title: Ventricular refractory periods in relation to rate and test-site VT intervals in anesthetized and conscious dogs: a canine model for conscious state measurements.
abstract: The functional relationship of ventricular effective refractory period (ERP) with basic cycle length (BCL) of stimulated ventricular depolarization and VT intervals of test-site unipolar ventricular electrograms were studied in five conscious and eight anesthetized (sodium pentobarbital, 30 mg/kg) open-chested dogs. The range of BCLs studied was 300 to 1000 ms, achieved through ventricular stimulation following chemically-induced complete AV block. In the conscious animal model developed for this study, two-to-four ventricular electrode leads were exteriorized and the ventricular rate was maintained by an implanted programmable VVI pacemaker. In all animals studied, the BCL-ERP relation was closely represented by the empirical equation ERP = A-B.Exp(-k.BCL), and the VT-ERP relation over the same range of BCLs was linear: ERP = C + D.VT. The correlation coefficients were in the range of 0.991 to 0.999. The mean values of the parameters in the above equations determined by the appropriate non-linear or linear regression analysis showed significant differences between the two groups of animals studied. In three conscious animals a strong linear correlation between the test-site VT intervals and simultaneously measured QT intervals measured from the lead II surface electrogram was demonstrated (r = 0.993 to 0.998). For a fixed site of stimulation, the morphology of ventricular depolarization complexes as well as the corresponding T-waves remained essentially unaltered with BCL for both myocardial and surface electrograms. The possible applications of developed canine model and the results of the present study include: (1) the study of the rate-dependent effects of cardioactive drugs on ventricular electrophysiology and, (2) the improved design of electronic refractory periods of rate programmable pacemakers.
mesh_terms: D000777:Anesthetics / Q000494:pharmacology; D000818:Animals; D004285:Dogs; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009431:Neural Conduction; D010424:Pentobarbital / Q000494:pharmacology; D012032:Refractory Period, Electrophysiological; D013997:Time Factors; D016276:Ventricular Function
chemical_list: D000777:Anesthetics; D010424:Pentobarbital