Journal of Pediatric Psychology Advance Access published online on December 20, 2006
Journal of Pediatric Psychology, doi:10.1093/jpepsy/jsl047
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© The Author 2006. Published by Oxford University Press on behalf of the Society of Pediatric Psychology. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org
Psychological and Cognitive Functioning in Children and Adolescents with Congenital Heart Disease: A Meta-Analysis
1University of Amsterdam, and 2Academic Medical Center, Amsterdam, The Netherlands
All correspondence concerning this article should be addressed to P.A. Karsdorp, Department of Clinical, Medical and Experimental Psychology, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands. E-mail: P.Karsdorp{at}DMKEP.unimaas.nl
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Abstract |
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Objective Findings in the literature are inconsistent on the impact of congenital heart disease (CHD) on the psychological and cognitive functioning of children and adolescents. The aim of the present study was to systematically review this empirical body of literature. Methods We conducted a meta-analysis to review studies on behavior problems and cognitive functioning in CHD. Results Only older children and adolescents with CHD displayed an increased risk of overall, internalizing, and to a lesser extent externalizing behavior problems. In addition, patients with severe CHD exhibited lower cognitive functioning than patients with less severe CHD, specifically with respect to performance intelligence. Moreover, decreased cognitive functioning remained relatively stable across different age groups. Conclusions Children with severe heart disease may benefit from interventions specifically targeting perceptual organizational abilities, such as visual–spatial abilities. Moreover, older children and adolescents with CHD may benefit from psychological interventions reducing anxiety symptoms and depression.
Key words: cognitive functioning; congenital heart disease; meta-analysis; pediatric chronic illness; psychopathology..
Congenital heart disease (CHD) refers to a heterogeneous group of diseases characterized by a structural heart defect at birth. The incidence of moderate to severe CHD is estimated to be 6/1000 live births, based on 62 studies from different countries (e.g., US, Europe, Australia, and China; Hoffmann & Kaplan, 2002
). This incidence rate rises to 19/1000 live births if the potentially serious bicuspid aortic valve is included and to 75/1000 live births if tiny muscular ventricular septum defects (VSDs) and other trivial lesions are included. Most patients with CHD are diagnosed in infancy and childhood and are expected to undergo an operation or interventional catheterization in infancy to correct or palliate their defect (Warnes et al., 2001). After cardiac intervention, residual anatomical abnormalities may remain and patients may still be at risk for premature death or comorbidities, such as arrhythmias, hypertension, pulmonary, renal, and myocardial disease or coronary artery disease. Most patients with CHD need to be seen regularly by a cardiologist and in the US almost 50% of the patients who have undergone surgery require additional surgery at an older age (Warnes et al., 2001). Advances in diagnostic and surgical techniques have increased survival rates in CHD remarkably. For example, in the US it is estimated that >85% of the children with complex CHD survive the first year of life as compared with 20% in the forties (Warnes et al., 2001). Due to increased survival rates, greater attention has been directed toward understanding the impact of CHD on psychological and cognitive functioning. The goal of medical care is not only to achieve long-term survival but also to achieve the best possible psychological and cognitive development.
A considerable number of studies have been conducted to assess the impact of CHD on children's and adolescents' psychological and cognitive functioning. The outcome measure that is used in the majority of these studies assessing psychological functioning is the Child Behavior Checklist (CBCL; Achenbach & Edelbrock, 1983) parent form. This is a parent report measure that provides an estimate of overall emotional and behavioral problems, and of internalizing (e.g., anxiety, depression, social withdrawal), and externalizing behavior problems (e.g., hyperactivity, oppositional behavior, aggression). The outcome measure that is used in the majority of studies assessing overall cognitive functioning, verbal (VIQ; e.g., verbal comprehensive abilities), and performance intelligence quotients (PIQ; e.g., perceptual organizational abilities) is the Wechsler Intelligence Tests for Children (WISC; Wechsler, 1991). Consensus among studies assessing psychological and cognitive functioning in CHD has not been reached. Authors report higher rates of behavior problems and reduced cognitive functioning among children and adolescents with CHD as compared with norms (e.g., Hövels-Gürich et al., 2002; Ikle, Hale, Fashaw, Boucek, & Rosenberg, 2003) or study-recruited control groups (e.g., Mahle et al., 2000; Oates, Turnbull, Simpson, & Cartmill, 1994), whereas others report no significant differences between patients with CHD and norms (e.g., Hövels-Gürich, Seghaye, Dabritz, Messmer, & Von Bernuth, 1997; Utens et al., 2001) or study-recruited control groups (e.g., Karl et al., 2004).
