Division of Paediatric Cardiology, Department of Paediatrics and Adolescent Medicine, Queen Mary Hospital, The University of Hong Kong
Fontan-type procedures are palliative for patients with functional single ventricles. The initial Fontan operation has since its description undergone several modifications from atriopulmonary connection through lateral tunnel to extracardiac conduit procedures. Notwithstanding, volume unloading of the systemic ventricle, acquired myocardial hypertrophy, and progressive ventricular remodeling still occur after the modified Fontan-type procedures and have impact on cardiac function. Ventricular diastolic functional abnormalities are characterized by early impairment of relaxation in association with incoordinate myocardial relaxation and late worsening of ventricular compliance. Progressive systolic ventricular dysfunction due to increased systemic afterload, atrioventricular regurgitation, and intrinsic alteration of myocardial architecture may eventually occur. Regular assessment of cardiac function is hence of paramount importance in long-term follow up of Fontan patients and echocardiography remains the most useful and convenient imaging modality. The complex anatomy of functional single ventricles may, however, invalidate the use of conventional geometric echocardiographic indices of systolic ventricular function. Non-geometric echocardiographic indices including the Doppler-derived mean ventricular pressure change during isovolumic contraction, myocardial performance index, and annular velocities can overcome some of the limitations. Introduction of speckle tracking echocardiography has further enabled direct interrogation of myocardial deformation, which may be less preload dependent and provide prognostic information on survival. Occurrence of mechanical dyssynchrony of the functional single ventricles is also increasingly recognized, assessment of which may guide resynchronization therapy for patients in heart failure. Apart from ventricular dysfunction and dyssynchrony, atrial dysfunction may potentially also play a pathophysiological role in Fontan circuit dysfunction and can be assessed echocardiographically. The ability to better define cardiac mechanics by noninvasive echocardiographic evaluation may help to decide on the institution of medical and surgical interventions to delay the failure of the Fontan circulation and to manage the failed ones.