小儿室上性心动过速的食管心电生理分型及演变

目的 :探讨小儿室上性心动过速 (SVT)的类型及其电生理特征 ,以及食管起搏对小儿SVT的干预作用。方法 :对 4 7例 8个月～ 15岁有SVT发作史的患儿进行了食管心电生理研究。结果 :4 7例SVT经食管心房调搏 (TEAP)确定分型 4 2例 (89.4 % ) ,其中旁路折返 2 8例 (6 6 .7% ) ,房室结内折返 10例 (2 3.8% ) ,心房内折返l例 ,窦房结折返l例 ,心房自律性增高 2例 ;不能定型 5例 (10 .6 % )。结论 :小儿SVT近 95 %为折返机制所致 ,以旁路折返最常见 ,其次为房室结内折返 ,与成人报道不同 ,可能与小儿传导系统发育规律以及旁路电生理特性发生演变有关     

Influence of Ventriculoatrial Timing on Hemodynamics and Symptoms During Supraventricular Tachycardia

Aims: Patients with reentrant supraventricular tachycardia (SVT) are often highly symptomatic and the mechanism of symptoms is not well understood. We hypothesized that variation in ventriculoatrial interval (QRS to P) modulates the left atrial pressure and symptoms during tachycardia.
Methods and Results: Three hundred twenty-six patients awaiting electrophysiological study completed a questionnaire regarding "neck pounding" or "shirt flapping" during tachycardia. Mean left atrial pressure was measured during simulated atrioventricular reentry tachycardia (AVRT) and atrioventricular nodal reentry tachycardia (AVNRT) in 18 patients. Pulmonary venous flow reversal was assessed using transesophageal echocardiography in 12 dogs when pacing at 220 bpm with different VA delays (0 to 250 ms). "Shirt flapping" is present more often during AVNRT than during AVRT (58.6% vs 43.8%, respectively, P < 0.05). Simulated AVNRT is associated with higher left atrial pressure compared with AVRT (19.4 ± 4.8 mmHg vs 13.7 ± 3.9 mmHg, respectively, P < 0.05). In dogs, pulmonary venous flow reversal during atrial systole was observed with significantly decreasing amplitude as VA delays increased: 668 ± 167% at 0 ms; 492 ± 138% at 100 ms; 278 ± 148% at 180/ms; and 134 ± 91% at 220 ms.
Conclusion: " Shirt flapping" and "neck pounding" frequently occur during AVNRT. LA contractions during AV valve closure increase left atrial pressure and may explain differences in certain symptoms between AVNRT and AVRT.     

Paradoxical responses to pacing maneuvers differentiating atrioventricular node reentrant tachycardia and junctional tachycardia

A 40-year-old female presented at our hospital because of heart palpitations. During an electrophysiological study, atrioventricular (AV) conduction showed dual AV nodal physiology. Three types of supraventricular tachycardia (SVT) were induced. The initiation of SVT was reproducibility dependent on a critical A–H interval prolongation. An early premature atrial contraction during SVT repeatedly advanced the immediate His potential with termination of the tachycardia, indicating AV node reentrant tachycardia (AVNRT). However, after atrial overdrive pacing during SVT without termination of the tachycardia, the first return electrogram resulted in an AHHA response, consistent with junctional tachycardia. The mechanism of paradoxical responses to pacing maneuvers differentiating AVNRT and junctional tachycardia was discussed.     

