January 25, 2008
Last Updated: 2008-01-23 18:18:45 -0400 (Reuters Health)
NEW YORK (Reuters Health) – An isolated corrected QT (QTc) interval below 500 ms is likely to be benign in elite athletes, according to a report by UK investigators.
American Heart Association and the European Society of Cardiology guidelines recommend that athletes with a long QT, even in the absence of symptoms or a family history, be disqualified from participating in sports, Dr. Sanjay Sharma told Reuters Health. However, the "significance of an isolated long QT in an asymptomatic athlete is unknown."
Dr. Sharma from University Hospital Lewisham/King’s College Hospital in London and associates investigated the prevalence of prolonged QTc in a large group of elite British athletes and evaluated its significance using Holter monitoring, exercise testing, cardiovascular evaluation of first-degree relatives, and genetic testing in consenting individuals. Males with a QTc value of > 440 ms and females with a QTc value of > 460 ms were considered to have an abnormally prolonged QTc interval,
Seven of 2000 athletes (six males, one female) had a prolonged QTc interval, for a prevalence of 0.4%, the researchers report in the December European Heart Journal. Three had baseline QTc values greater than 500 ms.
All seven athletes were asymptomatic, the report indicates, and none showed evidence of polymorphic ventricular tachycardia during 48 hours of monitoring or during exercise testing.
Among the athletes with baseline QTc value greater than 500 ms, two showed prolongation of the QTc interval during the initial stages of exercise and immediately postexercise, and two had first-degree relatives with a long QTc detected by 12-lead ECG screening.
One of the five athletes who underwent genetic testing had a positive genetic diagnosis (a single nucleotide substitution in KCNQ1 resulting in an amino acid change), the researchers report. His baseline QTc value was greater than 500 ms.
"It is highly unlikely that all 0.4% of athletes had true long QT syndrome, but more probable that the bradycardia associated with exercise results in an over-estimate of the QT interval or that the increase in left ventricular mass associated with exercise may also cause a slight prolongation of the QT interval," Dr. Sharma explained.
"Our results suggest that athletes with a QTc of 500 ms or more can be regarded to have definite long QT syndrome and should be disqualified appropriately," Dr. Sharma said.
"However, athletes with QTc of 440-490 ms may be able to compete in the absence of symptoms and in whom an exercise test, 24-hour ECG, and ECG in first-degree family members are normal — unless subsequent genetic testing proves otherwise."
"We are currently observing all athletes with a long QTc (less than 500 ms) on an annual basis," Dr. Sharma added. "These athletes continue to compete and remain asymptomatic over a 3-year follow-up period."
"It is clear that normal ventricular repolarization standards involving QT, heart rate, and QTc need to be developed in highly trained athletes, with clinical follow-up for outcome," writes Dr. Arthur J. Moss, from University of Rochester Medical Center in New York, in a related editorial.
Dr. Moss agrees that "QTc is only a surrogate marker for ventricular repolarization, and borderline QTc interval prolongation (460 ms < QTc < 500 ms) in trained athletes does not warrant disqualification from competitive sports in the absence of findings indicative of long QT syndrome or structural heart disease."
However, for those with "QTc greater than or equal to 500 ms, it is reasonable and prudent to recommend that they do not participate in competitive sports."
Eur Heart J 2007;28:2825-2826,2944-2949.
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