An important distinction among studies is the severity of heart disease of the patient sample. Studies provide estimates of behavior problems and cognitive functioning for separate patient groups with only simple or severe CHD, such as VSD or transposition of the great arteries (TGA; e.g., Clarkson, MacArthur, Barett-Boyes, Whitlock, & Neutze, 1980), or for a heterogeneous group of patients with CHD (Utens et al., 1993). The different findings among studies could be explained by the fact that patients with severe heart disease are at increased risk for psychological and cognitive problems. In the literature, however, no consensus has been reached on the effect of disease severity on psychological and cognitive functioning. That is, some authors report worse psychological and cognitive functioning in more severe CHD (e.g., Haneda, Itoh, Togo, Ohmi, & Mohri, 1996; Hesz & Clark, 1988), whereas others do not (e.g., Forbess, Visconti, Bellinger, Howe, & Jonas, 2002; Utens et al., 1993).
A second discrepancy among studies has been the age of the patients with CHD. Cognitive and psychological functioning is tested in patients varying in age from 4 months to 18 years old. The reliability and predictive validity of assessments of IQ and behavior problems is low in infancy and toddlerhood (e.g., Gruneau, Whitfield, & Petrie, 2000; McGrath, Wypij, Rappaport, Newburger, & Bellinger, 2004) and is moderate to high in children aged 4 years or above (Hofstra, van der Ende, & Verhulst, 2000; Sameroff, Seifer, Baldwin, & Baldwin, 1993). Therefore, the different findings across studies may reflect the low reliability and validity of the findings in infancy. Additionally, the different findings may reflect real differences between older and younger patients with CHD. Some studies showed age effects on psychological and cognitive functioning (e.g., Jedlicka-Köhler, Sinko-Sanz, Schlemmer, & Wimmer, 1995; Wray & Sensky, 1998).
Some reviews have been written to integrate the literature on psychological and cognitive functioning in CHD. However, the conclusions of these reviews as to whether patients with CHD are at increased risk of diminished psychological and cognitive functioning and whether disease severity is a risk factor have been inconsistent (Delamater, 2003; Foster et al., 2001; Gardner & Angelini, 1995; Griffin, Elkin, & Smith, 2003; Samango-Sprouse, & Suddaby, 1997; Shillingford & Wernovsky, 2004). Moreover, these reviews have not included all relevant literature and the criteria for inclusion are not always presented. Furthermore, these reviews rely on significance testing, increasing the likelihood of a type II error, as the sample sizes of the patients with CHD are often small.
The goal of the present study is to determine the impact of CHD on psychological and cognitive functioning in children and adolescents. We provide a systematic review of the current empirical body of literature on psychopathology and cognitive functioning in CHD, using meta-analytic techniques. Meta-analytic techniques provide a reliable overall estimate of effect sizes (ESs) and statistical tests to determine whether differences in methodological characteristics (e.g., control group used), and sample characteristics, such as chronological age and severity of heart disease, influence the findings.