食管心房调搏指标诊断室上性心动过速价值的评定

以射频消融结果为依据，评定Ｓ＿２Ｒ跃增值和ＲＰ＿Ｅ时距对４８例慢－快型房室结折返性心动过速（Ｓ－Ｆ型ＡＶＮＲＴ）和１４１例顺向型房室折返性心动过速（Ｏ－ＡＶＲＴ）患者的诊断及鉴别诊断价值，并讨论两类心动过速食管调搏的定量判别标准。结果表明：（１）Ｓ＿２Ｒ跃增以≥６０ｍｓ诊断ＡＶＮＲＴ为宜，但有一定局限性，其敏感性、特异性、诊断价值分别为９１．６％、８５．８％、７２．８％。（２）ＲＰ＿Ｅ时距≤７０ｍｓ和＞７０ｍｓ分别对Ｓ－Ｆ型ＡＶＮＲＴ、Ｏ－ＡＶＲＴ的诊断及鉴别诊断价值较高。敏感性、特异性、诊断价值分别为９３．８％、１００％、１００％与１００％、９３．８％、９７．９％．（３）少数（１７％）右侧壁旁道逆传性心动过速ＲＰ＿Ｅ／Ｐ＿ＥＲ可＞１．０。（４）Ｓ－Ｆ型ＡＶＮＲＴ与Ｏ－ＡＶＲＴ的定量判别Ｓ＿２Ｒ跃增、ＲＰ＿Ｅ标准宜分别取≥６０ｍｓ、≤７０ｍｓ与＜６０ｍｓ、＞７０ｍｓ。     

Latent Clerc-Levy-Cristesco syndrome as an electrophysiologic basis for paroxysmal reciprocal atrioventricular nodal tachycardia

An intracardiac electrophysiological investigation was performed in 15 patients with frequent episodes of supraventricular tachycardias (SVT) which are regarded, in terms of the present electrophysiological criteria, as episodes of reciprocal atrioventricular nodal tachycardia. It was demonstrated that accessory atrionodal junctions functioning only in the retrograde direction formed the basis for arrhythmias in 6 patients. This electrophysiological phenomenon was proposed to be termed the latent Clerc-Lery-Cristesco (CLC) syndrome. The main electrophysiological criteria for diagnosing the syndrome are the following: a) during a SVT episode, retrograde atrial excitation is recorded before or concomitantly with the initiation of ventricular excitation; b) during a SVT episode, H-A interval is no greater than 5 ms; c) during programmed ventricular stimulation, H2-A2 interval values remain constant. The latent CLC syndrome was shown to be commonly associated with discrete conduction in the antegrade atrioventricular junctions. Rhytmilen and gilurytmal (ajmaline) are the most potent antiarrhythmic agents for patients with reciprocal SVT due to the latent CLC syndrome.     

Usefulness of the delta HA interval to accurately distinguish atrioventricular nodal reentry from orthodromic septal bypass tract tachycardias

Surface electrocardiographic criteria may be inadequate to distinguish some cases of atrioventricular (AV) nodal reentrant supraventricular tachycardia (SVT) from those with orthodromic SVT incorporating a posterior septal bypass tract (orthodromic SVT) because of similarities in P-wave morphology and timing during SVT. Invasive electrophysiologic studies may occasionally leave uncertainty in the correct diagnosis, using currently accepted criteria. A new criterion for distinguishing these 2 forms of SVT was therefore devised and tested based on differences in the sequence of activation of the His bundle and atrium during SVT and ventricular pacing. Eighty-four patients underwent invasive electrophysiologic studies (60 with proved AV nodal SVT, 24 with proved orthodromic SVT), during which His to atrial (HA) intervals were measured during SVT as well as ventricular pacing at the same rate. The newly devised criterion, the delta HA interval (HApace-HAsvt) was found to accurately distinguish AV nodal SVT (delta HA greater than 0 ms) from orthodromic SVT (delta HA less than -27 ms). An intermediate value of delta HA = -10 ms was chosen which had a 100% sensitivity, specificity and predictive accuracy in differentiating the 2 forms of SVT. A clear retrograde His potential during ventricular pacing, which is essential for application of this criterion, was present in 78 of 84 (93%) cases. In summary, patients with delta HA intervals greater than -10 ms separate AV nodal reentry from orthodromic SVT incorporating a septal bypass tract, and no overlap exists between the 2 groups. This criterion may be useful in differentiating the mechanism of SVT in cases in which distinction is not possible by other methods.     

