Yamada, T., et al., Idiopathic mitral annular PVCs with multiple breakouts and preferential conduction unmasked by radiofrequency catheter ablation. Pacing Clin Electrophysiol, 2012. 35(5): p. e112-e115.
monomorphic PVCs were frequent and exhibited a right bundle branch block and inferior axis QRS morphology (PVC 1) ，
PVC 1 exhibited a QRS duration of 185 ms and maximum deflection index (MDI) of >0.55, 考虑心外膜起源。
Figure 1. Twelve-lead electrocardiograms exhibiting the first and second premature ventricular contractions (PVC 1 and PVC 2, respectively) and pace map, which was obtained by pacing from the first ablation site. Note that pacing from the first ablation site produced an excellent match to the QRS of PVC 2 with a long stimulus to QRS interval.
Activation mapping in the LV during PVC 1 revealed a centrifugal activation pattern from the site in the anterior aspect of the MA, where the local ventricular activation preceded the QRS onset by 33 ms (Figs. 2 and 3). Pacing from the site of the earliest ventricular activation did not produce an excellent match to the QRS morphology of PVC 1。
Irrigated radiofrequency (RF) current delivered in the power-control mode at 30 W with an irrigation flow rate of 30 mL/min eliminated the PVC 1 morphology.
PVC1消融成功后，出现了PVC2，形态不一致。
PVC 2 exhibited a right bundle branch block and right-inferior axis QRS morphology, QRS duration of 175 ms, and MDI of 0.45 (Fig. 1)
Figure 2. Cardiac tracings exhibiting the first and successful ablation sites (site 1 and site 2, respectively).
Figure 3. Activation map of the superior projection obtained during PVC 1 (left panel) and fluoroscopic images (right panels) exhibiting the ablation sites. The red tags in the activation map indicate the ablation sites. In the fluoroscopic images, the ablation catheter was positioned at the first ablation site and the stars indicate the successful ablation site.
Interestingly, the QRS morphology of PVC 2 was identical to that of the pace map at the first ablation site. 在第一次消融点起搏，QRS形态与PVC2完全一致。
Activation mapping in the LV during PVC 2 revealed a centrifugal activation pattern from a site adjacent but slightly lateral to the first ablation site. At this site, the local ventricular activation preceded the QRS onset by 45 ms
该病例尽管在第一点（二尖瓣环前侧壁）起搏形态不好，但一次消融就能成功消融PVC1。提示PVC1出口可能远离第一次消融点。虽然第一点起搏形态与PVC1匹配不好，但PVC1形态提示室早突破口可能位于心外膜(MDI>0.55) 。PVC2起源点可能与PVC1相同的原因有：1 在第一次消融前尚未记录到PVC 2；第一次消融点起搏形态与PVC2完全相似；3 在第一次消融点的邻近位点消融能终止PVC2。
起搏信号至QRS的距离及起搏形态完全一致也提示PVC2出口远离第一次消融点。尽管没有位点起搏形态与PVC2一致，PVC2形态提示出口可能在于心内膜。因此，这些发现提示这两种室早起源点相同而出口不一样（一个在心外膜，另一个在心内膜）。该病例可能由于绝缘心肌纤维将起源点连接至两个不同出口，并在两个出口之间有优先传导通路。
因为第一次消融揭示优先传导通路与PVC2相关，此外第一次消融只是消融了一根纤维，所以PVC2起源点以及心肌纤维还没受到影响，因此考虑第一次消融掉的心肌纤维间传导相比其他纤维更优先，可能由于传导速度快和至心肌纤维的距离短。
以上提示我们在临床也需要多观察消融过程形态发生改变，有可能由于起源点相同而突破口改变造成这种现象，需要多加鉴别。
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