Chronic recording from the His bundle of the awake dog

The conventional catheter method for measuring specialized A-V nodal and His-ventricular conduction times in the intact dog heart precludes an unanesthetized control. This control is necessary for meaningful studies of the effect of drugs or drug-drug interactions on A-V conduction times. At right thoracotomy (halothane anesthesia), mongrel dogs had bipolar electrodes sutured to the epicardial surface of both atrial appendages, junctions of the sulcus terminalis with both vena cavae, and right ventricle. A unipolar needle electrode, referenced to a unipolar electrode on the ascending aorta, was inserted into the interatrial septum from the aortic root for recording the His bundle electrogram. After one to three weeks for stabilization, weekly measurements were made of A-V nodal conduction time (AVN) and His-ventricular conduction time (H-V) for up to 52 weeks (4 to 52 weeks). Mean values (13 dogs) for spontaneous cycle length, AVN and H-V conduction times were 477 +/- 25, 82 +/- 3, and 30 +/- 1 msec, respectively. Simultaneous recordings from catheter and implanted His bundle electrodes were made during changes in atrial paced rate (five dogs, pentobarbital anesthesia). Values for AVN and H-V conduction times from catheter or implanted electrodes were the same. AVN conduction time increased, H-V conduction time remained constant during increases in atrial rate. Atropine shortened and propranolol prolonged AVN conduction time in six unanesthetized, unsedated dogs; neither affected H-V conduction time. Histologic examination of electrode sites in two dogs at 43 and 52 weeks showed no evidence of damage to underlying myocardial recording sites. This preparation provides reproducible awake values for AVN and H-V conduction times, and hence a more meaningful control for pharmacologic investigations.