Electrocardiographic and Electrophysiologic Characteristics of Anteroseptal, Midseptal, and Para-Hisian Accessory Pathways*

Transcription

1 Electrocardiographic and Electrophysiologic Characteristics of Anteroseptal, Midseptal, and Para-Hisian Accessory Pathways* Implication for Radiofrequency Catheter Ablation Ching-Tai Tai, MD; Shih-Ann Chen, MD; Chem-En Chiang, MD; Shih-Huang Lee, MD; and Mau-Song Chang, MD Study objective: To investigate the ECG characteristics, the electrophysiologic properties, and an effective radiofrequency catheter ablation technique in patients with septal accessory pathways. Patients: Forty-six consecutive subjects with septal accessory pathways located in the anteroseptal, midseptal, and para-hisian areas. Design and interventions: ECGs obtained during sinus rhythm and orthodromic tachycardia, conduction properties obtained from electrophysiologic study, and results of two different ablation techniques were analyzed. Measurements and results: (1) Twenty-four (52.2%) had manifest preexcitation and 15 (32.6%) had multiple accessory pathways; (2) midseptal pathways could be differentiated from anteroseptal and para-hisian pathways by a negative delta wave in lead III and a biphasic delta wave in lead a VF during sinus rhythm, and a negative retrograde P wave in two inferior leads during orthodromic tachycardia; (3) midseptal pathways had better antegrade conduction properties and a significantly higher incidence (61.5%) of inducible atrial fibrillation; (4) radiofrequency catheter ablation using lower energy (2:::'::6 W) had a comparable effect to ablation using higher energy (36:±5W), but without impairment of atrioventricular (AV) node conduction or development of AV block; and (5) during the follow-up period of 26:::'::14 months (range, 5 to 54 months), three (6.5%) patients had recurrence. Conclusions: Midseptal accessory pathways had ECG and electrophysiologic characteristics that were distinctive from those of anteroseptal and para-hisian pathways. Catheter ablation of these septal pathways using low radiofrequency energy was safe and effective. (CHEST 1996; 19:73-4) A V =atrioventricular Key words: accessory pathway; anteroseptal; midseptal; para-hisian; radiofrequency catheter ablation The septal region is a complex anatomic entity containing major parts of the specialized conduction system. Anteroseptal, midseptal, and para-hisian accessory pathways, which are the least common in Wolff-Parkinson-White syndrome, may course through this region in close anatomic proximity to the His bundle and atrioventricular (A V) node. Surface ECGs of the preexcitation pattern, or orthodromic tachycardia mediated by the accessory pathways located in the anteromidseptal area, varied widely. Whether the short distance between these pathways and A V node might affect the ECG findings and electrophysiologic param- *From the Division of Cardiology, Department of Medicine, National Yang-Ming University, SChool ofmedicine, and Veterans General Hospital-Taipei and' Kaohsiung, Taiwan, Republic of China. Supported in part by grants from the National Science Council (NSC 82-llS-B7S-llO, B1-83), Taipei, Taiwan. Manuscript received April 21, 1995; revision accepted August 3. Rer,rint requests: Dr. Chen, Division of Cardiology, Veterans General Hospital-Taipei, 21 Sec 2, Shili-Pai Road; Taipei, Taiwan, ROC 73 eters was unknown. 14 Furthermore, to our knowledge, differences of electrophysiologic characteristics among the patients with anteroseptal, midseptal, and para Hisian accessory pathways had not been reported previously. Although surgical division of these pathways, guided by electrophysiologic activation mapping, has evolved into a curative therapeutic approach with high success and low mortality rate, s i ~ i f risk i c of a ncomplete t A V block cannot be avoided. -ll Some investigators have shown that the results of radiofrequency ablation for these septal pathways had a comparable efficacy with preservation of A V node-his bundle conduction, but another has reported that the success rate is only modest, and that complications with complete A V block were high.i 2-15 The purpose of this study was to investigate the unique ECG and electrophysiologic characteristics and an effective radiofrequency catheter ablation technique in a large series of patients with anterosep- Clinical Investigations

