Lateral Tunnel Total Cavopulmonary Connection Research Articles

The long-term outcome of extra cardiac lateral tunnel total cavopulmonary connection

Abstract Background Although early results of total cavopulmonary connection (TCPC) using an extracardiac conduit are favorable, the patients' growth leads to linearization of the Fontan route causing energy loss by collision of blood flow from the SVC and the IVC, and PV compression. Use of oversized conduit in young children also causes energy loss due to caliber change, and a risk of thrombosis by flow stagnation. We have performed TCPC with the Extra Cardiac Lateral Tunnel (ECLT) technique using e-PTFE patch to make an angled route design for laminar IVC and SVC blood flow confluence, and to avoid caliber change of the IVC-Fontan route. Purpose To clarify the long-term outcome of the Extra Cardiac Lateral Tunnel TCPC (ECLT-TCPC) using e-PTFE patch. Methods Medical records of the patients who underwent staged ECLT-TCPC from April 2003 to March 2020 were reviewed retrospectively. The surgical technique consists of creation of IVC and PA opening connected by atrial appendage and free wall as a floor and suturing a cut-open e-PTFE graft over the anterior external wall of the right atrium to make a Fontan route 14–16 mm in diameter entering the PA from the ventral aspect to merge the SVC flow with an angle. Sixty five patients were included in the study: 46 cases of functional single ventricle, 10 HLHS, 9 tricuspid atresia. Age at surgery were 33.0±22.2 month and the weight was 11.1±3.7 kg. Preoperative catheterization data were following; PA pressure: 10.3±4.0 mmHg, PVR: 1.9±0.65 woods. Results We had one in-hospital death (1.8%) and three long-term deaths (6.2%) during a follow-up period of 7.3±4.3 years. Long-term complications included 6 cases of arrhythmias requiring medical or surgical treatment. Other complication included 2 cases of thrombotic complications, and 1 case of hemorrhagic complication. Two patients underwent re-operation for TCPC: 1 cyanosis due to residual shunt and 1 cases for occlusion of the Fontan route. The anticoagulant therapy was usually terminated eight months after surgery. At the latest follow-up, 55 (84.6%) patients were anticoagulantion-free. At the one-year follow-up, the diameters of the Fontan route were 11.0±2.4mm at the PA anastomosis level, 10.8±2.5mm at the middle level, 10.0±2.5mm at the IVC anastomosis level. At the latest follow-up, the diameters of the Fontan route at the three levels were 14.9±3.4mm, 13.0±3.2mm, and 13.6±4.9mm, respectively. Using the normal IVC diameter as a reference, the Fontan route diameter at the three levels were 127±35%, 123±28%, and 143±44% of Normal, respectively, remaining above 100%Normal. The pressure gradient between IVC and PA was 1.5±1.0mmHg at the latest follow-up, and no significant changes in the route design were noted. Conclusion The long-term results of ECLT TCPC using e-PTFE patch seemed acceptable. This technique may provide advantages of a long-term maintenance of the Fontan route diameter and design, and an option of a long-term freedom form anticoagulation. Funding Acknowledgement Type of funding sources: None.

The Epidemiology of Persons Living with Fontan in 2020 and Projections for 2030: Development of an Epidemiology Model Providing Multinational Estimates.

IntroductionFontan surgery is a palliative procedure performed in children with a functionally univentricular heart. Improvements in surgical technique over the past 30 years have increased life expectancy in this rare population. However, the epidemiology of persons living with Fontan is poorly understood. This study aimed to estimate the 2020 and 2030 prevalence of persons living with a Fontan circulation in 11 countries across the US, Europe, Australia and New Zealand, by procedure type: [atriopulmonary connection (AP), lateral tunnel total cavopulmonary connection (LT-TCPC) or extracardiac total cavopulmonary connection (EC-TCPC)]; and age group: [children (< 12 years), adolescents (12–17 years), and adults (≥ 18 years old)] by building an epidemiologic model.MethodsThe annual number of Fontan surgeries by country in 2010–2020 were extracted from hospital or claims databases, via procedure codes. The epidemiology of persons living with Fontan was modelled by applying these surgery frequencies to mid-year populations from 1972 to 2020 and overlaying an uptake curve. A literature search identified: 30-day mortality rates, long-term survival, and median age at surgery. Averages of these estimates were inputted into the model to project prevalence in 2030.ResultsThe number of persons living with Fontan in 2020 across the 11 countries was estimated to be 47,881 [66 people per million (ppm)], rising to 59,777 (79 ppm) by 2030. In 2020, this population was 55% adults, 17% adolescents and 28% children shifting to 64%, 13% and 23%, respectively, in 2030. Among all persons living with Fontan, 74%/18%/9% are estimated to have EC-TCPC/LT-TCPC/AP, respectively, in 2020, and 83%/14%/4% in 2030.ConclusionsAccording to this epidemiology model, the Fontan population is growing, partly driven by increased survival rates with the more recent LT-TCPC and EC-TCPC procedures (compared with AP). The 2020/2030 prevalence of persons living with Fontan is 66/79 ppm.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12325-021-02002-3.

