A long-term study of children with a potentially life-threatening heart condition called hypertrophic cardiomyopathy (HCM) found that the risk of death or need for immediate heart transplantation was greatest for those who developed certain subtypes of this disease as infants with congestive heart failure and for children who also had inborn errors of metabolism, a group of rare genetic disorders in which one or more of the body’s key metabolic processes are disrupted. These findings present an immediate opportunity to improve outcomes for affected children.
The findings were published online September 3 in The Lancet to coincide with a presentation at the European Society of Cardiology Congress 2013 meeting in Amsterdam.
“Predicting the clinical outcome for children with hypertrophic cardiomyopathy, or HCM, is challenging because of the complexity and diversity of causes and symptoms,” said Steven E. Lipshultz, M.D., director of the Batchelor Children’s Research Institute from the University of Miami Leonard Miller School of Medicine and principal investigator of the study. “Although children with HCM comprise the smallest proportion of children with cardiomyopathy listed for heart transplantation, selected patient groups may benefit from early listing for heart transplantation given the malignant course and high death rates shown in certain subgroups.”
Hypertrophic cardiomyopathy, a type of pediatric cardiomyopathy (diseases of the heart muscle) with varied causes and outcomes, is characterized by increased thickness (hypertrophy) of the heart wall. HCM is rare, with less than one out of 100,000 children (ages birth to 18 years) diagnosed annually in the U.S. The condition is more frequently diagnosed in infants (under the age of one year), with 2-3 out of every 100,000 identified each year.
Despite all that modern medicine has to offer, too many infants and children with HCM still die unexpectedly or prematurely. To better understand how diagnostic factors and patient characteristics predict the risk of death or the need for immediate heart transplantation in this rare condition, researchers from the University of Miami Miller School of Medicine, along with colleagues from other institutions, spent 19 years amassing data on more than 1,000 affected children at 98 pediatric cardiology centers in the U.S. and Canada through the National Heart, Lung, and Blood Institute (NHLBI)-funded Pediatric Cardiomyopathy Registry.
They found that children with HCM caused by inborn errors of metabolism had the lowest rate of transplant-free survival within two years after diagnosis (43 percent). At two years after diagnosis, the rate of transplant-free survival was 55 percent for children with a mixed version of the disease that included thickening of the heart walls and enlargement and weakening of the heart and 62 percent for those with a restrictive form of the disease characterized by both a thickening and hardening of the heart walls. Children diagnosed after age one with hypertrophic cardiomyopathy of unknown cause had the most favorable outcome, a 97 percent rate of transplant-free survival.
Infants and children who had two or more of the following risk factors at HCM diagnosis (depending on the cause of HCM) — lower weight or body size, female gender, diagnosis during infancy, congestive heart failure, and abnormal heart function — had an increased risk of poor outcomes (death or need for immediate heart transplantation).
“Progress has been slow in properly diagnosing and finding treatments for this heart disease that took the life of my two young sons at age 11 months and 9 months,” said Lisa Yue, founding executive director of the Children's Cardiomyopathy Foundation. “When my second son was diagnosed with hypertrophic cardiomyopathy in 2000, very few children had this condition and there was not an understanding that his symptoms were life-threatening and required immediate evaluation for heart transplantation. These new population-based findings will allow families to work with medical professionals to make more informed treatment decisions.”
The study’s findings are expected to assist clinicians in identifying which children are likely to have the worst outcomes (death or need for heart transplantation) within two years of diagnosis thereby enabling medical teams, genetic counselors, and family planners to jointly and quickly determine the best treatment approach.
“This study is a good example of public-private collaboration to address one of the most serious and complex heart conditions that affects children,” said Gail Pearson, M.D., Sc.D., a pediatric cardiologist and director of the Adult and Pediatric Cardiac Research Program in the NHLBI’s Division of Cardiovascular Sciences. “Where we don't have good treatment options, such as with hypertrophic cardiomyopathy, determining risk level takes on more importance. The long-term follow-up made possible through the Pediatric Cardiomyopathy Registry has improved our ability to determine which children are at the highest risk for needing a heart transplant and for dying from this condition and thus need more intensive monitoring or earlier listing for transplantation."
The NHLBI and the Children’s Cardiomyopathy Foundation supported this research.