2 tal, midseptal, and para-hisian accessory pathways. Patient Characteristics MATERIALS AND METHODS From May 199 to August 1994, a total of 62 patients with accessory pathway-mediated tachyarrhythmia were referred to this institution for electrophysiologic study and radiofrequency catheter ablation. Twenty-three patients (group A) had anteroseptal accessory pathways; there were 13 male and 1 female patients, with a mean age of 39:±:18 years (range, 17 to 77 years). Thirteen patients (group B) had midseptal accessory pathways; there were 9 male and 4 female patients, with a mean age of 4:±: 15 years (range, 13 to 64 years). Ten patients (group C) had para-hisian accessory pathways; there were five male and five female patients, with a mean age of 35:±:1 years (range, 23 to 5 years). These patients were refractory to or intolerant of 2:±:1 antiarrhythmic drugs. Baseline Electrophysiologic Study After informed written consent had been obtained, each patient underwent baseline electrophysiologic study while in the fasting, unsedated state, at least five half-lives after discontinuation of antiarrhythmic drug therapy. As described previously, three multipolar catheters (interelectrode space, 2 mm; Mansfield-Webster) were introduced from the femoral vein and placed in the right atrium, His bundle area, and right ventricle for recording and stimulation. One or two orthogonal electrode catheters (Mansfield Webster) were percutaneously introduced into the right internal jugular vein and placed in the coronary sinus to record left atrial activation. Intracardiac electrograms were simultaneously displayed with surface ECG leads I, II, and V 1 on a multichannel oscilloscopic recorder (Electronics for Medicine; VR-13; PPG Biomedical Systems, Cardiovascular Division; Pleasantville, NY), and were recorded at a paper speed of 1 to 15 mm/s using a Hlter frequency setting of 3 to 5 Hz. A programmed digital stimulator (Bloom Associates Ltd; Reading, Pa) was used to deliver electrical impulses of 2. ms at approximately twice diastolic threshold. Programmed electrical stimulation consisting of atrial and ventricular incremental pacing and extrastimulation was performed to assess the conduction properties of atrium, ventricle, AV node, and accessory pathway (antegrade and/or retrograde), and to induce reciprocating tachycardia. If tachycardia was not induced under the baseline state, isoproterenol (at graded dosages from 1 to 4 pglmin) or atropine (.1 to.2 mglkg) was infused IV to facilitate its induction. Various types of supraventricular tachyarrhythmias were defined by classic criteria 18 ECG Analysis ECG recordings were obtained in all patients during the invasive electrophysiologic study. The ECGs were recorded at a paper speed of25 mm/s and evaluated by two independent observers. Preexcited 12-lead ECGs were obtained during sinus rhythm. The initial4 ms of the preexcited QRS complex in each of the frontal leads and the initial 6 ms of the preexcited QRS complex in each of the precordial leads were taken as the delta wave. If the delta wave was above the baseline without any part below the baseline in a given lead, it was designated as positive for that lead. If the delta wave was below the baseline without any part above the baseline, it was designated as negative. The isoelectric delta wave was designated as the whole delta wave on the baseline. The delta wave that was composed of both positive and negative deflections was designated as biphasic.l9 In addition, 12-lead ECGs of narrow QRS complex were obtained during sinus rhythm and orthodromic tachycardia. The characteristics of presumed retrograde P wave in each of 12 leads were analyzed by comparison of both ECGs during sinus rhythm and orthodromic tachycardia. If the presumed P wave was above the baseline of ST segment, it was designated as positive. If the presumed P wave was below the baseline of ST segment, it was designated as negative. If the presumed P wave had components above and below the baseline, it was designated as biphasic. However, if the presumed P wave was on the oblique part of ST segment, we used a line connecting the end point of Q RS complex to the peak (positive Twave) or nadir (negative T wave) oft wave to define P wave polarity during tachycardia. If the P wave was above this line, it was designated as positive. If the P wave was below this line, it was designated as negative. If the P wave had both positive and negative components, it was designated as biphasic. Endocardial Mapping and Radiofrequency Catheter Ablation Technique The patients were randomized to receive either of the two different ablation techniques. In brief, a multipolar electrode catheter with a deflectable, large-tip electrode (7F; length, 4 mm; Mansfield-Webster) was used for mapping and ablation via the femoral vein approach. Using the His bundle and coronary sinus catheters for reference, the tip electrode was positioned against the right-side atrial septum to map anteroseptal, midseptal, and para Hisian pathways. The presumed ablation sites showed typical AV fusion with ventricular activation preceding delta wave (for manifest accessory pathways), typical ventriculoatrial fusion with earliest retrograde atrial activation (for concealed accessory pathways), or a possible accessory pathway activation potential. In 23 group 1 patients, radiofrequency energy (3 to 4 W; 4 to 6 s) was applied during sinus rhythm, ventricular pacing, or orthodromic tachycardia. In 23 group 2 patients, lower radiofrequency energy (1 to 3 W) was applied by titration method and delivered during sinus rhythm, atrial pacing, or ventricular pacing; all applications were begun using a power setting of 1 W; if accessory pathway