选择性刺激犬心房窦房结脂肪垫的电生理观察

目的 位于右心房及右肺静脉交界处的窦房结(SAN)脂肪垫含有丰富的支配心房的副交感神经纤维节.本实验通过选择性直接刺激心脏SAN脂肪垫,观察其对SAN功能、房室传导、心房有效不应期(AERP)及心室有效不应期(VERP)、心房颤动(AF)诱发易感性等电生理参数的影响,以明确心房SAN脂肪垫的副交感神经功能分布特点及探讨AF发生机制.方法 入选杂种犬33只,右侧开胸暴露SAN脂肪垫.将标准的电生理导管置于右心房、希氏束、右心窒心尖部及右心室流出道,记录基础窦性周期长度(SCL)、AH及HV间期、房室结文氏点、AERP及VERP、AF诱发窗口(WOV)及快速右心房起搏诱发AF的RR间期.以逐级递增的能量直接刺激SAN脂肪垫直至AF诱发,测定不同能量状态下SCL及AF诱发阈值.以引起SCL较基线延长50%的固定能量再次刺激SAN脂肪垫,观察其对上述电生理参数的影响.AF诱发成功后,继续逐级增加刺激能量直至最人值10.0 mA.记录不同能量状态下诱发AF的连续10个RR间期,取其平均值.结果 100%犬在直接SAN脂肪垫刺激下诱发AF,AF诱发阈值为(4.0±1.3)mA.AF诱发前,SAN脂肪垫刺激导致窦性心率减慢SCL:(588±77)ms对(994±293)ms,P<0.001].AF诱发后,直接刺激诱导AF RR间期进行性延长(461±204)ms对最长(636±260)ms,P<0.001],个别犬出现高度房室阻滞.在以延艮SCL 50%的固定能量刺激SAN脂肪垫时,AERP与刺激前比较明显缩短(P<0.001)、WOV增宽(P<0.001),而AH、HV、房室结文氏点、VERP无变化(P>0.05).结论 直接SAN脂肪垫刺激延长SCL,缩短AERP,增加AF诱发易感性,而对房窒结下区传导及心室无影响.以前文献报道SAN脂肪垫只有单一调节SAN的功能,而本实验结果显示当刺激能量足够时,SAN脂肪垫还町减慢AF时房窜传导.

Electrophysiological response to selective stimulation of atrial sinoatrial nodal fad pad in canine heart

Objective Parasympathetic innervations of atrium can be selectively stimulated via sinoatrial nodal (SAN) fat pad located at the junction of right atrium (RA) and right pulmonary vein. This study was de signed to evaluate the electrophysiological response of SAN, atrioventricular conduction, atrial (AERP) and ventricular effective refractory period (VERP),and atrial fibrillation (AF) inducibility in response to direct SAN fat pad stimulation. Methods In 33 adult mongrel dogs,via right lateral thoracotomy,SAN fat pad was di rectly stimulated. EP catheters were placed in RA, His bundle, right ventricular apex and right ventricular out flow tract Baseline sinus cycle length (SCL),AH and HV intervals, A V node Wenckebach point, AERP, VERP, window of vulnerability (WOV) and RR intervals during AF induced by rapid RA pacing were tested. Under SAN fat pad stimulation with stepwise incremental stimulation energy, SCL and AF threshold were recor ded until AF induction. With the stimulation energy at inducing 50% prolongation in SCL,SAN fat pad was re stimulated and the above-mentioned EP parameters were re-tested. After AF was successfully induced, the stim ulation energy was continually increased stepwise until maximum 10.0 mA. Successive 10 RR intervals during stimulus-induced AF with various stimulation current settings were recorded and averaged. Results 100% animals were repeatedly induced AF by SAN fat pad stimulation. The AF threshold was (4. 0 ± 1. 3)mA. Before AF induction, SAN fat pad stimulation prolonged SCL from (588 ± 77) ms to (994 ± 293) ms (P<0. 001). After AF induction, SAN fat pad stimulation produced graded prolongation of RR during AF((461 ±204)ms vs. Max (636 ±260)ms,P<0. 001],and even led to complete atrioventricular block in one animals. During stimulation at fixed energy inducing 50% prolongation in SCL, AERP was shortened (P <0. 001) and VOW was widened,but no obvious change was found in AH,HV,AV node Wenckebach point,and VERP(P=NS). Conclusion Direct SAN fat pad stimulation prolonged SCL, shortened AERP and increased AF inducibility which had no effect on HV and VERP. Our data also showed that SAN fat pad retarded atrioventricular conduction with AF when the stimulation was high enough.