PROLONGED QT INTERVAL - A TRICKY DIAGNOSIS

Prolonged heart-rate adjusted QT intervals on the electrocardiogram (E CG) are associated with an increased risk for coronary heart disease a nd sudden death. However, the diagnosis of the prolonged QT interval i s hampered by lack of standards. We studied variations in the prevalen ce of prolonged QT, based on different common definitions, in a large nonhospitalized population, and compared our results with other studie s applying the same definitions. The study population consisted of 2,2 00 men and 3,366 women participants of the Rotterdam Study, greater th an or equal to 55 years old, The QT interval was computed by our Modul ar ECG Analysis System (MEANS), Three different formulas to adjust QT for heart rate were used: Bazett's formula (QT(c)), a linear regressio n equation (QT(lr)), and the QT index (QTI). Prolonged QT occurred fre quently in both men and women, and its prevalence increased with age. Women had longer heart-rate adjusted QT intervals than men (mean QT(c) 433 ms vs 422 ms), and mean values for QT(lr), were lower than for QT , (mean QS(lr), 422 ms in women and 412 ms in men). Prevalence was hig hest for prolonged QT(lr), (31% in men and 26% in women) and lowest fo r prolonged QTI (6% in men and 9% in women), Comparison with other stu dies applying the same correction formulas showed large discrepancies in prevalence estimates of prolonged QT(c) and QT(lr), and to a lesser degree of prolonged QTI, possibly due to differences in measurement t echniques. Future research is needed to relate QT interval to prognosi s, to obtain measurement technique specific reference values of heart- rate adjusted QT measurements, and to obtain age-and sex-specific thre shold values for prolonged QT. Such data are needed to use the QT inte rval with confidence, (C) 1997 by Excerpta Medica, Inc.