Hemodynamic and electrophysiologic interactions between antiarrhythmic drugs and beta blockers, with special...

The administration of beta-receptor blocking drugs and antiarrhythmic drugs in close proximity may result in hemodynamic, electrophysiologic, or pharmacokinetic interactions. We examined the hemodynamic and electrophysiologic effects of 0.20 mg/kg intravenous metoprolol followed by a 15-minute infusion of 0.75 mg/kg/min tocainide. In the six patients sutided, metoprolol produced a fall in cardiac rate and output which was not further altered by tocainide. Both drugs decreased peak left ventricular (LV) dP/dt, ejection fraction, and mean Vcf. There was no change in LV end-diastolic pressure or echo dimension and in clinical ill effects. In eight patients without sinus A-V nodal disease electrophysiologic studies showed mild depression of A-V conduction by metoprolol. Tocainide depressed sinus node function and shortened the functional refractory period of the His-Purkinje system. There were no clinical sequelae. However, three patients with preexisting electrophysiologic abnormalities developed asystole. There was no evidence of pharmacokinetic interaction. It is concluded that metoprolol and tocainide can be given concurrently with reasonable safety to cardiac patients without electrophysiologic abnormalities.