Abstract 51: Potential Gradient Fields and Earliest Post Shock Activity Following External Defibrillation of Long Duration Ventricular Fibrillation in Swine
Background: Though many studies have evaluated internal defibrillation during short duration VF (SDVF), the shock potential gradient (VV) field and activation immediately following external defibrillation of long duration VF (LDVF) has not been well studied. We tested the hypothesis that the timing of post-shock activation following LDVF is different than following SDVF and is due to shock gradient differences between shocks delivered following short and long duration VF.
Methods: In 6 pigs, 115–120 plunge needles each with 3– 6 electrodes were inserted throughout the ventricles. After the chest was closed, external defibrillation pads were placed in a left lateral to right lateral configuration. Defibrillation threshold (DFT) strength biphasic shock potentials were recorded during SDVF (20 s of VF) and LDVF (7 min of VF). A VV 3-D map was generated. Earliest activation following each shock was determined.
Results: The shock size required for defibrillation of LDVF (1660±446 stored V) was not significantly different from the SDVF DFT strength shocks (1632±429 stored V). Comparison of recorded potential distribution generated by different shocks within the same animal was similar between SDVF and LDVF shocks (R2 =0.81– 0.98) also. The time from the shock until first recorded cardiac activation was significantly longer for LDVF (3845±4511ms) than SDVF (841±1739ms) p<0.05.
Recorded potential distribution required for defibrillation is very similar between shocks delivered to animals in SDVF and LDVF.
The external defibrillation energy for LDVF is not greater than for SDVF; however, the time from the shock until first recorded activation is significantly longer.
This difference is not due to a difference in shock field and likely represents changes in the tissue physiology secondary to the ischemia of long duration VF.