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The effects of ventricular fibrillation duration and site of initiation on the defibrillation threshold during early ventricular fibrillation

John S. Strobel, MD^a, Bruce H. KenKnight, PhD^{* *}, Dennis L. Rollins, MS^a, William M. Smith, PhD^a and Raymond E. Ideker, MD, PhD, FACC^{* *}

^a Department of Medicine, the University of Alabama at Birmingham, Birmingham, Alabama, USA
^* Department of Physiology, the University of Alabama at Birmingham, Birmingham, Alabama, USA
Biomedical Engineering, the University of Alabama at Birmingham, Birmingham, Alabama, USA
^* CPI/Guidant Corp., St. Paul, Minnesota, USA

View larger version (13K): [in a new window]   Figure 1 A bipolar electrogram recorded from the integrated tip of the catheter electrode demonstrates the induction of VF followed by shock delivery after five VF activation cycles. The S2 stimulus artifact is labeled S2. The time scale is shown at the bottom left.

View larger version (14K): [in a new window]   Figure 2 The mean DFT ± 1 SD for each number of VF activation cycles in protocol 1. The DFT rises sharply for shocks given after one to four VF cycles, and then more gradually for shocks given after up to 25 VF activations. An asterisk (*) signifies the DFT is significantly less at that number of VF cycles than for the control (C) DFT after 10 s of VF. The filled circles (•) represent the test DFTs. The control DFT is indicated by the open circle ().

View larger version (14K): [in a new window]   Figure 3 The mean DFT ± 1 SD for each number of VF activation cycles in protocol 2. Filled circles (•) indicate DFTs for VF initiated from the RV. Filled squares () indicate DFTs for VF initiated from the LV. The open circle () indicates the control DFT determined for shocks given after 10 s of VF. An asterisk (*) signifies that the DFT is significantly less at that number of VF cycles than for the control DFT after 10 s of VF. The right-sided DFTs were significantly less than the left-sided DFTs.