Discussion

This complex case of a teenage boy with massive, mobile right ventricular thrombi culminating in life-threatening pulmonary embolism despite therapeutic anticoagulation highlights critical dilemmas in management. It underscores that in the presence of high-risk thrombus morphology, conventional first-line therapy may be inadequate, and a multidisciplinary strategy guided by advanced imaging is imperative.

The initial diagnostic challenge centred on the definitive characterization of the right ventricular masses. While echocardiography served as the cornerstone, our case exemplifies the complementary value of a multimodal approach. Transthoracic echocardiograph identified three distinct right ventricular masses, notably two highly mobile lesions. Although this morphology was highly suggestive of Type A (“in-transit”) thrombi and conferred an extremely high embolic risk, ^{1,Reference Dinesh Kumar, Nareppa and Shetty2} echocardiography alone proved insufficient to definitively characterize the masses. Crucially, cardiac MRI with late gadolinium enhancement provided definitive characterization by demonstrating complete avascularity, effectively ruling out neoplasm. ^{Reference Motwani, Kidambi and Herzog3,Reference Barbagallo, Naef and Köpfli4} Both echocardiography and MRI revealed severe right ventricular dysfunction and pulmonary hypertension. Concurrently, CT pulmonary angiography detailed the massive, bilateral pulmonary embolism burden, and unveiled characteristic features of chronic thromboembolic pulmonary hypertension. This imaging triad did not merely diagnose right ventricular thrombus; it painted a complete picture of high embolic potential (morphology), definitive nature (avascularity), and severe physiological impact (massive pulmonary embolism, pulmonary hypertension, and right ventricular dysfunction).

The patient’s clinical deterioration despite therapeutic anticoagulation underscores the recognized limitation of anticoagulation for mobile, high-risk right ventricular thrombus. ^{Reference Athappan, Sengodan and Chacko5,Reference Sakellariou, Efstathopoulos and Stamatis6} Given the type A morphology and the already-manifested large pulmonary embolism, the risk of further, potentially fatal embolization was deemed unacceptable. Our patient met the criteria for American Heart Association/American College of Cardiology pulmonary embolism category C3 (symptomatic, elevated severity score, abnormal right ventricular function, and positive biomarkers). As such, current guidelines provide a Class 2a recommendation for advanced therapies over anticoagulation alone to mitigate clinical deterioration. ^{Reference Creager, Barnes and Giri7} While systemic thrombolysis is an option, the concern for fragmentation of such large, highly mobile thrombi and exacerbation of pulmonary hypertension favoured a definitive surgical approach. Specifically, underlying chronic thromboembolic pulmonary hypertension drove the decision to pursue a single-stage surgical approach encompassing both emergent thrombectomy and pulmonary endarterectomy—a procedure best achieved surgically. This strategy allowed for complete removal of the right heart thrombotic source, extensive pulmonary endarterectomy to address chronic changes, and incidental atrial septal defect repair in a single procedure. The immediate postoperative result—a dramatic drop in mean pulmonary arterial pressure from 59 mmHg to 22 mmHg—confirms the haemodynamic rationale for this aggressive intervention and aligns with outcomes sought in pulmonary endarterectomy for chronic thromboembolic pulmonary hypertension management. ^{Reference Delcroix, Torbicki and Gopalan8}

A comprehensive thrombophilia workup, extending to whole-exome sequencing, yielded no definitive cause. The transient depression of protein C and S levels was likely acute-phase/reactant, given the confounding effect of heparin therapy and the negative genetic screen. The lack of deep vein thrombosis argues against a simple “in-transit” phenomenon from the periphery, suggesting possible in situ formation in a predisposed heart, though no structural or arrhythmogenic cardiomyopathy was identified. This diagnostic ambiguity directly informed long-term management. Despite surgical clearance of the major thrombi, the presence of residual peripheral emboli and the idiopathic nature of the event justified the recommendation for lifelong anticoagulation, consistent with guidelines for similar high-risk scenarios. ^{Reference Delcroix, Torbicki and Gopalan8} Bosentan was utilized in the context of the preoperative chronic thromboembolic pulmonary hypertension diagnosis.

In conclusion, this case highlights a refined approach in managing paediatric right ventricular thrombi. Multimodal imaging—specifically cardiac MRI—was pivotal for tissue characterization, allowing for definitive differentiation of the right ventricular mass and risk stratification. Crucially, the combination of a highly mobile right ventricular thrombus and underlying chronic thromboembolic pulmonary hypertension drove the decision to pursue a single-stage surgical approach encompassing both emergent thrombectomy and pulmonary endarterectomy—a procedure best achieved surgically. This case underscores the necessity of individualized, multidisciplinary evaluation to balance the risks of embolism against intervention, ultimately leading to successful salvage.