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Literature Search
Because medical technology and medical treatment have changed dramatically over the last 25 years (Griffin et al., 2003
), the literature search was restricted to articles published between 1980 and May 2005. We performed a search in Medline and Psychinfo databases using the following keywords: "congenital heart defects or disease", paired with the descriptors "mental disorders", "behavior", "psychology", and "cognitive". In addition, we searched reference lists of studies included in this meta-analysis. To ascertain the likelihood of a publication bias, a file drawer analysis was conducted. A file drawer analysis is a method to estimate the number of additional studies (x) averaging null findings that would be necessary to bring small and medium ESs for psychopathology and cognitive functioning (dk) to negligible ESs (dc) using the formula dc = 
dk/(k + x), with k being the number of studies included in the analysis (Hunter & Schmidt, 1990).
Inclusion Criteria
Criteria for inclusion in the meta-analysis were as follows: (a) studies had to be published in a peer-reviewed English- or German-language journal; (b) studies solely included patients with CHD; (c) studies included patients between 2 and 19 years old, and with a mean age of 4 years or above; (d) studies included solely patients who had undergone surgery or interventional catheterization; (e) studies included the CBCL (Achenbach, 1991; Achenbach & Edelbrock, 1983) parent form to measure psychopathology; (f) and/or studies included a measure of cognitive function: British Ability Scale (BAS; Elliot, 1983), Bayley Scales of Infant Development (BSID; Bayley, 1969), Differential Ability Scale (DAS; Elliot, 1990), Hamburger Wechsler Intelligence Test for Adults (HAWIE; Wechsler, 1964), Hamburger Wechsler Intelligence Test for Children (HAWIK; Bondy, 1966), Hamburger Wechsler for Children in Pre-school Age (HAWIVA; Eggert, 1975), Kaufman Assessment Battery for Children (K-ABC; Kaufman & Kaufman, 1983), Leiter International Scale (LIS; Arthur, 1952), McCarthy Scales of Children's Abilities (MCSA; McCarthy, 1972), Stanford Binet Scale (SB; Terman & Merrill, 1961; Thorndike, Hagen, & Sattler, 1986), Wechsler Intelligence Test for Children (WISC; Wechsler, 1974, 1991), Wechsler Preschool and Primary Scale of Intelligence (WPPSI; Wechsler, 1967, 1989); (g) studies reported sufficient data necessary to compute ESs; (h) studies included a control group (healthy controls, siblings, individuals with innocent heart murmur, or published norms).
Studies were excluded that tested patients with only syndromes in which CHD was part of the total syndrome, like Williams, Marfan, or velo-cardio-facial syndrome.
Variables Coded from Each Study
To determine between-rater agreement, two independent judges coded 19 randomly selected studies of the sample. Information coded from each study included: meeting inclusion criteria, year of publication, age of the patients, name of questionnaires, construct measured, type of heart disease, type of control group, sample sizes, inferential statistics, and mean and standard deviation of psychopathology and cognitive functioning. Discrepancies in coding were measured with Kappa's coefficient and Pearson's correlation for categorical and noncategorical data, respectively (e.g., Whittington, Podd, & Kan, 2000). Between-rater agreement showed that the coding for each variable was very reliable (mean agreement for the variables coded: r = .93, SD = 13). Discrepancies in coding were solved through discussion between judges. A cardiologist classified the heart defects into complex (e.g., transposition of the great arteries), moderate (e.g., tetralogy of Fallot), and simple CHD (e.g., ventricular septum defect) based on risk of morbidity and mortality, according to the classification system presented at the 32nd Bethesda Conference (Warnes et al., 2001).
Meta-analytic Procedures
The basic approach primarily focused on ESs and was modeled on the meta-analytic techniques of Hunter and Schmidt (1990). This method provides the opportunity to determine how much of the variance in ESs across studies is due to sampling error. Moreover, this method allows adjusting for the effect of sampling error, yielding an estimate of the true population variability of study outcomes. Finally, it provides a method to test whether ESs across studies are uniform (homogeneous). This method is less vulnerable to type II error (i.e., concluding that the ES are uniform when in fact they are not) than the often-used chi-square statistics (Hedges & Olkin, 1985).
