Total Cavopulmonary Connection is Superior to Atriopulmonary Connection Fontan in Preventing Thrombus Formation: Computer Simulation of Flow-Related Blood Coagulation

Pulmonary vascular disease and optical coherence tomography imaging in patients with Fontan palliation

INTRODUCTION

The Fontan procedure is the palliative procedure of choice for patients with single ventricle physiology. Pulmonary vascular disease (PVD) is an important contributor to Fontan circulatory failure.

AREAS COVERED

We review the pathophysiology of PVD in patients with Fontan palliation and share our initial experience with optical coherence tomography (OCT) in supplementing standard hemodynamics in characterizing Fontan-associated PVD. In the absence of a sub-pulmonary ventricle, low pulmonary vascular resistance (PVR; ≤2 WU/m2) is required to sustain optimal pulmonary blood flow. PVD is associated with adverse pulmonary artery (PA) remodeling resulting from the non-pulsatile low-shear low-flow circulation. Predisposing factors to PVD include impaired PA growth, endothelial dysfunction, hypercoagulable state, and increased ventricular end-diastolic pressure. OCT parameters that show promise in characterizing Fontan-associated PVD include the PA intima-to-media ratio and wall area ratio (i.e. difference between the whole-vessel area and the luminal area divided by the whole-vessel area).

EXPERT OPINION

OCT carries potential in characterizing PVD in patients with Fontan palliation. PA remodeling is marked by intimal hyperplasia, with medial regression. Further studies are required to determine the role of OCT in informing management decisions and assessing therapeutic responses.

Pulse wave-based evaluation of the blood-supply capability of patients with heart failure via machine learning

Pulse wave, as a message carrier in the cardiovascular system (CVS), enables inferring CVS conditions while diagnosing cardiovascular diseases (CVDs). Heart failure (HF) is a major CVD, typically requiring expensive and time-consuming treatments for health monitoring and disease deterioration; it would be an effective and patient-friendly tool to facilitate rapid and precise non-invasive evaluation of the heart's blood-supply capability by means of powerful feature-abstraction capability of machine learning (ML) based on pulse wave, which remains untouched yet. Here we present an ML-based methodology, which is verified to accurately evaluate the blood-supply capability of patients with HF based on clinical data of 237 patients, enabling fast prediction of five representative cardiovascular function parameters comprising left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter (LVDd), left ventricular end-systolic diameter (LVDs), left atrial dimension (LAD), and peripheral oxygen saturation (SpO2). Two ML networks were employed and optimized based on high-quality pulse wave datasets, and they were validated consistently through statistical analysis based on the summary independent-samples t-test (p > 0.05), the Bland-Altman analysis with clinical measurements, and the error-function analysis. It is proven that evaluation of the SpO2, LAD, and LVDd performance can be achieved with the maximum error < 15%. While our findings thus demonstrate the potential of pulse wave-based, non-invasive evaluation of the blood-supply capability of patients with HF, they also set the stage for further refinements in health monitoring and deterioration prevention applications.

New intra-conduit thrombus detected using transesophageal echocardiography immediately after weaning from cardiopulmonary bypass during the Fontan procedure: a case report

This study reports a case wherein a new thrombus was detected by transesophageal echocardiography in the conduit during extracardiac conduit Fontan procedure. Immediately after weaning from the cardiopulmonary bypass and administration of protamine, a thrombus was noted in the conduit by transesophageal echocardiography. Since the patient was hemodynamically stable, anticoagulation therapy was initiated after admission to the intensive care unit. One week post-surgery, imaging results showed residual thrombus, but the patient was safely discharged. Even during Fontan procedure, careful observation with transesophageal echocardiography is important because of the possibility of thrombus formation in the conduit.

Coagulation and Anticoagulation in Fontan Patients

Patients with a Fontan circulation for single-ventricle physiology are at increased risk of developing thromboembolic events. Thromboembolic events can lead to failure of the Fontan circulation, chronic sequelae in case of stroke, and early mortality. Controversies exist regarding the substrates, risk factors, and optimal detection methods for thromboembolic events. Despite the major clinical implications, there is currently no consensus regarding the optimal antithrombotic therapy to prevent or treat thromboembolic events after the Fontan procedure. In this review we aimed to untangle the available literature regarding antithrombotic prophylaxis and treatment for pediatric and adult Fontan patients. A decision-tree algorithm for thromboprophylaxis in Fontan patients is proposed. Additionally, the current state of knowledge is reviewed with respect to the epidemiology, pathophysiology, and detection of thromboembolic events in Fontan patients, and important evidence gaps are highlighted.

