AB

ST

RA

CT

S

S130 Abstracts Heart, Lung and Circulation2008;17S:S1–S209

In the septum, there was no significant difference inmean CV (75 ± 44 cm/s vs. 95 ± 46 cm/s, p = 0.66); voltage(1.5 ± 1.4 mV vs. 1.8 ± 1.4 mV, p = 0.6); and % low voltageareas (23 ± 24% vs. 25 ± 20%, p = 0.9) in AA vs. controls.There were no regional differences in AA v controls in% of scar (lateral 4 ± 9% vs. 2 ± 5%, p = 0.4; septal 4 ± 7%vs. 3 ± 9%, p = 0.9) or in % of FS/DP (lateral 38 ± 21% vs.32 ± 17%, p = 0.5; septal 17 ± 14% vs. 15 ± 13%, p = 0.9).Conclusion: In ASD patients, substrate abnormalities con-ducive to development of AA are most marked in thelateral wall cf. the septum and in patients with AA cf. ASDcontrols. This remodeling is out of proportion to extent ofsurgical intervention and may be due to the underlyingdefect and/or electrical remodeling.

doi:10.1016/j.hlc.2008.05.308

308Effect of Chronic Atrial Stretch on Pulmonary VeinRemodelling

Bobby John ∗, Martin Stiles, Dennis Lau, Hany Dimitri,Pawel Kuklik, Anthony Brooks, Lauren Wilson, DarylLeong, Glenn Young, Prashanthan Sanders

Cardiovascular Research Centre, Royal Adelaide Hospital andDisciplines of Medicine and Physiology, University of Adelaide,Adelaide, South Australia, Australia

MS Controls P

Proximal ERP (ms) 270 ± 39 231 ± 25 0.008

Distal ERP (ms) 278 ± 37 258 ± 50 0.3

Proximal conduction time, S1 (ms) 54 ± 15 40 ± 17 0.04

Distal conduction time, S1 (ms) 63 ± 8 42 ± 8 <0.0001

Proximal intra-PV CB, S2 (ms) 62 ± 26 50 ± 19 0.4

Distal intra-PV CB, S2 (ms) 61 ± 22 39 ± 24 0.04

doi:10.1016/j.hlc.2008.05.309

309Right Ventricular Outflow Tract Septal Pacing: Long-TermFollow-Up of Ventricular Lead Performance

Caroline Medi ∗, Harry Mond

The Royal Melbourne Hospital, Melbourne, VIC, Australia

Introduction: The detrimental effects of right ventricular(RV) apical pacing on LV function has driven interest inselective site pacing, predominantly on the right ventric-ular outflow tract (RVOT) septum. There is currently noinformation on long-term ventricular lead electrical per-formance from this site.Methods: One hundred patients (mean age 73.4 year,range 16–92) with indications for single or dual chamberpacemaker implantation had ventricular lead positioningat the RVOT septum. Successful RVOT position was con-

Introduction: Chronic stretch is known to modify the sub-strate of atrial fibrillation (AF). However, its role on thetriggers of AF is not known.Methods: Ten (29 ± 8 years) patients with rheumatic mitralstenosis (MS) mitral valve area (MVA; 0.8 ± 0.1 cm2) hav-ing percutaneous mitral commissurotomy (MC) and tenage-matched controls undergoing ablation of left-sidedaccessory pathways (33 ± 8 years) underwent electrophys-iological study of the pulmonary veins (PV) using amulti-electrode basket catheter. We determined effectiverefractory period (ERP) and conduction time (CT) whilepacing the proximal and distal PV. Activation maps werecreated to identify regions of intra-PV conduction block(CB; ≥30 ms between adjacent bipoles) during the drivetrain (S1) and maximum pre-excited stimulus (S2).Results: Patients with MS had elevated left atrial meanpressure (31 ± 4 mmHg vs. 11 ± 5 mmHg, p = 0.04) asso-ciated with higher proximal PV but not distal PV ERPcompared to controls. CT was prolonged both during sinusrhythm (41 ± 9 ms vs. 32 ± 8 ms, p = 0.02) and during thedrive train (S1) in MS patients. Longer intra-PV CB wasobserved with distal S2 in MS patients compared to con-trols but did not differ from proximal PV. In addition,mean bipolar voltage was lower in MS (1.2 ± 0.4 mV vs.1.8 ± 0.8 mV, p = 0.04).Conclusion: Patients with MS demonstrated significantelectrical remodelling within the PV characterized chieflyby conduction delay, intra-PV CB and areas of low voltage.These abnormalities may result in circuitous activationwithin the veins contributing to triggers and maintenanceof AF.

firmed by four fluoroscopic views. Stimulation threshold,R wave sensing and bipolar lead impedance were assessedat implant, 24 h, 6 months and 1 year. Long-term follow uprate was 92%.Results: RVOT lead positioning was successful in allpatients with no significant procedural complications.Electrical parameters at implant included: mean stim-ulation threshold of 0.84 V (±0.40 V), range 0.2–2.2 V; Rwave sensing of 10.9 mV (±5.3 mV), range 3.0–24.5 mV;and impedance of 732 � (±150 �, range 350–1144 �). At24 h, the ventricular lead pacing threshold fell to a meanof 0.55 V (±0.22 V), range 0.25–1.3 V. At the 1-year follow-up, the stimulation threshold had increased to a mean of0.71 mV (±0.25 mV), range 0.25–1.50 mV (p < 0.001).Conclusion: The selection of the RVOT septum as theprimary pacing site in the majority of patients with brady-cardia indications is further supported by these resultswhich indicates that the long-term electrical performanceat this site is excellent. Long-term physiologic studies toprove if the RVOT septum is better than the RV apex arenow required.

doi:10.1016/j.hlc.2008.05.310