Fontan circulation: unraveling the individual determinants of functional limitation

Fontan palliation is associated with a long list of factors that can contribute to functional impairment. Some of them are directly related to the very nature of the Fontan circulation (systemic venous hypertension, low cardiac output, pulmonary vascular disease), while others are still poorly understood (lymphatic abnormalities, Fontan associated liver disease). A third and very heterogeneous group depends on the baseline cardiac anatomy (ventricular morphology, associated valvular or vascular anomalies) or arise from complications of staged surgeries needed to achieve Fontan circulation (pulmonary vein compression after atrio-pulmonar Fontan or hepatopulmonary syndrome after the Kawashima procedure). To top it all, other cardiac problems arise during follow up, including diastolic and systolic dysfunction, arrhythmias, or development of new veno-venous and systemic to pulmonary anomalous collateral vessels.

This complex and sometimes overwhelming landscape paves the road of what we call Fontan failure (1), a broad term that can be drastically different from one patient to another, thus allowing many different approaches and therapies to tackle it. The importance of thorough and extensive evaluation of each patient to unravel the main determinants of worsening functional class cannot be emphasized enough.

Miranda et al describe in this recent communication (2) the useful role of exercise catheterization as a diagnostic tool for failing Fontan. Albeit a short one, the series of cases exemplifies brilliantly the strengths of invasive hemodynamics during exercise to unmask various conditions, from AV valve or conduit stenosis to severe diastolic ventricular dysfunction. Some of the main take-home messages are:

• Gradients at rest, especially in the Fontan circuit, can be deceivingly low or even normal, and significant stenosis may only be detected during exercise. Suspicion based on anatomic appearance or on secondary FALD may prompt dynamic evaluation if basal pressures are normal, and percutaneous treatment of the stenosis if needed and feasible.
• Exertional dyspnea may be associated with marked elevation of Fontan pressure, even in patients with apparently normal pressures at rest. This elevation is usually driven by diastolic dysfunction, characterized during effort by a high ratio between the increase of filling pressures and the increase of cardiac output (ΔPAWP/ ΔCO, mmHg/l/min) (3), but can also be related to AV valve stenosis, evaluated by echo or measuring simultaneously the telediastolic ventricular pressure. Alternatively, a mild elevation of pulmonary vascular resistance can also be detected suggesting the possible use of pulmonary vasodilators.
• Peripheral impairment, which has been studied in the context of heart failure with preserved ejection fraction, can be an important factor contributing to functional limitation (4). Sarcopenia, abnormal skeletal muscle function, and deconditioning are all involved in this condition and are all frequent among congenital heart disease patients. Insufficient peripheral oxygen uptake coupled with normal resting and exercise pressures can point in this direction, which may benefit from a prescribed exercise program.
  Although exercise catheterization has been around for a long time, its use has never been widespread because it is time-consuming, technically nuanced, and difficult to standardize. That being true, the reawaked interest for its potential use in many different situations, from heart failure with preserved ejection fraction to pulmonary arterial hypertension, is slowly making it more available. This work shows how it may help to further tailor the care of Fontan patients and could be considered if the initial diagnostic workup is normal, contradictory, or insufficient to explain the patient’s clinical status. Whether this approach will lead to a therapeutic changes with an impact on the prognosis remains to be determined.