房室结折返性心动过速患者房室结功能曲线连续性的电生理分析

分析房室结折返性心动过速 (AVNRT)中房室结功能曲线呈连续性者的电生理特点。将AVNRT分为房室结功能曲线连续组 (Ⅰ组 )及房室结功能曲线不连续组 (Ⅱ组 ) ,行慢径消融 ,进行消融前后和组间的电生理比较 ,分析房室结功能曲线呈连续性者的特点。结果 :I组心房程序刺激对AVNRT的诱发率仅 42 % (5 / 12 ) ,低于Ⅱ组的 6 6 %(2 3/ 35 )。Ⅰ组房室结前传有效不应期 (ERP AVN)消融前后无显著变化 (2 18.2± 2 9.3msvs 2 5 3.3± 80 .3ms,P >0 .0 5 ) ;心房程序刺激最长A2 H2 间期 (AHmax)消融前后无显著变化 (2 2 5 .8± 71.8msvs 175 .4± 41.9ms,P >0 .0 5 )。Ⅱ组ERP AVN消融后显著延长 (2 78.9± 5 8.9msvs 2 35 .8± 39.6ms,P <0 .0 5 ) ;AHmax消融后显著缩短 (172 .0± 6 7.1msvs 331.6± 86 .6ms ,P <0 .0 5 ) ;消融后房室结快径前传有效不应期 (ERP FP)显著缩短 (2 78.9± 5 8.9msvs 330 .0±5 5 .3ms,P <0 .0 5 )。消融前Ⅰ组AHmax短于Ⅱ组 (P <0 .0 5 ) ,Ⅰ组心动过速时A2 H2 间期 (AHSVT)与消融前AHmax比较差异无显著性 (P >0 .0 5 ) ;Ⅱ组AHSVT短于消融前AHmax(P <0 .0 5 )。结论 :房室结功能曲线连续性者较难经常规心房程序刺激诱发心动过速 ;慢径消融后曲线“尾巴”消失可作为消融终点的一项指     

短P—R综合征合并室上性心动过速的电生理观察

为探讨短Ｐ－Ｒ综合征合并室上性心动过速的电生理机制,对７例短Ｐ－Ｒ综合征合并室上性心动过速的患者进行心内电生理检查。结果发现：随着心房负扫描程序刺激,６例Ａ－Ｈ间期逐渐延长,１例间歇性延长,６例有Ａ－Ｈ间期跳跃现象;室上性心动过速时６例最早心房激动部位在希氏束,Ｖ－Ａ间期〈７０ｍｓ,１例在左后游离壁,Ｖ－Ａ间期〉７０ｍｓ。提示短Ｐ－Ｒ综合征合并室上性心劝过速的电生理机制是房室结加速传导合并房室结双     

Characterization of right atrial substrate in patients with supraventricular tachyarrhythmias

Right atrial substrate of supraventricular tachyarrhythmias. BACKGROUND: Voltage mapping has been used to detect diseased myocardium. However, accurate determination of the local atrial voltage at the same site, and simultaneous recordings from multiple mapping sites were limited. The purpose of this study was to investigate the right atrial (RA) substrate properties in patients with supraventricular tachyarrhythmias (SVT). METHODS AND RESULTS: Forty patients (aged 55+/-20 years) undergoing noncontact mapping and ablation of SVT constituted the study population. There were eight patients with atrioventricular node reentrant tachycardia (AVNRT), eight patients with focal atrial tachycardia (AT), 14 patients with atrial flutter (AFL), and 10 patients with atrial fibrillation (AF). The mean peak negative voltage (PNV) was analyzed in virtual unipolar electrograms, which were obtained from 256 equally distributed RA endocardial sites during sinus rhythm (SR), atrial pacing, and tachycardia. The mean PNV of global RA during SR (-1.34+/-0.22 vs. -0.90+/-0.40 vs. -1.00+/-0.36 vs. -0.85+/-0.35 mV, P=0.04), atrial pacing at cycle lengths of 500 ms (-1.30+/-0.29 vs. -0.70+/-0.35 vs. -0.76+/-0.25 vs. -0.64+/-0.26 mV, P=0.02), and 300 ms (-1.54+/-0.47 vs. -0.94+/-0.21 vs. -0.75+/-0.27 vs. -0.57+/-0.22 mV, P<0.01) were significantly greater in patients with AVNRT compared to AT, AFL, and AF. Furthermore, the mean PNV decreased during atrial pacing with shorter pacing cycle length was demonstrated only in patients with AFL and AF. CONCLUSION: Negative unipolar voltage analysis of global RA showed different RA substrate characteristics during various SVT. The substrate property of activation and cycle length-dependent voltage reduction may be related to the development of AFL and AF.     

