CIRCADIAN VARIATION OF SUSTAINED VENTRICULAR-TACHYCARDIA IN PATIENTS SUBJECT TO STANDARD ADRENERGIC-BLOCKADE

Morning peeks in the circadian variation of sustained ventricular tach ycardia (VT) may reflect the contribution of sympathetic activation to onset of VT, We hypothesized that adrenergic blockade would eliminate this morning peak. Fifty-four patients using a defibrillator had 1114 time-stamped episodes of VT requiring therapy with a device: 1012 epi sodes with and 102 episodes without antiadrenergic medications. Nine p atients had episodes both with and without antiadrenergic medication a nd were examined separately. In patients taking antiadrenergic agents, data fitted to a harmonic regression model revealed a morning peak at 9:00 AM (R-2=0.542; p < 0.05), with a secondary peak at 4 PM. Those n ot receiving antiadrenergic therapy had a similar morning peak. Antiad renergic agents as used in standard clinical practice do not prevent c ircadian variation in onset of VT. This variation may be mediated by s ystems other than adrenergic receptor-linked activation or may reflect inadequacy of adrenergic blockade in standard clinical dosing.