was not interrupted after 1 to 15 s, the step-up energy was increased 5 W for every 1 to 15 s. When accessory pathway conduction was lost within 1 to 15 s without any impairment of A V nodal conduction, a second application of the same energy was delivered at the successful ablation site for 15 to 2 s, but was terminated immediately in the event of an increase in impedance, displacement of the ablation catheter, or atrio-hisian interval prolongation. The end point of ablation procedures was complete elimination of antegrade and retrograde accessory pathway conduction during isoproterenol infusion. The total procedure time and radiation exposure time were calculated (including the time for the diagnostic procedure). Radiofrequency current (continuous wave, 5 KHz) was generated by an electrosurgical generator (Radionics model RFG-3C; Burlington, Mass). Real-time monitoring of root-mean-square voltage, current, and impedance was provided. Radiofrequency current was usually delivered between the tip electrode and a standard adhesive electrosurgical dispersive pad (3M, Medical and Surgical Division; St. Paul, Minn) applied to the posterior chest wall. Definitions of Anteroseptal, Midseptal, and Para-Hisian Accessory Pathways Localization and identification of an accessory pathway were based on the large-tip, mapping, and ablation catheter in right and left anterior oblique fluoroscopic views. An anteroseptal accessory pathway was defined as one situated above the His bundle with ventricular activation cephalad and anterior to the membranous septum. A midseptal accessory pathway was defined as one situated in the area anterior and superior to the coronary sinus orifice, but below the His bundle. A para-hisian accessory pathway was defined as one situated in the His bundle area with a large His bundle potential of more than.1 mv.' Postablation Monitoring and Evaluation All patients were monitored in the Coronary Care Unit for 24 h CHEST I 19 I 3 I MARCH,

3 Table 1-Clinical and ECG Characteristics in Patients With Anteroseptal (Group A), Midseptal (Group B), and Para-Hisian (Group C) Accessory Pathways* Patient No. Age, yr Sex Location(s) of AP Clinical Tachyilll)1hmia AFib SVT Polarity of Delta Wave Transition of RIS Ratio II III avf avl avr Vt V2 V3 V4-V5 >1 Polarity of Retrograde Wave During SVT II III avf avl avr V 1 Group A (n=23) 1/32JF V55/M 3/17/M 4/24/F 5132JF 6t54!M 7/17/M 8/35/F 9n7/M 1172/!vl ll/6/m 12131/F 13/48/F 14/64/M 15/43/F 16/29/M 17/18/F 18/37/F 19 1 /22JM 2 1 /28/M 21 1 /25/M 22162JF 23122/M 24/33/M 25/15/M 26/33/M 27/57!M 28/46/F 29/44/M 3/33/M 31 1 /48/M 32 1 /64/F 33 1 /58/M 34137/M 35/13/F 36/39/F 37/35/M 38/24/M 39/23/F 4/32JF 41133/F /F /24/M 44 1 /5/M 45 1 /39/F 46 1 /38/M AS(M) AS(M) AS(M) AS(M) AS(M) AS(!) AS(!) AS(C) AS(C) AS(M),RAL(M) AS(C),RP(M) AS(C),RP(M),RPL(M) AS(C),LPS(M) AS(C), LPS(C) MS(C),RPS(M) MS(C),LL(C) MS(C),LL(C),RP(M),RL(C) MS(C), RPS(C), RAL(M) PH(M) PH (I) PH(1) PH(!) PH(C) PH(C) PH(M),LL(M) PH(M), RAL(M) PH(M),RPS(C) PH(C), RPL(M) + + I\ A :-.la Group B (n=l3) Group C (n=lo) + : :!: :!: :!: ± :t ::!:: ± :±: ± :t ::!: ::!: ::!: ::!: :t :t ± ::!: ::!: ::!: ::!: ± :±: :t ± :±: :±: ± :±: ± :±: * AFib=atrial fibrillation; AP=accessory pathway; AS=anteroseptal; C=concealed;!=intermittent; LL=ieft lateral; LPS=Ieft posteroseptal; M =manifest; MS=midseptal; =not applicable; PH=para-Hisian; RAL=right anterolateral; RL=right lateral; RP=right posterior; RPL=right posterolateral; RPS=right posteroseptal; SVT=supraventricular tachycardia; =unknown. ±=biphasic polarity; -=negative polarity; O=no; +=positive polarity. 'Polarity of the delta wave or retrograde P wave could be analyzed after successful ablation of other pathways. after the ablation procedures. Serial creatine kinase and creatine kinase MB fraction levels were measured. After hospital discharge, all patients were seen in the outpatient clinic at 1 week, 1 month, and then every 3 months, at which time a history of recent symp- 732 toms was taken, and a physical examination, 12-lead ECG, and 24-h Holter monitoring were performed. Patients were followed up without antiarrhythmic drugs. Serial follow-up electrophysiologic studies (early, 5 to 7 days; and late, 3 months after ablation) were Clinical Investigations

4 FIGURE 1. Panels A and B: Twelve-lead ECG showed different ventricular preexcitation patterns in two patients with an anteroseptal accessory pathway. C and D: ECGs showed orthodromic tachycardia with a retrograde P wave in two patients with an anteroseptal accessory pathway. E and F: ECGs showed ventricular preexcitation and orthodromic tachycardia in a patient with a midseptal accessory pathway, respectively. A: The delta wave is positive in leads I, II, Ill, avf, avl, and Vz to V5, and biphasic in VI. The precordial R/S ratio becomes more than 1 in lead V3. B: The delta wave is positive in leads I, II, avf, avl, and V3 to V 6, and negative in leads III and VI to V 2. The R/S ratio becomes more than 1 in lead V4. C: The retrograde P wave is positive in leads II, III, and