非器质性心脏病的房室传导裂隙现象分析

了解非器质性心脏病的患者在作食管电生理检查时裂隙现象发生的情况及类型 ,并观察药物及不同刺激方式对裂隙现象的影响。对在我院作食管电生理检查的 2 2 0例患者 ,先采用S1S2 法 ,每次递减 10ms进行反扫 ,直至S1S2 间期小于 2 0 0ms ,并且连续 3次以上的早搏刺激无下传 ;其中 6 2例患者同时作了S1S2 与S1S2 S3 法检查 ,2 6例用异丙肾上腺素前后行早搏刺激 ,观察裂隙现象的发生情况。 2 2 0例患者中 6 9例患者出现裂隙现象 ,总共 83例次 ,8例有双裂隙 ,裂隙带时限 45 .3± 32 .1(10～ 12 0 )ms;裂隙类型有房室结及结下组织形成的裂隙 42例次、房室结与束支形成的裂隙 2 8例次、束支裂隙 11例次、旁道裂隙 2例 ;房室结双径路的裂隙现象发生率高于其他患者 ;S1S2 法的裂隙现象发生率高于S1S2 S3 法 ;用异丙肾上腺素后的裂隙现象发生率高于用药前。裂隙现象是无器质性心脏病的患者作食管电生理检查时常见的电生理现象 ,它的发生与激动传导径路、早搏刺激的方式和用药有关。     

Transesophageal study of infant supraventricular tachycardia: electrophysiologic characteristics

Programmed electrical stimulation of the heart to initiate and terminate tachycardia and analysis of the temporal relation between ventricular and atrial activation during tachycardia have been useful in the evaluation of supraventricular tachycardia (SVT). Such techniques have rarely been applied to evaluate infants with SVT. We used a silicone rubber-coated bipolar electrode catheter (15 or 22 mm interelectrode spacing), positioned in the esophagus, for electrical stimulation of the heart and recording of electrograms for the evaluation of 14 infants aged 1 to 84 days with SVT. Three infants had electrocardiographic features of Wolff-Parkinson-White syndrome, and no infant had other manifestations of congenital heart disease. Tachycardia cycle lengths ranged from 180 to 295 ms and ventriculoatrial intervals recorded from the esophagus were 80 to 220 ms. In 12 infants, transesophageal atrial stimulation was used to terminate and initiate SVT using stimuli of 9.9 ms and 10 to 20 mA. Initiation and termination of SVT by electrical stimulation suggest that SVT in infants is due to reentry, and the presence of ventriculoatrial intervals greater than 70 ms further suggests that accessory atrioventricular connections (usually concealed) constitute a portion of the reentry circuit.     

