A Johns Hopkins study has provided the most comprehensive description to date of people most likely to develop a relatively rare heart condition, called arrhythmogenic right ventricular dysplasia (ARVD), known to be among the top causes of sudden cardiac death among young athletes.
Estimates from researchers and the Heart Rhythm Society suggest that ARVD accounts for up to 5 percent of the 300,000 deaths each year in the United States from sudden cardiac death.
"Our results are a sobering reminder that if a young person faints, especially in association with exercise, their physicians should evaluate them carefully for cardiac diseases, including ARVD," says study lead author Darshan Dalal, M.D., M.P.H., a cardiology research fellow at Hopkins.
A family history of sudden cardiac death at a young age is considered a major risk factor for the disorder. Athletes are also at particular risk, but the precise biological reasons for this remain unknown.
According to senior study investigator and cardiac electrophysiologist Hugh Calkins, M.D., "physicians need to know that this is a serious disease, and they should be on the lookout for its early signs and symptoms because it is an important cause of sudden cardiac death in apparently healthy young individuals.
"Preventive treatment with an implantable defibrillator appears to eliminate the risk of sudden death," he adds.
Calkins, a professor of medicine and pediatrics at The Johns Hopkins University School of Medicine and its Heart Institute, notes that the disease frequently strikes people who are relatively young and that symptoms may appear up to 15 years before diagnosis. Initial symptoms include palpitations, dizziness and fainting.
Researchers found that symptoms usually appear after puberty and before age 50. Eight of the 31 patients who died before diagnosis had shown signs of the disease when alive, including five who had passed out, suggesting they could have been treated and saved, the researchers say.
In their study, published in the journal Circulation online, the Hopkins scientists analyzed characteristics of 100 ARVD patients, including 69 while still alive and 31 diagnosed postmortem.
The subjects, who included men and women of many ethnic backgrounds, with a median age of 31, were part of Hopkins' registry of U.S. patients with the condition, which appears on MRI scans as either a protruding or pouch-like bulge from the right side of the heart or a dilated, poorly functioning right ventricle.
ARVD is composed of a range of symptoms, including irregular heartbeat and the presence of excess amounts of fatty tissue in the heart's right ventricle, the lesser known of the heart's two main pumping chambers and the one that pumps blood to the lungs.
As a result, the abnormal and often weakened and scarred right ventricle dramatically increases the risk of harmful ventricular arrhythmias and possible sudden cardiac death.
Diagnosis of ARVD is based on a four-point scale, and up to 10 cardiac tests are required to confirm a diagnosis.
Electrocardiograms, or EKGs, and echocardiograms are performed to verify the origins of arrhythmia, and MRI tests -- backed up by tissue biopsy -- are done to confirm the buildup of fat and fibrous tissue in the right ventricle.
According to Calkins, who founded Hopkins' ARVD registry in 1998 and is also director of its arrhythmia programs, these confirmatory tests are important because the illness is often misdiagnosed if physicians rely on a single diagnostic test, such as MRI.
His earlier research, in 2004, showed that more than half of patients are misdiagnosed, with physicians correctly diagnosing only 27 percent of true cases of ARVD.
In the new study, of the 47 patients who were diagnosed early and implanted with defibrillators that shock the heart to correct irregular rhythms, only one died of cardiac arrest, when the heart suddenly stops functioning from a runaway heartbeat.
Twenty-nine of the patients' defibrillators "fired" within two years. This was, says Dalal "the good news that most patients do quite well if protected by a defibrillator."
Of 22 patients without defibrillators and maintained on drug therapy alone, two died of cardiac arrest, in addition to the 31 who died before diagnosis.
While the exact cause of ARVD remains unknown, the scientists believe it to be an inherited syndrome and that improved awareness and better diagnosis are steps toward their goal of developing a screening test for those at risk.