avf, and biphasic in lead VI. D: The retrograde P wave is biphasic in leads II, III, and avf, and negative in lead V 1. E: The delta wave is positive in 1eads I, II, avl, and V3 to V5, negative in leads III and V1, and biphasic in leads avf and V2. The precordial R/S ratio becomes more than 1 in lead V4. F: The retrograde P wave is negative in leads II, Ill, and avf, and biphasic in lead V1. performed in 15 patients, and the other patients were encouraged to receive follow-up electrophysiologic studies if they had frequent complaints of palpitation. A second ablation session was arranged if the patient had recurrence of conduction through the accessory pathway. Statistical Analysis All data are expressed as mean±sd. Comparisons between different groups were evaluated by x 2 test with Yates' correction or Fisher's Exact Test for categorical data and one-way analysis of variance for continuous data. A p value less than.5 was consid- CHEST I 19 I 3 I MARCH,

5 FIGURE 2. Twelve-lead ECGs showed ventricular preexcitation (A to C) and orthodromic tachycardia with a retrograde P wave (D to F) from three patients with a para-hisian accessory pathway. A: The delta wave is positive in leads I, II, avf, avl, and Y4 to Y5, and negative in leads III and Yr to Y3. The R/S ratio in the precordial leads becomes more than 1 in lead Y4. B: The delta wave is positive in leads I, II, ayf, ayl, and Y3 to Y 6, biphasic in lead III, and negative in leads Yr to Y2. The R/S ratio becomes more than 1 in lead Y3. C: The delta wave is r.ositive in leads I, II, III, avf, ayl, and Yr to Y5. The R/S ratio becomes more than l in lead Y2. D: The retrograde P wave is biphasic in leads II, III, ayf, and Yr. E: The retrograde P wave is positive in leads II, III, and avf, and negative in lead Yr. F: The retrograde P wave is negative in leads III and avf, and biphasic in leads II and Yr. ered statistically significant. EGG Characteristics RESULTS Of the 31 patients with a single accessory pathway, all the 12-lead ECGs recorded during sinus rhythm and/or orthodromic tachycardia were included for analysis; of the 15 patients with multiple accessory 734 pathways, only 1 patients with a residual septal pathway after successful ablation of other associated pathways were included for analysis to assure one ECG pattern resulting from a single accessory pathway (Table 1). Delta Wave: Eight patients with the anteroseptal accessory pathway had ventricular preexcitation; six had persistent and two had intermittent ventricular Clinical Investigations

6 Table 2-ECG Finding to Differentiate Anteroseptal (Group A), Midseptal (Group B), and Para-Hisian (Group C) Accessory Pathways* Group A Group B Group C p Value Patients with preexcitation, n Delta wave positivity, % II III avf Two of above Transition of RIS >1, % v V V Patients with OT, n Retrograde P-wave negativity, % II III avf Two of above *n=patient number; OT =orthodromic tachycardia. preexcitation. All the eight patients had a positive delta wave in frontal leads I, II, a VF, a VL, and precordial leads V3 through V5, and a negative delta wave in frontal lead avr. Seven patients (87.5%) had a positive delta wave in frontal lead III and one (12.5%) had a negative delta wave. Four patients (5%) had a biphasic delta wave in lead V1 and a positive delta wave in lead V2; four (5%) patients had a negative delta wave in leads V1 and V2. Precordial QRS transition (RIS>1) was noted in leads V3 or V4 (Fig 1, A and B). Seven patients with the midseptal accessmypathway had persistent ventricular preexcitation. All these patients had a positive delta wave in frontal leads I, II, a VL, and precordial leads V 4 through V 6, a negative delta wave in lead III, a VR, and V 1, and a biphasic delta wave in lead avf. Five patients (71.4%) had a positive delta wave in precordial leads V 2 and V 3; one patient ( 4.3%) had a negative delta wave in these leads; one patient ( 4.3%) had a negative delta wave in lead V 2 and a positive delta wave in lead V3. Precordial QRS transition (RIS>1) was noted in lead V 2, V3, or V 4 (Fig 1, E). Seven patients with the para-hisian accessory pathway had ventricular preexcitation; four had persistent and three had intermittent ventricular preexcitation. Seven patients had a positive delta wave in frontal leads I, II, avf, avl, and precordial leads V4 through V6, and a negative delta wave in lead avr. Four patients (57.1%) had a positive delta wave, one (14.2%) had a negative delta wave, and two (28.6%) had a biphasic delta wave in lead III. Four patients (57.1%) had a negative delta wave and two patients (28.6%) had a positive delta wave in leads V1 and V 2. Precordial QRS transition (RIS>1) was noted in leads V2, V3, or V4 (Fig 2, panels A to C). Retrograde P Wave: Sixteen patients with the anteroseptal, nine patients with the para-hisian, and six patients with the midseptal accessory pathway had a retrograde P wave clearly visible on the 12-lead ECG (Fig 1, panels C, D, and F; and Fig 2, panels D to F). All the patients with the midseptal pathway