A novel procedure of puncture to access the pulmonary venous atrium in complex congenital heart disease with surgical correction

BackgroundIn complex congenital heart disease, supraventricular arrhythmia develops long term after surgical repair. The arrhythmia could have pharmacological tolerance and sometimes be fatal. We report our experiences with puncturing tough or calcified surgical repair material to access the pulmonary venous atrium for the purpose of the management of arrhythmia in complex congenital heart disease with surgical correction. MethodsFrom June 2016, subsequent 9 patients underwent the procedure. Their age at the procedure ranged from 11 to 43 years old (median 26.4 years old). Surgical procedures were Mustard procedure (XenomedicaⓇ) in 6, lateral tunnel total cavo-pulmonary connection with autologous pericardium in 2, and extra-cardiac total cavo-pulmonary connection with expanded polytetrafluoroethylene (ePTFE) tube in 1. ResultsMulti-planar reconstruction imaging by cardiac computed tomography was done for making plans before the procedures. Under intracardiac echocardiography guidance, an 8 French steerable sheath was perpendicularly adjusted to target objects. The sharpened edge of 0.014 inch guide wire penetrated with gentle forward force. Subsequently, the puncture site was dilated from a small balloon to a large one step by step. In all patients, penetration was successfully completed. Catheter ablation was achieved in 8 patients and a pacemaker was implanted through the re-canalized superior caval vein in 1 patient. No complications were recorded. ConclusionThe trans-catheter puncture of the synthetic or calcified material is safe and feasible, although careful planning is required with imaging. A steerable sheath could easily be controlled to the make appropriate angle to the target object for preventing slippage and conveying effective force.

Cardiopulmonary exercise performance after total cavopulmonary connection with or without prior superior cavopulmonary connection.

To compare cardiopulmonary exercise capacity of patients undergoing primary total cavopulmonary connection (TCPC) with those undergoing TCPC after a prior bidirectional Glenn (BDG). Out of 42 patients in this study, 24 had undergone primary TCPC while 18 had undergone staged TCPC. The peak oxygen consumption (O(2) peak), O(2) pulse, chronotropic index, and other exercise parameters were studied. There were no significant differences in O(2) peak (940 ± 538 vs. 1010 ± 417 mL/min, p=0.42) and O(2) pulse (5.76 ± 3.52 vs. 6.85 ± 2.95) of patients undergoing staged TCPC versus primary TCPC, respectively; however, chronotropic index (0.43 ± 0.23 vs. 0.30 ± 017, p=0.047) was significantly different. Exercise tolerance was the same in fenestrated versus nonfenestrated TCPC groups and age at TCPC less than or more than 7 years. However, O(2) peak and O(2) pulse of patients with extracardiac TCPC was better than patients with lateral tunnel TCPC (p values 0.05, 0.04 and respectively). Some parameters of exercise tolerance of patients with antegrade pulmonary blood flow (APBF) interrupted at the time of BDG were better than those with APBF open. There were no differences in the exercise parameters of patients undergoing a staged versus a primary TCPC, fenestrated versus nonfenestrated TCPC, and age at surgery less than or more than 7 years. Exercise parameters were better in the extracardiac conduit group versus lateral tunnel TCPC groups. Patients who had a TCPC after prior interruption of APBF had better exercise parameters.

