Commentaries

Rheumatic heart disease remains a leading cause of valvular heart disease in children and adolescents in low-and middle-income countries, with a disproportionately high burden in sub-Saharan Africa. ^{Reference Zühlke, Karthikeyan and Engel1,Reference Watkins, Johnson and Colquhoun2} While these challenges are not unique to the region, their magnitude and clinical impact are greater in resource-limited healthcare systems. Early disease onset, late diagnosis, and restricted access to prevention favour progression to advanced valvular injury in childhood, often requiring surgical intervention. In this scenario, mechanical valve replacement is often preferred due to its durability, especially in young patients. ^{Reference Zilla, Human and Pennel3}

This intervention, however, imposes a critical dependence on lifelong anticoagulation with vitamin K antagonists. In children, management is particularly complex, given age-related pharmacokinetic variability, growth, dietary fluctuations, and caregiver dependence. In environments with structural limitations, these difficulties become even more relevant.

We define silent anticoagulation failure as a composite, often unrecognised, condition characterised by persistently suboptimal time in therapeutic range, recurrent subtherapeutic INR values, interruptions in access to treatment, and long-term follow-up fragilities. It is a “silent” failure because it tends to manifest only when serious complications arise, such as valve thrombosis or systemic embolism.

This concept differs from the post-valvular anticoagulation gap, which describes the disconnect between the expansion of cardiac surgery and the capacity of healthcare systems to sustain safe anticoagulation. While the latter represents a structural problem, silent failure constitutes its clinical expression.

The scarcity of specific paediatric evidence remains a central limitation. Therapeutic targets and anticoagulation strategies are largely extrapolated from adults or general paediatric thrombosis guidelines. ^{Reference Choaib, AlKhader and Azzam4} This gap reflects the lower need for valve replacement in children in high-income countries, contrasting with low-and middle-income countries, where early rheumatic heart disease progression often leads to surgery at young ages. ^{Reference Carapetis, Beaton and Cunningham5}

In sub-Saharan Africa, studies predominantly in adults or mixed populations show inadequate anticoagulation control, with time in therapeutic range often below 40–50% and fewer than 20% of patients achieving adequate levels. ^{Reference Mwita, Francis and Pillay6,Reference Erba, Tosetto and Langer7} A significant proportion of INR measurements remain subtherapeutic, suggesting a consistent pattern of under-anticoagulation. These data should be interpreted primarily as indicators of healthcare system performance, rather than direct estimates of paediatric risk.

Despite this, limited paediatric data point in the same direction. A study conducted in Dakar found that about one-third of children on anticoagulation experienced haemorrhagic or thrombotic complications, with the risk of death associated with under-anticoagulation and inadequate monitoring often exceeding the haemorrhagic risk, questioning the applicability of conventional strategies derived from high-income contexts. ^{Reference Kane, Fall and Dione8} In paediatric age, therapeutic instability can also compromise neurocognitive development and long-term functional outcomes.

The choice of prosthesis thus raises a clinical and ethical dilemma. Mechanical valves offer greater durability but require reliable anticoagulation; bioprosthetic valves avoid this need but degenerate more quickly in young patients. In contexts where follow-up is inconsistent, the implantation of mechanical valves can expose children to predictable and preventable risks. ^{Reference Manuel9} This raises the question of whether it is ethically justifiable to use a technology that relies on a system that is often not secure.

The fact is that structural and social determinants exacerbate this scenario. INR monitoring is often centralised, implying long journeys and indirect costs. Irregular availability of drugs, fragmented follow-up, and limitations in health literacy hinder adherence. Dependence on caregivers, often constrained by informal work demands, adds an additional layer of vulnerability.

Despite this, isolated experiences on the African continent demonstrate that improvements are possible. In Rwanda, national initiatives integrated guidelines, structured follow-up, and care organisation, showing gains in care continuity. ^{Reference Nkoko, Rusingiza and Mlambo10,Reference Manuel, Bernardo and Gouveia11} Similarly, in Angola, the development of a paediatric medical-surgical centre showed that the expansion of cardiovascular capacity can be achieved through international collaboration and local capacity building. ^{Reference Nunes, Magalhães and Uva12} These examples indicate that the post-valvular anticoagulation gap is not inevitable but results from the misalignment between surgical capacity and follow-up systems.

Overcoming the silent failure of anticoagulation requires coordinated interventions. In cardiac centres, standardised protocols and structured discharge planning are essential. At the community level, decentralisation of INR and involvement of health agents can improve continuity of care. Nationally, integrating anticoagulation into universal coverage and essential medicines lists is fundamental. Globally, equitable partnerships and contextualised research are needed to sustain these changes. Strengthening local leadership will be crucial to ensure continuity and sustainability.

In summary, improving outcomes in children with mechanical valves depends on the alignment between surgical capacity and long-term care infrastructure. Without this alignment, initial survival gains remain vulnerable to preventable complications. The silent failure of anticoagulation thus constitutes not only a clinical challenge but also a concrete manifestation of structural inequalities in global cardiovascular health.