心腔内超声心动图指导下经导管射频消融治疗左心室后乳头肌室性早搏

Radiofrequency catheter ablation of premature ventricular contraction originating from left ventricular posterior papillary muscle by intracardiac echocardiography

目的左心室后乳头肌起源的室性早搏（室早）因其体表心电图与左后分支参与的特发性室性心动过速（室速）一样，都表现为心电轴左偏，伴右束支阻滞合并左前分支阻滞，因此有相当一部分被误认为分支室早。为了明确二者起源点的异同，我们采用术中心腔内超声心动图（ICE）来实时监测消融靶点的确切解剖位置。方法选择3例频发室早患者（男2例，女1例），平均24h室早30000多次，超声心动图均未见心脏结构异常。在三维电解剖系统（CartoXP）指导下，跨主动脉瓣逆行送入3．5mm冷盐水磁定位标测电极导管于左心室，以激动标测构建左心室内膜图。以室早时提前最多；起搏时能得到12／12导联一致的QRS波以及放电20S内室早逐渐减少和消失作为理想靶点标准。在理想靶点确认后，经ICE确认消融导管在左心室内的确切位置，并记录和分析其局部双极电位图。以既往消融成功的经典左后分支室速作为对照，比较两者之间心电图的异同，为以后的标测和消融提供真实可靠的参照。结果ICE证实该3例室早靶点均位于左心室后乳头肌根部或中段，其解剖位置与左心室特发性室速靶点明显不在同一位置，其消融位点较特发性室速更靠心尖部；其局部双极电位在窦性心律时偶尔也可记录到浦肯野电位，但在早搏时都不能记录到浦肯野电位，说明其为肌源性起源，而特发性室速靶点无论窦性心律下还是室速时均可记录到清晰的浦肯野电位；体表心电图尽管可鉴别的特征不多，但后乳头肌起源的室早较特发性室速胸前导联（V：～V。导联）QRS时限明显增宽（前者平均124ms，后者仅86ms），R／S≤1移行也早于特发性室速（后乳头肌室早在V，导联移行为R／S≤1，特发性室速在V，导联才移行为R／S≤1）。消融10余小时后，室早复发。1个月时复查动态心电图，24h平均室早10000余次，二尖瓣功能未受到任何影响。结论通过实时ICE证实，后乳头肌室早无论起源位置、体表心电图形态还是局部靶点电图均与特发性室速有区别，这类室早消融效果较差，易复发。如何在增强消融强度、扩大消融范围和避免乳头肌损伤之间找到平衡点是该类室早消融的重点和难点。

Objective Premature ventricular contractions （PVCs） originated from posterior papillary muscle （PPM） of left ventricle are often misdiagnosed as PVCs originated from left posterior brunch which usu- ally mediate idiopathic left ventricular taehycardia（ILVT） .Because PPM-PVCs share the similar electrocardio- gram morphology with ILVT, both of their QRS morphology show right bundle brunch block （RBBB） incorpo- rated into left anteriorfascicle block （LAB） with left axis deviation.To distinguish the origin,intracardiac echo- cardiography （ICE） was used to monitor the location of optimal ablation sites for PPM-PVCs. Methods Three patients （ 2 male, 1 female） with frequent PVCs（ 〉30 000 beats/24 h） were selected for catheter ablation therapyguided by Carto mapping system and ICE.An irrigation ablation catheter was introduced into the left ventricle retrograde across the aortic valve, and activated electroanatomic left ventricular model were constructed.Optimal ablation sites were identified as：earliest active site during PVCs, obtained QRS morphology identical to PVC in all 12 leads during pace mapping, and PVCs were eliminated within 20 s when radiofrequency were delivered. Once optimal ablation site was identified, ICE catheter was positioned at the inferior septum of right ventricular outflow tract （RVOT） to identify the anatomical location of ablation sites.Then,local bipolar electrograms were analyzed and compared with that of idiopathic ventricular tachycardia. Results ICE identified that the ablation sites of these three patients were all located at posterior papillary muscle.The ablation site for PPM-PVCs was more left and near the heart apex compared to that of ILVT.Further, to PPM-PVCs, its bipolar electrograms at ablation sites occasionally presented P potential during sinus rhythm but never during PVC itself,indicating its muscle origin.While to ILVT,P potential constantly presented both during sinus rhythm and PVCs and being a marker of optimal ablation site for ILVT.As to QRS morphology of ECG, there existed two obvious differences between PPM-PVCs and ILVT.One difference was QRS width：the PPM-PVCs in V2- V4 was much wider than that of ILVT（ 124 ms vs 86 ms） .Another difference was R/S~〈 1 transition earlier in PPM-PVCs than that of IL- VT（ PPM at lead V3 ,while ILVT after lead V5 ）.PVCs recurred 10 hours after the procedure in all 3 patients, and remained onemonth follow-up.No impaired function occurred associated with mitral valve. Conclusion Real- time ICE monitoring demonstrats that PPM-PVCs is a special kind of PVCs with distinctive origination, ECG morphology and local bipolar electrogram. However, PPM-PVCs have high ablation recurrence. How to balance the more intensive and enlarger ablation with impaired PPM function is still beyond resolved.