The Journal of laboratory and clinical medicine . the junctional tis- Regular Ectopic Rhythms 479 sues they are usually referred to as atrioventricular rhythms. Such rhythmsmay arise spontaneously, most often during the course of certain acute diseasesespecially diphtheria- and acute rheumatic fever.^ IVIore often they may be pro-duced by stimulation of the vagus.* They may also occur after the adminis-tration of digitalis.^ \\e have recently been able to show that such rhythms maybe produced in the majority of young adults by vagus stimulation between eightand fifteen minutes after the admini
The Journal of laboratory and clinical medicine . the junctional tis- Regular Ectopic Rhythms 479 sues they are usually referred to as atrioventricular rhythms. Such rhythmsmay arise spontaneously, most often during the course of certain acute diseasesespecially diphtheria- and acute rheumatic fever.^ IVIore often they may be pro-duced by stimulation of the vagus.* They may also occur after the adminis-tration of digitalis.^ \\e have recently been able to show that such rhythms maybe produced in the majority of young adults by vagus stimulation between eightand fifteen minutes after the administration of one-fiftieth of a grain of atropinsulphate.^ This drug appears to increase the susceptibility to atrioventricularrhythm by a selective action upon the vagus endings in that it paralyzes thosethat are found in the auriculoventricular node before it paralyzes those thatlie in the sinus node. We have been able to obtain a large number of atrioven-tricular rhvthms bv this method. Thev are usuallv of short duration and are ., c a </ /:. f\\ \ ? \v,\ Fig. 3.—Lead III. An A-V rhythm of type I, with the transition to the normal rhythm. Dur-ing the A-V rhytlim the P-wave is inverted and tlie I-R and a-c intervals are slightly reduced. In thetliird cycle the P-wave is invisible although there is a definite a-wave in the venous pulse. The absenceof the P-wave is due to the fact that two excitation waves met in the auricular walls and neutralizedeach other electrically. The cardiac mechanism is diagramed below the tracing. This A-V rhythm orig-inated high up in the junctional tissues or possibly in the coronary sinus region. not accompanied by symptoms except that palpitation is occasionally experiencedwhen auricles and ventricles contract simultaneously. For convenience in theirdescription atrioventricular rhythms may be divided into three types; type 1 inwhich the P-R interval is present but reduced, type 2 in which the P-R intervalis zero, and type 3 in which there is a
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