implantation in the two groups were as shown in the table below. All thepatients in DFT class 4 had subcutaneous array implanted successfullyachieving safety margin. By multivariate analysis DCM was found to be anindependent predictor of poor defibrillation thresholds (�21J, DFT class 3and above).Conclusion: Patients with dilated cardiomyopathy have higher defibrilla-tion thresholds than ischemic cardiomyopathy.

AB2-4

MAGNETICALLY ASSISTED BIVENTRICULAR DEVICEIMPLANTATION: COMPARISON USING A STANDARDGUIDESHEATH OR A “BARE” WIRE APPROACH WITHOUT AGUIDESHEATH*Peter L. Gallagher, MD, Laura Martin, RN, Lori Angel, RN,Aaron Hesselson, MD and *Gery Tomassoni, MD. CentralBaptist Hospital, Lexington, KY.

Background: Biventricular (BiV) devices have been shown to significantlybenefit patients with electro-mechanical dyssynchrony and severe heart failure.The implantation of BiV devices remains technically challenging and theselection of lateral coronary sinus (CS) branch vessels can be time consuming.This study is the first to evaluate the initial experience using magnetic navi-gation and a magnetic guidewire in the implantation of BiV devices usingeither a traditional CS guidesheath or a “bare” wire (no CS guidesheath).Methods: 50 patients (67 � 17 years) with an ejection fraction (21 � 6%),ischemic CHF (82%) and non-ischemic CHF (18%). The CS was accessedwith an AL-2 guide catheter. A tear-away CS sheath was placed in 70%and a 0.014” magnet-tipped guidewire (Stereotaxis Inc.) was directlyintroduced into the distal CS in 30% (“bare” wire). When a “bare” wire wasplaced, the OTW CS lead was advanced directly into the CS without CSsheath support. The lead and wire were retracted to the proximal CS; novenography was performed. When a guidesheath was used, venographywas performed in 50% of the cases. When no venography was performed,a lateral magnetic vector was placed on the 0.014” wire and manually“probed” until the best lateral vessel was selected.Results: CS leads were placed in all patients. The CS lead locations wereantero-lateral (14%), mid-lateral (46%) and postero-lateral (40%). Themean procedure time with a guidesheath was 103 � 32 min and 84 � 18min without a guidesheath (p�0.029). The mean lead positioning time witha guidesheath was 20 � 9 min and 10 � 4 min without a guidesheath(p�0.001). The mean fluoroscopy time with a guidesheath was 28 � 16min and 13 � 4 min without a guidesheath (p�0.0007). The mean numberof wires used per case was 1.06.Conclusions: The use of Magnetic navigation and the “bare” wire, noguidesheath approach to the placement of CS leads is associated with asignificant reduction in procedure time, lead placement time and fluoros-copy time. Further improvements in magnetic guidewire and lead technol-ogy will continue to reduce the technical challenges of CS lead placement.

AB2-5

CT GUIDANCE FOR PERCUTANEOUS, TRANS-THORACICPLACEMENT OF LEFT VENTRICULAR PACING LEADSTimm-Michael Dickfeld, MD, PhD, Ronald Berger, MD,PhD, Saman Nazarian, MD, Hugh Calkins, MD, Henry R.Halperin, MD and Stephen Solomon. Johns HopkinsHospital, Baltimore, MD.

Background: Cardiac resynchronization therapy (CRT) has been shown toimprove morbidity and mortality in patients with chronic heart failure.However, in some patients placement of the left ventricular (LV) lead viathe coronary sinus can be challenging and requires more aggressive sur-gical approaches. This study sought to evaluate the feasibility of CT-guidedpercutaneous trans-thoracic placement of LV leads.Methods: 45-50kg swine (n�4) were placed in a CT scanner with real-timecapabilities and underwent cardiac imaging to define the safest percutane-ous access strategy. Under CT guidance a 17G needle was advanced froma left antero-lateral approach to the LV epicardium and placed tangentially

in the myocardium. A 3.5F active fixation pacing lead was advancedthrough the introducer needle and fixated in the myocardium under directvisualization. After the needle was removed pacing thresholds, R-waveamplitudes, and pacing impedance were assessed repeatedly. Post-mortemin-situ pathology was compared to real-time images.Results: CT successfully defined the safest percutaneous access route in all7/7 lead placements and no pneumothorax or intrathoracic hematoma wasobserved. CT was successfully used to direct the percutaneous needle to theLV epicardium and successful placement of the pacing lead in the myo-cardium was achieved in all 7 cases. Lead thresholds were 2.5�1.5mV,R-waves 11.0�5.6 V, impedance 686�108 mV, impedance 521�49ohms. While no cardiac complications was observed with tangential leadplacement in the myocardium (6/7), a perpendicular approach was at-tempted in 1/7 experiments resulting in a pericardial effusion requiringpericardioscentesis. At autopsy CT images correlated well with the in-situpathological results.Conclusion: Percutaneous placement of LV pacing leads under CT guid-ance is feasible and might offer in alternative to more invasive surgicalapproaches in patients with complicated LV lead placement.

AB2-6

ICD-IMPLANTATION IN INFANTS AND SMALL CHILDREN:THE EXTRACARDIAC TECHNIQUEThomas Kriebel, MD, Matthias Sigler, MD, Maja Kroll, MD,Wolfgang Ruschewski, MD and Thomas Paul, MD. Georg-August-University, Gottingen, Germany.

Introduction: There is no standard approach for the implantation of aninternal cardioverter-defibrillator (ICD) in infants and small children. De-spite technological advancements, implantation of transvenous systems isnot feasable in infants and small children. Epicardial patch electrodes, asused often in the past, are associated with extensive trauma and highdefibrillation thresholds.Patients and Methods: Since July 2004 an extracardiac ICD-system wasimplanted in 4 patients (age: 6 months-6 years; body weigt: 5-25 kg).Indications included Long-QT syndrome after successful resuscitation in 3patients and ventricular tachycardia with recurrent syncopes in one patient.Under fluoroscopic guidance a transvenous defibrillator lead (MedtronicTransvene 6937 SN, 35 cm) was tunneled starting from the anterior axillarline in a subscapular fashion along the course of the 6th rib until almostreaching the vertebral column. After a partial inferior sternotomy, bipolarsteroid-eluting sensing and pacing leads (Capsure Epi 4968, 25 cm) weresutured to the atrial wall (n�1) and to the anterior wall of the rightventricle (n�4). The ICD (Marquis DR 7274) was implanted as “activecan” in the right upper abdomen (see figure). Sensing, pacing, defibrillationthreshold (DFT) and impedance were verified intraoperativly.Results: In 3 of the 4 patients intraoperative DFT (between subcutaneouslead and device) was � 15 J. In one patient DFT exceeded 20 J requiringrevision of the system. Up to now, an appropriate ICD discharge was notedin one patient.Conclusions: In infants and small children an extracardiac ICD-system istechnically feasible. Experience is still limited. The course of the DFT isunknown facing further growth of the patients.

S4 Heart Rhythm, Vol 2, No 5, May Supplement 2005