Abstract 6071: Phenotypic Heterogeneity and Outcomes of Restrictive Cardiomyopathy in Childhood - A Report from the NHLBI Pediatric Cardiomyopathy Registry
Restrictive cardiomyopathy (RCM), the rarest form of cardiomyopathy in childhood, has been associated with poor prognosis. An overlapping phenotype with hypertrophic cardiomyopathy (HCM) has been recognized in adults. The goal of the present analysis was to compare outcomes of childhood RCM considered to have a “pure” RCM phenotype with those with additional features of HCM using the North American Pediatric Cardiomyopathy Registry (PCMR). We analyzed the PCMR for all cases of RCM. Cases were defined as “pure” when this was the only assigned diagnosis at all time points. Additional documentation of HCM at any time was used as the criteria for defining a mixed RCM/HCM phenotype. Overall prevalence of RCM in the PCMR was 5%. In 102 cases (66%), pure RCM was diagnosed; in 52 (34%) there was mixed RCM/HCM phenotype. Median age at diagnosis was not significantly different between groups (6.0 vs. 4.5 years), but 9.8% of the RCM group was diagnosed in infancy versus 23.1% of the RCM/HCM group. Ninety-three per cent of the pure group was labeled as having idiopathic disease, compared to 77% of the mixed group. Inborn errors of metabolism (9.6 vs. 1%) and familial history of cardiomyopathy (43.8 vs. 14.1%) were more common in the mixed group. Freedom from death (censored for transplant) was comparable for the two groups with 1, 2 and 5 year survival of RCM 82, 80, 66% vs. RCM/HCM 77, 74, 68% (log rank P=0.780). Freedom from transplant differed significantly between groups: RCM 60, 45, 35% vs. RCM/HCM 85, 72, 62% (log rank P=0.002). Event-free survival (freedom from death or transplant) was 49, 36, 23% and 65, 53, and 43% for RCM and RCM/HCM respectively (log rank P=0.017). Survival for “pure” idiopathic HCM in the PCMR is 94, 93 and 90% at 1, 2 and 5 yrs. Event-free survival is poor for RCM in childhood; however, the mixed RCM/HCM phenotype has significantly better event free survival. Both groups fare significantly worse than those with “pure” HCM within the PCMR, suggesting that the RCM/HCM phenotype is a distinct (though likely heterogeneous) entity. Genetic studies are indicated to determine if the genotype spectrum is comparable to that for pediatric HCM, and to potentially enhance prognostic information.