Calculation of Effect Sizes
The standardized mean difference, d (Cohen, 1988), was used as the estimate of ES. The d statistics can be defined as the difference between the group means divided by the pooled standard deviation. Where a study reported the percentages of patients with CHD who exceeded a cutoff score, the ES was determined by consulting a table using probit transformation methods to convert differences in proportions to ES (Glass, McGaw, & Smith, 1981). ESs expressed in eta squared were transformed to Cohen's d (Cohen, 1988). Where published norms or standard scores were provided, the sample size of the control group was equated with the sample size of the patient group. Where standard deviation of the patient group was missing, the standard deviation of the control group was substituted. For psychopathology, a positive ES reflects more psychopathology in CHD relative to controls. For cognitive functioning, a negative ES reflects decreased cognitive functioning in CHD relative to controls.
To correct for differences in sample size, the weighted mean ES and variance were computed (Hunter & Schmidt, 1990). To correct for sampling error, the population (residual) variance was then computed by subtracting the sampling error variance from the observed variance (Hunter & Schmidt, 1990). Sampling error variance was computed using the formula Se2 = [(N – 1)]/[(N – 3)] [(4/N)] [(1 + D2/8)], N being the average sample size across all groups and D the weighted average of Cohen's d. The estimate of the population variance served as the multiplier in the formula for the 95% confidence interval. Finally, an unbiased ES (d*) was calculated by removing a small sample bias. The unbiased ES was computed by d* = d/a, where a = 1 + .75/(N–3) (Hunter & Schmidt, 1990).
To reliably interpret the estimated population ES, the ESs should be uniform across studies, (i.e. homogenous). To test to what extent the ESs are homogenous, we determined the degree in which any residual variance of the ESs (i.e., variance after removal of sampling error) could be explained by artifacts not corrected for. This was calculated by the percentage of observed variance explained by sampling error variance. The data set can be considered homogeneous if 
75% of the observed variance is explained by sampling error (Hunter & Schmidt, 1990). If <75% of the observed variance is explained by sampling error, the data set can be considered heterogeneous. This may indicate that there are moderating variables explaining the residual variance of the ESs.
To examine the effect of moderating variables, the data set was subdivided as a function of the moderator. For continuous moderator variables, Pearson product-moment correlation coefficients were calculated between the unbiased ESs and the moderator variable. According to Cohen (1988), small, medium, and large ESs were d = 0.20, 0.50, and 0.80, respectively.
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Psychopathology
Eleven studies were selected for inclusion in the meta-analysis, providing 16 ESs for overall behavior problems and 14 for internalizing (e.g., anxiety, depression) and externalizing (e.g., hyperactivity, aggression) behavior problems (Table I). The analysis showed that patients with CHD exhibited more overall (medium ES), internalizing (medium ES), and externalizing (small ES) behavior problems than controls (Table II). However, only for externalizing behavior problems a homogeneous data set was obtained, indicating that significant moderators were present with respect to overall and internalizing behavior problems.
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Correlations between age and ESs for behavior problems showed that only older patients with CHD showed more overall, internalizing, and externalizing problems as compared with a comparison group, r(16) = .67, p = .005; r(14) = .77, p = .001; and r(14) = .73, p = .003 respectively. Separate analysis of younger children (mean age <6 years) and older children and adolescents (mean age >10 years) showed homogeneous data sets (Table II). Younger children with CHD showed less internalizing (negligible ES) and externalizing behavior problems (small ES) than controls. In contrast, older children and adolescents showed more internalizing (medium ES) and to a lesser extent externalizing problems (small ES) than controls. Disease severity was not significantly related to overall: r(13) = .18, p = ns, internalizing: r(12) = .11, p = ns, and externalizing: r (12) = –.05, p = ns problems.1
Overall Cognitive Functioning
Twenty-five studies were selected for inclusion in the meta-analysis, providing 50 ESs for overall cognitive functioning (Table III). There was considerable heterogeneity in the data set (Table IV), which points to significant moderators. Because healthy controls, patients with innocent heart murmurs, and siblings scored significantly higher on cognitive functioning (medium ES) as compared with normative data (Table IV), we substituted their means and SDs by means and SDs of the norm, in order to create a more homogeneous data set. However, the data set remained heterogeneous.
