Effects of Septal Pacing on P Wave Characteristics: The Value of Three-Dimensional Echocardiography TAMAS SZILI-TOROK, NICO BRUINING, MARCOEN SCHOLTEN, GEERT-JAN KIMMAN, JOS ROELANDT, and LUC JORDAENS From the Department of Cardiology, Erasmus Medical Center, Rotterdam, the Netherlands SZILI-TOROK, T., ET AL.: Effects of Septal Pacing on P Wave Characteristics: The Value of Three- Dimensional Echocardiography. Interatrial septum (IAS) pacing has been proposed for the prevention of paroxysmal atrial fibrillation. IAS pacing is usually guided by fluoroscopy and P wave analysis. The authors have developed a new approach for IAS pacing using intracardiac echocardiography (ICE), and examined its effects on P wave characteristics. Cross-sectional images are acquired during pullback of the ICE transducer from the superior vena cava into the inferior vena cava by an electrocardiogram- and respiration-gated technique. The right atrium and IAS are then three-dimensionally reconstructed, and the desired pacing site is selected. After lead placement and electrical testing, another three-dimensional reconstruction is performed to verify the final lead position. The study included 14 patients. IAS pacing was achieved at seven suprafossal (SF) and seven infrafossal (IF) lead locations, all confirmed by three- dimensional imaging. IAS pacing resulted in a significant reduction of P wave duration as compared to sinus rhythm (99.7 ± 18.7 vs 140.4 ± 8.8 ms; P < 0.01). SF pacing was associated with a greater reduction of P wave duration than IF pacing (56.1 ± 9.9 vs 30.2 ± 13.6 ms; P < 0.01). P wave dispersion remained unchanged during septal pacing as compared to sinus rhythm (21.4 ± 16.1 vs 13.5 ± 13.9 ms; NS). Three- dimensional intracardiac echocardiography can be used to guide IAS pacing. SF pacing was associated with a greater decrease in P wave duration, suggesting that it is a preferable location to decrease interatrial conduction delay. (PACE 2003; 26[Pt. II]:253–256) atrial fibrillation, septal pacing, atrial mapping, echocardiography Introduction Alternative pacing approaches have recently been introduced for the management of patients with paroxysmal atrial fibrillation (PAF). 1-3 Pac- ing the interatrial septum (IAS) has been reported to be effective in slowing the progression of atrial fibrillation (AF). 4-6 Fluoroscopy does not allow the visualization of the fossa ovalis, aortic arch, aortic valve, crista terminalis, and tricuspid valve. Thus, the accuracy of lead positioning when se- lecting septal pacing sites with fluoroscopy is lim- ited. The aim of the present study was to develop a new approach for IAS pacing based on three- dimensional intracardiac echocardiography (ICE) and to test its feasibility. Using this technique, the effects of septal pacing on P wave characteristics were examined. Patients and Methods Patient Population Fourteen consecutive patients (7 women; mean age 63.1 ± 15.4, range 32–77 years) who un- derwent dual chamber (DDD, n = 13) or atrial (AAI, n = 1) pacemaker implantation were included in Address for reprints: Tamas Szili-Torok, M.D., Dept. of Clin- ical Electrophysiology, Thoraxcentre, Rotterdam, Dr Molewa- terplein 40, 3015 GD, Rotterdam, the Netherlands. Fax: 31-10- 4634420; e-mail: szili@card.azr.nl this study, which was reviewed by the Medical Ethical Committee of the Thoraxcentrum. Three-Dimensional ICE The ClearView system (CardioVascular Imag- ing Systems Inc., Fremont, CA, USA) was used with an 8 Fr sheath-based ICE imaging catheter that incorporated a 9-MHZ beveled single ele- ment transducer rotating at 1,800 rpm (model 9900, EP Technologies, Boston Scientific Corp., San Jose, CA, USA). A custom-made electro- cardiogram (ECG) and respiratory-gated pullback device and a three-dimensional ultrasound work- station (EchoScan, TomTec GmbH, Munich, Germany) were used to acquire and process the ICE images. 7,8 The custom-made pullback device is controlled by the three-dimensional workstation and uses a stepping motor to move the catheter stepwise and linearly through the right atrium. The workstation receives video input from the ICE sys- tem and an ECG and respiration signal (impedance measurement) from the patient. In accordance to their timing in the cardiac cycle, all images are for- matted in volumetric data sets (256*256*256 pix- els/each 8 bits). Insertion of ICE Transducer and Pacemaker Implantation A 12-lead ECG was initially recorded with a high resolution electrophysiology system (Prucka PACE, Vol. 26 January 2003, Part II 253