Discussion

The current literature suggests that 5–33% patients following a Fontan palliation may incur a thrombotic and embolic complication. The overwhelming majority of these are right atrial/Fontan conduit thrombus (38%), pulmonary embolus (32%), intracardiac thrombus (14%), and ischemic stroke (13%).^{Reference Egbe, Connolly and Niaz1} There are only four reported patients with left ventricle thrombus following a Fontan palliation.^{Reference Lee, Baek and Kim2–Reference Coon, Rychik and Novelle4} Of these, only Lee et al. have furnished a descriptive report of a male patient with double outlet right ventricle and recurrent thrombosis within the rudimentary left ventricle. This patient was diagnosed with cerebral infraction and presented 4 years (age of 7 years) pursuant to a lateral tunnel Fontan palliation with associated symptoms of syncope, motor weakness, and vomiting. The thrombus occurred despite continuous medication with warfarin. Subsequently, the patient required thrombectomy. The authors emphasised the clinical significance of thrombosis an intracardiac blind pouch, formed by the pulmonary stump or rudimentary ventricle, after a Fontan operation.^{Reference Lee, Baek and Kim2} Our patient may also require thrombectomy in the future in consideration of possible systemic embolisation from the thrombus in the rudimentary left ventricle. However, the plan is to continue warfarin therapy at present since there was an improvement in the size of thrombus over the 3 months of treatment. The other three reported patients are not well elaborated.^{Reference Rosenthal, Friedman and Kleinman3,Reference Coon, Rychik and Novelle4}

In older patients following Fontan palliation, the images of echocardiogram are suboptimal due to multiple surgeries, scar formation, and change in the shape of chest. In addition, the slow passive flow within the Fontan conduit and pulmonary arteries makes visualisation of thrombus in these areas quite challenging. However, despite this low sensitivity (23%), the specificity of transthoracic echocardiogram remains high (96%).^{Reference Srichai, Junor and Rodriguez5} So given the low false positivity, a “possible” diagnosis when rendered even in an asymptomatic patient should mandate initiation of therapeutic anticoagulation to avoid serious complications. In such circumstances, it is always preferable to establish a confirmatory diagnosis utilising a cardiac MRI (sensitivity 88%; specificity 99%) rather than a transesophageal echocardiography (sensitivity only 40%).^{Reference Srichai, Junor and Rodriguez5}

Cardiac MRI circumvents the issue of suboptimal images and can differentiate thrombus from tumours.^{Reference Slonimsky, Konen and Di Segni6} Although there was no suspicion of left ventricle tumour in our patient, the cardiac MRI more importantly excluded any additional intracardiac thrombus. The recommended imaging sequences pertinent for evaluation of intracardiac masses include post-contrast sequences such as steady-state free precession, T1, and delayed gadolinium enhancement. These methodologies are useful since thrombi are typically not enhanced after contrast administration.^{Reference Slonimsky, Konen and Di Segni6} A long inversion time (600 ms) for delayed gadolinium enhancement as employed in our case may increase in the sensitivity of this technique for thrombus detection.^{Reference Hoey, Mankad and Al-Chalabi7}

In summary, this case highlights the perplexing clinical triad of (i) a late onset, but fortuitously identified, clinically silent thrombus, (ii) an unexpected location such as the rudimentary left ventricle, (iii) an unsuspecting patient with Fontan palliation devoid of the “usual” thrombogenic risk factors. Antithrombotic prophylaxis with aspirin failed in this patient, but warfarin therapy proved effective in reducing the size of thrombus. Cardiac MRI remains the gold standard for this diagnosis. However, the clinical caveat that a “positive” result noted on transthoracic echocardiogram merits prompt initiation of therapeutic anticoagulation should not be overlooked.