Abstract
- 1.
All patients with ACHD and AF, atrial flutter, or intraatrial reentrant tachycardia should undergo transthoracic and transesophageal echocardiography to rule out a thrombus prior to cardioversion.
- 2.
In patients with Fontan operation presenting with AF, flutter, or IART, the search for an intracardiac thrombus should be performed regardless of the duration of the arrhythmia and prior anticoagulant therapy.
- 3.
Fontan patients with a large intracardiac thrombus should be considered for surgical removal of the thrombus. Conversion to a newer style Fontan can be combined with the thrombectomy operation.
Keywords
Atrial arrhythmia, Atrial fibrillation, Failing Fontan, Fontan circulation, Thrombosis, Ventricular dysfunction
Case Synopsis
A 38-year-old gentleman presented to a routine clinic appointment describing a 4-month history of daily episodes of palpitations lasting between 10 and 20 min and declining exercise tolerance. Although he was continuing to work full time as a support worker in a care home, the severity of his symptoms meant that he was struggling to complete daily activities of living without becoming limited by breathlessness.
His background was that of situs solitus, tricuspid atresia with a rudimentary right ventricle, severe pulmonary stenosis, and normally related great vessels. When the patient was 2 months old, a right Blalock-Taussig shunt was performed, and he subsequently underwent a classic atriopulmonary Fontan at 10 years of age. During his childhood, the patient suffered from severe kyphoscoliosis, for which he underwent a spinal fusion procedure at the age of 18 years.
The patient was under regular follow-up at a specialist adult congenital heart disease (ACHD) institution and had enjoyed a long preceding period of clinical stability. During his previous clinical review, he had described symptoms consistent with New York Heart Association Class II–III. At that point, a cardiac MRI had showed reduced left ventricular function (LVEF 42%), long-standing severe right atrial dilatation, and patent Fontan pathways, without evidence of intracardiac thrombus. His regular medications included enalapril 2.5 mg twice daily and warfarin, with a target INR range between 2 and 3.
At presentation, he was found to be slightly hypotensive (95/57 mmHg) and tachycardic (120 bpm), with normal oxygen saturations (97%) measured on room air. Auscultation of his chest revealed that he was in an irregular cardiac rhythm, with a single second heart sound present and no additional murmurs audible. He had normal vesicular breath sounds and no hepatosplenomegaly or ascites were detected. There was no sign of peripheral edema and peripheral pulses were easily palpated.
An electrocardiogram performed on admission showed atrial fibrillation (AF) with fast ventricular response (120 bpm), normal axis, and a normal QRS interval ( Fig. 18.1 ). His previous resting electrocardiogram had showed sinus rhythm with stable first-degree atrioventricular block, normal QRS interval, and signs of right atrial dilatation. In addition, a recent 48-h Holter monitor, requested prior to his clinic attendance, had not revealed any significant arrhythmias.
The patient was admitted to hospital for further evaluation, including blood pathology and imaging. His laboratory data revealed a significantly elevated BNP and a mild rise in CRP, with normal renal and liver functions ( Table 18.1 ). A chest radiograph showed clear lung fields, with cardiomegaly due to a prominent bulging at the right heart border relating to the grossly enlarged atrium ( Fig. 18.2 ).
| Value | Normal Range | |
|---|---|---|
| Hemoglobin (g/L) | 144 | [134–166] |
| Hematocrit (%) | 45 | [40–49] |
| MCV (fL) | 88 | [84–98] |
| MCH (pg) | 28 | [28.3–33.3] |
| Platelets (10 9 /L) | 205 | [136–343] |
| WBC total (10 9 /L) | 6.9 | [4.4–10.1] |
| Neutrophils (10 9 /L) | 4.8 | [2.1–6.7] |
| Lymphocytes (10 9 /L) | 1.5 | [1.3–3.7] |
| INR | 2.5 | [2–3] |
| Sodium (mmol/L) | 134 | [133–146] |
| Potassium (mmol/L) | 4.6 | [3.5–5.3] |
| Creatinine (μmol/L) | 60 | [60–120] |
| Bilirubin (μmol/L) | 20 | [<20] |
| ALP (U/L) | 122 | [30–130] |
| ALT (IU/L) | 37 | [8–40] |
| Total protein (g/L) | 80 | [60–80] |
| Albumin (g/L) | 43 | [35–50] |
| BNP (ng/L) | 563 | [<20] |
| CRP (mg/L) | 14 | [<10] |
Transthoracic echocardiography demonstrated a nondilated single left ventricle with moderately to severely impaired systolic function (LVEF 36%). A small rudimentary right ventricle was present, with a nonrestrictive VSD. The mitral valve was of normal function. The aortic valve was trileaflet, with no sign of significant stenosis or regurgitation. The Fontan connections were patent with low velocity, phasic flow. Of particular note, a large thrombus was detected within the severely dilated right atrium, extending from the mouth of the inferior vena cava (IVC) up to the right atrium (RA) connection (7.9 × 3.3 cm, area: 24.6 cm 2 ).
