EVALUATION OF QT INTERVAL DURATION AND DISPERSION AND PROPOSED CLINICAL-CRITERIA IN DIAGNOSIS OF LONG QT SYNDROME IN PATIENTS WITH A GENETICALLY UNIFORM TYPE OF LQT1

Objectives. This study investigated the ability of QT duration, QT dis persion (QTD) and clinical diagnostic criteria to correctly identify g enetically documented LQT1 type long QT syndrome (LQTS) patients, and to separate symptomatic and asymptomatic LQT1 patients. Background. Ve ntricular repolarization has played an essential role both in diagnosi s and risk assessment of LOTS. Today, molecular genetic techniques per mit unequivocal identification of many LQTS patients. Methods. QT inte rval and QTD in 12 symptomatic and 18 asymptomatic LQT1 patients and t heir 43 healthy relatives were evaluated. The sensitivity and specific ity of upper normal limits of QT interval two QT interval adjustment m ethods (Bazett's and Fridericia's formulas), and the proposed clinical criteria for LQTS were assessed. Occurrence of a mutant (D188N) KVLQT 1 gene was considered as the basis of classification into affected and nonaffected individuals. Results. Diagnostic sensitivity and specific ity values were 90% and 88% using Bazett's formula, and 80% and 100% u sing Fridericia's cubic root formula or upper normal limits for QT int erval. Suggested diagnostic criteria for LOTS reached 100% specificity , but 47% of the DNA-documented LQT1 patients were classified into the category of low or intermediate probability of LOTS. QT interval and heart rate did not differ between symptomatic (464 +/- 47 ms, 70 +/- 9 min(-1)) and asymptomatic 460 +/- 41 ms, 65 +/- 13 min(-1)) LQT1 pati ents. QTD was increased in symptomatic LQT1 patients compared to unaff ected relatives (66 +/- 48 vs. 37 +/- 15 ms, p = 0.02), but symptomati c patients LQT1 did not differ from asymptomatic (45 +/- 19 ms). Concl usions. Not all LQT1 patients can be distinguished from healthy relati ves by assessment of QT duration or clinical criteria. Presence of LQT 1 gene can carry the risk of cardiac events even with no or only margi nal prolongation of QT interval.