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What can haemodynamic profiles teach us about heart failure in the paediatric population?

An often-recited teaching point in most medical schools holds that ‘children are not just small adults’. This tenet reminds students and clinicians that many paediatric conditions exhibit different signs and symptoms compared to their adult counterparts. Further, the same disease often arises from different aetiologies and requires different treatments in children, compared with adults. Thus, diagnostic tests, differential diagnoses, and treatment strategies must be based on separate evidence bases from respective paediatric and adult populations. This concept certainly holds true for the syndrome of heart failure (HF). In adults, for example, HF accounts for the largest proportion of hospitalizations in industrialized nations. Adult HF can arise from multiple aetiologies, though in practice the vast majority of HF occurs after pathological insult to the heart (chronic pressure overload, myocardial infarction, or metabolic disease, for example), and develops from the maladaptive responses to these insults. This current paradigm, advanced by basic and translational research, that the adult HF syndrome arises from a common pathological remodelling response to these varied stresses, has paved the way for successful clinical trials studying broad populations of HF patients, generally without regard to the causative nature of the syndrome. These clinical trials represent great successes of evidence-based medicine and came to fruition, in part, by drawing on a large base of epidemiological and physiological research in adults. In stark contrast, HF in children differs in prevalence, in both absolute and relative numbers, from adult HF. Importantly, the aetiologies of HF differ between adults, in which coronary artery disease accounts for the largest proportion of cardiomyopathy, and children, in which congenital heart conditions have a much higher prevalence, and coronary disease remains rare. Furthermore, HF in children can occur at ages ranging from infancy to early adulthood, and therefore may have different pathophysiological effects during these varied stages of active growth and development. For these and other reasons, clinicians hesitate to apply adult HF therapies and guidelines to paediatric populations. The varied epidemiology and unique challenges in paediatric HF populations described above have also limited the opportunities for clinical investigation in this population. Specifically, the haemodynamic profiles of children with HF, and how these relate to outcomes, symptoms, and organ function, remain poorly studied and represent important knowledge gaps in the field. In this issue of European Heart Journal, Chen and colleagues have therefore taken an important step by studying the haemodynamic features specific to children with end-stage HF listed for heart transplant, for which clinical data and guidelines remain particularly sparse. The investigators specifically analyzed the Paediatric Heart Transplant Study database, a large international registry, to investigate the association of haemodynamic profiles with other clinical variables and outcomes. The major findings of the study are that: (i) elevated left-sided filling pressures are highly prevalent in this population and (ii) elevations in pulmonary capillary wedge pressure chiefly predict clinical outcomes and clinical deterioration in this population, whereas decreased cardiac output appears less strongly associated with ultimate change in clinical status. Specifically, their multivariate analysis identified that congestion, as opposed to decreased cardiac output, predicted the severity of symptoms, clinical outcomes, worsening clinical status, and abnormalities of markers of renal and hepatic function. Although the combination of low cardiac output and left-sided congestion predicted worsening outcomes, isolated congestion, but not isolated low output, independently predicted death or clinical deterioration. In other words, reverse or ‘warm’ HF both occurred more frequently and better predicted prognosis than forward or ‘cold’ HF (Figure 1). This study represents the largest effort to date to examine haemodynamics in paediatric patients with end-stage HF. This is of particular importance due to the relative lack of data in the field. Further, the population in this well-designed study encompassed a broad range of HF aetiologies and patient ages, comparable to the populations reflected in clinical practice. In addition to representing a critical piece