Blood Flow Simulation to Determine the Risk of Thrombosis in the Fontan Circulation: Comparison between Atriopulmonary and Total Cavopulmonary Connections

Three-dimensional computational fluid dynamics (CFD) simulations were performed in the anastomotic region of the Fontan route between the venae cava and pulmonary arteries to investigate the risk of thrombosis due to blood stasis in the Fontan circulation. The finite volume method based on the time-averaged continuity and Navier–Stokes equations combined with the k-ω SST turbulent model was used in the CFD simulations. Low shear rate (SR) and SR on the wall (WSR) of <10 s−1 were used as markers to assess blood stasis as a cause of blood coagulation. Simulated blood flow velocity and both SR and WSR were reduced in the right atrium (RA) as the cavity of a flow channel in the atriopulmonary connection (APC) Fontan model, whereas the values increased in the total cavopulmonary connection (TCPC) Fontan model, which has no cavity. The volume of SR <10 s−1 and wall surface area of WSR <10 s−1 were, respectively, 4.6–261.8 cm3 and 1.2–38.3 cm2 in the APC Fontan model, and 0.1–0.3 cm3 and 0.1–0.6 cm2 in the TCPC Fontan model. The SR and WSR increased in the APC model with a normal-sized RA and the TCPC model as the flow rate of blood from the inferior vena cava increased with exercise; however, the SR and WSR in the RA decreased in the APC model with a dilated RA owing to the development of a recirculating flow. These findings suggest that the APC Fontan has a higher risk of thrombosis due to blood stasis than the TCPC Fontan and a higher RA dilation is associated with a higher risk of thrombosis from a fluid mechanics perspective.

Clinical Importance of Fontan Circuit Thrombus in the Adult Population: Significant Association With Increased Risk of Cardiovascular Events

BACKGROUND

The impact of Fontan circuit thrombus is poorly understood. The objectives of this study were to determine (1) the incidence of Fontan circuit thrombus and proportion of silent thrombus; (2) any association between Fontan circuit thrombus and markers of Fontan circulatory dysfunction; and (3) the association of Fontan circuit thrombus with adverse cardiac outcomes.

METHODS

We conducted a retrospective review of adult patients who underwent the Fontan procedure (aged > 18 years) followed at St. Paul's Hospital who underwent cardiac computed tomography or magnetic resonance imaging assessment (n = 67). Fontan circulatory dysfunction markers included clinical heart failure, N-terminal pro-brain natriuretic peptide, ventricular dysfunction, atrioventricular valvular regurgitation, refractory arrhythmias, declining exercise capacity, and hepatic/renal dysfunction. Adverse cardiac outcomes were death, heart transplantation, or surgery for Fontan revision or atrioventricular valve replacement.

RESULTS

Fontan circuit thrombus was present in 15 of 67 patients (22%): 41% (7/17) classic/modified Fontan and 16% (8/50) total cavopulmonary connection. Incidence was 36% among those suspected to have Fontan circuit thrombus; 14% in those with no clinical/echocardiographic suspicion; and clinically silent in 40% diagnosed with Fontan thrombus. The time from Fontan surgery to Fontan circuit thrombus diagnosis was 22 ± 6 years in the classic/modified group vs 14 ± 8 years in the total cavopulmonary connection group (P = 0.03. Fontan circuit thrombus was associated with adverse cardiac outcomes (27% [4/15] vs 8% [4/52], P = 0.02), but there was no difference in Fontan circulatory dysfunction markers.

CONCLUSION

Given the incidence of Fontan circuit thrombus and association with adverse cardiac outcomes, routine surveillance of the Fontan circuit should strongly be considered. The identification of thrombus should lead to anticoagulation implementation/optimization, along with screening/intervention for reversible Fontan circulatory issues in an attempt to prevent adverse cardiac outcomes.

Risk of thromboembolic complications in adult congenital heart disease: A literature review

Adult congenital heart disease (ACHD) is a constantly expanding population with challenging issues. Initial medical and surgical treatments are seldom curative, and the majority of patients still experience late sequelae and complications, especially thromboembolic events. These common and potentially life-threating adverse events are probably dramatically underdiagnosed. Better identification and understanding of thromboembolic risk factors are essential to prevent long-term related morbidities. In addition to specific situations associated with a high risk of thromboembolic events (Fontan circulation, cyanotic congenital heart disease), atrial arrhythmia has been recognized as an important risk factor for thromboembolic events in ACHD. Unlike in patients without ACHD, thromboembolic risk stratification scores, such as the CHA₂DS₂-VASc score, may not be applicable in ACHD. Overall, after a review of the scientific data published so far, it is clear that the complexity of the underlying congenital heart disease represents a major risk factor for thromboembolic events. As a consequence, prophylactic anticoagulation is indicated in patients with complex congenital heart disease and atrial arrhythmia, regardless of the other risk factors, as opposed to simple heart defects. The landscape of ACHD is an ongoing evolving process, and specific thromboembolic risk scores are needed, especially in the setting of simple heart defects; these should be coupled with specific trials or long-term follow-up of multicentre cohorts.

