Volume 124

Number 3 Symposium abstracts 939

OPTIMIZING THE SUBCUTANEOUS ELEC- TRODE OF A NEW NONTHORACOTOM-Y LEAD SYSTEM IN PIGS. Bruce H. KenKnight, David K. Swanson, Roger W. Dahl, John E. Heil, Stephen J. Hahn. CPI, 4100 Hamline Ave., St. Paul, MN 55112, U.S.A.

To investigate the impact of element (E) number and interelement spacing of a multi-E sub- cutaneous electrode (SQE), we determined acute defibrillation strength requirements (DSR) in pigs (n=B, 30-40 kg) for three electrode configurations employing different left thoracic S&Es: 4-E at 2cm spacing (4N); 2-E at 2cm (2N2); 2-E at Bern (2W). Defibrillation catheters (3.4cm ) were positioned in RV 8nd SVC. Results were obtained by giving biphasic shocks (RV -+ SVC+SQE) and later con- structing sigmoidal defibrillation probability curves (DPC) for energy delivered (E), peak voltage (V) and peak current (I). DPC mid-points, E50, V50, and 150, were extracted, averaged, and compared. Data are mean&SD.

SQE E50(J) V5O(V) 150(A) W)

4N 9.7&2.8 328f49 10.4&1.6 32*2 2w ll.lf2.8 353&42 10.8M.9 33&2 2N 10.0+2.5 333f40 10.0*1.0 33+3

There were no significant differences amongst DSR or Z for S&Es constructed from 4 or ‘L-elements, either narrowly or widely spaced in pigs.

ABSOLUTE VENTRXXLAR FIBRILLATION VOLTAGE AND PATCH-TO-PATCH IMPED- ANCE ARE ASSOCIATED WITH SUCCESSFUL DEFIBRILLATION DURING FIXED LOW ENERGY DC SHOCKS. Penn-Wie E. Hsia. Kathv F. Kuelc. Robert M. Wise, Rehan Mah’mud, and Ralph ‘J. Damiano. Surgery and Biomedical Engineering Program, S-015 Sanger Hall, Medical College of Virginia, Richmond, VA 23288-068, U.S.A.

At higher absolute ventricular fibrillation vol- tages (AVFV) the heart may be more vulnerable to defibrillation. This study investigated in a canine model whether voltage integration I) of the AVFV and patch-to-patch impedance defibrillation success. The Lead h

\ PP ) could predict IAVFV was eom-

puted over various sample sizes including 1, 4, 8, 16, 32, 64 & 128 me immediately prior to the DC shock (DCS). Fibrillation was induced and a truncated exponential shock wan delivered through a pair of epicardial patches. For each of a total 84 DCS

L4 40% successes, 60% failures) delivered energy,

VFV, and PPI immediately prior to the- DCS were analyzed. If all trials were included, delivered energy (4.3*2.3 vs. 4.0*2.1 joules, p=NS) was similar for successful (S) or unsuccessful (US) DCS. However, the L4VFV over all window sizes except 32 ms were greater for S as compared to US attempts (1 ms: 0.30*.25 vs. 0.20+.14 mV p<.O15, 4 ms: 0.30M.24 vs. O.lOM.15 p<.O14, 8 ms: 0.29fl.24 vs. 0.19fo.14 p<.O13, etc. . Patch-to-patch impedance was lower in S versus t S DCS (72.3 Il.4 vs. 77.9 f 1.2 ohms, p<.OO4). Higher values of IAVFV are associated with successful DC shocks.

n ATRIAL CARDIOVl3RSION

EVALUATION OF A SHEEP MODEL OF ATRIAL FIBRILLATION. Gregory M. Ayers, Clif A. Alferness, Marina I. Ilina, Darrell 0. Wagner, and Paul Kreyenhagen. InControl, Inc., 6675 185th Ave. NE, Ste 100, Redmond, WA 98052, U.S.A.

The goal of this study was to measure the hemodynamic and electrical characteristics of an animal model of atria1 fibrillation (AF). We com- pared the R-R intervals in six sheep during sinus rhythm SR) and AF. AF was induced with 60 Hz current 6 elivered to the atria1 epicardium. 100 beat electrograms as well as femoral arterial blood pres- sure (BP) were obtained during SR and AF. The R-R mterval and corresponding BP parameters were analyzed. Data from all animals were pooled for comparison of SR to AF. We found the mean R-R interval was 560*1.7 msec (1 s.d.) for SR and was 438f84.8 msec for AF. During AF, many of the ventricular depolarizations do not result in produc- tive contractions as evidenced by BP pulses. We found that 62.6% of ventricular depolarizations produced a measurable BP. The mean interval between productive beats was 704f268 msec for AF. The heart rates seen in these animals in NSR and AF were similar to those previously reported for humans. There appears to be a substantial negative hemodynamic effect of AF on perfusion pressures. This compromise may result in the mor- bidity associated with AF and may justify the need for rapid treatment with electric counter-shock.

CARDIOVERSION OF ATRLAL FIBRILLATION IN SHEEP. Randolph A. S. Cooper, Clif A. Alferness, William M. Smith, and Raymond E. Ideker. Box 3140 Duke University Medical Center, Durham, NC, 27710, U.S.A.

We studied cardioversion in a sheep model of atria1 fibrillation (AF) induced by rapid atria1 pac- ing. In 6 sheep, 3 mternal lead systems--ri

t ht atria1

appendage to left \

RA) to distal coronary sinus pu monary artery (LPA ,

Rl

CS), R.A and RA to

CS+LPA--were compared to a catheter elec- trode to left chest patch system. Four truncated exponential waveforms were tested with each lead system: 6 ms and 12 ms monophasic pulses, and 3/3 ms (3B) and 6/6 ms single capacitor biphasic pulses. The 3 internal lead systems had lower cardioversion requirements than the catheter to patch system. In 6 other sheep a left to right lead system RA to CS

LA LR) was compared to a totally right sided system

to SVC (RR). Eight waveforms were tested: 1.5 ms, 3 ms, 4.5 me, and 6 ma monophasic; 1.5/1.5 ms, 313 ms, 4.514.5 ms, and 6/6 ms biphasic. For all waveforms the LR configuration had lower cardi- oversion requirements than the RR configuration. The 3B waveform with the LR lead system for both groups of sheep had the lowest cardioveraion requirements with a mean 80% successful energy requirement of 1.5M.4 joules.