Exercise in children with common congenital heart lesions: Balancing benefits with risks
- Conflict of interest: No conflicts of interest to report for any authors.
Children with corrected common congenital heart lesions are often withheld from regular exercise by their parents. While there are some modest risks with exercise, they should be seen in perspective, and the life-long benefits of regular exercise on general health, mood and well-being should be emphasised.
- The impact of reduced habitual activity has significant consequences for all children on long-term outcomes such as cardiovascular health, weight and level of fitness, which may be more pronounced in those with surgically corrected congenital heart lesions who are electively declining participation in exercise.
- Exercise limitation may be a clinical manifestation of the complex cardiopulmonary interdependency.
- Long-term follow-up should include assessments of cardiac structure and function, exercise, lung function and growth parameters.
Exercise is an important aspect of the physical and mental well-being of children. This is especially evident in a country such as Australia where the climate and life-style are conducive to exercise. The impact of reduced habitual activity has significant short and long-term consequences. In the short term, a negative feedback loop can be created where reduced exercise capacity leads to reduced habitual activity, and declining participation in sport, further reducing exercise capacity.[1-3] This may impact on a child's general health and well-being, their mood as well as their self-esteem. Moreover, there are long-term consequences for the individual who has become deconditioned, such as an increased risk for cardiovascular disease, osteoporosis and obesity.
For parents of children with congenital heart disease (CHD), there is an added concern of whether their child is able to be active, or whether exercise will have a detrimental effect on their child's health. Few studies have been conducted on this question and as such, there is a limited evidence base for any recommendations regarding habitual exercise. Consequently, in an era of evidence-based medicine, existing guidelines are suboptimal when assisting clinicians and parents in deciding upon an appropriate prescription for exercise in children with haemodynamically significant CHD.
Benefits and Risks of Exercise
In the general population, regular exercise combined with a balanced diet has been shown to reduce the risk of Type II diabetes and cardiovascular disease, strengthen bone health and assist with weight management. Exercise also helps reduce the risk of colon and reproductive cancers and is efficacious in reducing levels of stress. The benefits of exercise are apparent across the age range.
Regular exercise in childhood helps to establish good habits for life and improves overall health.[1-3] It has been shown that the amount of regular, moderate and vigorous physical activity started early in childhood is a significant predictor of bone mineral density (BMD) in later childhood. If a higher BMD is maintained, an increase in peak bone mass would be expected, which is thought to be a critical factor in the reduction of fracture risk during adulthood. Children who exercise regularly have healthier lipid profiles, which is expected to help reduce the risk of atherosclerosis and hypertension later in life. Furthermore, positively reinforcing good exercise habits early in life makes it easier to continue to exercise into adulthood.
It is widely accepted that exercise participation decreases during adolescence, with girls being less active than boys.[1, 2] It was suggested by Malina that this decrease in exercise during adolescence is a result of changing interests, the social demands of adolescence and the transition from school to work or university. Strong suggested that girls stop participating in exercise because they perceive that the activities are no longer fun, are too competitive or demand too much time. Interestingly, Ammouri et al. found that increased screen time was not associated with less exercise participation and thought it was likely that, although adolescents spend large amounts of time in front of a screen, they still attain adequate amounts of exercise. Adolescents and young adults are more likely to be active if they were active as children, with this trend continuing into adulthood. Therefore, to produce healthy and active adults, the importance and habits of regular exercise should be instilled in childhood and reinforced during the adolescent years.
Regular exercise is associated with a decrease in all-cause mortality. Exercise can lower blood pressure, improve lipoprotein profile, enhance insulin sensitivity and play an important role in weight management. These health benefits can be attained by a minimum of three weekly sessions of vigorous activity. By way of example, this could include activities that would increase the heart rate to above 80% of maximal heart rate in interval training sessions (e.g. running). Interestingly, several studies have shown that at only half the volume of exercise of these recommendations, significant risk reductions for cardiovascular disease and premature mortality can be observed.
Osteoporosis is a common disease that most often presents in the elderly because of the increase in the loss of bone minerals with age. Osteoporosis is associated with an increased fracture risk, especially fractures of the hip, vertebrae and wrist. Most fractures in the elderly are the result of a fall occurring on a background of osteoporosis. Hip fractures are the most debilitating and are associated with significant morbidity and mortality in the elderly. Exercise interventions have been shown to both increase BMD through weight-bearing exercise and decrease the risk of falls through increasing balance and muscle strength.
