In vivo recording of monophasic action potentials in awake dogs.

Assessment of cardiac repolarization in dogs in vivo is of interest in numerous experimental canine models. Previous studies have used monophasic action potentials (MAPs) to investigate repolarization in vitro and in vivo in anesthetized animal models. Therefore, an approach for recording MAPs in awake dogs without the interference of anesthesia is desirable. We describe an experimental technique to record MAPs in conscious dogs by means of conventional rubber introducers which are implanted into the internal jugular vein. Atrial as well as ventricular MAPs can be simultaneously measured without complications. Pacing thresholds are low and stable over time. Continuous MAP recordings of stable amplitude can be achieved from the same endocardial site for periods up to 1h. Antegrade and retrograde atrioventricular nodal conduction properties can be assessed. Programmed stimulation can be performed to simultaneously determine local refractory periods and MAP duration at cycle lengths from 500 to 200ms. In awake, unsedated dogs measuring MAPs via rubber introducers permits safe, long-term recording of MAPs. Such recordings may be useful for safety pharmacologic studies in evaluating cardiovascular and noncardiovascular drugs with respect to their effects on repolarization. In various canine in vivo models including in vivo models of long QT syndrome, heart failures or sudden cardiac death, the present technique permits electrophysiologic measurements without the interference of anesthesia.