and two (22.2%) patients with the para-hisian pathway had a negative P wave in at least two inferior leads; whereas, a positive P wave in at least two inferior leads was observed in 13 (81.3%) patients with the anteroseptal pathway and in 6 (66.7%) patients with the para-hisian pathway. A biphasic P wave in V 1 was observed in 12 ( 75%) patients with the anteroseptal pathway, 7 ( 77.8%) patients with the para-hisian pathway, and all ( 1%) the patients with the midseptal pathway. Comparisons Among the Three Groups of Patients: Midseptal pathways could be differentiated from anteroseptal and para-hisian pathways by a negative delta wave in lead III (p=.32) and a biphasic delta waveinleadavf (p<.1), and a negative retrograde P wave in two of the three inferior leads (p<.1) (Table 2). Electrophysiologic Characteristics Multiple accessory pathways were found in 5 ( 21.7%) of 23 group A patients, 6 (46.2%) of 13 group B patients, and 4 (4.%) of 1 group C patients (p=.242). A bidirectional pathway was noted in 7 (3.4%) group A, 8 (61.5%) group B, and 7 (7.%) group C patients (p=.221); a concealed pathway was noted in 15 (65.2%) group A, 4 (3.8%) group B, and 3 (3.%) group C patients (p=.81). One (4.3%) group A and one (7.7%) group B patient had an accessory pathway with antegrade conduction only (Table 3). Neither the incidence of inducible orthodromic tachycardia (95.7%, 69.2%, and 88.9%; p=.79) nor the mean tachycardia cycle length (331::±:47, 335::±:66, and 356::±:45 ms; p=.4547) differed significantly among the three groups of patients. Group B patients had a significantly higher incidence (61.5%) of inducible atrial fibrillation than either group A (13.%) or group C (1.%) patients (B vs A, p=.64; B vs C, p=.31), and the mean shortest RR interval during atrial fibrillation with ventricular preexcitation was significantly shorter in group B patients (227::±:31 vs 28::±:36 ms; p=.1). Group B patients also had a significantly shorter antegrade effective refractory period of the accessory pathway (253 ±39 ms) than either group A (348::±:44 ms) or group C (338::±:28 ms) patients (p<.5). There were no significant differences in retrograde effective refractory period of the accessory pathway, and minimal atrial and ventricular pacing cycle length with 1:1 conduction through the accessory pathway among the three groups of patients. Of the total46 patients, there were 15 (32.6%) pa- CHEST / 19 /3/ MARCH,

7 Table 3-Electrophysiologic Characteristics and Radiofrequency Ablation in Patients With Anteroseptal (Group A), Midseptal (Group B), and Para-Hisian (Group C) Accessory Pathways* Group A Group B Group C p (n=23) (n=13) (n=1) Value Total No. of APs Multiple APs (% 5 (21.7) 6 (46.2) 4 (4.).242 of patients) Direction of AP (%) Bidirectional 7 (3.4) 8 (61.5) 7 (7.).221 Antegrade only 1 (4.3) 1 (7.7) (O).69 Retrograde only 15 (65.2) 4 (3.8) 3 (3.).81 Types of tachyarrhythmia Orthodromic(%) 22 (95.7) 9 (69.2) 9 (9.).79 TCL, ms 331::t47 335::t66 356::t AFib (%) 3 (13.) 8 (61.5) 1 1 (lo.o).34 SRR,ms 28::t36 227::t31.1 AP 1:1 conduction, ms Ante grade 382::t59 37::t55 362::t3.641 Retrograde 317::t36 334::t43 32::t AP ERP, ms Antegrade 348::t44 253::t39; 338::t28.68 Retrograde 29::t3 296::t13 28::t *Unless otherwise indicated, values presented are mean ::t SD and number (%) of patients. AP=accessmy pathway; ERP=effective refractory period; RF=radiofrequency; SRR=shortest preexcited R-R interval during atrial fibrillation; TCL=tachycardia cycle length. 1 p=.64, group B vs A, and p=.31, group B vs C. *p <.5, group B vs A and group B vs C; other abbreviations as Table l. tients with multiple accessory pathways. Locations of accessory pathways and types of tachycardia were shown in Table 1. Thirteen patients had double pathways and two patients had triple pathways. Right free-wall pathways are the most common among the associated pathways. Patients with multiple accessory pathways did not have a significantly higher incidence of atrial fibrillation than those who had a single pathway (53.3% vs 29%; p=.441). During the electrophysiologic study, evidence supporting multiple accessory pathways included the following: (1) different patterns of ventricular preexcitation during sinus rhythm, atrial pacing, or atrial fibrillation in six patients; (2) different sites of atrial activation during right ventricular pacing or orthodromic reciprocating tachycardia in nine patients; (3) preexcited tachycardia with the use of a second accessory pathway as the retrograde limb of the tachycardia in two patients; and ( 4) one additional pathway found after successful radiofrequency ablation of the initially attempted pathway in ten patients. Catheter Ablation and Follow-up In group 1 and group 2 patients, all the accessory pathways were ablated successfully in the primary ablation session (Table 4). Radiofrequency ablation pulse number, total procedure time, and fluoroscopic exposure time were similar between the two groups of patients. Radiofrequency energy of the successful pulse was significantly lower in