Value of esophageal pacing in evaluation of supraventricular tachycardia

Esophageal stimulation was performed in 40 patients who had spontaneous paroxysmal supraventricular tachycardias (SVTs). The purpose of this study was to look for the most sensitive stimulation protocol and criteria that would help to define the mechanism of reentry. In 20 patients (group I) atrial pacing up to second-degree atrioventricular block was performed under control conditions and isoproterenol, and SVT was induced in 14 patients (70%), 11 in the control state and 3 while receiving isoproterenol. In 20 patients (group II) atrial pacing and programmed atrial stimulation using 1 and 2 extrastimuli delivered at 2 cycle lengths (600 and 500 ms) was performed in the control state and while receiving isoproterenol. SVT was induced in all patients, in 13 patients in the control state and in 7 while receiving isoproterenol. Programmed stimulation always induced SVT and was the only method capable of tachycardia induction in 14 patients. The mechanism of SVT could be established in 91%. The measurement of the ventriculoatrial interval was the most useful sign to define the site of reentry. Occurrence of a bundle branch block helped to delineate the mechanism in 4 patients. When a positive P wave in V1 preceded the esophageal atrial electrocardiogram, it suggested that there was reentry through a left-sided accessory atrioventricular connection in 6 patients. SVT could always be induced by programmed atrial stimulation in the control state and under isoproterenol. The location of the P wave in V1 compared to the ventriculogram and the esophageal electrocardiogram helped to define the mechanism of tachycardia.     

冠状静脉窦不同部位起搏拖带心动过速对房性心动过速的诊断价值

目的:探讨心动过速时分别在冠状静脉窦近端(CSp)和远端(CSd)快速起搏拖带心动过速的操作方法鉴别房性心动过速(AT)的价值。方法:入选67例室上性心动过速患者,在心动过速时分别以短于心动过速周长10~40 ms的间期起搏CSp和CSd,确认夺获心房后停止起搏。如果心动过速不终止,测量每次起搏停止后的第一个QRS波群起始至第一个自身A波的间期(VA间期),计算两个VA间期差值(DVA)。结果:67例患者平均年龄(41±17)岁,其中15例为AT患者,25例为房室结内折返性心动过速患者,27例为房室折返性心动过速患者(后两类患者为非AT患者)。AT患者的DVA[(79±29)ms]大于非AT患者[(4±2)ms],差异有统计学意义(P<0.01)。所有AT患者的DVA均>10 ms,而非AT患者中无一例DVA>10 ms。结论:在冠状静脉窦不同部位起搏拖带心动过速,计算停止起搏后第一个DVA是一种快速、简单、有效的诊断或除外AT的方法,在使用较少标测电极时更为实用。     

导管消融具有双向传导特性的Mahaim结室纤维

目的介绍具有双向传导特性Mahaim结室纤维的电生理机制及导管消融方法。方法患者女性,34岁,反复发作性心动过速病史7年。外院心电图示“阵发性室上性心动过速”。心动过速可被维拉帕米及普罗帕酮终止。入院各项检查排除器质性心脏病后行电生理检查及导管消融术。结果电牛理检查示窦性心律时AH=73ms、HV=42ms,QRS时限100ms。心动过速时QRS波形态与窦性心律时相似,伴有轻度电交替。心动过速在多数情况下室房呈分离状态,HV问期为42ms,与窦性节律时相同,有时室房呈1：1传导,最早心房激动位于希氏束记录处。右心室心尖部以400ms周长刺激时室房呈分离状态。心房增频刺激时QRS波逐渐增宽,直至充分预激。在QRS波增宽过程中,HV逐渐缩短直至H波融合于QRS波之中,刺激信号至QRS波的间期逐渐延长,反映了递减传导的过程。继续缩短心房刺激周长后突然旁路传导受阻,经房室结下传并出现传导跳跃现象,继传导跳跃后心动过速被诱发。心动过速可被三磷酸腺苷（ATP）终止,终止后房室经旁路前传,其QRS波形态与充分预激时相似。在心房刺激保持充分预激的前提下,沿三尖瓣环标测,于左前斜位45。三尖瓣环4点钟处标测到最早V波,此处较体表心电图QRS波提前25ms,单极记录呈Qs型,HA波与V波之间未见高频电位。于该点消融放电（60W×60℃）,2S后旁路传导消失。放电过程中未出现交界性心律。消融结束后心房程序电刺激仍有房室传导跳跃现象。随访18个月,未再有心动过速发作。结论本病例心动过速系Mahaim结室纤维所介导,该纤维具有双向传导功能,其上插入端位于房室结慢径区域,下插入端位于邻近房室沟的局部心室肌。心动过速时房室结-希氏-浦肯野系统为前传支,结室纤维作为逆传支。     