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Correlations between CHD severity and ESs of cognitive functioning revealed that patients with more severe CHD exhibited lower cognitive functioning than patients with less severe CHD; r(46) = –.45, p = .002.1 In addition, older patients showed less adverse cognitive outcome than younger patients; r(50) = .31, p = .03. The effect of disease severity on cognitive functioning remained after controlling for mean age; r(43) = –.39, p = .009. The effect of chronological age did not reach significance after controlling for disease severity; r(43) = .23, p = ns.
Table IV provides the ESs of overall cognitive functioning for the various congenital heart defects including: hypoplastic left heart syndrome (HLHS), TGA, tetralogy of Fallot (ToF), atrium septum defect (ASD), and VSD. The data sets are homogeneous, except for ToF. Mean cognitive functioning was higher among patients with VSD than normative data (small ES). Cognitive functioning of patients with ASD was within the normative range. Patients with HLHS and TGA had significantly lower cognitive functioning than normative data, respectively a large and small ES. For patients with ToF, the analysis showed that older patients tended to exhibit higher cognitive functioning than younger patients, but this effect did not reach significance; r (7) = .77, p = .08. For the other patient groups separately (VSD, ASD, TGA, and HLHS), no association was observed between mean age and cognitive functioning, all ps = ns. For these patient groups together, a significant relation between chronological age and cognitive functioning was found; r(25) = .40, p < .05. However, when patients with HLHS were excluded from the analysis, the age effect dissipated; r(21) = .16, p = ns, indicating that age effects were observed because patients with HLHS were tested at an earlier age. This suggestion was confirmed by t tests showing that patients with HLHS were significantly younger than patients with ASD, t (8) = 3.37, p = .01 (ASD: M = 10.63, SD = 2.09; VSD: M = 9.31, SD = 3.05; TGA: M = 8.26, SD = 2.37; ToF: M = 7.96, SD = 3.08; HLHS: M = 5.82, SD = 2.08). It is noteworthy that no other significant differences were found in mean chronological age between the patient groups. This indicates that differences in cognitive functioning among patients with VSD, ASD, TGA, and ToF could not be explained by differences in chronological age.
Verbal and Performance IQ
Twelve studies (Table III) were selected for inclusion in the meta-analysis, providing 21 ESs for verbal IQ (VIQ; verbal comprehensive abilities) and performance IQ (PIQ; perceptual organizational abilities). The analysis demonstrated that the data sets of PIQ and VIQ were characterized by considerable heterogeneity (Table V). Follow-up analysis demonstrated that patients with more severe CHD exhibited lower PIQ and VIQ than would be expected by normative data; respectively, r (20) = –.62, p = .003 and r(20) = –.59, p = .006. Moreover, younger patients with CHD exhibited lower PIQ but not lower VIQ than normative data, respectively, r (21) = .53, p = .01 and r(21) = .38, p = .09. The effect of age on PIQ dissipated after excluding patients with HLHS or after controlling for disease severity; respectively, r(17) = .39, p = ns and r (16) = .32, p = ns. The effect of disease severity on PIQ and VIQ remained after controlling for mean age, respectively, r(17) = –.42, p = .07 and r(17) = –.47, p = .04.
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Table V provides the ESs of VIQ and PIQ for HLHS, TGA, VSD, and ASD; the data sets are homogeneous. Patients with ASD and VSD had significantly higher VIQ and PIQ than normative data, respectively a small and negligible ES. Patients with HLHS had lower VIQ and PIQ than normative data, respectively a medium and large ES. Patients with TGA had lower VIQ than normative data (a negligible ES). With respect to PIQ, no homogeneous data set was obtained for the patients with TGA. Exclusion of one study in which full-flow cardiopulmonary bypass was used as a surgical technique (ES = 0.34; Karl et al., 2004
), resulted in a homogeneous data set with lower PIQ scores for patients with TGA as compared with normative data (small ES).