Risks for people with structural heart disease
It has been reported that light to moderate physical activity poses no greater risk of sudden cardiac death (SCD) than you would expect of chance alone in the healthy adult population. However, in individuals with known cardiovascular disease, vigorous exercise increases the risk of SCD substantially. On autopsy, the major cause of unexpected SCD in younger athletes is previously unidentified, inherited structural heart abnormalities with hypertrophic cardiomyopathy, the most common, followed by structural malformations of the coronary arteries. The American Heart Association states that the incidence of SCD during exercise performed at light to moderate intensities is similar to what would be expected by chance and stratifies risks accordingly (Table 1). It therefore appears that it is a combination of strenuous exercise and an unidentified, structurally abnormal heart that leads to SCD.
Table 1. New York Heart Association (NYHA) Functional Classifications
|I||No symptoms and no limitation in ordinary physical activity, e.g. shortness of breath when walking, climbing stairs, etc.|
|II||Mild symptoms (mild shortness of breath and/or angina) and slight limitation during ordinary activity.|
|III||Marked limitation in activity due to symptoms, even during less-than-ordinary activity, e.g. walking short distances (20–100 m). Comfortable only at rest.|
|IV||Sever limitations. Experiences symptoms even while at rest. Mostly bedbound patients.|
Respiratory and Cardiac Interaction
The cardiovascular and respiratory systems are interdependent. Therefore, the respiratory system must be considered when treating patients with CHD. CHD is associated with abnormal pulmonary haemodynamics and altered gas exchange. Respiratory compromise may be associated with increased pulmonary blood flow and raised pulmonary artery pressure.
It has been suggested that early full repair of patients with tetralogy of Fallot (TOF) improves lung development. Gaultier et al. showed that patients who had a full TOF repair (aged 4–19 months) had higher values on pulmonary function tests at a mean age of 3.9 years compared with those with a later age at repair of their tetralogy. This age range of tetralogy repair is now considered broad and current procedures differ from 25 years ago, in that, many children have their definitive repair prior to 6 months of age. Consequently, children undergoing corrective surgery for their tetralogy in the first 6 months of life today may have better results on spirometry testing in childhood than those in previously reported series.
Left-to-right shunts, such as in atrial septal defects (ASDs) and ventricular septal defects (VSDs), are a cause of raised pulmonary arterial pressures and potentially mild hypoxaemia, which may be seen in infants with CHD. After cardiac surgery in patients with previously normal lungs, respiratory mechanics decline acutely. This decline is usually the result of an increase in airway resistance and lung stiffness. However, there is comparatively little data on long-term outcomes on lung mechanics in children with repaired CHD.
One of the most serious complications of CHD is pulmonary vascular disease in those patients where pulmonary blood flow is increased for long periods. Persisting elevation of pulmonary blood flow results in elevated pulmonary vascular resistance and pulmonary hypertension. When the pulmonary hypertension reaches supra-systemic levels, it may become irreversible and preclude successful surgical correction of CHD. It is unclear whether mild to moderately raised pulmonary arterial pressures in early childhood are associated with significantly altered lung function and exercise tolerance in later childhood.
Clinical and Physiological Outcomes
It is often assumed that after an early repair of an ASD, the heart functions completely normally. In contrast, sinus node dysfunction, atrial fibrillation, right ventricular dilatation, pulmonary hypertension, atrial flutter and left ventricular dysfunction may uncommonly occur post-operatively in children and adults following ASD repair in series reported over the last 15 years.[22-24]
VSDs are the most common congenital heart defect.[25-27] They are usually non-life threatening, especially small muscular VSDs that usually close spontaneously over months to years.[25, 27] Typically, it is suggested that patients with small unrepaired VSDs remain asymptomatic from the exercise viewpoint, as children.
