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(Circulation. 1999;99:1516-1522.)
© 1999 American Heart Association, Inc.

Basic Science Reports

Effect of Biphasic Shock Duration on Defibrillation Threshold With Different Electrode Configurations and Phase 2 Capacitances

Prediction by Upper-Limit-of-Vulnerability Determination

Patrick N. Schauerte, MD; Kathrin Ziegert, MD; Matthias Waldmann, BSE; Friedrich A. Schöndube, MD; Frank Birkenhauer, BSE; Karl Mischke, BSE; Marius Grossmann, MD; Peter Hanrath, MD; Christoph Stellbrink, MD

From the University of Technology, Department of Cardiology (P.N.S., K.Z., M.W., F.B., K.M., P.H., C.S.) and Department of Cardiovascular Surgery (F.A.S., M.G.), Aachen, Germany.

Correspondence to Dr Patrick N. Schauerte, Cardiovascular Section, Department of Internal Medicine, University of Oklahoma Health Sciences Center, D.V.A. Medical Center/Research Service 151-F, 921 NE 13th St, Oklahoma City, OK 73104. E-mail Patrick-Schauerte{at}ouhsc.edu

Background—The defibrillation threshold (DFT) may be affected by biphasic shock duration (BSD), electrode configuration, and capacitance. The upper limit of vulnerability (ULV) may be used to estimate the DFT. For different lead configurations and phase 2 capacitances, we investigated in 18 pigs whether the use of ULV may predict waveforms with lowest DFT.

Methods and Results—DFT and ULV were determined by up-down protocols for 10 BSDs. ULVs were measured by T-wave scanning during ventricular pacing (cycle length 500 ms). In protocol 1 (n=6), a pectoral "active can" was combined with an electrode in the superior vena cava as common cathode and a right ventricle electrode as anode (AC+SVC). In protocol 2 and protocol 3 (n=6 each), only the "active can" was used as proximal electrode (AC). Capacitance was 150 µF during both phases in protocol 1 and protocol 3 but 150 µF (phase 1) and 300 µF (phase 2) in protocol 2. ULV and DFT demonstrated a linear correlation in each protocol (r=0.78 to 0.84). Lowest DFTs were found at 10 ms for AC+SVC and at 14 ms for AC (P<0.001). At optimal BSDs, voltage DFTs did not differ significantly between AC (527±57 V) and AC+SVC (520±70 V). Switching capacitors for phase 2 in a way that reduced leading-edge voltage by 50% while doubling capacity did not change BSD for optimal voltage DFT but increased minimum DFT from 527±57 V to 653±133 V (P=0.04).

Conclusions—The BSD with lowest DFT is shorter for AC+SVC than for AC. There is no significant difference in voltage DFT between both at optimal BSD. A lower phase 2 capacitance reduces DFTs irrespective of BSD. Because strength-duration curves for DFT and ULV correlate for different BSDs, lead systems, and phase 2 capacitances, ULV determination may allow the prediction of waveforms with lowest DFT.

Key Words: defibrillation • fibrillation • waves