In vivo recording of monophasic action potentials in awake dogs - new applications for experimental electrophysiology

Introduction Despite enormous developments in the field of clinical and exp erimental electrophysiology there is still a gap in evaluating repolarizati on in the awake animal. Numerous previous studies have used monophasic acti on potentials (MAP) to assess repolarization in vitro and in vivo in anesth etized animal models. However, an approach for recording MAP in awake dogs without interference of anesthesia has not yet been developed. Methods and results We developed an experimental technique to record MAP in conscious d ogs by means of conventional rubber introducers which were implanted into t he internal jugular vein. In seven awake dogs, atrial as well as ventricula r MAP were simultaneously measured without complications. Pacing thresholds were low and stable over time ranging from 0.2 to 4.0 mA. The MAP amplitud es ranged from 10 to 30 mV for ventricular and from 5 to 15 mV for atrial M AP. Continuous MAP recordings of stable amplitude could be made from the sa me endocardial site for periods of up to one hour. Antegrade and retrograde AV-nodal conduction properties could be assessed. Programmed stimulation w as performed to simultaneously determine local refractory periods and MAP d uration at cycle lengths from 500 to 200 ms. Conclusion In awake, unsedated dogs the measurement of MAP via rubber introducers permits safe, long-term recording of MAP. Such recordings may be useful for safety pharmacological studies in evaluating cardiovascular and non-cardiovascular drugs with reg ard to their effects on repolarization. In various canine in vivo models in cluding in vivo models of long QT syndrome, heart failure or sudden cardiac death, the present technique permits electrophysiological measurements wit hout interference of anesthesia.