QT variability before and after episodes of nonsustained ventricular tachycardia in patients with hypertrophic cardiomyopathy

This study examined the changes in QT dynamics occurring during 5-minute intervals sampled immediately before and 1 hour after episodes of nonsustained ventricular tachycardia (VT) in patients with hypertrophic cardiomyopathy (HCM). Twenty-four hour Holter recordings were performed in 10 patients with HCM in the absence of antiarrhythmic medications and processed by the ELA Medical QT analysis software. All sinus complexes were averaged over 30-second segments and 2,880 templates were created. For each template, a mean corrected QT(ec) (time interval between the onset of QRS and the end of the T wave) and QT(ac) (time interval between the onset of the QRS and the peak of the T wave) were calculated, with their standard deviations (SDQT(e) and SDQT(a)) taken as indices of QT variability. The slopes of the regression line for the QT(e) and QT(a) against the corresponding RR also were calculated. Forty 5-minute segments were analyzed immediately before (sample A) and 1 hour after (sample B) 20 episodes of nonsustained VT. QT(ac) was significantly longer in group A than in group B (321 +/- 20 vs 312 +/- 22, P < 0.0001) and SDQT(a) was significantly lower (2.8 +/- 1.2 vs 4.7 +/- 3.7 P < 0.03). There were no significant differences in QT(ec), SDQT(e), QT(e)/RR and QT(a)/RR before and after the episodes. Our data indicate that in patients with HCM, the averaged QT,, is significantly longer and the QT(a) variability significantly lower before episodes of nonsustained VT.