Cardiac arrhythmias and atrioventricular (A-V) conduction disturbances remain an important cause of anesthetic morbidity and mortality. They interfere with the mechanical performance of the heart and impair myocardial oxygenation. Significant advances have been made by both basic and clinical cardiac electrophysiologists in determining mechanisms for arrhythmias and A-V conduction disturbances, particularly those observed in cardiac special care units. This has led to more effective means for their prevention and management. Similar advances have not been made in anesthesiology, but are urgently needed since arrhythmias and A-V conduction disturbances occur in as many as 62 percent of anesthetized patients. Our work to date (in situ dog heart) using catheter electrophysiologic methods, indicates that further systematic study will be of definite value in elucidating mechanisms underlying observed anesthetic-related arrhythmias and A-V conduction disturbances. Catheter electrophysiologic methodology, however, precludes measurements in conscious dogs. Such measurements are necessary to make meaningful comparisons between anesthetic drugs for their effects on the electrical activity of the heart. We have developed a dog model with chronically implanted electrodes that permits conscious-anesthetized comparisons. This has not been done previously. In eleven dogs, and after two to three weeks for electrode stabilization following thoracotomy for electrode implantation, conscious state measurements of A-V nodal, His-Purkinje and ventricular specialized A-V conduction times have been reproducible over two to thirty-one week periods. We propose using this model to determine anesthetic and combined drug effects on specialized A-V conduction times, cardiac refractory periods, electrically stimulated atrial and ventricular arrhythmias, and subsidiary atrial pacemaker location. Our findings should further the current understanding of mechanisms for anesthetic-related arrhythmias and A-V conduction disturbances. It is hoped this will lead to the improved anesthetic management of patients with pre-existing arrhythmias and A-V conduction disturbances, as well as to the more effective prevention and management of such disturbances caused by anesthetics or combined drugs.
