3-LEAD MEASUREMENT OF QTC DISPERSION

Introduction: QTc dispersion has traditionally been calculated from al l 12 leads of a standard electrocardiogram (EGG), It is possible that alternative, quicker methods using fewer than 12 leads could be used t o provide the same information. Methods and Results: We have previousl y shown a difference in QTc dispersion from ECGs recorded at least 1 m onth after myocardial infarction between patients who subsequently die d and long-term survivors, In the current study, we recalculated QTc d ispersion in these ECGs using different methods to determine if the ob served difference in QTc dispersion measurements between the two group s, as calculated from 12-lead ECGs, persisted when using smaller sets of leads, QTc dispersion was recalculated by four methods: (1) with th e two extreme QTc intervals excluded; (2) from the six precordial lead s; (3) from the three leads most likely to contribute to QTc dispersio n (aVF, V-1, V-4); and (4) from the three quasi-orthogonal leads (aVF, I, V-2), For each of the 270 12-lead ECGs examined, a mean of 9.9 lea ds (SD 1.5 leads) had a QT interval analyzed; the QT interval could no t be accurately measured in the remaining leads, Using the standard 12 -lead measurement of QTc dispersion, there was a difference in the fal l in QTc dispersion from early to late ECG between the groups: 9.1 (SD 60.8) msec for deaths versus 34.4 (55.2) msec for survivors (P = 0.01 6), This difference in QTc dispersion between early and late ECGs was maintained using either three-lead method (quasi-orthogonal leads: -2. 6 [56.2] msec for deaths vs 26.9 [54.3] msec for survivors [P = 0.003] ; ''likeliest'' leads: 8.6 [64.9] msec vs 29.5 [50.2] msec [P = 0.05]) , but not when using the other two methods (precordial leads: 19.1 [55 .5] msec vs 22 [50.8] msec [P = 0.76]; extreme leads removed: 9.2 [50. 1] msec vs 21.8 [42] msec [P = 0.13]). Conclusion: QTc dispersion calc ulated from three leads may be as useful a measurement as QTc dispersi on calculated from all leads of a standard EGG. Its advantages over th e standard measurement are its simplicity and the lack of problems Wit h lead adjustment.