Effect of verapamil on retrograde conduction in atrioventricular nodal reentrant tachycardia

Using His bundle electrograms, incremental ventricular pacing and the ventricular extrastimulus (V2) technique, the effects of intravenous verapamil, 0.2 mg/kg, on retrograde atrioventricular (AV) nodal conduction during ventricular pacing, premature ventricular stimulation (H2A2 interval) and paroxysmal supraventricular tachycardia (SVT) (H-Ae interval) were evaluated in 11 patients with AV nodal reentrant tachycardia. During the control study, SVT could be induced in all 11 patients. After verapamil administration, SVT or atrial echo beats could be induced in 5 patients. Verapamil produced ventriculoatrial (VA) block at a longer cycle length than that during the control study in 10 of 11 patients (295 +/- 27 vs 352 +/- 40 ms, p less than 0.01), but prolonged H2A2 interval in only 5 of 11 patients (37 +/- 6 vs 60 +/- 31 ms, p less than 0.05). In all 5 patients with persistence of inducible SVT or atrial echo beats after verapamil treatment, the H-Ae interval remained unchanged even though in 4 of these 5 patients VA conduction time or H2A2 interval was prolonged. Correlation between the paced cycle length which induced VA block, the shortest V1H2 interval achieved during premature ventricular stimulation and the cycle length of SVT revealed that in all instances in which verapamil induced VA block at a longer cycle length than in controls but did not prolong H2A2 or H-Ae interval, the shortest V1H2 interval and the cycle length of SVT (H-H interval) were significantly longer than the ventricular paced cycle length which produced VA block.(ABSTRACT TRUNCATED AT 250 WORDS)     

A new method for estimating preexcitation index without extrastimulus technique and its usefulness in determining the mechanism of supraventricular tachycardia.

The preexcitation index has been shown to be useful in determining the mechanism of paroxysmal supraventricular tachycardia (SVT) and the site of the accessory pathway in atrioventricular (AV) reentrant tachycardia. To test whether a preexcitation index could be computed analytically instead of by scanning the whole SVT cycle with extrastimuli, 19 patients with SVT were studied. The new index was computed using the following formula: (AV conduction time during SVT) + (ventriculoatrial conduction time during ventricular pacing at the SVT cycle length) - (SVT cycle length). There was a strong correlation between the preexcitation index determined by the extrastimulus technique and the new index in 15 patients in whom the preexcitation index could be determined (r = 0.99, p less than 0.01). The value on the new index was greater than 90 ms only in patients with dual AV nodal pathways. In the 4 patients in whom the preexcitation index could not be determined by the extrastimulus technique, the new index could differentiate AV reentrant tachycardia (index for 2 patients, 60 and 60 ms, respectively) from AV nodal reentrant tachycardia (index for 2 patients, 100 and 105 ms, respectively). In conclusion, the new index provided help in determining the mechanism of SVT, even when retrograde atrial preexcitation by a ventricular extrastimulus did not occur.     

Identification of slow anterograde conduction of excitation in patients with paroxysmal reciprocal atrioventricular nodal tachycardia

Basing on results of examination of a cohort of patients with typical paroxysmal reciprocal atrioventricular tachycardia a group of patients with continuous curve of anterograde conduction was distinguished. The use of incremental doses of adenosine triphosphate (ATP) during transesophageal atrial pacing allowed in some cases to identify slow conduction through atrioventricular node and to initiate paroxysmal nodal tachycardia. The dose of ATP causing conduction block over fast pathway depended on the duration of effective refractory period.     