the group 2 patients (2±6 vs 36±5 W; p=o.oool). In group 1 patients, one with the anteroseptal and one with the para-hisian pathway 736 had the complication of complete A V block; one with the midseptal pathway had the complication of firstdegree A V block immediately after successful radiofrequency ablation. Patients with complete A V block received implantation of a physiologic model permanent pacemaker. None of the group 2 patients had any impairment of AV node function. Four (8.7%) of the 46 patients had mechanical trauma of the accessory pathway during the procedures. Significant impairment of antegrade A V node conduction properties, including effective refractory period (287±31 vs 247±27 ms; p<.1) and minimal atrial pacing cycle length with 1:1 conduction (41 ±29 vs 326±4 ms; p<o.ol) was found in the group 1 patients with successful ablation. During the follow-up periodof26±14 months (range, 5 to 54 months), three patients (one group 1 and two group 2 patients) had recurrence of tachycardia (one anteroseptal and two para-hisian pathways); all had a successful result in the second ablation session. The other patients were free of arrhythmias without any antiarrhythmic drug (Table 4). Main Findings DISCUSSION This study showed the following: (1) midseptal accessory pathways could be differentiated from anteroseptal and para-hisian pathways by characteristic ECGs during sinus rhythm and orthodromic tachycardia; (2) patients with midseptal pathways had a higher incidence of inducible atrial fibrillation and a shorter Clinical Investigations

8 Table 4-Radiofrequency Catheter Ablation of Septal Accessory Pathways* Group 1 Group 2 (n=23) (n=23) AP Location AS MS 7 6 PH 5 5 RF ablation Pulse No. 8:!:7 9 :!:8 Power, W 36:!:5 2:!:6 Procedure time, h 2.6::':: l.o 2.6 ::'::.8 Radiation time, min 35.4:!: ::'::12.9 Recurrence rate (%) 1 (4.3) 2 (8.7) AV block (%) 3 (13.) 1 (O) p Value *AS=anteroseptal; MS=midseptal; PH=para-Hisian; RF=radiofrequency; other abbreviations as in Table l. 1 Two with third-degree and one with first-degree AV block. anterograde effective refracto:ry period of the accesso:ry pathway; and (3) radiofrequency catheter ablation using lower energy was effective in eliminating septal pathways without impairment of A V node conduction. ECG Characteristics ECG recognition of anteroseptal, midseptal, and para-hisian accesso:ry pathways had been demonstrated by several investigators, but the ECG patterns varied widely and some of the pathway localizations were not confirmed by radiofrequency catheter ablation In this study, all the pathway locations correlated with surface ECGs were confirmed by radiofrequency catheter ablation. Preexcitation Pattern: Regarding the anteroseptal pathways, Rodriguez et al 2 reported that 11 patients with anteroseptal pathways showed positive delta waves in all inferior leads and transition of RIS ratio more than 1 occurred mainly in lead V3 and V4. Fitzpatrick et al 3 reported that anteroseptal pathways had an inferior frontal plane Q RS vector with positive delta wave in at least two of the three inferior leads. Xie et al 4 also showed that there was a positive QRS complex in lead avf and a negative QRS complex in leads III and VI. The present study showed that seven of the eight patients with manifest anteroseptal accesso:ry pathways had a positive delta wave in leads I, II, III, avf, and avl (one patient had a negative delta wave in lead III) and all the eight patients had transition of RIS ratio more than 1 in precordial leads V 3 and V 4. The results suggested the anterosuperior position of these anteroseptal pathways. Regarding the midseptal pathways, various patterns of ECGs might be observed. Kuck et al 12 demonstrated that four of the five patients with these pathways had a delta wave polarity predominantly negative in lead III and a VF, but positive in leads I, II, and a VL; they were located in closer to the corona:ry sinus ostium than to the A V node. The other one patient also had a positive delta wave in leads I, II, and a VL, but an isoelectric delta wave in leads III and avf. 12 The preexcitation pattern described by Epstein et al 11 for their "type 1" intermediate septal pathways showed a positive delta wave in leads I, II, and a VL, but a negative delta wave in lead III and an isoelectric delta wave in lead avf; these pathways were located in the midpoint (paranodal area) of Koch's triangle. In the series of Gallagher et al, 1 patients with intermediate septal pathways also had a positive delta wave polarity in the leads I, II, and a VL, but isoelectric polarity in leads III and a VF; this finding indicated that these pathways might be located in the anterior portion of Koch's triangle. The preexcitation pattern of midseptal pathways in this study was comparable to the report of Epstein et al 11 (type 1 intermediate septal pathways) and showed that a positive delta wave was present in leads I, II, and avl, a negative delta wave was in leads III, avr, and V1, and a biphasic delta wave was in lead avf; precordial