Exercise capacity in pediatric heart transplant candidates: is there any role for the 14 ml/kg/min guideline?

A Systematic Approach for the Interpretation of Cardiopulmonary Exercise Testing in Children with Focus on Cardiovascular Diseases

Cardiopulmonary exercise testing (CPET) is the clinical standard for children with congenital heart disease (CHD), heart failure (HF) being assessed for transplantation candidacy, and subjects with unexplained dyspnea on exertion. Heart, lung, skeletal muscle, peripheral vasculature, and cellular metabolism impairment frequently lead to circulatory, ventilatory, and gas exchange abnormalities during exercise. An integrated analysis of the multi-system response to exercise can be beneficial for differential diagnosis of exercise intolerance. The CPET combines standard graded cardiovascular stress testing with simultaneous ventilatory respired gas analysis. This review addresses the interpretation and clinical significance of CPET results with specific reference to cardiovascular diseases. The diagnostic values of commonly obtained CPET variables are discussed using an easy-to-use algorithm for physicians and trained nonphysician personnel in clinical practice.

Oxygen Uptake Efficiency Slope Predicts Adverse Outcome Following Atrial Switch Procedure

Prior to the 1990s, d-TGA was palliated with the atrial switch procedure resulting in a systemic right ventricle associated with significant long-term morbidity and mortality. Determining the optimal timing of heart transplantation (HT) in these patients has been difficult. While cardiopulmonary exercise testing (CPET) is commonly used to try and risk stratify these patients, traditional exercise parameters have lacked the sensitivity and specificity to assess long-term risk. We sought to assess changes in exercise parameters over time in order to determine if any CPET parameter or combination of parameters could reliably identify risk for adverse outcome in this patient group. A retrospective review of serial CPET for 40 patients over 17 years was completed. Patients with adverse event within 6 months prior to CPET were noted. CPET parameters were compared and linear mixed model regression with repeated measures was performed on serial tests for longitudinal assessment. The linear mixed model regression identified OUES indexed to BSA to be the most sensitive parameter in identifying patients at risk of adverse event and became a stronger predictor of adverse event when combined with peak heart rate. CPET is useful in identifying patients with atrial switch at increased risk of adverse outcome. Indexed OUES and peak heart rate are better prognostic indicators than VO₂ and VE/VCO₂.

Clinical utility of preoperative pulmonary function testing in pediatrics

Perioperative respiratory adverse events pose a significant risk in pediatric anesthesia, and identifying these risks is vital. Traditionally, this is assessed using history and examination. However, the perioperative risk is multifactorial, and children with complex medical backgrounds such as chronic lung disease or obesity may benefit from additional objective preoperative pulmonary function tests. This article summarizes the utility of available pulmonary function assessment tools as preoperative tests in improving post-anesthetic outcomes. Currently, there is no evidence to support or discourage any pulmonary function assessment as a routine preoperative test for children undergoing anesthesia. In addition, there is uncertainty about which patients with the known or suspected respiratory disease require preoperative pulmonary function tests, what time period prior to surgery these are required, and whether spirometry or more sophisticated tests are indicated. Therefore, the need for any test should be based on information obtained from the history and examination, the child's age, and the complexity of the surgery.

Biomarkers in pediatric heart disease

A biomarker is a characteristic that can be used as an indicator of a biological state. A biomarker can be a clinical observation, laboratory test or an imaging parameter. In this review, we discuss the use of biomarkers in differentiating cardiac from noncardiac disease; predicting the prognosis of patients with heart failure, pulmonary hypertension and dilated cardiomyopathy; diagnosing subclinical cardiac involvement in muscular dystrophy and postchemotherapy cancer patients; detecting acute rejection following heart transplantation; diagnosing Kawasaki disease; aiding the management of postoperative cardiac patients; and managing both common (tetralogy of Fallot) and complex (single-ventricle physiology) congenital heart diseases.

Prognostic Value of Exercise Testing During Heart Transplant Evaluation in Children

Background—

Maximum oxygen consumption (peak VO 2 ) <50% predicted on exercise testing is a class I indication for heart transplant (HT) listing in children. This recommendation is based on exercise data in adults. We assessed the association of peak VO 2 <50% predicted during HT evaluation with freedom from death or deterioration in children.

Methods and Results—

We analyzed all children who underwent exercise testing during HT evaluation at our center between 2002 and 2011. Patients with peak VO 2 <50% predicted were compared with those with peak VO 2 ≥50% predicted for the composite outcome of death before HT, initiation of mechanical circulatory support, and HT at highest urgency status, using time-to-event analyses. There were 50 children in the study (median age, 15 years; interquartile range, 13–17 years; 24 girls; 18 with palliated single ventricle). Overall, 24 children reached the composite end point. Peak VO 2 <50% predicted was associated with outcome in children with biventricular circulation (hazard ratio, 4.7; 95% confidence interval, 1.8–12.3; P <0.001) but not in those with a palliated single ventricle (hazard ratio, 1.3; 95% confidence interval, 0.1–12.0; P =0.80). Similarly, VE/VCO 2 slope ≥34 was associated with outcome in children with biventricular circulation (hazard ratio, 2.7; 95% confidence interval, 1.1–7.1; P <0.001) but not in children with a palliated single ventricle.

Conclusions—

Exercise testing during HT evaluation in children with biventricular circulation identified those at higher risk of death or deterioration in this small study. Larger studies are needed to assess the role of exercise testing during HT evaluation in children with a palliated single ventricle.

