Dispersion of ventricular repolarization: A new marker to identify high risk patients with long QT syndrome

QT interval dispersion, measured as interlead variability of QT has been proposed as a marker of dispersion of ventricular repolarization (DVR) and therefore of electrical instability. In the present study we tested the hypothesis that DVR may be differently affected by intervention destined to provide complete or incomplete protection against malignant arrhythmias in patients with long QT syndrome (LQTS). Dispersion of QT and QTc (QT/√RR), was calculated using two indexes: 1) the difference between the longest and the shortest value measured in each of the twelve ECG leads (QT max-QT min; QTc max-QTc min); the relative dispersion (RD) of QT and QTc (STD of QT/QT average 100, STD of QTc/QTc average 100). A group of 15 healthy volunteers, with an age comparable to that of the LQTS population served as control (group 1). Twenty-eight patients affected by the Romano-Ward form of idiopathic LQTS entered the study and divided into 3 groups; LQTS patients not receiving pharmacologic therapy (group 2), responders (group 3) and non-responders (group 4) to beta-blockers therapy. Similar results have been observed also for QT interval. Diagnostic value of dispersion of repolarization has been also calculated: a cut-off value of 100 ms QT max-QT min had a 80% sensitivity a 82% specificity a 80% positive and a 77% negative predictive value. A cut-off value of 6 for relative dispersion of QT had a 80% sensitivity, a 73% specificity, a 73% positive and a 75% negative predictive value, in identifying responders to beta blockers. Non responders patients (group 4), underwent left cardiac sympathetic denervation (LCSD) and thereafter remained asymptomatic. LCSD significantly reduced DVR to values comparable to group 1 (QT max-QT min: 78 ± 45 vs. 137 ± 52, p <0,002; QTc max-QTc min; 78 ± 45 vs. 156 ± 58, p <0,001. QT RD 5,1 ± 3,7 vs. 8,6 ± 3,9, p <0,001 and QTc RD 5,2 ± 3,4 vs. 9,5 ± 4, p <0,001). Thus these data demonstrate that DVR measured by means of QT and QTc dispersion can be modified by antiadrenergic intervention and that its changes may be related to clinical outcome. Therefore QT and QTc dispersion indexes may become useful markers to quantify electrical instability in patients with LQTS and clinically valuable tools in making therapeutic decisions