File Drawer Analysis
We estimated the number of additional studies averaging null findings that would be necessary to bring the small and medium ESs for psychopathology and cognitive functioning below a negligible ES, d = |0.1| (Cohen, 1988). The results provide confidence that the effects found would not be invalidated even if a publication bias existed, since an increase of 50–850% in existing numbers of studies would be necessary.
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Discussion |
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The findings of the present study indicate that the sole presence of CHD does not adversely affect behavior problems among children and adolescents. The variance in ESs across studies with respect to psychopathology could not solely be attributed to sampling error; chronological age appeared to be significantly related to psychopathology in CHD, whereas disease severity was unrelated to psychopathology. The findings indicate that only older children and adolescents with CHD display an increased risk of overall, internalizing (medium ES), and to a lesser extent externalizing behavior problems (small ES). These findings suggest that exposure to potential risk factors during the course of a patient's life may increase the development of specifically internalizing behavior problems in older children and adolescents with CHD.
The finding that older children and adolescents with CHD exhibited more internalizing than externalizing problems is consistent with other reviews of pediatric chronic disease (Lavigne & Faier-Routman, 1992; Lebovidge, Lavigne, Donenberg, & Miller, 2003). Future research may focus on the mechanism that may explain increased levels of internalizing problems among older children and adolescents with CHD. An overprotective parenting style in CHD (Casey, Sykes, Craig, Power, & Mulholland, 1996; Linde, 1982) may be a possible risk factor for internalizing problems (Gilliom & Shaw, 2004). Alternatively, hormonal and brain changes during adolescence triggering the expression of genetic vulnerabilities in combination with potential stressful disease experiences may increase internalizing behavior problems (Walker, Sabuwalla, & Huot, 2004).
The findings of the present study indicate that CHD does not adversely impact on cognitive functioning among all children and adolescents. The variance in ESs across studies with respect to cognitive functioning could not solely be attributed to sampling error; disease severity was significantly related to overall cognitive functioning. Patients with HLHS (large ES) and patients with TGA (small and medium ES) demonstrated decreased cognitive functioning compared with study-recruited control groups and normative data, specifically in the area of perceptual organizational abilities. Patients with ASD and VSD showed cognitive functioning within the normative range. An additional finding is that cognitive functioning in CHD remained relatively stable across age groups. For the patients with VSD, ASD, TGA, and HLHS separately, no effect of chronological age was observed. Moreover, although for the patients with CHD overall, chronological age was related to cognitive functioning, additional analysis demonstrated that the observed effect was confounded by disease severity. That is, patients with severe CHD, specifically those with HLHS, were tested at an earlier age than were patients with less severe CHD. Removal of the patients with HLHS from the analysis yielded no age effects.
The finding that severe CHD resulted in more impaired cognitive functioning relative to their counterparts with less severe CHD may possibly be explained by the fact that severe CHD is associated with risk factors that have a cumulative adverse effect on cognitive functioning. For example, patients with more severe disease are at increased risk for congenital brain anomalies (Glauser, Rorke, Weinberg, & Clancy, 1990b) that may be associated with prenatal physiological events (Kaltman, Tian, & Rychik, 2005) and by chromosomal anomalies (Tennstedt, Chaoui, Korner, & Dietel, 1999). Moreover, patients with severe heart disease are at increased risk for acquired cognitive impairments (Glauser, Rorke, Weiberg, & Clancy, 1990a; Trittenwein, et al., 2003) as a result of more difficult and frequent surgery (Clarkson et al., 1980; Stavinoha, Fixler, & Mahony, 2003), pre- and postoperative poor cerebral perfusion, seizures, and physical incapacity (Forbess et al., 2002; Goldberg et al., 2000; Newburger, Silbert, Buckley, & Fyler, 1984).
