. The principles of clinical pathology, a text-book for students and physicians; . 98 CLINICAL PATHOLOGY Disturbances in the conduction of impulses from the auri-cles to the ventricles are much more common and are ofgreater importance. Clinically we may estimate the timetaken in the transmission of the contraction wave from theauricles to the ventricles by the duration of the a-c intervalon the jugular venous pulse, where a represents the auric-ular contraction and c the carotid pulse (ventricular con-traction) (Fig. 8). This a-c interval normally does not second, but where the cond
. The principles of clinical pathology, a text-book for students and physicians; . 98 CLINICAL PATHOLOGY Disturbances in the conduction of impulses from the auri-cles to the ventricles are much more common and are ofgreater importance. Clinically we may estimate the timetaken in the transmission of the contraction wave from theauricles to the ventricles by the duration of the a-c intervalon the jugular venous pulse, where a represents the auric-ular contraction and c the carotid pulse (ventricular con-traction) (Fig. 8). This a-c interval normally does not second, but where the conduction is poor it may be pro-longed to second or more. If the conductivity be stillfurther reduced, the impulse may fail altogether to reach theventricles, and we then observe an auricular, but no ventricular Fig. 7. t- 00 00 i> i> 00 OS co co co CD CD co CD CD O l- rt to c* I- O I- 0 CO 0 c» 0 CO co t- t- tr - ei co CM Tf a -* C* T* a -«ji 0* ?* CJ •* CO CO eo CO CO. A pulsus bigeminus with the transition to a regular pulse. Notice that the double inter-val of the former ( fifths of a second) is less than twice the period of a single interval ofthe latter (2 X 3-75 = 7-5), from which fact we may infer that the extrasystoles were probablyof auricular origin. beat (see Fig. 8). When the next auricular wave reachesthe connection with the ventricle it passes over with unwontedrapidity on account of the rest given to the fibres from theprevious missed beat. The a-c period is then shortened. Thiscondition of partial heart block, as it is called, may attain vary-ing degrees of severity. Only occasional impulses may fail topass the auriculo-ventricular junction; again, only every otherone may pass (2:1 rhythm), or one out of three or four maypass (3:1 and 4: 1 rhythms), etc. Finally, none at all pass, in which case we get complete THE HEART 99 heart block. In such a case the ventricles take on their ownrhythm, which is about 30 per minute, and maintain
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