Journal of electrocardiology
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Multicenter Study Comparative Study
A comparison of commonly used QT correction formulae: the effect of heart rate on the QTc of normal ECGs.
The corrected QT interval (QTc) is widely used in pharmaceutical studies and clinical practice. Bazett's QT correction formula is still the most popular, despite Simonson's warning in 1961 that it could not be recommended. Other QTc formulae, e.g. ⋯ Numerous references recommend 420 to 440 ms as the threshold for reporting prolonged QTc when using Bazett's formula. Based on this database, 30% of apparently normal ECGs would be reported as having abnormal QT intervals for the 440 ms threshold, or 10% if 460 ms is chosen, compared to <2% for the other formulae. It was also noted that QT has a linear trend with HR but not with RR.
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A new computerized acute coronary syndrome (ACS) computer algorithm has been developed with the aim of improving the electrocardiographic detection of acute myocardial ischemia and infarction in the emergency department (ED). The purpose of this study was to determine the added value of the new ACS algorithm in assisting ED physicians to obtain a more accurate diagnosis in patients with ACS. The new algorithm combines a rule-based decision tree, which uses well-known clinical criteria and a data-centered neural network model for more robust pattern recognition. ⋯ The results demonstrated that with the assistance of the new algorithm, the emergency physician and cardiologist improved their sensitivity of interpreting acute myocardial infarction by 50% and 26%, respectively, without a loss of specificity. The new algorithm also improved the emergency physician's acute ischemia interpretation sensitivity by 53% and still maintained a reasonable specificity (91%). The new ACS algorithm provides added value for improving acute ischemia and infarction detection in the ED.
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This article reports a case of tachycardia-dependent right bundle branch block (RBBB) occurring during atrial fibrillation. In some sections of the recording, an alternans occurs between complexes with a complete RBBB pattern and complexes showing normal intraventricular conduction or incomplete RBBB. Alternans is frequently observed during phases of fast and nearly regular rhythm, but it occurs even in the presence of a markedly irregular ventricular response. The RBBB alternans associated with short and regular RR intervals is likely to represent a manifestation of 2:1 bundle branch supernormal conduction, whereas alternans occurring with irregular cycles expresses a complex interaction between the RR cycle length and some mechanisms affecting intraventricular conduction, such as tachycardia-dependent bundle branch block, supernormal conduction and concealed retrograde activation of the anterogradely blocked bundle branch (the so-called "linking" phenomenon).