Fontan completions over 10 years after Glenn procedures

Despite the broadened indications for Fontan procedure, there are patients who could not proceed to Fontan procedure because of the strict Fontan criteria during the early period. Some patients suffer from post-Glenn complications such as hypoxia, arrhythmia, or fatigue with exertion long after the Glenn procedure. We explored the possibility of Fontan completion for those patients. Between 2004 and 2010, five consecutive patients aged between 13 and 31 years (median 21) underwent Fontan completion. These patients had been followed up for more than 10 years (10 to 13, median 11) after Glenn procedure as non-Fontan candidates. We summarise these patients retrospectively in terms of their pre-operative physiological condition, surgical strategy, and problems that these patients hold. Pre-operative catheterisation showed pulmonary vascular resistance ranging from 0.9 to 3.7 (median 2.2), pulmonary to systemic flow ratio of 0.3 to 1.6 (median 0.9), and two patients had significant aortopulmonary collaterals. Extracardiac total cavopulmonary connections were performed in three patients, lateral tunnel total cavopulmonary connection in one patient, and intracardiac total cavopulmonary connection in one patient, without a surgical fenestration. Concomitant surgeries were required including valve surgeries--atrioventricular valve plasty in three patients and tricuspid valve replacement in one patient; systemic outflow tract obstruction release--Damus-Kaye-Stansel procedure in two patients and subaortic stenosis resection in one patient; and anti-arrhythmic therapies--maze procedure in two patients, cryoablation in two patients, and pacemaker implantation in two patients. All patients are now in New York Heart Association category I. Patients often suffer from post-Glenn complications. Of those, if they are re-examined carefully, some may have a chance to undergo Fontan completion and benefit from it. Multiple lesions such as atrioventricular valve regurgitation, systemic outflow obstruction, or arrhythmia should be surgically repaired concomitantly.

What is a Modern Fontan?

The Fontan procedure has undergone multiple modifications since its original description in 1971 [1]. However, all modifications before 1988 focused on somehow connecting the right atrial appendage to the pulmonary arteries. This forced the caval blood to take a curved path to the pulmonary arteries, with the inferior caval return following an S-shaped route and the superior caval return taking a 180 turn. Consequently, the caval return lost significant kinetic energy [2]. To improve this, another modification of Fontan was described in 1988 whereby the caval return was ‘‘streamlined’’ (the caval veins took a straight path to the pulmonary arteries), with significantly better kinetic energy and outcome. This was the lateral tunnel total cavopulmonary connection (lateral tunnel TCPC) [2]. Then, 2 years later, an alternative form of streamlined Fontan was described, the extracardiac conduit [3]. Streamlining the Fontan circuit was very significant and marked the transition from the classic to the modern Fontan. The description of modern Fontan seemed simple: if the caval return follows a straight path to the pulmonary arteries, it is modern; otherwise it is classic. Both lateral tunnel TCPC and extracardiac Fontans are therefore modern. The rare cases of intra-atrial tube Fontans, as may be used in the setting of isomerism, also would be considered modern because the inferior caval blood takes a straight path toward the pulmonary arteries. However, this description is incomplete. Another important difference between classic and modern Fontans is worth noting because it may have contributed to the improvement in outcome. In modern Fontans, the coronary sinus is not included in the Fontan circuit. Rather, it drains into the atrium, where the pressure is 7 or 8 mmHg lower than in the Fontan circuit. If the coronary sinus drains into the Fontan circuit (classic Fontan), it may subject the myocardium to the same deleterious effects of chronic venous hypertension seen in other organs (e.g., proteinlosing enteropathy, hepatic and renal dysfunction, ascites). It is interesting that, at least in my experience, cardiac dysfunction usually is a prominent component in the clinical picture of a failing classic Fontan, whereas the clinical picture of a failing modern Fontan tends to be dominated by peripheral complications (e.g., protein-losing enteropathy, renal and hepatic dysfunction) with relatively wellpreserved cardiac function. Perhaps the definition of modern Fontan should consist of both criteria: streamlining and maintaining the drainage of the coronary sinus within the atrium.

Presurgical Evaluation of Fontan Connection Options for Patients With Apicocaval Juxtaposition Using Computational Fluid Dynamics

Apicocaval juxtaposition (ACJ) is a rare congenital heart defect associated with single ventricle physiology where optimal positioning of the Fontan conduit for completion of total cavopulmonary connection (TCPC) is still controversial. In ACJ, the cardiac apex is ipsilateral with the inferior vena cava (IVC), risking kinking and collapse of the Fontan conduit at the apex of the heart. The purpose of this study is to evaluate two viable routes for Fontan conduit connection in patients with ACJ, using computational fluid dynamics. Internal energy loss evaluations were used to determine contribution of conduit curvature to the energy efficiency of each cavopulmonary anastomosis configuration. This percentage of energy loss contribution was found to be greater in the case of a curved extracardiac conduit connection (44%, 4.1 mW) traveling behind the ventricular apex, connecting the IVC to the left pulmonary artery, than the straighter lateral tunnel conduit (6%, 1.4 mW) installed through the ventricular apex. In contrast, net energy loss across the anastomosis was significantly lower with extracardiac TCPC (9.3 mW) in comparison with lateral tunnel TCPC (23.2 mW), highlighting that a curved Fontan conduit is favorable provided that it is traded off for a superior cavopulmonary connection efficiency. Therefore, a relatively longer and curved Fontan conduit has been demonstrated to be a suitable connection option independent of anatomical situations.