The present results suggest that specifically perceptual organizational abilities are impaired in TGA and HLHS as compared with normative data. Although some caution is warranted, as the number of studies was small, the present findings are in accordance with other studies of children with early brain damage (Ewing-Cobbs, Barnes, & Fletcher, 2003; Muter, Taylor, & Vargha-Khadem, 1997). The basis for the detrimental effects on perceptual organizational abilities is unclear. One possibility is that reduced motor abilities resulting from CHD and operative recovery time may specifically impede the normal development of motor and spatial relation skills (Goldberg et al., 2000; Muter et al., 1997). Alternatively, left-hemisphere injury may result in functional re-organization of language functions from the left to the right hemisphere to preserve language functions. This compensation may be achieved at the expense of visuospatial abilities (Muter et al., 1997). The present finding, that patients with CHD have verbal abilities within the normal range, despite the fact that they may have missed considerable schooling due to hospitalizations, may support this notion. Nevertheless, the present findings also indicate that overall IQ, VIQ, and PIQ are relatively stable in patients with TGA, HLHS, ToF, ASD, and VSD across different age groups, suggesting that decreased verbal and perceptual abilities may remain after compensation for language functions. A possible explanation for the observed stability of decreased cognitive functioning in CHD is that patients with CHD suffer from neurological impairment at an early age. Brain damage at an early age has been shown to be a risk factor for enduring decreased cognitive functioning (Ewings-Cobbs et al., 2003; Levin, 2003; Mutter et al., 1997). One possibility is that, young patients are more vulnerable to brain damage because they have a less-well-established skill repertoire (Ewings-Cobbs et al., 2003) and because myelination takes place during this period (Levin, 2003).
Several potential limitations of this review should be considered. The present meta-analysis excluded studies that tested patient groups with a mean age of <4 year, because the reliability and predictive validity of assessments of IQ and behavior problems is low in infancy and toddlerhood (e.g., Gruneau et al., 2000; McGrath et al., 2004). As a result, the findings of the present study may not apply to infants and toddlers with CHD. Additionally, the meta-analysis is based on the assumption that IQ is normally distributed among patients with CHD. However, some studies have shown a non-normal distribution of IQ that is skewed to the left (e.g., Mahle et al., 2000). This may indicate that the present meta-analysis underestimates the extent to which patients with CHD evidence diminished functioning.
Research has shown a rise in mean intelligence scores during the 20th century (Rowe & Rodgers, 2002). This so-called Flynn effect may explain why patients with simple CHD (e.g., VSD) showed higher cognitive functioning than suggested by normative data. If this Flynn effect influenced the present findings, the adverse effect of CHD on cognitive outcome may be underestimated.
In the present study, the ESs of cognitive functioning were computed using normative data as opposed to data of a study-recruited control group. However, a study-recruited control group provides the opportunity to carefully match patients and controls on demographic characteristics and to control for a Flynn effect. The present study reveals that the study-recruited control groups evidence higher cognitive functioning than would be suggested by normative data. This indicates that comparison of patients with CHD with a recruited control group could have resulted in larger ESs than a simple comparison of patients with normative data. These findings may be interpreted to suggests that the present data underestimate the degree of cognitive dysfunction in CHD.
The present meta-analysis included only studies that employed tests of overall cognitive functioning. It is possible, however, that patients with CHD exhibit a deficit in a specific area of cognitive functioning. Because IQ scores may average scores on unaffected and affected areas (Schatz, Finke, Kellett, & Kramer, 2002) the present study may underestimate cognitive dysfunction in CHD.
Some caution is warranted with respect to the observed effect of chronological age on psychopathology. The meta-analysis is cross-sectional, and may therefore be subject to potential confounds such as cohort effects across studies or sampling biases. Therefore, the association between chronological age and psychopathology should be viewed only as suggestive. Prospective studies of children with CHD and control groups are needed to clearly establish the age effect posited in this review.
