title: An analysis of the electrocardiogram QT interval.
abstract: No reports testing the efficacy of the use of the QT/RR ratio <1/2 for detecting a normal QTc interval were found in the literature. The objective of the present study was to determine if a QT/RR ratio < or =1/2 can be considered to be equal to the normal QTc and to compare the QT and QTc measured and calculated clinically and by a computerized electrocardiograph. Ratios (140 QT/RR) of 28 successive electrocardiograms obtained from 28 consecutive patients in a tertiary level teaching hospital were analyzed clinically by 5 independent observers and by a computerized electrocardiograph. The QT/RR ratio provided 56% sensitivity and 78% specificity, with an area under the receiver operator characteristic curve of 75.8% (95%CI: 0.68 to 0.84). The divergence in QT and QTc interval measurements between clinical and computerized evaluation were 0.01 +/- 0.03 s (95%CI: 0.04-0.02) and 0.01 +/- 0.04 s (95%CI: -0.05-0.03), respectively. The QT and QTc values measured clinically and by a computerized electrocardiograph were similar. The QT/RR ratio < or =1/2 was not a satisfactory index for QTc evaluation because it could not predict a normal QTc value.
authors.affiliation: Serviço de Cardiologia, Departamento de Clínica Médica, Faculdade de Medicina and Hospital São Lucas, Pontifícia Universidade Católica, Porto Alegre, RS, Brasil.
authors.forename: N R
authors.initials: NR
authors.lastname: Koehler
authors.forename: J P
authors.initials: JP
authors.lastname: Zouvi
authors.forename: L A
authors.initials: LA
authors.lastname: Acevedo
authors.forename: B J
authors.initials: BJ
authors.lastname: Sukienik
authors.forename: M
authors.initials: M
authors.lastname: Rabin
mesh_terms: D001145:Arrhythmias, Cardiac / Q000175:diagnosis*; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D012372:ROC Curve; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted