Diagnostic accuracy of screening electrocardiograms in long QT syndrome I

Objective. Inherited long QT syndrome (LQTS) may present with syncope, seiz ures, and/or sudden death as a result of ventricular tachyarrhythmias. Iden tification of family members who are at risk because they harbor the geneti c substrate for LQTS is critical. Presently, such identification relies on the 12-lead electrocardiogram (ECG). The purpose of this study was to evalu ate the efficacy of the automated ECG as a screening tool for LQTS. Method. Molecular testing of a proband and 22 additional family members for the KVLQT1 mutation and symptomatic status facilitated the classification of each family member into the following patient groups: non-carriers (13), asymptomatic carriers (5), and symptomatic carriers (5). Each individual h ad a standard 12-lead ECG from which the computer and manual (lead II) corr ected QT interval were determined. In addition, we determined the accuracy of the computer ECG diagnostic interpretation for each patient group. Results. With the use of a corrected QT interval of greater than or equal t o 460 ms as a diagnostic cutoff, the positive and negative predictive value s for identifying at-risk individuals were 100%. Despite this, the computer -generated ECG diagnostic interpretation erroneously classified 6 of 23 fam ily members. Moreover, half of the family members, proved to have the ion c hannel defect, received the diagnostic interpretation "normal ECG." Conclusion. Reliance on the computer-generated ECG diagnostic interpretatio n alone will fail to identify many at-risk family members. It is suggested that all first-degree relatives of an identified LQTS proband have a 12-lea d ECG that is reviewed independently by a physician who is familiar with LQ TS in an effort to improve screening for this potentially lethal syndrome.