Amiodarone reduces QT dispersion in patients with hypertrophic cardiomyopathy

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.