Vortex Flow in the Right Atrium Surrogates Supraventricular Arrhythmia and Thrombus After Atriopulmonary Connection-Type Fontan Operation: Vortex Flow Analysis Using Conventional Cine Magnetic Resonance Imaging

We developed a novel imaging technique, designated as vortex flow (VF) mapping, which presents a vortex flow visually on conventional two-dimensional (2D) cine MRI. Using it, we assessed circumferential VF patterns and influences on RA thrombus and supraventricular tachycardia (SVT) in AP connection-type Fontan circulation. Retrospectively, we enrolled 27 consecutive patients (25.1 ± 9.2 years) and 7 age-matched controls who underwent cardiac MRI. Conventional cine images acquired using a 1.5-Tesla scanner were scanned for axial and coronal cross section of the RA. We developed "vortex flow mapping" to demonstrate the ratio of the circumferential voxel movement at each phase to the total movement throughout a cardiac cycle towards the RA center. The maximum ratio was used as a magnitude of vortex flow (MVF%) in RA cine imaging. We also measured percentages of strong and weak VF areas (VFA%). Furthermore, in 10 out of 27, we compared VF between previous CMR (3.8 ± 1.5 years ago) and latest CMR. Of the patients, 15 had cardiovascular complications (Group A); 12 did not (Group B). A transaxial image showed that strong VFA% in Group A was significantly smaller than that in Group B or controls. A coronal view revealed that strong VFA% was also smaller, and weak VFA% was larger in Group A than in Group B or controls (P < 0.05, and P < 0.05). Maximum MVF% in Group A was significantly smaller than in other groups (P < 0.001). Univariate logistic analyses revealed weak VFA% on a coronal image, and serum total bilirubin level as factors affecting cardiovascular complications (Odds ratio 1.14 and 66.1, 95% CI 1.004-1.30 and 1.59-2755.6, P values < 0.05 and < 0.05, respectively). Compared to the previous CMR, smaller maximum VMF%, smaller strong VFA%, and larger weak VFA% were identified in the latest CMR. Circumferentially weak VFA% on a coronal image can be one surrogate marker of SVT and thrombus in AP connection-type Fontan circulation. This simple VF assessment is clinically useful to detect blood stagnation.

Prevalence and outcome of thrombotic and embolic complications in adults after Fontan operation

There are limited studies of thrombotic and embolic complications (TEC) in the adult Fontan population. The purpose of the study was to determine the prevalence, risk factors, and outcomes of TECs in this population.

METHODS

Retrospective review of adults with a previous Fontan operation, with follow-up at Mayo Clinic, 1994-2014. Systemic TEC was defined as intracardiac thrombus, ischemic stroke, or systemic arterial embolus. Nonsystemic TEC was defined as Fontan conduit/right atrial thrombus or pulmonary embolus.

RESULTS

We identified 387 patients with a mean (SD) age of 28 (7) years and a mean follow-up of 8 (2) years. An atriopulmonary connection (APC) was done for 286 patients (74%). Atrial arrhythmias were present in 278 (72%). There were 121 TECs (systemic n=36, nonsystemic n=85) in 98 patients (25%). Risk factors for systemic TEC were atrial arrhythmia (hazard ratio 2.28, P=.001) and APC (hazard ratio 1.98, P=.02); nonsystemic TEC also had similar risk factors. All 98 patients received warfarin. Warfarin was discontinued in 10 of 98 because of bleeding, and 8 of these 10 subsequently had a second TEC. Among the 82 patients who had follow-up imaging, 16 (20%) had resolution of thrombus. In total, 24 of 98 patients had a second TEC, most of whom had inadequate anticoagulation.

CONCLUSIONS

Thrombotic and embolic complication was not uncommon; risk factors for TEC were APC and atrial arrhythmias. Most patients were treated successfully with warfarin alone. A second TEC occurred in most patients whose anticoagulation was discontinued because of bleeding events.