His bundle electrography in the dog. Normal values and findings with verapamil

An exact analysis of the intracardiac conducting system can be performed by the His bundle electrography. It allows a differential representation of individual parts of this system and, therefore, a more accurate determination of the site of action of compounds. Today this method belongs to the diagnostic routine in large cardiologic centres. However, His bundle electrography is seldom applied in experimental pharmacology. Our control values of 97 anaesthetized dogs under non-stimulated conditions are as follows: PA time = 41 +/- 1 ms, AH time = 66 +/- 2 ms, HV time = 37 +/- 1 ms; under stimulated conditions: PA = 40 +/- 1, AH = 88 +/- 2, HV = 36 +/- 1, QRS = 51 +/- 1 ms, sinus node recovery time (SNRT) = 1087 +/- 26 ms, corrected sinus node recovery time (CSNRT) = 370 +/- 17 ms, effective refractory period of the atrium = 267 +/- 8 ms, and of the AV node = 266 +/- 8 ms, functional refractory period of the atrium = 276 +/- 8 ms, and of the AV node 345 +/- 7 ms. With intravenous injections of 0.03 and 0.1 mg/kg verapamil, only a tendency to prolongation of the AH time, CSNRT and the refractory parameters was achieved. Immediately after 0.3 mg/kg verapamil given as i.v. injection or infusion over a period of 5 min, heart rate was increased and sinus node recovery time was shortened transitorily. After the rapid disappearance of these effects, AH time was prolonged while PA, HV and QRS remained unaffected, also under stimulated conditions. All refractory periods measured were prolonged significantly.(ABSTRACT TRUNCATED AT 250 WORDS)