Andersons pediatric cardiology 608

Conditions Where Exercise Testing Is of Value Congenital Cardiac Disease More formal exercise studies have been performed in children with congenitally malformed hearts than any other group of children There is also a robust and growing literature on exercise testing in adults with congenital heart defects Exercise testing in such patients can aid the decision-making process as to whether an intervention such as surgery is needed and can help in assessing the success of a previously performed intervention Unrepaired Congenital Cardiac Lesions Left-sided obstructive lesions, including aortic stenosis, have been the subject of numerous studies and are common reasons for referral of the patient for stress testing The exercise test should evaluate for the presence of subendocardial ischemia A blunted rise in systolic blood pressure may occur in severe cases Results of exercise testing alone are seldom a definitive reason for surgical intervention but may be useful as part of an overall assessment of the severity of obstruction Surgically Repaired Congenital Cardiac Disease Transposition of the Great Arteries Atrial redirection operations were widely used during the 1960s and 1970s, with identified later sequels of atrial arrhythmias, diminished right heart function, chronotropic impairment, and reduced exercise performance.78 Improvements in surgical technique and postsurgical management resulted in the advent of the arterial switch operation in the late 1970s, still used as the procedure of choice at the time of this writing Both physical working and aerobic capacities are clearly superior in patients after an arterial compared with an atrial switch.78,118 Preadolescent patients who have undergone the arterial switch operation as a group have normal consumption of oxygen and maximal cardiac indexes compared with healthy subjects, which is not the case with patients after atrial redirection.92 There is a decline in aerobic capacity in in the adolescent and young adult populations after the arterial switch The reason for this decline is not entirely clear and is most likely multifactorial The potential late-term sequels of reimplanted coronary arteries remain to be seen Published studies to date indicate an incidence of approximately 10% in exercise-induced ischemic changes in patients after an arterial switch.92,119 Studies of myocardial perfusion imaging in this population were discussed earlier Tetralogy of Fallot Most studies of exercise performance before 1990 in patients after surgical repair of tetralogy of Fallot found mild-to-moderate reduction of aerobic capacity compared with healthy controls.69,80,120–127 However, some have reported near normal physical working and aerobic capacities.128 The presence of free pulmonary insufficiency and right ventricular dilation, as well as residual outflow tract obstruction, are considered to be key factors in limiting aerobic capacity in this population, although empiric investigation has found very modest correlation between cardiac magnetic resonance variables and exercise response (e.g., right ventricular ejection fraction was the sole MR correlate of peak VO2 in one study and explained only approximately 19% of peak VO2 variability).129 In adults, both low peak VO2 and elevated VE:VCO2 slope are associated with adverse outcomes including mortality, although it should be noted that increased risk is mainly seen when these values are markedly abnormal.130 The role of exercise testing in the assessment of the efficacy and timing of pulmonary valve replacement in this population is not clearly established at the time of this publication but will most certainly be an evolving subject over the coming years In addition, patients with repaired tetralogy of Fallot often have depolarization and repolarization abnormalities, such that QRS prolongation (≥180 ms) has been attributed to significant arrhythmias and a predictor of late sudden cardiac death Repair of Anomalous Coronary Arteries No significant differences were found in rate of work or consumption of oxygen in patients with anomalous left coronary artery from the pulmonary trunk when repair was performed at less than 2 years of age compared with those repaired beyond infancy,53 albeit that the clinical significance of these findings remains to be seen.53 Exercise testing is considered an essential part of the evaluation of patients with anomalous aortic origin of the coronary artery from the opposite sinus of Valsalva However, its utility in risk stratifying patients for athletic sudden death appears to be poor In the absence of better diagnostic testing, it remains a mainstay of both screening and postoperative assessment for this anomaly.131,132 Fontan Physiology Many studies have shown that patients with the Fontan circulation almost universally have diminished physical working and aerobic capacities and have a high prevalence of chronotropic impairment, reduced stroke volume, intracardiac and intrapulmonary shunting, and abnormal pulmonary mechanics.133–139 Exercise performance in the first decade of life following the Fontan operation is often relatively preserved Maximal oxygen consumption and especially the ventilatory anaerobic threshold are often in the normal range for healthy agematched peers140,141 As this population progresses through adolescence and into young adulthood, there is a steady decline in exercise capacity Studies from this age range indicate that a falling aerobic capacity, especially to less than 50% of predicted, is a strong harbinger for onset of clinical heart failure and increased risk of sudden death.142 Based on these findings, measures of exercise performance are being used to assess clinical efficacy of various therapeutic interventions in the Fontan population.143,144 Heart rate responses are often impaired in patients with the Fontan circulation, and rate responsive pacemakers have been implanted to make the response during exercise as close to normal physiology as possible, but the limited data available have failed to demonstrate an improvement in exercise performance with greater pacemaker rate response despite higher peak heart rate Lower peak VO2 is associated with worse outcomes in the Fontan population, as is a decrease in peak VO2 over time between tests.145–147 Notably, the relationship between VE:VCO2 and outcomes may be less robust in these patients because VE:VCO2 is commonly elevated for various reasons unrelated to outcomes.145,148,149 A specific abnormal ventilatory pattern called exercise oscillatory ventilation is also often present in ambulatory patients with the Fontan circulation and appears to be predictive of worse