Effect of adrenergic stimulation and blockade on ventricular defibrillation in the rat

Ventricular fibrillation was electrically induced in 60 rats and the effects of adrenergic stimulation ad blockade on the time taken to spontaneous reversion to sinus rhythm were determined. Alpha adrenergic stimulation by norepinephrine and phenylephrine infusion shortened ventricular fibrillation from 3.21 +/- 0.42 (+/- S.E.M.) to 1.48 +/- 0.17 sec (P less than .001) and from 5.13 +/- 0.77 to 2.18 +/- 0.27 sec (P less than .001), respectively. Nonselective beta adrenergic stimulation with isoproterenol prolonged the time to defibrillation from 1.65 +/- 0.20 to 7.01 +/- 0.95 sec (P less than .001), whereas beta-2 adrenergic stimulation with salbutamol produced no change. Alpha adrenergic stimulation antagonized the effect of a concomitant isoproterenol infusion (P less than .05). Alpha adrenergic blockade with phenoxybenzamine prolonged ventricular fibrillation (P less than .001) whereas beta blockade with propranolol or metoprolol shortened the duration of fibrillation. It was concluded that these effects were due to direct stimulation and blockade of cardiac adrenergic receptors. These actions were associated with changes in ventricular refractoriness. Cardiac alpha adrenergic stimulation prolonged the ventricular effective refractory period and promoted spontaneous defibrillation. Beta adrenergic stimulation shortened the ventricular effective refractory period and prolonged the time to defibrillation.