A cardiac magnetic resonance (CMR) examination confirmed the presence of a large thrombus (9.1 × 2.3 cm) situated inferiorly and anteriorly from the IVC-RA connection ( Fig. 18.3 ). The left ventricular ejection fraction was significantly reduced at 36%, a clear deterioration from the preceding CMR study (LVEF 43%). There was unobstructed flow within the Fontan connections.
Questions
- 1.
Should an attempt be made to restore sinus rhythm in this symptomatic patient?
- 2.
Assuming that electric cardioversion is deemed too risky, what are the pros and cons of chemical cardioversion?
- 3.
Should one go with a rate control strategy?
- 4.
What drugs do you recommend for rate control?
- 5.
What anticoagulation strategy would you recommend for this clot?
- 6.
Is he a candidate for surgery to remove the clot + convert to a newer style Fontan with a biatrial Maze?
- 7.
If the thrombus can be made to get smaller and denser-appearing on imaging, can he be considered for cardioversion? Electric cardioversion? Or is that still too risky? What about chemical cardioversion?
- 8.
If the thrombus can be resolved with anticoagulation, can he be considered for ablation?
- 9.
If ablation is not an option, what would be the drug of choice for antiarrhythmic management?
Consultant Opinion #1
- Madhukar S. Kollengode, MD
- Duy T. Nguyen, MD
Since the introduction of a surgical technique to separate the systemic and pulmonary circulations in 1971 by Dr. Fontan and associates, single ventricle palliation has undergone numerous modifications. The initial atriopulmonary (AP) approaches incorporated contractile right atrial tissue into the systemic venous circulation, resulting in marked RA dilation and a high burden of atrial arrhythmias. Although these approaches have been largely abandoned in favor of lateral tunnel or extracardiac conduits, the aging population of patients who underwent AP Fontan palliation means that many adult patients may have a surgical history of this type of Fontan. The ACHD specialist should be familiar with management decisions unique to these patients. This particular case presents a complex set of circumstances not infrequently seen in this population and is an important therapeutic challenge to highlight and discuss.
Thromboembolism is an important cause of late mortality in Fontan patients. The RA dilation seen in AP Fontan patients often results in hemodynamic derangement with atrial stasis with a predisposition to thrombus development. Right-sided thrombus in the setting of AF is associated with an increased risk of pulmonary embolism. In 38% of noncongenital patients with an intracardiac thrombus, a manifest pulmonary embolism has been found. Prior studies in Fontan patients have demonstrated a prevalence of 9%–33% of RA thrombus and up to 16% of asymptomatic pulmonary embolism. Pulmonary embolism results in ventilation-perfusion mismatch and an elevation in pulmonary vascular resistance, both of which are deleterious to Fontan hemodynamics. Thrombus within the Fontan pathway and AF are independent predictors of thromboembolic death.
The first consideration in this patient with AF associated with hypotension and worsening ventricular systolic function is whether or not restoration of sinus rhythm should be attempted . AF with rapid ventricular response is poorly tolerated in patients with the Fontan circulation, where pulmonary blood flow is highly dependent on low filling pressures and diastolic filling. Therapeutic options include rate control or restoration of sinus rhythm (via pharmacologic or electric cardioversion or catheter ablation). Unfortunately, management is confounded by the presence of newly discovered RA thrombus, as restoration of sinus rhythm may result in embolization. Although electric cardioversion is more efficacious than pharmacologic cardioversion, both carry an equivalent risk of embolization and postconversion atrial stunning. Regardless, isolated cardioversion without use of concurrent antiarrhythmic medications in Fontan patients is unlikely to be effective. Catheter ablation of AF in Fontan patients is challenging, and, in this case, carries additive risk of thrombus dislodgement. Thus, we do not advocate initial rhythm control strategy in this situation. We would favor temporizing with a rate control strategy with the intent to improve hemodynamics and allow recovery of systolic function, which has likely deteriorated due to tachycardia-induced cardiomyopathy. β-Blockade should be initially utilized, although dose tolerance may be limited secondary to depressed systolic function and hypotension. Alternative rate control options include digoxin or short-term low dose amiodarone (while an antiarrhythmic, the low dose of amiodarone will have low likelihood of pharmacologic cardioversion, the risks of which are offset by its rate control properties and relative tolerance in those with severe systolic dysfunction). Calcium channel blockers are likely to be poorly tolerated.