The Ross classification for heart failure in children after 25 years: a review and an age-stratified revision

Accurate grading of the presence and severity of heart failure (HF) signs and symptoms in infants and children remains challenging. It has been 25 years since the Ross classification was first used for this purpose. Since then, several modifications of the system have been used and others proposed. New evidence has shown that in addition to signs and symptoms, data from echocardiography, exercise testing, and biomarkers such as N-terminal pro-brain natriuretic peptide (NT-proBNP) all are useful in stratifying outcomes for children with HF. It also is apparent that grading of signs and symptoms in children is dependent on age because infants manifest HF differently than toddlers and older children. This review culminates in a proposed new age-based Ross classification for HF in children that incorporates the most useful data from the last two decades. Testing of this new system will be important to determine whether an age-stratified scoring system can unify the way communication of HF severity and research on HF in children is performed in the future.

Peak oxygen uptake correlates with survival without clinical deterioration in ambulatory children with dilated cardiomyopathy

BACKGROUND

Children stable at home with dilated cardiomyopathy remain at risk of death; there is evidence of survival benefit for transplantation out to 4 years postoperatively. The limited supply of donor organs makes risk stratification imperative, but although cardiopulmonary exercise test is well established as a powerful tool in adults with heart failure, no published studies have linked oxygen uptake to prognosis in children.

METHODS AND RESULTS

Between 2001 and 2009, using cardiopulmonary exercise test and echocardiography, we studied 82 children (mean age, 13.5±2.3 years) with dilated cardiomyopathy. All were ambulatory, outpatients, and >120 cm in height. All children completed a symptom-limited maximal exercise test. Resting left ventricular shortening fraction was 20±9%; peak heart rate was 87±13% of predicted; peak oxygen uptake (VO(2)) was 67±22% of predicted; and ventilatory efficiency was 32±8. Follow-up was available for 100% of the children, and was a mean of 32.3±7.5 months. Eighteen patients reached the defined clinical end point of death or listing for urgent heart transplantation. On univariate analysis, left ventricular shortening fraction, peak heart rate, peak VO(2), peak systolic blood pressure, and ventilatory efficiency were all associated with adverse outcome. On multivariable Cox analysis, only peak VO(2) (P=0.003) was associated with the study end point. Patients with a peak VO(2) ≤62% of predicted had a higher 24-month event rate (50.6% versus 4.4%; hazard ratio, 10.78).

CONCLUSIONS

We have demonstrated that a cardiopulmonary exercise test is feasible in ambulatory children with dilated cardiomyopathy who are >120 cm height and for the first time have linked peak VO(2) with outcome in children.

Living at an altitude adversely affects exercise capacity in Fontan patients

BACKGROUND

Data assessing the effect of altitude on Fontan haemodynamics are limited to experimental models and case reports. Both suggest a detrimental impact. This study describes exercise performance in patients with Fontan circulation and matched controls at a low altitude versus at sea level. We sought to assess the impact of increasing altitude on functional capacity in patients with Fontan palliation.

METHODS

A retrospective review of 22 patients at low altitude (1602 metres) and 119 patients at sea level with Fontan circulation, as well as age-, gender-, and altitude-matched controls, underwent maximal cardiopulmonary exercise testing. Linear regression models were created to determine the influence of altitude on differences in exercise variables between Fontan patients and their matched controls.

RESULTS

Peak oxygen consumption was 28.4 millilitres per kilogram per minute (72% predicted) for the sea-level cohort and 24.2 millilitres per kilogram per minute (63% predicted) for the moderate altitude cohort. The matched case-control differences for patients at moderate altitude were greater for peak oxygen consumption (-29% against -13%, p = 0.04), anaerobic threshold (-36% against -5%, p = 0.001), and oxygen pulse (-35% against -18%, p = 0.007) when compared with patients living at sea level. When compared to institution-matched controls, the same parameters fell by 3%, 8.9%, and 4.2%, respectively, for each increase of 1000 feet in residential altitude (p = 0.03, p = 0.001, and p = 0.05, respectively).

CONCLUSIONS

Patients with Fontan circulation at a higher altitude have impairment in aerobic capacity when compared with patients at sea level. Reduction in exercise capacity is associated with a reduction in stroke volume, likely related to increased pulmonary vascular resistance.

Peak circulatory power as an indicator of clinical status in children after Fontan procedure

Peak circulatory power (CircP), a product of peak exercise oxygen uptake (VO(2)) and peak mean or systolic arterial blood pressure, has proved to be a strong predictor of poor outcome in adults with congenital heart disease. This study sought to compare CircP with other cardiopulmonary exercise (CPX) test variables and to assess whether CircP is superior in categorizing patients into well-functioning vs. poorly functioning at-risk groups in the pediatric population after a Fontan procedure. The CPX test reports of 50 patients were retrospectively reviewed after the Fontan procedure. The patients were divided into two groups. The well-functioning group included patients in New York Heart Association (NYHA) classes 1 and 2 (n = 36). The poorly functioning at-risk group included patients in NYHA classes 3 and 4 and those with significant indicators or outcomes of a poor prognosis (n = 14). The patients in the well-functioning group had significantly higher CircP values based on mean blood pressure (MBP) (P < 0.001), higher CircP values based on systolic blood pressure (SBP) (P < 0.001), and higher peak VO(2) (P = 0.004) than those in the poorly functioning at-risk group. At a cutoff value less than 2100.4 mmHg/mlO(2)/kg/min, CircP MBP had a sensitivity of 85% in categorizing children to the poorly functioning at-risk group. CircP correlated well with the clinical status of our patients. CircP and peak VO(2) did not differ significantly in ability to identify poorly functioning patients. Further prospective analysis is needed to assess whether CircP can serve as a prognostic marker for the pediatric population after Fontan procedure.