title: Electrocardiographic and electrophysiologic characteristics of midseptal accessory pathways.
abstract: BACKGROUND
  The purpose of the present study was to investigate the electrocardiographic and electrophysiologic characteristics of right midseptal (RMS) and left midseptal (LMS) accessory pathways (APs), and to develop a stepwise algorithm to differentiate RMS from LMS APs.
  
  
  RESULTS
  From May 1989 to February 2004, 1591 patients with AP-mediated tachyarrhythmia underwent RF catheter ablation in this institution, and 38 (2.4%) patients had MS APs. The delta wave and precordial QRS transition during sinus rhythm, retrograde P wave during orthodromic tachycardia, and electrophysiologic characteristic and catheter ablation in 30 patients with RMS APs and 8 patients with LMS APs were analyzed. There was no significant difference in electrophysiologic characteristics and catheter ablation between RMS and LMS APs. The polarity of retrograde P wave during orthodromic tachycardia also showed no statistical difference between patients with RMS and LMS APs. The delta wave polarity was positive in leads I, aVL, and V3 to V6 in patients with RMS and LMS APs. Patients with LMS APs had a higher incidence of biphasic delta wave in lead V1 than patients with RMS APs (80% vs. 15%, P=0.012). The distributions of precordial QRS transition were different between RMS APs (leads V2; n = 10, V3; n = 7 and V4; n = 3) and LMS APs (leads V1; n = 1 and V2; n = 4) (P = 0.03). The combination of a delta negative wave in lead V1 or precordial QRS transition in lead V3 or V4 had a sensitivity of 90%, specificity of 80%, positive predictive value of 95%, and negative predictive value of 66% in predicting an RMS AP.
  
  
  CONCLUSIONS
  Delta wave polarity in lead V1 and precordial QRS transition may differentiate RMS and LMS APs.
authors.affiliation: Department of Medicine and Cardiovascular Research Center, National Yang-Ming University, Fu Jen Catholic University, Veterans General Hospital, Taipei, Taiwan, ROC.
authors.forename: Shih-Ling
authors.initials: SL
authors.lastname: Chang
authors.forename: Shih-Huang
authors.initials: SH
authors.lastname: Lee
authors.forename: Ching-Tai
authors.initials: CT
authors.lastname: Tai
authors.forename: Chern-En
authors.initials: CE
authors.lastname: Chiang
authors.forename: Jun-Jack
authors.initials: JJ
authors.lastname: Cheng
authors.forename: Yenn-Jiang
authors.initials: YJ
authors.lastname: Lin
authors.forename: Ming-Hsiung
authors.initials: MH
authors.lastname: Hsieh
authors.forename: Kung-Tai
authors.initials: KT
authors.lastname: Lee
authors.forename: Hsuan-Ming
authors.initials: HM
authors.lastname: Tsao
authors.forename: Jen-Yuan
authors.initials: JY
authors.lastname: Kuo
authors.forename: Yi-Jen
authors.initials: YJ
authors.lastname: Chen
authors.forename: Shih-Ann
authors.initials: SA
authors.lastname: Chen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D017115:Catheter Ablation; D003331:Coronary Vessels / Q000503:physiopathology*; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006346:Heart Septum / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013610:Tachycardia / Q000503:physiopathology*