QRS transition (RIS>1) was present in leads V2 through V4. These different findings suggested that midseptal accesso:ry pathways activate the ventricles in a complex manner depending on the location of the accesso:ry pathway in the midseptal area. However, a posteroseptal pathway may well have a negative delta wave in lead III and biphasic delta wave in lead avf. 2 Furthermore, although posteroseptal pathways often have a dramatic transition in lead V2, this occasionally overlaps with midseptal pathways. The present study showed that two (28.6%) of the seven patients with midseptal pathways had a dramatic transition in lead V 2 Thus, it might be difficult to separate midseptal from posteroseptal accesso:ry pathways by the analysis of delta waves only. 19 Regarding the para-hisian accesso:ry pathways, no ECG criteria were distinctive because the presence of a His bundle potential without measuring its amplitude is not specific since a small His bundle potential is frequently observed in the locations of anteroseptal and midseptal accesso:ry pathways. Therefore, they might be misclassified as either anteroseptal or midseptal accesso:ry pathways.l 5 Haissaguerre et al 15 reported that the ECG of para-hisian pathways showed a positive delta wave in leads I, II, and a VF in all the eight patients and a predominantly negative delta wave in lead V1 and V2 in six patients. This pattern had a sensitivity of 75%, a specificity of 96%, a positive predictive value of 86%, and a negative predictive value of 93% for a para-hisian location in comparison with a group of 28 patients with anteroseptal pathways. 15 The present study showed that four (57.1%) of the seven manifest para-hisian pathways had this ECG pattern. However, four (5%) of the eight manifest anteroseptal pathways also had this ECG pattern. Retrograde P Waves: Although the patterns of delta CHEST I 19 I 3 I MARCH,

9 waves in patients with manifest anteroseptal, midseptal, and para-hisian accessory pathways have been well described by several investigators, information about retrograde P wave is limited. Scheinman et al 1 found an overlap in polarity of the retrograde P wave during orthodromic reciprocating tachycardia in patients with anteroseptal, intermediate seytal, and right anterior accessory pathways. Yeh et al 1 reported that a positive retrograde P wave in inferior leads during orthodromic reciprocating tachycardia favored an accessory pathway in the anteroseptal or right anterior location. The present study and previous experience in this laboratory showed that a negative or biphasic retrograde P wave in lead V 1 and a positive or biphasic retrograde P wave in all inferior leads favor an anteroseptal or para-his ian pathway; a negative or biphasic retrograde P wave in lead V 1 and a negative retrograde P wave in at least two of the three inferior leads favor an midseptal accessory pathway; a positive retrograde P wave in lead V 1 and a negative retrograde P wave in all the three inferior leads favor a posteroseptal pathway. These results are compatible with those of the study of Waldo et al Waldo et al demonstrated that when the atria were paced from sites in the A V junction, increasing more anterior relative to the coronary sinus ostium, biphasic and finally frankly positive P waves in leads II, III, and a VF are produced; when the atria are paced from the region of the coronary sinus ostium, negative P waves or negative P waves with a small late positive component in ECG lead II, III, and a VF are produced. The findings of a positive P wave in the inferior leads during orthodromic tachycardia in patients with an anteroseptal pathway may suggest rapid activation of superior right atrial areas along anterior internodal pathway with later spread to inferior atrial areas Electrophysiologic Characteristics Comparisons of the electrophysiologic characteristics among these three septal pathways had not been reported previously (to our lmowledge). This study showed that patients with midseptal accessory pathways tended to have a lower incidence of induced orthodromic tachycardia and a significantly higher incidence of induced atrial fibrillation than anteroseptal and para-hisian accessory pathways. Better antegrade and poorer retrograde conduction properties of midseptal pathways might predispose to lower inducibility of sustained orthodromic tachycardia and higher inducibility of atrial fibrillation. Bella et al 23 had reported that the antegrade rather than the retrograde conduction properties of the accessory pathway are the critical determinants of atrial fibrillation in the Wolff Parkinson-White syndrome. The reason why midseptal accessory pathways had such unusual electrophysiologic characteristics was not clear. 