Visualization of flow structures in Fontan patients using 3-dimensional phase contrast magnetic resonance imaging

Our objective was to analyze 3-dimensional (3D) blood flow patterns within the total cavopulmonary connection (TCPC) using in vivo phase contrast magnetic resonance imaging (PC MRI). Sixteen single-ventricle patients were prospectively recruited at 2 leading pediatric institutions for PC MRI evaluation of their Fontan pathway. Patients were divided into 2 groups. Group 1 comprised 8 patients with an extracardiac (EC) TCPC, and group 2 comprised 8 patients with a lateral tunnel (LT) TCPC. A coronal stack of 5 to 10 contiguous PC MRI slices with 3D velocity encoding (5-9 ms resolution) was acquired and a volumetric flow field was reconstructed. Analysis revealed large vortices in LT TCPCs and helical flow structures in EC TCPCs. On average, there was no difference between LT and EC TCPCs in the proportion of inferior vena cava flow going to the left pulmonary artery (43% ± 7% vs 46% ± 5%; P = .34). However, for EC TCPCs, the presence of a caval offset was a primary determinant of inferior vena caval flow distribution to the pulmonary arteries with a significant bias to the offset side. 3D flow structures within LT and EC TCPCs were reconstructed and analyzed for the first time using PC MRI. TCPC flow patterns were shown to be different, not only on the basis of LT or EC considerations, but with significant influence from the superior vena cava connection as well. This work adds to the ongoing body of research demonstrating the impact of TCPC geometry on the overall hemodynamic profile.

Growth of the lateral tunnel in patients who underwent a total cavopulmonary connection at less than 5 years of age☆

A lateral tunnel-total cavopulmonary connection (LT-TCPC) using a right atrial (RA) free wall is the first choice of treatment for patients with a small body weight in this institute. Whether the growth of the LT is appropriate or not according to the growth of the body remains controversial. In addition, the optimal initial diameter of an LT is unknown. The purpose of this study was to verify the growth of the LT. Ninety-one patients of a total of 267 TCPC cases underwent an LT-TCPC at less than 5 years of age in this institute between March 1991 and June 2008. The data on 47 of the 91 patients, which were available to investigate the LT growth, were retrospectively reviewed. The mean age at LT-TCPC was 37+/-11 months (16-57 months). The mean body weight at TCPC was 12.4+/-2.4 kg (7.6-20.0 kg). The initial LT diameter was determined with Hegar's sizer of the estimated half-pulmonary arterial (PA) diameter, which is a diameter that results in half of the dimension of the normal pulmonary valve. The measured maximum LT diameter (mm) divided by the estimated half-PA diameter (mm) was considered as the LT index. The size of the LT was evaluated using either echocardiography or angiography. The mean follow-up period was 7.4+/-3.5 years (1.6-13.5 years). The LT index was initially 2.0+/-0.7 (1.3-4.5), 2.0+/-0.4 (1.3-3.2) at 1 year after operation, 2.1+/-0.5 (1.5-3.2) at 5 years after operation, 1.9+/-0.4 (1.5-2.8) at 10 years after operation and 2.1+/-0.5 (1.6-2.5) at 13 years after operation, respectively. LT growth suitable for the body growth can be expected. Although there was some variation in the initial LT diameter, the LT index tended to converge at 2.0 with growth.

Intermediate-term outcome following the fontan operation: a survival, functional and risk-factor analysis☆

