To compare QT interlead variability (dispersion) in patients who receive a class III antiarrhythmic with those not on antiarrhythmic
therapy, we measured QT in all 12 leads of a standard ECG in 24 patients with
hypertrophic cardiomyopathy, 12 (50%) of whom were on
amiodarone monotherapy and 12 (50%) who were not on
amiodarone or other cardioactive medication which could affect QT. Age, functional class, chamber dimension or the degree of
left ventricular hypertrophy expressed by maximal wall thickness (21 +/- 5 vs 20 +/- 4 mm; p = NS) was not different between the
amiodarone and the non-
amiodarone group. Maximal corrected QT (QTc) was greater in patients receiving (488 +/- 25 ms) compared to those not receiving
amiodarone (451 +/- 23 ms) (p less than 0.001). However, QTc dispersion defined as the difference of maximum minus minimum QTc was decreased in the
amiodarone (48 +/- 10 ms) compared to the non-
amiodarone group (78 +/- 17 ms) (p less than 0.001). We conclude that in patients with
hypertrophic cardiomyopathy,
amiodarone prolongs QTc but reduces QTc dispersion. These results agree with expected changes in ventricular recovery time in patients who receive Class III antiarrhythmic agents and provide further support to the theory that QTc dispersion reflects regional differences in ventricular recovery time.