左侧隐匿性房室旁道频率依赖性室房传导及心动过速特点

Properties of Tachycardia and Rate-Dependent Ventriculoatrial Conduction of The Left Concealed Accessory Pathway

报道4例经导管射频消融证实的左侧隐匿性房室旁道（LCAP）空房（VA）传导及心动过速特点。4例室上性心动过速患者均接受了心内电生理检查（EPS）：①4例均于右空心尖（RVA），其中1例于多个部位（右室流出道、左室及旁道在室端)行分级递增起搏（S1S1），观察VA传导情况；②于高位右房行S1S1及程控期前（S1S2）刺激诱发心动过速，观察有无房室给双径路。结果显示,RVA起搏经LCAP1：1VA传导窗口为40～120m，上限为400～350ms，下限为360～270ms；若RVA起搏周长在窗口之外，VA完全分离或偶经LCAP逆传。其中1例多部位起搏结果与RVA起搏结果相似。4例均对诱发心动过速，周长为330～360ms，但不能持续，A波逆传受阻于旁道而自动终止。提示LCAP若受到3相、4相阻滞或旁道之外如其他旁道竞争传导、房室结逆传干扰等因素的影响，可发生频率依赖性VA传导，EPS诱发的心动过速可能不持续。因此，认识这些特点，有助于LCAP的诊断，避免误诊、漏诊。

Four patients with paroxysmal supraventricular tachycardia underwent electrophysiologic study (EPS).In order to observing the properties of ventriculoatrial (VA) conduction,incremental pacing (S1S1 ) was per formed in right ventricular apex (RVA) in all patients,and in multiple sites including right ventricular output tract,left ventricular and the inserted site of the accessory pathway in one case. S,S, and single extrastimuli (S1S2) were also performed in high right atrium. Results :A "window't of 1: 1 VA conduction through the left concealed accessory pathways (LCAPs) from the RVA pacing was identified. The duration of the window ranged from 4O to 120 ms,the upper limlt was 400-350 ms,and the low limit 360-270 ms. If the RVA pacing cycle lengths were beyond the window,VAs were dissociated completely or retrograded by LCAPs accidently. The results of the patient paced in multiPle sites were similar to those from the RVA Pacing. Nonsubstained tachycardia could be iniciated in each patlent, and the tachycardla cycle lengths were 330-360 ms. The retrograde A waves were blocked in LCAPs,and the tachycardias were terminated. These results suggest that the VA conduction of the LCAPs would be rate-dependent if they are affected by factors,such as phase 3 or Phase 4 block,contested conduction of other accessory pathways and retrogradation of atrioventricular node. The tachycardia induced in EPS may be nonsubstained. Understanding these characteristics may be useful to avoid false or missed diagnosis.