To investigate survival and risk factors influencing intermediate outcome after the Fontan procedure. Retrospective analysis of 122 patients operated between April 1991 and September 2002. Poor outcome was defined as late death or poor functional status (intractable supraventricular arrhythmias/NYHA 3-4) necessitating revision surgery. 64(52%) patients had an intermediate bi-directional cavo-pulmonary shunt (BCPS). 91 (76%) patients had a lateral tunnel total cavo-pulmonary connection, 21(17%) patients had an atrio-pulmonary connection and 10 (8%)patients had a Kawashima connection. There were 6 (5%)early deaths. Over a median follow up of 54 months (1-133), 12 (10%)patients have had surgical revision for poor functional status. There were 7 (6%) late deaths, 5 of which occurred after revision surgery. Univariate analysis identified older age at operation (>4 years) (P=0.04), higher postoperative pulmonary artery pressure at 24h (P=0.012), arrhythmia postoperatively (P=0.03) or during follow-up (P=0.01) and the requirement for anticoagulation during follow-up (P=0.03) as significant predictors of poorer outcome. Patients who had an intermediate BCPS (P=0.002) or Norwood Stage 1 (P=0.05) had a better outcome. Multivariate analysis identified an intermediate Glenn shunt and lower postoperative pulmonary artery pressure as significant predictors of better outcome. Actuarial freedom from death or revision is 93% (+/-2), 88% (+/-3), 86% (+/-4) and 69% (+/-7) at 1, 5, 7 and 9 years respectively. Actuarial freedom from death or revision for the lateral tunnel group is 92% (+/-2), 89% (+/-3), 85% (+/-5) and 66% (+/-10) respectively. Atrio-pulmonary connection results in a higher incidence of arrhythmias and failure than the lateral tunnel Fontan. Even in patients with a lateral tunnel Fontan there is a continuing hazard phase in the intermediate term. Mid-term outcome appears to be favorably influenced by an intermediate BCPS.

Extracardiac total cavopulmonary connection using a tissue-engineered graft

Objective Extracardiac and lateral tunnel total cavopulmonary connection are currently 2 major options for patients with a single ventricle physiology. However, each procedure has some disadvantages over the other. We developed a new technique of extracardiac total cavopulmonary connection using a tissue-engineered graft to overcome some of the disadvantages previously associated with both the extracardiac and lateral tunnel procedures. Methods Between February 2001 and October 2002, 8 patients underwent an extracardiac total cavopulmonary connection using a tissue-engineered graft in our institution. Collected bone marrow cells (1 × 10 8 mononucleocytes) from a patient (∼1-4 mL/kg body weight) were seeded onto a biodegradable scaffold composed of polycaprolactone-polylactic acid copolymer reinforced with woven polylactic acid. After a 2- to 4-hour cultivation, the seeded scaffold was implanted as an extracardiac conduit during the total cavopulmonary connection operation. Results There were no hospital or late deaths. At a mean follow-up of 13.4 months (range 4-25 months), all patients are alive and asymptomatic with no need for repeat surgery. A postoperative catheter examination or computed tomography showed all tissue-engineered grafts to be patent and revealed no stenosis, obstruction, or aneurysmal change in the 8 patients. Conclusion We believe that extracardiac total cavopulmonary connection using a tissue-engineered graft has the potential to overcome some of the disadvantages previously associated with extracardiac or lateral tunnel total cavopulmonary connection. However, an extended follow-up period is required to clarify the long-term clinical outcome for the tissue-engineered graft.

In vivo flow dynamics of the total cavopulmonary connection from three-dimensional multislice magnetic resonance imaging

Background. The total cavopulmonary connection (TCPC) design continues to be refined on the basis of flow analysis at the connection site. These refinements are of importance for myocardial energy conservation in the univentricular supported circulation. In vivo magnetic resonance phase contrast imaging provides semiquantitative flow visualization information. The purpose of this study was to understand the in vivo TCPC flow characteristics obtained by magnetic resonance phase contrast imaging and compare the results with our previous in vitro TCPC flow experiments in an effort to further refine TCPC surgical design. Methods. Twelve patients with TCPC underwent sedated three-dimensional, multislice magnetic resonance phase contrast imaging. Seven patients had intraatrial lateral tunnel TCPC and 5 had extracardiac TCPC. Results. In all patients in both groups a disordered flow pattern was observed in the inferior caval portion of the TCPC. Flow at the TCPC site appeared to be determined by connection geometry, being streamlined at the superior vena cava–pulmonary junction when the superior vena cava was offset and flared toward the left pulmonary artery. Without caval offset, intense swirling and dominance of superior vena caval flow was observed. In TCPC with bilateral superior vena cavae, the flow patterns observed included secondary vortices, a central stagnation point, and influx of the superior vena cava flow into the inferior caval conduit. A comparative analysis of in vivo flow and our previous in vitro flow data from glass model prototypes of TCPC demonstrated significant similarities in flow disturbances. Three-dimensional magnetic resonance phase contrast imaging in multiple coronal planes enabled a comprehensive semiquantitative flow analysis. The data are presented in traditional instantaneous images and in animated format for interactive display of the flow dynamics. Conclusions. Flow in the inferior caval portion of the TCPC is disordered, and the TCPC geometry determines flow characteristics.

