Circadian variation of sustained ventricular tachycardia in patients subject to standard adrenergic blockade

Morning peeks in the circadian variation of sustained ventricular tachycardia (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 episodes with and 102 episodes without antiadrenergic medications. Nine patients had episodes both with and without antiadrenergic medication and 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 not receiving antiadrenergic therapy had a similar morning peak. Antiadrenergic agents as used in standard clinical practice do not prevent circadian variation in onset of VT. This variation may be mediated by systems other than adrenergic receptor-linked activation or may reflect inadequacy of adrenergic blockade in standard clinical dosing.