QT dispersion analysis of a transplant assessment group

QT dispersion has been shown to be a marker of those at risk of sudden death due to cardiac arrhythmias. One of the most vulnerable groups of subjects are those waiting for heart transplantation, many of whom die before receiving a donor heart. We assessed the difficulties in measuring QT dispersion in these patients, by studying an initial group of 10 patients. Simultaneous 12-lead ECGs were recorded for each subject on admission to hospital for transplant assessment. The recordings were saved directly to computer at a sampling rate of 500 Hz. Q wave onset, T wave offset and T wave amplitude were measured in each lead using an on screen interactive analysis tool. The QT interval in 40% of the leads could not be measured. 7 patients had fewer than 8 measurable leads. Repeat measurements showed greatest differences for the T wave end measurements in the chest leads with mean (SD) difference of 16.2 ms (16.7 ms) compared with 9.1 ms (5.8 ms) in limb leads. The smallest differences were obtained for Q wave start points in the chest leads with mean (SD) difference of 2.4 ms (1.2 ms). Mean T wave amplitude was 0.21 mV (0.12 mV) across all leads, and for limb and chest leads was 0.15 mV (0.09 mV) and 0.28 mV and (0.17 mV) respectively. QT dispersion, measured as the difference between maximum and minimum QT intervals across all leads, for the group was 118 ms with range 35 ms to 330 ms.