Pulmonary and caval flow dynamics after total cavopulmonary connection

ObjectiveTo assess flow dynamics after total cavopulmonary connection (TCPC).DesignCross-sectional study.SettingAarhus University Hospital.PatientsSeven patients (mean age 9 (4–18) years) who had previously undergone a lateral tunnel TCPC mean 2 (0.3–5) years...

Anatomically based ablation of atrial flutter in an acute canine model of the modified Fontan operation

Background: Lateral tunnel total cavopulmonary connection, also called the modified Fontan operation, uses a baffle through the right atrium. We established, in an acute canine model, that atrial flutter after total cavopulmonary connection revolves around a line of conduction block imposed by the free wall lateral tunnel suture line. We hypothesized that a line of conduction block between the free wall total cavopulmonary connection suture line and the tricuspid anulus would interrupt atrial flutter in this model. Objective: Our objective was to determine whether a cryolesion placed between the free wall total cavopulmonary connection suture line and the tricuspid anulus would terminate atrial flutter in an acute canine model. Methods: Seven adult dogs underwent median sternotomy and institution of cardiopulmonary bypass. A suture line was placed through a right atriotomy to simulate total cavopulmonary connection lateral tunnel construction. Form-fitting 253-point biatrial endocardial mapping electrodes were placed via bilateral ventriculotomies. Atrial flutter was induced by atrial burst pacing. A cryothermal lesion was then placed between the free wall total cavopulmonary connection suture line and the tricuspid anulus in the low lateral right atrium (i.e., CRYO 1 procedure), and reinduction of atrial flutter was attempted. If atrial flutter was reinduced, the cryolesion was modified superiorly to include the caudal portion of the atriotomy (i.e., CRYO 2 procedure). Activation sequence maps were generated for sinus rhythms before and after the cryolesions were placed and for induced arrhythmias. Results: In all seven cases, atrial flutter was inducible after suture line placement, before placement of a cryolesion. The reentrant circuit incorporated both caval orifices in five of seven cases and was successfully ablated by the CRYO 1 approach in each case. Atrial flutter was not inducible after placement of the CRYO 2 lesion in the remaining two cases, in which breakthrough of the wave front occurred across the lateral tunnel suture line in the intercaval region. Activation sequence maps of sinus rhythm after placement of the cryolesions demonstrated a conduction block at the site of the lesion. Conclusions: A linear cryothermal lesion placed between the free wall aspect of the total cavopulmonary connection suture line and the tricuspid anulus created a line of conduction block that successfully ablates atrial flutter in the canine model. (J T HORAC C ARDIOVASC S URG 1996;112:898-907)

CONNECTION GEOMETRY AFFECTS RESISTANCE TO FLOW IN FONTAN CONNECTIONS: IN VITRO STUDIES † 174

Recent modifications to the original Fontan procedure have placed emphasis on the nature of the connection between the cavae and the pulmonary arteries. Since there is no ventricle acting as a pump to drive blood through the pulmonary circulation, a critical determinant of outcome is the overall resistance to flow across the surgical connection and pulmonary circuit. This study addressed the hypothesis that Fontan connection geometry significantly affects resistance to flow. Methods: Connections of the following three types were performed on explanted canine hearts; (1) atriopulmonary connection (APC), (2) lateral tunnel total cavopulmonary connection (TCPC) and(3) partial cavopulmonary connection (intra-atrial baffle with posterior cavo-atriopulmonary connection) (PCPC). Anatomically correct transparent urethane flow models were constructed using injection molding and casting procedures. The models were perfused using a blood analog fluid at flow rates ranging from 2-7 L/min. A variable voltage pumping system allowed input voltage, which can be related to the rate of energy expenditure, to be recorded for each flow condition. Results: Resistances at constant flow differed for each geometry (p<.01). The TCPC had the lowest values of resistance for equivalent flows through each model followed by the PCPC and the APC. Resistance differentials increased with flow rate for each model(p<.05). Conclusions: Based on these experiments, we conclude that a lateral tunnel TCPC offers the least resistance flow among these commonly used connections. The observed increase in resistance differentials with flow may have implications regarding exercise capacity and suggests that minimizing resistance in the Fontan circuit may have significant implications for postoperative morbidity and survival. Figure