FREQUENCY-DEPENDENT ELECTROPHYSIOLOGIC PROPERTIES OF VENTRICULAR REPOLARIZATION IN PATIENTS WITH CONGENITAL LONG QT SYNDROME

Objectives, This study was performed to evaluate the frequency depende ncy of ventricular repolarization and the effect of epinephrine in pat ients with congenital long QT syndrome (LQTS), Background. The efficac y of pacemakers in addition to antiadrenergic therapy in the treatment of congenital LQTS has been reported, Methods, Monophasic action pote ntials were recorded from right and left ventricular endocardium durin g atrial pacing at heart rates from 70 to 140 beats/min at baseline an d from 100 to 140 beats/min during epinephrine infusion (0.1 mu g/kg b ody weight per min) in 11 patients with congenital LQTS and 10 control patients, The response of monophasic action potential duration at 90% repolarization (MAPD90) and the dispersion of MAPD90 were examined. R esults. At baseline, both the MAPD90 and the dispersion of MAPD90 were significantly (p < 0.001) longer in the congenital LQTS group than th e control group, The differences in these variables between the two gr oups significantly decreased (MAPD90: from 105 to 31 ms; dispersion of MAPD90: from 55 to 13 ms, p < 0.001) as heart rate was increased, Epi nephrine prolonged the MAPD90 and increased the dispersion of MAPD90 s ignificantly (p < 0.001) at all paced heart rates in the congenital LQ TS group without frequency dependency but did not change in the contro l group, Thus, epinephrine increased the differences in these variable s between the two groups, Conclusions, The repolarization abnormalitie s in congenital LQTS were attenuated by increasing the heart rate, whi ch supported the efficacy of pacemaker therapy, However, during sympat hetic stimulation, the effects of increased heart rate on these repola rization abnormalities were limited.