Pacing and clinical electrophysiology : PACE
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Pacing Clin Electrophysiol · Jun 2004
Selective site pacing: defining and reaching the selected site.
Selective site right ventricular pacing has been suggested as an approach to reduce the incidence of ventricular dysfunction and hopefully influence the morbidity resulting from traditional right ventricular apical pacing. Pacing from the right ventricular apex allows a stable ventricular rate, and together with atrial pacing and sensing, helps maintain atrioventricular synchrony but does not allow physiological activation of the left ventricle. ⋯ This lack of definition consensus may have contributed to the apparent conflict of data, particularly in the right ventricle. There is an urgent need for a standardization of terms and identifying measures for selective pacing sites.
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Pacing Clin Electrophysiol · Jun 2004
Differences between study-specific and subject-specific heart rate corrections of the QT interval in investigations of drug induced QTc prolongation.
A computational study was designed to investigate the differences between the so-called study-specific and subject-specific heart rate corrections of QT interval. In 53 healthy subjects (25 women, mean age 26.7 +/- 8.7 years), serial 10-second electrocardiograms (ECG) were obtained during daytime hours. In each subject, 200 ECGs were selected representative of the individual QT/RR relationship. ⋯ The subject-specific corrections led to maximum errors in single milliseconds (error range of 2.4, 5.7, and 2.6 ms with linear, log/log linear, and exponential models, respectively) while the study-specific corrections led to substantially greater errors (error range of 17.8, 19.4, and 16.9 ms with linear, log/log linear, and exponential models, respectively). Both Bazett and Fridericia corrections led not only to substantial errors (error range of 28.3 and 16.9 ms) but also to regular bias with systematically false negative and false positive conclusions dependent on modeled heart rate acceleration and deceleration. Thus, subjects-specific corrections should be used in the intensive and definite studies aimed at providing the final answer on the ability of a drug to prolong the QT interval.