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High dispersion of ventricular repolarization after an implantable defibrillator shock predicts induction of ventricular fibrillation as well as unsuccessful defibrillation

Jean B. Moubarak, MD^* , Pamela E. Karasik, MD^* , Ross D. Fletcher, MD, FACC^* and Michael R. Franz, MD, PhD, FACC^*

^* Veterans Administration, Washington, DC, USA
Georgetown University Medical Center, Washington, DC, USA. / %

View larger version (28K): [in a new window]   Figure 1 Measurements of the dispersion of repolarization (DR) between the right ventricular outflow tract (RVOT) and the right ventricular apex (RVA) following an electrical shock. Simultaneous recordings of the surface electrocardiogram (ECG), the monophasic action potential (MAP) in the RVOT and the MAP in the RVA. The coupling interval (CI) is the time between the upstroke of the MAP and the shock artifact. The post-shock repolarization time (PSRT) is the time between the shock artifact and the full repolarization following the shock. Post-shock DR (PSDR) is the difference between the PSRTs in the RVOT and RVA (time between the two dashed lines). This is an example of a successful induction of ventricular fibrillation (VF) by a T wave shock. Post-shock repolarization time in the RVA is 180 ms; PSRT in the RVOT is 90 ms. PSDR is 90 ms and is followed by VF.

View larger version (22K): [in a new window]   Figure 2 Simultaneous recordings of the electrocardiogram (ECG) and the monophasic action potential (MAPs) in the right ventricular outflow tract (RVOT) and right ventricular apex (RVA) during failed induction of ventricular fibrillation (VF). Post-shock repolarization time (PSRT) is 110 ms in the RVOT; PSRT is 95 ms in the RVA. The post-shock dispersion repolarization (PSDR) is 15 ms. The T wave shock generated one ventricular beat with no VF induction.

View larger version (21K): [in a new window]   Figure 3 Simultaneous recordings of the ECG and the MAPs in the RVOT and RVA during successful internal defibrillation shock delivered by the implantable cardioverter defibrillator (ICD). The PSRT in the RVOT is 205 ms; the PSRT in the RVA is 200 ms. The PSDR is 5 ms with termination of VF. Abbreviations as in Figure 1.

View larger version (21K): [in a new window]   Figure 4 Simultaneous recordings of the ECG and the MAPs in the RVOT and RVA during failed internal defibrillation shock delivered by the implantable cardioverter defibrillator (ICD). The PSRT in the RVOT is 125 ms; the PSRT in the RVA is 210 ms. The PSDR is 85 ms. The VF persisted following the shock. Abbreviations as in Figure 1.

View larger version (18K): [in a new window]   Figure 5 Post-shock repolarization time (PSDR) expressed as mean ± standard error. Left: the PSDR generated by T wave shocks which induced ventricular fibrillation (VF) is significantly higher than the PSDR generated by T wave shocks which failed to induce VF. Right: the PSDR generated by the internal defibrillation shocks that failed to terminate VF is significantly higher than the PSDR generated by the successful defibrillation shocks.