Andersons pediatric cardiology 1906

less than 16.6 mL/kg/min CI, Confidence interval HR, heart rate (From Fernandes S, Alexander ME, Graham DA, et al Exercise testing identifies patients at increased risk for morbidity and mortality following Fontan surgery Congenit Heart Dis 2011;6[4]:294–303.) Consequent to improved survival the Fontan population is becoming older, with the average age predicted to increase from 18 years in 2014 to 23 in 2025 and 31 years in 2045.32 The effective management of these patients will depend on the identification of those at greatest risk of decline, as well as potentially modifying the current approach to staged reconstruction on an individual basis Well-defined patient surveillance strategies will allow physicians to deliver timely targeted interventions with the aim of increasing longevity and quality of life (QOL) Consequences of the Fontan Circulation The Fontan circulation is characterized by elevated central venous pressure (CVP) and a low or low-normal cardiac output with a limited capacity to increase cardiac output with exercise Arrhythmias are common and may be caused by atrial distension, especially in the case of the atriopulmonary Fontan, or by scarring subsequent to surgical interventions Elevated CVP and reduced cardiac output adversely affect the function of a number of organs, including the hematologic, renal, liver, and lymphatic systems Many of the resulting problems have an insidious onset, but, as the time passes, they contribute very significantly to morbidity, mortality, and QOL late after the Fontan procedure Impaired Exercise Capacity (see also Chapter 23) Performance of the Fontan circulation is limited at rest and with exercise, even with optimal anatomic and circulatory conditions This remains an issue regardless of the type of Fontan procedure13,34–37 and suggests that the problem relates in a large part to the inherent limitations of the circulation itself In the normal circulation, the subpulmonary ventricle has an important role to play in augmenting cardiac output with exercise Its absence is central to the limited exercise capacity observed in the Fontan population (Fig 73.7) The magnitude of the reduction in exercise capacity is best demonstrated by cardiopulmonary exercise testing.34,38–40 Maximal exercise capacity is determined by the highest uptake and utilization of oxygen by the body during maximal exercise (VO2 max) based on achieving a plateau of VO2 despite an increase in workload.41,42 The highest achieved VO2 value (VO2 peak) is used as a substitute when this plateau is not achieved; a common occurrence in the Fontan population (Fig 73.8) In a structurally normal heart, the major factor limiting VO2 max is cardiac output, which accounts for 70% to 85% of variance, with the remainder being derived by other factors, including pulmonary and skeletal muscle function and cellular metabolism.41,43 Multiple studies have demonstrated reduced VO2 peak or VO2 max in Fontan patients.31,37–39,44–46 Importantly, a lower VO2 peak is associated with an increased risk of morbidity and mortality.21,31,45 There is also reduced workload at maximal effort, a variable reduction of VO2 at ventilatory anaerobic threshold, a reduced peak O2 pulse, and chronotropic incompetence with a blunted peak heart rate response.37–40,44–46