Gabriel et al. studied a population of adults (mean age 30 ± 10 years) with small VSDs that did not require surgical correction. The VSDs were classified as perimembranous (84.8%), trabecular (13.1%), outlet infracristal (1.7%) and inlet (0.4%). They reported that 13% of their study population had a ventricular arrhythmia. Roos-Hesselink et al. found that 8% of their study population (median age of surgical closure 4 years) showed ventricular tachycardia on 24-h ambulatory monitoring at a follow-up of 30 years of age (range 21–44 years). Rodriguez et al. studied the prevalence of hospitalisations of adults with CHD with septal defects in America. Their study population was aged 18–50+ years with an ASD, VSD or atrioventricular septal defect. They reported that arrhythmias accounted for 31% of cardiovascular hospital admissions with 9% being ventricular arrhythmias. The limitations of such an audit include multiple centres with differing levels of expertise and protocols for intra-operative and perioperative management (e.g. myocardial protection strategies).
Long-term survival is now excellent after a complete repair of TOF with up to 85% of patients surviving more than 30 years.[30, 31] However, there are three major long term sequealae: the haemodynamic manifestations of chronic pulmonary valve incompetence, recurrent or residual pulmonary stenosis and ventricular arrythmias. The study by Rathore et al. found that postoperatively 65% of their patients (aged 7.9 ± 3.6 years) had right ventricular restrictive physiology because of reduced diastolic function of the right ventricle, 71% had mild to moderate pulmonary valve regurgitation, 24% had right bundle branch block and 4% had first degree atrioventricular block. Factors influencing these findings may have included the age at repair and the number of subjects with transannular patches. Bacha et al. reported similar findings with pulmonary regurgitation and also stated that 14% of their patients had mild right ventricular outflow tract obstruction, which was not thought to be haemodynamically important. The unresolved issue for teenagers and young adults following early repair of TOF is the optimal timing of further interventions to treat severe pulmonary regurgitation or pulmonary stenosis, both complications which may present with exercise limitation. Consequently, the clinician has to juxtapose life-style limitations and quality of life for the patient with limiting the number of lifetime surgical interventions and the likely associated risks and benefits. In this setting, exercise testing provides a useful source of objective information to consider along with reported alterations in exercise tolerance and echocardiographic findings related to right ventricular outflow tract blood flow dynamics.
Exercise Methods and Protocols
The treadmill and cycle ergometer are considered the ‘gold standard’ for exercise testing. However, they require equipment that is expensive, and they do not imitate a child's normal physical activity. Testing performed in a laboratory setting can be intimidating, especially for small children, and they may therefore not perform the test correctly. Field testing is a way to overcome these hurdles as they replicate the ‘gold standard’ of the treadmill and cycle ergometer, but are performed without the use of expensive and specialised equipment and are undertaken in a non-intimidating environment.
The 6-minute walk test (6MWT) is one of the most widely used field tests because it ‘is easy to administer, better tolerated, and more reflective of activities of daily living than other walk tests’. The 6MWT measures the distance a patient can walk in 6 minutes on a hard flat surface. The 6MWT is a self-paced test that assesses a patient's submaximal functional capacity. Patients choose the intensity they would like to walk at and are able to stop and rest during the test. Therefore, most patients do not reach maximal exercise capacity during the 6MWT. Nonetheless, because most habitual activity is performed at a submaximal level, the distance a patient walks in a 6MWT may better reflect their functional capacity. Along these lines, the 6MWT has been used previously to monitor progress in children with other chronic conditions associated with reduced exercise capability including haemophilia, juvenile idiopathic arthritis and spina bifida.
Cycle ergometer and treadmill testing
The cycle ergometer and treadmill ergometer are considered to be the two ‘gold standard’ ergometers for measuring maximal oxygen consumption (VO2 max). It has been demonstrated that treadmill testing elicits a VO2 7–19% greater than that of cycle testing, requiring specific norms to be established for each ergometer. The cycle ergometer is often difficult to use in children as it has to be modified for different body sizes during growth. The cycle ergometer is more likely to cause local leg muscle fatigue whereas the treadmill ergometer requires a more habitual movement and does not require modifications for different body sizes. During a cycle ergometer test, children are required to maintain a pace set by the tester, whereas during a treadmill ergometer test the pace is set by the incremental protocol used by the treadmill.
There are several different protocols that can be used to measure VO2 max with a treadmill ergometer.[37-39] The most common are the Bruce and Balke protocols, which were originally developed for use in adults. However, the Balke protocol goes for too long and requires too high a gradient for children. The Bruce protocol is the most widely used protocol in children. However, the increments between stages are too large for young children. The modified Bruce protocol has been established as the protocol of choice when using the treadmill to test VO2 in children as it requires smaller increments between stages. Exercise testing in children younger than 7 or 8 years is not advised as it is difficult for them to understand the test and therefore achieve a maximal effort.
