MYOCARDIAL IRRITABILITY— HEGNAUER and COVINO 



349 



1 



BP 



125 



'/85 



Fig. 2. — Effect of procaine injection of superior vena caval-atrial junction upon electro- 

 cardiogram (lead 2), pulse and blood pressure in hypothermic dog, temperature 27 degrees. 

 From Riberi, ct al. (Surgery, Nov., 1955.) 



mals^ the stimulus of very rough external manipulation or vigorous massage of the 

 ventricular septum by a finger passed into the right ventricle through the right 

 atrium and tricuspid valve resulted in ventricular fibrillation in all control animals 

 and in none protected by procaine injection (table II). When animals were stimu- 

 lated by right ventriculotomy, or by ventriculotomy and placement of sutiu"es in 

 the ventricular septum, similar results were obtained. Ventricular fibrillation oc- 

 curred in all control animals and in none of those injected with procaine. The series 

 of animals was not enlarged because the results were so conclusive and because 

 Radigan, Lombardo, and Morrow, who repeated our experiments, obtained the 

 same results.** When the experiment was carried out upon dogs cooled to a lower 

 temperature, only 56 per cent of the control animals developed fibrillation.^ Those 

 with procaine blockade showed a remarkable degree of protection. Fibrillation was 

 prevented in 94 per cent. 



We have also investigated the influence of the extrinsic nerve supply to the heart 

 on the incidence of ventricular fibrillation^ (table III). In moderately cooled dogs 

 subjected to a 10-mintite period of venous inflow occlusion, right ventriculotomy 

 and placement of sutures in the ventricular septum, upper dorsal and stellate 

 ganglionectomy protected all animals from ventricular fibrillation. The use of in- 



TABLE I 



Average Pulse, Blood Pressure and Electrocardiographic Changes in Dogs with Procaine 

 Block of Atrial- Superior Vena Caval Area 



(Adapted from Surgery, Nov., 1955.) 



Normothermic animals 



