窦房结优势起搏点兴奋向心房传导方式的探讨

本文采用同步双标测法,研究了窦房结(SN)优势起搏点兴奋向心房传导的规律。在14只麻醉狗心脏界沟部缝上一装有32个电极的电极板,标测优势起搏点(P点),最早起始负电位点(N点),心房激动过程图及最早激动点(O点)。在用异丙肾上腺索、心得安或刺激迷走神经使P点移位后,我们研究了P点位置与P—O、P—N的关系。在计60次实验中:(1)P—O、P—N多数并不重叠(分别为46次和40次);(2)随着P点从SN头部向尾部移位,O(N)点在P点头侧的出现率下降,在P点尾侧的出现率上升;(3)出现两个O点者23次,出现两个N点者11次,但P点始终只有一个。 本文提出了SN兴奋在SN内优先向头、尾两端扩布,再传向心房肌的窦房传导模式。并对心房激动多中心起源、界沟部兴奋超速传导等现象及Boiaeau的“心房综合起搏”假说进行了讨论。

STUDY ON THE WAY OF EXCITATION PROPAGATION FROM THE DOMINANT PACEMAKER OF THE SINUS NODE TO THE ATRIUM

By means of synchronizing two kinds of mapping, we have studied the role of excitation propagation from the dominant pacemaker of the sinus node ( S N ) to the atrium. In 14 dogs, 32 electrodes arranged in a template were affixed to the sulcus terminalis of the heart of each dog. The potential received from every electrode was recorded and treated with a computer to determine the position of the dominant pacemaker point ( P point ) , the point showed the earliest primary negativity ( N point ) , the atrial active sequence maps and the points of the earliest atrial activation ( O point ). By using isoproperenol and propranolol and stimulating the vagal nerve, we studied the changes of P-O and P-N relationship induced by changing the position of the P point. In 60 sets of maps, we found. (1) P-O and P-N overlapping did not occur in most cases ( 46, 40 in each );(2) as the P points shifted caudally, the rate of O points and N points appearing in caudal direction of the P points increased. While that of O ( or N ) points appearing in cranial direction of P points decreased;(3)in 20 sets of maps, there were two O points in one set of maps, and in 9 sets there were two N points as well, but there was only one P point in each set of maps.We supposed that in SN the excitation propagated more easily in direction to the cauda and cranium of SN and excited the atrial muscles there earliest.With this model, we discussed the cause of the multicentric ori gin of atrial impulse and ultra-rapid conduction phenomenon in sulcus termina-lis, and also the Boineau's "atrial pacemaker complex" hypothesis.