Effect of QT interval correction during autonomic blockade in combination with changes in posture

The measurement of QT interval on ECG is a marker for malignant ventricular arrhythmias. When QT is measured, it must be corrected to become independent of heart rate (HR) and become a comparable measure of repolarization between different conditions. The objective of this work was to evaluate different types of QT interval correction (Bazzett, Individual and Hodges) for different QT/RR relations. This was accomplished with selective blockade of sympathetic and vagal autonomic systems by using combinations of postural changes and drugs. When comparing vagal condition (supine) versus sympathetic condition (standing atropine) a significant shortening of 43 ms (P<0.006) was observed. Whereas when comparing sympathetic (standing) versus vagal condition (supine propranolol) a significant lengthening of 23 ms (P<0.005) was observed. The Individual correction method achieved the best uncorrelation between QT and RR interval, making QT more independent of HR and ANS status