Current recommendations regarding exercise participation in children with CHD
The health benefits of exercise are widely known for the general population. However, there is limited literature available on sports participation in patients with CHD. As a result, a conservative approach is usually taken, with an emphasis on non-contact sports and activities with mild to moderate physical exertion.
The European Society of Cardiology suggests that if a patient with CHD wishes to participate in competitive sports, their pre-participation screening should be extensive. A patient is eligible to participate in competitive sports if they have had a full surgical correction, are New York Heart Association class I (Table 1), their electrocardiography is normal, are haemodynamically stable and their spirometry values are within normal range.
Both the European Society of Cardiology recommendations (2006) and the results of the Bethesda Conference (2005) suggest that patients with a closed or non-significant ASD or VSD have no restrictions on sport participation.[39, 40] Patients with successfully repaired TOF are restricted to low to moderate dynamic and static sports such as diving, gymnastics, baseball and golf. Patients who have TOF with marked pulmonary regurgitation, significant right ventricular hypertension or tachyarrhythmias are restricted to low dynamic and static sports such as bowling, cricket and golf.
It remains presumed rather than proven that once a child has had a complete surgical repair of their CHD, especially early in life, if their heart function is ‘normal’ or ‘satisfactory’, then pulmonary function and exercise capacity should be ‘normal’ also. However, the limited literature suggests that a range of complications can occur in even the simplest cardiac lesions, and lung mechanics may be altered, compromised by the early abnormal heart function, the general anaesthetic required or the bypass surgery needed to correct the cardiac lesion in infancy or early childhood. Exercise limitation may be a clinical manifestation of the complex cardiopulmonary interdependency. Therefore, long-term follow-up is required of these children and should include assessments of cardiac structure and function, lung function and growth parameters. Furthermore, the effects of physiological challenges such as exercise and hypoxia in children with repaired CHD need to be further evaluated.
Three Multiple Choice Questions
- 1.Regular exercise
- Has no impact on blood lipid levels. (False)
- Is not encouraged in children with CHD. (False)
- Participation in early childhood is a predictor of BMD in later childhood. (True)
- Declines similarly in males and females in adolescence. (False)
- Typically increases in the adolescent years. (False)
Regular exercise in childhood is of benefit for lipid profiles and BMD and may reduce the risks of atherosclerosis and hypertension in later life. Participation rates for exercise decline in adolescence, more so in girls. Children with CHD benefit like all children, although some restrictions on intensity of exercise may be appropriate for certain cardiac conditions.
- 2.Children with TOF
- Rarely have conduction abnormalities following definitive repair. (False)
- Often have significant pulmonary regurgitation or residual right ventricular outflow obstruction, which can present with exercise limitation. (True)
- Who have an early definitive repair may have worse lung function than children who have a later definitive repair. (False)
- Who have exercise limitation should not undergo an exercise test. (False)
- Have a life expectancy of 20 years. (False)
Earlier definitive repair may result in improved lung function. Pulmonary regurgitation and pulmonary stenosis are common sequelae of the repair but in more severe cases may be associated with exercise limitation. Exercise testing is an appropriate dynamic test of cardiorespiratory well-being and is an appropriate tool when attempting to determine the aetiology of exercise limitation. Survival rates of 80% beyond 30 years for repaired TOF are reported.
- 3.Exercise testing in children
- Treadmill or cycle ergometry are routine tests that occur in clinical practice. (False)
- The 6MWT is a maximal test of exercise capacity. (False)
- The 6MWT has not been used in children with chronic disease states. (False)
- The modified Bruce protocol is the protocol of choice using the treadmill to determine VO2 max in children. (True)
- Does not correlate with questionnaire data. (False)
Treadmill testing or cycle ergometry are the gold standards for conducting maximal exercise tests in children. The modified Bruce protocol (from the Adult protocol) is the instrument of choice for maximal exercise testing on a treadmill. Field tests, such as the 6MWT, have been useful in monitoring chronic conditions such as juvenile arthritis and haemophilia, but are self-paced and so most children will not reach their maximal exercise capacity. Questionnaire data, such as from the ‘Habitual Activity and Estimation Scale’ (HAES questionnaire), correlates reasonably well with measured exercise capacity.