1. Patient characteristics at the time of diagnosis of pediatric hypertrophic cardiomyopathy predict risk of death or heart transplantation.
2. Worse outcomes were associated with diagnosis at age less than 1 year, inborn errors of metabolism or mixed hypertrophic cardiomyopathy.
Evidence Rating Level: 2 (Good)
Study Rundown: This retrospective, multicenter study identified patient characteristics that could be used to assess the risk of death or heart transplantation in children with hypertrophic cardiomyopathy. Patients with cardiomyopathy secondary to inborn errors of metabolism had poor outcomes, as did children with mixed (hypertrophic and either dilated or restricted) cardiomyopathy. In contrast, children with idiopathic hypertrophic cardiomyopathy diagnosed at 1 year of age or older had much lower rates of death or heart transplantation. Other patient characteristics associated with increased risk included young age at diagnosis, congestive heart failure, low weight, and higher left ventricular end-diastolic posterior wall thickness at diagnosis; however, these risk factors varied by cardiomyopathy subgroup.
Although prior studies have previously identified risk factors for poor outcome in this population, this study is the first to focus on patient characteristics present at the time of diagnosis. These findings may help physicians to provide families with more timely prognostic information, and could allow earlier identification of children likely to require heart transplantation. As illustrated by this study, pediatric hypertrophic cardiomyopathy is a heterogeneous disease with varying outcomes, making risk stratification especially important. Given the rarity of the disease, the relatively large sample size is one of the greatest strengths of this study. However, the largest phenotypic subgroup was composed of patients with idiopathic hypertrophic cardiomyopathy; it may be possible that some of these patients belonged to another causal subgroup but were incorrectly diagnosed. In order to apply the findings of this study to practice, physicians will need to identify the appropriate subgroup for each patient.
In-Depth [retrospective cohort study]: This study used data from the Pediatric Cardiomyopathy Registry, which collected demographic and longitudinal clinic data, including echocardiographic measurements, from 1085 patients seen at 98 centers in North America. Cases were classified as pure hypertrophic cardiomyopathy or mixed (hypertrophic with either dilated or restrictive) cardiomyopathy. Pure hypertrophic cases were further subdivided by presumed cause (e.g. idiopathic, malformation syndrome, inborn errors of metabolism, neuromuscular disease, familial).
The primary outcome was heart transplantation or death (whichever occurred earlier). Kaplan-Meier plots were used to calculate time to death or heart transplantation for different subgroups. Cox proportional-hazards regression was used to identify variables predicting the primary outcome. Children with inborn errors of metabolism had the poorest outcomes; the rate of death or heart transplantation 1 year after diagnosis was 48% (95% CI 36 – 60). The mixed hypertrophic and dilated phenotype was also associated with high rates of death or transplantation at 1 year (43%, 95% CI 50 – 56), as was the mixed hypertrophic and restrictive phenotype (30%, 95% CI 18 – 43). In contrast, children diagnosed with idiopathic hypertrophic cardiomyopathy at greater than 1 year of age had much better outcomes, with a 0.5% (95% CI 0.0 – 1.2) rate of death or transplantation at 1 year. Multiple variables were found to have prognostic value; including congestive heart failure at diagnosis, young age, and being underweight were associated with worse outcomes in patients with idiopathic hypertrophic cardiomyopathy.
By Hayley Walker and Mimmie Kwong
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