The meta-analysis relied only on studies using the CBCL as a measure of child psychopathology. However, concerns have been raised regarding the use of the CBCL in research with children with chronic disease, because the internalizing problem scale includes items that tap physical symptoms (Perrin, Stein, & Drotar, 1991). One study on CHD addressed this issue and demonstrated that the difference between patients and the reference group remained after excluding items with a somatic content (Utens et al.,1993). Moreover, the present study provided results indicating that severity of heart disease was unrelated to internalizing problem scores. Therefore, it is unlikely that the specific medical diagnosis explained an increased report of internalizing problems in older children and adolescents.
Another limitation of the meta-analysis is the potential impact of rater bias on reported psychopathology in CHD. Assessment of behavior problems was exclusively based on parents’ reports. However, studies comparing parent and child reports have found that children tend to report more behavior problems (specifically internalizing) than their parents (Utens et al., 1993). Consequently, the ratings of caregivers of psychopathology in the current study may have underestimated the level of internalizing problems of children and adolescents of CHD.
One of the most frequent criticisms leveled against meta-analysis in general is the argument that the studies available for analysis are biased samples of all available studies. It is often suspected that published studies will show results that are more often statistically significant and have larger ESs than unpublished studies. However, this argument applies equally well to the narrative review (Hunter & Schmidt, 1990). Moreover, there is evidence that the availability bias is much less severe than some have believed (Glass, McGaw, & Smith, 1981; Hunter & Schmidt, 1990). Finally, the number of "lost" studies averaging null results that would be necessary to derive negligible ESs is so large in the present study that it is unlikely that there has been an availability bias.
Another frequent argument against meta-analysis is that it combines studies that are so different that they are not comparable (Hunter & Schmidt, 1990). First, a meta-analysis does not analyze studies; it analyzes study results. Any set of numbers can be compared or averaged. Second, the question of whether study results differ across settings is an empirical question rather than a semantic or logical question. The question of whether a potential moderator variable (study characteristic) is an actual moderator variable is impossible to answer without a meta-analysis of some kind (Hunter & Schmidt, 1990).
The present study suggests that the sole presence of CHD may not affect the development of overall, internalizing, and externalizing problems. Only older children and adolescents show behavior problems in this investigation, specifically with respect to internalizing difficulties. Moreover, the present study suggests that severe CHD may adversely impact cognitive functioning, specifically in the area of perceptual organizational abilities. To promote psychological and cognitive functioning, future research should attempt to unravel the role of possible risk factors such as diminished cerebral perfusion, treatment characteristics, overprotective parents, or hospitalizations. Although, a lot of work has been done is this area (e.g., Casey et al., 1996; Ellerbeck et al., 1998; Karl et al., 2004; Wernovsky et al., 2000), the findings are difficult to integrate, because different surgical techniques have been applied, different patient groups have been tested, or because many risk factors are highly interrelated. Therefore, future studies are required in which cognitive and psychological functioning are assessed longitudinally and in which homogeneous patient groups are randomly assigned to medical treatments (e.g., McGrath et al., 2004). Once the impact of individual risk factors is clarified, adverse psychological and cognitive functioning in CHD can be prevented. Another important direction for future research is to move beyond the broad focus on internalizing and externalizing problems and verbal and performance IQ toward the examination of specific domains of psychopathology and cognitive functioning (e.g., anxiety, depression, and visual–spatial skills). Overall, the current study suggests that young children with severe heart disease (HLHS and TGA) may benefit from interventions specifically targeting perceptual organizational abilities (e.g., visual – spatial abilities). Moreover, older children and adolescents with CHD may benefit from psychological interventions that reduce anxiety symptoms and depression.
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We gratefully acknowledge Kiki Hohnen for her grammatical advice.
The report was written as part of a project funded by the Dutch Heart Foundation (No. 99.038).
Conflict of interest: None declared.
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Footnotes |
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1 Year in which the study was conducted was unrelated to ESs of psychopathology and cognitive functioning, p > .05.
Received November 7, 2005; revision received April 15, 2006; accepted November 3, 2006
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References |
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