An analysis of the electrocardiogram QT interval

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 <=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 percent sensitivity and 78 percent specificity, with an area under the receiver operator characteristic curve of 75.8 percent (95 percentCI: 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 percentCI: 0.04-0.02) and 0.01 ± 0.04 s (95 percentCI: -0.05-0.03), respectively. The QT and QTc values measured clinically and by a computerized electrocardiograph were similar. The QT/RR ratio <=1/2 was not a satisfactory index for QTc evaluation because it could not predict a normal QTc value.

An analysis of the electrocardiogram QT interval.

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.

[Left arterial overload. Electro-echocardiographic correlations]. / Sobrecarga atrial esquerda. Correlação eletro-ecocardiográfica.

PURPOSE: To compare the accuracy of left atrial enlargement (LAE) diagnosis made by electrocardiographic criteria with those obtained using M-mode echocardiography. METHODS: We studied 273 patients age 17 to 87 (mean 49) years, 115 men, white 95.5%, black 3.5% mulattos 1%, with or without heart disease of different etiologies. The ECG criteria studied were: a) P terminal force in V1 > or = 0.04 mmx s; b) Pt force in V1 duration > 0.04s; c) Pt force in V1 depth > or = 1 mm; d) P wave notching in D2 with interpeak distance > or = 40ms; f) presence of atrial fibrillation. The gold-standard for LAE was left atrial dimension > 40 mm obtained by echocardiography. RESULTS: The percentage of correct diagnosis were: atrial fibrillation (88%), Morris index (75%), PtfV1 negativity > or = 1 mm (74%), notched P wave in D2 with interpeak distance > or = 0.04 s (70%), PtfV1 with duration > 0.04 s (64%) and P wave duration in D2 > 0.11s (46%). CONCLUSION: Conventional ECG has limited value for detecting LAE. A higher correlation was found between atrial fibrillation and changes in P wave in V1 and the echocardiographic LAE.