].

Growth Potential
Direct connection of both cavae to the pulmonary artery would be the ideal right heart bypass by virtue of elimination of prosthetic material and extensive atrial suture lines [13]. When direct connection is impossible, this may be accomplished by a prosthetic graft or a viable in situ pedicled pericardium [2, 7, 8, 13].

The prosthetic tube lacks growth potential. An adult-sized conduit (20 to 22 mm) may avoid reoperations, and may accommodate flow rates necessary for exercise. This limits the operation to patients of a minimum age, weight, and size. We selected patients older than 3 years of age and weighing more than 10 kg to avoid reoperations and achieve adequate exercise tolerance. Minimum patient weight for an extracardiac Fontan candidate should be approximately 10 to 15 kg because a 20- to 22-mm conduit in a smaller child is relatively oversized and risks the formation of thromboses [2].

To address the problem of growth potential, some including us have used viable in situ pericardial tunnel, pedicled on its lateral blood supply [7, 8]. The technical details, postoperative clinical course, and the hemodynamics have been addressed in our earlier publication [7]. It appears that patients with situs solitus, levocardia, L-malposition or L-transposition of the aorta or situs inversus, dextrocardia, and D-transposition or D-malposition of the aorta or those with anteroposterior disposition of the aorta and main pulmonary artery may be the ideal candidates for this operation. Because the pericardial tube is vascularized, it is viable and also pliable, thus capable of absorbing cardiac pulsations as well as being affected by respiratory bellow mechanisms. Serial echocardiograms postoperatively have demonstrated continued growth of the tube. Cavopulmonary angiograms in the late postoperative period have demonstrated smooth, nonturbulent, and somewhat pulsatile flow without gradients. Because of nonthrombogenicity of the native pericardium, anticoagulation could be avoided in all patients and there was no peel or thrombus formation. Owing to reduction in right atrial distension, wall stress, absence of extensive suture lines, and avoidance of damage to the sinoatrial node, atrial dysrhythmias could be eliminated in all patients. The pericardium is known to follow Laplace’s law, and does not dilate unless there is distal obstruction.

Thromboembolism and Thrombotic Obstruction
Thromboembolic complications have ranged from 3% to 20% and are unrelated to the modifications of the Fontan circulation [1–3, 10, 12]. There is no consensus about candidate selection and type or duration of anticoagulation [1–3, 10].

Although used worldwide, prosthetic conduits in the venous circulation carry the inherent risks of thrombosis and obstruction [2, 12]. Thrombosis of the Fontan pathway is often silent and may remain undetected until there is significant elevation of venous pressures. Radionuclide studies may be useful for early detection of this complication [1–3, 5, 12]. In this study, we observed three instances of conduit thrombosis despite adequate oral anticoagulation. The anastomoses were technically unrestrictive, and there was no evidence of kinking or mechanical compression of the conduit in any patient. Low cardiac output was the possible cause of graft thrombosis in 1 patient.

Radionuclide angiography detected conduit obstruction in all patients, in particular, by paradoxic intense visualization of both lungs after femoral injection. These obstructions allowed inferior vena caval blood to flow upward into the superior vena cava-pulmonary artery connection through the paravertebral and epidural veins and azygos system. These may have reduced blood flow in the conduit and favored its thrombosis. There was no evidence of low cardiac output in 2 patients. Four similar reports of paradoxic filling of the right lung after lower limb injection of microspheres have been described in patients with conduit obstruction [14]. The above findings were confirmed by Doppler echocardiography and angiocardiography before revision surgery.

Routine anticoagulation for all patients undergoing the Fontan operation has been recommended [1–3, 12]. Our institutional policy is to use warfarin and aspirin for the first 6 months and then switch to aspirin alone with regular echocardiographic or radionuclide follow-up. A viable pericardial extracardiac tunnel may eliminate the need for anticoagulation. Although the observed instances of PTFE conduit obstruction would make their use questionable, we have continued to use them as they are easily available in all sizes and their use has been widespread [2, 3, 5, 12]. However, with our growing experience with the viable tunnel procedure, we would be inclined to consider the viable tunnel as the first option whenever possible.

Supraventricular Arrhythmias
To date, the optimal surgical approach for avoidance of postoperative arrhythmias after Fontan repair has not been determined. Their incidence varies widely (12% to 48%), reflecting difference in definitions, methods of detection, changes in patients treated, and long-term follow-up [1–5, 10, 12]. Extracardiac Fontan may minimize the atrial arrhythmias by so-called atrial no-touch surgery, avoiding manipulation or injury to the sinoatrial node, avoiding exposure of the right atrium to elevated systemic venous pressure, and limiting the extensive atrial suture lines and scarring commonly seen with the lateral tunnel Fontan operation [1–4, 7, 8].

Sinoatrial node function is best evaluated by 24-hour Holter monitoring, which was done only once in the great majority during the period of this study. Although this is a potential source of error in this retrospective study, the bias is more likely toward the underdetection of arrhythmias rather than an overestimation. In this series, patients with systemic ventricular dysfunction, heterotaxy syndrome, anomalous systemic venous drainage, and previous BDG exhibited a higher incidence of arrhythmia (Table 1).

Patients with preoperative systemic ventricular dysfunction (n = 9) were at moderate risk according to Texas Heart Institute Fontan risk score and had mean systemic venous pressure ranging between 16 and 19 mm Hg postoperatively. The increased incidence of supraventricular arrhythmias in this subset of patients was statistically significant (Table 1). It manifested in the perioperative period and continued in the late follow-up, indicating the effects of ongoing hemodynamic factors.

Abnormalities of the conduction system are known to exist in patients with heterotaxy syndrome, which may provoke tachyarrhythmia and bradyarrhythmia irrespective of the type of Fontan connection [1, 2, 10, 15]. Cohen and colleagues [16] demonstrated that avoidance of surgery near the sinus node had no effect on the development of sinus nodal dysfunction.

Our study suggests that despite the best surgical efforts, we must accept a certain incidence of sinus nodal dysfunction in this patient population. Continued surveillance is necessary to determine which patients will develop clinically significant arrhythmia.

Staged surgical correction of the functionally univentricular heart with the addition of an intermediate BDG exposes the sinoatrial nodal area to dissection twice, thus potentially risking dysfunction caused by direct injury to the sinoatrial node or sinoatrial nodal artery [17]. Our data suggest an additive risk of abnormal sinoatrial nodal function with a staged Fontan connection (Table 1).

In patients with bilateral superior venae cavae, the superior vena cava-right atrial junction may be too small to accommodate the entire inferior vena caval return. Patients in this series with bilateral superior venae cavae requiring enlargement of the right superior cavoatrial junction exhibited sinus nodal dysfunction probably as a result of damage to the sinoatrial nodal artery. The technique of viable extracardiac lateral tunnel presented herein provides an alternative method of cavopulmonary connection that attempts to avoid this complication.

Systemic Ventricular Function
Intact systolic and diastolic performance is critical for the successful establishment of an atrial-dependent circulation. The literature documents variable systemic ventricular performance after the Fontan operation [1–3, 10].

In spite of performing the operation on a normothermic, beating heart, there was transient significant depression of ejection fraction in all patients in the immediate postoperative period (p = 0.000). This could be related to a decrease in left ventricular end-diastolic volume from preoperative to postoperative measurements, mostly because of elimination of systemic-pulmonary shunts or pulmonary artery band and improvement in myocardial oxygen supply.

Varying ventricular morphologies (right, left, indeterminate, or biventricular) in the Fontan cohort make calculation of ejection fraction by conventional angiocardiograms unreliable [18]. Radionuclide-derived ejection fraction is probably more accurate as it is devoid of geometric assumptions. The ability to obtain serial measurement of ejection fraction after a single isotope injection makes this modality particularly appealing [5, 18].

Study Limitations
This study is retrospective and nonrandomized. Because of the transient and intermittent nature of some arrhythmias, their incidence may be underestimated. Long suture lines in the atrial wall of the viable tunnel may predispose to late atrial arrhythmias [7, 8]. Second, the floor of the extracardiac lateral tunnel contains the pulmonary veins. There are isolated reports of anterior compression of the pulmonary veins by a markedly enlarged right atrium [8]. The issue of energy losses in the extracardiac Fontan circuit as compared with the lateral tunnel Fontan has been discussed recently [11]. However, we did not measure this and are unable to comment on this aspect. Finally, the incidence of thromboembolic complications is probably underestimated because only clinically suspected cases were investigated.

Further investigations on a larger number of patients with prospective longitudinal evaluation are needed to confirm the midterm results, especially atrial dysrhythmias, pulmonary venous obstruction, thromboembolic complications, and growth.

Conclusions
Supraventricular arrhythmias after extracardiac Fontan operation are probably multifactorial and mandate continuous surveillance. Patients with systemic ventricular dysfunction, bilateral superior venae cavae, and heterotaxy syndrome and those undergoing completion Fontan may exhibit a high incidence of these arrhythmias. The viable extracardiac Fontan may be the operation of choice in a selected subset of patients. Serial dynamic radionuclide studies may be useful for evaluation of anatomic and functional flaws of the Fontan circuit.

	Acknowledgments

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
The authors are grateful to Mr Shankar Sharma for the preparation of the manuscript.

	References

Top Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

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