738 Of the 15 patients with multiple pathways, 1 ( 66.7%) had one additional pathway found after successful ablation of the initially attempted pathway. Failure to detect the additional pathways may be explained by the inherent limitations of endocardial mapping, transient pathway trauma during manipulation of electrode catheters, or concealed conduction Regarding the occurrence of true antidromic tachycardia (retrograde conduction through AV node), Bardy et af 6 demonstrated that all but two episodes of true antidromic tachycardia in the 22 patients with a single accessory pathway had the location of accessory pathway at least 4 em from the A V node. Because these septal pathways are located near the A V node and His bundle, true antidromic tachycardia (using A V node for retrograde conduction) occurs with difficulty. However, if preexcited reciprocating tachycardia really occurs, multiple accessory pathways must be considered.26 In the present study, two patients with multiple accessory pathways had preexcited reciprocating tachycardia and none of the patients with a single anteromidseptal accessory pathway developed true antidromic tachycardia. Catheter Ablation Several investigators have demonstrated that radiofrequency catheter ablation was effective in interrupting the anteroseptal, midseptal, and para-hisian accessory pathways with preservation of A V node conduction. Kuck et al 12 and Schluter et al 13 reported that radiofrequency ablation using the power level of 26.4±4. Wand 25.3±4.7 W was enough to eliminate midseptal and anteroseptal pathways, respectively, and to avoid functional damage of the A V node-his bundle system. Haissaguerre et al 15 also showed that all the para-hisian accessory pathways were successfully ablated without causing heart block using 5 to 2 W of radiofrequency energy in their study. However, in the series ofyeh et a1, 14 the success rate of radiofrequency ablation using energy power 3±8 W for intermediate septal pathways is modest (71%), whereas complications with heart block ( 36%) or comrlete right bundle branch block (29%) were high.l 2 - In the present study, patients were randomized to receive radiofrequency ablation using high energy (group 1, 36±5 W) or low energy (group 2, 2±6 W). Although the success rate and recurrence rate were similar between these two groups, group 1 had a higher incidence of impaired A V conduction properties. These results suggested that radiofrequency ablation using lower energy with titration method was effective in eliminating septal accessory pathways with preservation of A V conduction properties. Future study to prove the safety of temperature monitoring in ablating these septal pathways is necessary. Clinical Investigations

10 Possible Anatomic Relation and A V Block Catheter-induced mechanical trauma of these septal pathways has been reported in recent studies and the incidence was not rare These findings and the results of radiofrequency ablation using lower energy suggested a subendocardial location of these septal pathways. From the findings of surgical ablation, His bundle was located within the central fibrous body and anteroseptal as well as para-hisian pathways were close to this specialized conduction fiber. Midseptal accessory pathways occupy in reality the true A V septum, which also contains the compact part of the A V node. 27 Therefore radiofrequency ablation using higher energy might impair the conduction properties of A V node and His bundle by thermal injury and lead to various degrees of A V conduction block. Study Limitations First, we looked at the QRS complex during sinus rhythm. Although a sufficient amount of ventricular preexcitation was analyzed, a completely preexcited Q RS complex obtained by atrial pacing probably would allow a more precise ECG differentiation between these septal pathways, whereas an invasive procedure was required. Second, although 4 patients had 12- lead ECGs during orthodromic tachycardia in this study, the polarity of retrograde P wave could be recognized in 31 (77.5%) patients. Four patients were excluded for analysis due to conflicting interpretation of the 12-lead ECGs and five due to participation of multiple accessory pathways. Future prospective studies of retrograde P wave are necessary to confirm these findings. CoNCLUSIONS The present study showed that a midseptal accessory pathway might be recognized by a negative delta wave in lead III, a biphasic delta wave in lead avf, and a positive delta wave in lead II during sinus rhythm, and a biphasic retrograde P wave in lead V 1 with a negative P wave in at least two inferior leads during orthodromic tachycardia. Furthermore, patients with a midseptal pathway had better antegrade conduction properties and a higher incidence of atrial fibrillation. Catheter ablation of these septal pathways using optimal titration of radiofrequency energy appears to be safe and effective. REFERENCES 1 Scheinman MM, Wang YS, Van Hare GF, et a!. Electrocardiographic and electrophysiologic characteristics of anterior, midseptal and right anterior free wall accessory pathways. J Am Coil Cardiol1992; 2: Rodriguez LM, Smeets JLMR, de chillou C, et a!. The 12-lead electrocardiogram in midseptal, anteroseptal, posteroseptal and right free wall accessory pathways. 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