An increase in awareness of congenital long QT syndrome may have led to diagnosis and treatment of a significant number of unaffected people, according to an article in the May 22 issue of Circulation.

In a review of 176 patients referred to the Mayo Clinic, Rochester, MN, USA, for a second opinion, specialists there found that about 40 percent of patients did not show sufficient evidence to merit that diagnosis. Most of these patients were eventually cleared as normal.

Of the 176 who sought a second opinion, most were taking drugs to correct presumed long QT syndrome and were restricted from strenuous physical activity, including competitive sports. About 10 percent had undergone surgery to have an implantable cardioverter defibrillator placed.

“Two of every five patients who were referred to us with the diagnosis of Long QT Syndrome (LQTS) left Mayo Clinic without the diagnosis,” said Michael Ackerman, MD, PhD, the pediatric cardiologist who directs Mayo’s Long QT Syndrome Clinic and is the director of the Mayo Clinic Windland Smith Rice Sudden Death Genomics Laboratory.

“This is dramatic evidence of just how challenging LQTS is to correctly diagnose because it can present with such a large variety of symptoms,” Ackerman said. “There’s a real need for cautious, comprehensive evaluation by experienced LQTS specialists because there is a risk for overdiagnosis. And when that happens, some of the treatments that patients may receive when they carry this diagnosis -- such as taking medications for life, having a defibrillator implanted, or being restricted from competitive sports -- can have a profound effect on quality of life.”

Ackerman emphasized that this subset of patients seen at Mayo Clinic may not be representative of all patients. Their cases may not have been clear in the first place, prompting the families to seek a second opinion. He cautioned against interpreting the results of this study to mean that 40 percent of all patients have errors in diagnosis. “Instead, this study has exposed the fact that sometimes the clues we use to suspect the diagnosis of LQTS can be misread, misinterpreted, mismeasured and mistaken,” he said.

Long QT syndrome is a genetic disorder that occurs in about 1 in 3,000 people. Approximately 5 percent to 10 percent of the time, its first symptom is sudden death, often related to physical exertion or auditory triggers such as an alarm clock. However, most cases can be diagnosed following warning signs that suggest its potential presence and from objective data derived from an electrocardiogram, exercise or adrenalin stress testing, and genetic testing. Genetic testing for this condition has been available as a clinical diagnostic test for only three years. A number of treatments can then be prescribed.