Reanalysis of the "pseudo A-A-V" response to ventricular entrainment of supraventricular tachycardia: importance of his-bundle timing

BACKGROUND: The sequence of atrial and ventricular electrograms following termination of ventricular pacing during supraventricular tachycardia has been shown to reliably differentiate atrial tachycardia from atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT). However in patients with long HV intervals, this may be misleading due to a pseudo "A-A-V" response. The aim of the present study is to see if inclusion of the timing of the His-bundle in the electrogram response (ER) following ventricular pacing would reliably identify the mechanism of tachycardia in patients with long HV intervals. METHODS: Eight patients (7 men) with AVNRT and underlying bundle branch block and long HV (>55 msec) intervals underwent ventricular pacing at 10-40 msec shorter than the tachycardia cycle length during SVT. The ER was classified as "A-A-H" or "A-H" depending on the number of atrial electrograms (A) prior to His deflection following VEP. RESULTS: The ER following ventricular pacing was classified as A-H in all 8 patients. However, using conventional classification the response was A-A-V in 5 of 8 patients due to delayed ventricular activation secondary to long HV intervals and would erroneously suggest atrial tachycardia. The ER was A-V in only 1 of 8 patients. In the remaining 2 patients the A and V electrograms were simultaneous. CONCLUSIONS: Incorporating the His-bundle in the ER following ventricular pacing would eliminate the pseudo "A-A-V" response in patients with AVNRT and long HV intervals. Labeling the response to ventricular pacing as "A-H" or "A-A-H" is simple and more accurate.     

A technique for diagnosis of accessory pathway using the H-H and A-A intervals of the first entrained cycle during ventricular overdrive pacing

Although advancement of succeeding atrial activation by a ventricular extrastimulus (VES) on His refractoriness during supraventricular tachycardia (SVT) has been used as evidence of an accessory pathway (AP), the sensitivity of this method is suboptimal. This study was designed to compare the His-His (H-H) and atrial-atrial (A-A) intervals of the first entrained cycle during ventricular overdrive pacing (VOD) for the diagnosis of AP, in comparison to the conventional VES method. In 55 patients with SVT, a VES was elicited on His refractoriness during SVT. VOD was subsequently performed at cycle lengths 30 to 40 ms shorter than SVT cycle lengths. When the A-A interval became equal to the pacing cycle length after some beats of VOD, the cycle was considered the first entrained cycle and the H-H interval preceding the A-A interval was measured. VES advanced the next atrial activation in 16 patients (52%) with an AP, but in no patient without an AP. The H-H interval of the first entrained cycle was longer than the pacing cycle length by > or =15 ms in all patients with an AP, but was equal to the pacing cycle length in all patients without an AP. The criterion of H-H greater than A-A by > or =15 ms for the first entrained cycle provided higher diagnostic yield for AP compared with the VES method(100% vs 52%, p <0.001). In conclusion, this new criterion reliably diagnoses the presence of an AP in patients with SVT, with higher sensitivity compared with the VES method.     

Shortening of conduction time over arborized atrioventricular accessory pathway with Mahaim fibers physiology just before interruption during radiofrequency ablation

A 21-year-old woman had paroxysmal wide QRS tachycardia with a left bundle branch block configuration and a retrograde conducted P wave just behind the QRS complex. An electrophysiological study revealed antidromic atrioventricular tachycardia involving an atrioventricular connection with decremental conduction as the anterograde limb and normal atrioventricular node as the retrograde limb. During constant pacing from the high right atrium (HRA) at the cycle length (CL) of 600 ms, the QRS configurations were not identical to those during the wide QRS tachycardia or constant pacing at the CL of less than 500 ms. The process by which this arborized atrioventricular accessory pathway with the Mahaim fibers physiology was interrupted by radiofrequency catheter ablation is described. Radiofrequency energy was delivered to the site recording a Mahaim potential at the tricuspid annulus during constant pacing from the HRA at the CL of 429 ms. The stimulus-QRS interval gradually shortened as it reached the power plateau without changing the preexcited QRS configuration. Shortening of the conduction time over the Mahiam pathway might have resulted in changing of the propagation from a slow to fast conduction zone or acceleration in response to thermal effect in a node-like structure on the atrial insertion site.