Because this patient developed a thrombus while ostensibly on therapeutic warfarin, a review of anticoagulation strategy is warranted. Thromboprophylaxis with both aspirin and warfarin has been shown to reduce the incidence of thromboembolism in Fontan patients, but there is ongoing uncertainty about which strategy is best suited for long-term therapy. In a recent single-center retrospective review of Fontan patients with atrial arrhythmias, treatment with warfarin rather than aspirin was associated with lower rates of thromboembolism. We agree with the utilization of warfarin over antiplatelet therapy with aspirin in this patient. Lack of adequate intensity of anticoagulation is the primary reason for thrombosis while on therapeutic anticoagulation. To prevent clot propagation, we recommend the utilization of high-intensity warfarin therapy (goal INR 2.5–3.5). Alternative considerations include the addition of aspirin or transition to an alternative regimen such as low-molecular-weight heparins. Although non–vitamin K oral anticoagulants (NOACs) have not been studied extensively in patients with congenital heart disease, early reports are encouraging. NOACs may have an increasing role in this population in the future. There is no role for thrombolytic therapy in the absence of hemodynamic instability.
It is unlikely that the thrombus will resolve with 4–6 weeks of increased intensity of anticoagulation. If thrombus is resolved, rhythm control with antiarrhythmic therapy and/or catheter ablation is an option. Antiarrhythmic medications can be considered as an initial option, concurrently with electric or pharmacologic cardioversion. Vaughan Williams Class III agents are good first options. Dofetilide may be a more appealing choice than sotalol if ventricular function remains depressed, to avoid excessive negative inotropy and allow for the addition of guideline-directed medical therapy of ventricular systolic dysfunction. Amiodarone is an efficacious short-term agent, but should be avoided long-term due to toxicity. Given his impaired NYHA functional classification, ventricular dysfunction, and arrhythmias consistent with Fontan failure, dronedarone should ideally be avoided. Vaughan Williams Class Ic agents are probably best avoided in this patient with structural heart disease and poor ventricular function. Catheter ablation can also be considered. Although catheter ablation of atrial arrhythmias in Fontan patients is challenging, a focused ablative approach targeting mechanisms of AF initiation and maintenance can provide durable results.
Fontan conversion with thrombus evacuation and arrhythmia surgery or cardiac transplantation should be considered in this patient with a failing Fontan as evidenced by poor functional status, depressed ventricular function, atrial arrhythmias, and poor flow dynamics. However, he has multiple risk factors for early mortality following Fontan conversion, including gender, age, abnormal hemodynamics, and presence of an intratrial thrombus. Ideally, hemodynamic evaluation with heart catheterization to evaluate and optimize filling pressures would be undertaken prior to consideration of both surgical options. Attempts at rate control and medical therapy for ventricular dysfunction should be utilized and, if unsuccessful or not tolerated, then Fontan conversion with thrombus evacuation and arrhythmia surgery should be attempted.
Summary
AF is associated with ventricular dysfunction, and functional deterioration in Fontan patients should be managed aggressively. Ideally, if no intracardiac thrombus is present, initial management strategies should incorporate prompt cardioversion and initiation of antiarrhythmic therapy as well as anticoagulation. Catheter ablation, either as isolated or adjunctive therapy, can be considered. The presence of an intracardiac thrombus is an important finding that precludes initial rhythm control strategies due to risk of embolism. Attempts to intensify anticoagulation for a period of 4–6 weeks, or as long as patient is stable and improving hemodynamically, and thereafter assess for thrombus resolution are reasonable; however, efforts should be made in the interim to optimize rate control and encourage ventricular functional recovery. Fontan conversion or cardiac transplantation should be considered if medical management is not tolerated or unsuccessful to allow time for thrombus resolution.
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