A study on entrainment; with special reference to the continuation mechanism of tachycardia

作为夹带的标准之一，Wellens提出在起搏停止后，第一个心动过速波群出现在起搏频率上。这并不总是如此，这取决于宏观折返回路上的起搏位置。第一个心动过速周期长度延长，然后恢复到原来的心动过速周期长度。为了了解这种现象发生的原因和方式，我们研究了隐匿性WPW综合征的房室折返性心动过速和犬实验性心房扑动起搏时和起搏后即刻各记录部位周期长度的变化。在房室折返性心动过速中，第一个心动过速周期长度的延长需要在折返回路中存在慢传导区域(如房室结)。延长的程度相当于起搏和心动过速时通过SCA的传导时间之差。从近端起搏至右高位心房时，位于SCA近端但位于起搏部位下游的低位右心房可见延长。从远端起搏到右心动过速时，所有记录部位均有延长，因为这些部位位于起搏部位的下游。然而，在实验性心房扑动中，由7个局部心房电信号组成的心房兴奋序列在房性早搏和心动过速时略有不同。再入回路(母环)的精确刺激失败或回路路线的相反改变可能是潜在的机制。在实验性心房扑动中未发现SCA的存在。

As one of the criteria of entrainment, Wellens has proposed that after cessation of pacing, the first tachycardia complex occurs at the pacing rate. This is not always so, depending upon the pacing site on the macro reentrant circuit. The first tachycardia cycle length prolongs before returning to the original tachycardia cycle length. In order to see why and how this occurs, we have studied the change of cycle length at each electrogram-recording site during and immediately after pacing in A-V reentrant tachycardia of concealed WPW syndrome and experimental atrial flutter of dog.In A-V reentrant tachycardia, prolongation of the first tachycardia cycle length necessitates the presence of slow conduction area (SCA),e.g. AV node, in the reentrant circuit. The degree of prolongation equals to the difference of conduction times through SCA during pacing and tachycardia. On pacing from proximal site to SCA (high right atrium), low right atrium, seated proximal to SCA but downstream to pacing site, shows the prolongation. On pacing from distal site to SCA (right vantricle), all recording sites show the prolongation, because these sites lie downstream to the pacing site.In experimental atrial flutter, however, atrial excitation sequence, constructed by 7 local atrial electrograms, differs slightly during atrial premature stimulation and tachycardia. The failure of precise stimulation of reentry circuit (mother ring) or contrnuously changing of the route of the circuit could be the underlying mechanism. The presence of SCA could not be identified in experimental atrial flutter.