Abstract 2009: Matching the Transthoracic Defibrillation Vector to the Fibrillation Vector Improves Shock Success
Background: Depolarization of myocytes requires less energy when electrical current flows along the longitudinal axis compared to the transverse axis of myocytes. Since ventricular fibrillation (VF) amplitude in ECG leads reflects the functional electrical orientation of the majority of myocytes, we hypothesized that a defibrillation shock would be more effective if the shock vector was oriented along the functional electrical axis of the majority of myocytes, and this axis could be determined in real time from the relative amplitudes of the VF signal measured in three orthogonal ECG leads.
Methods: In closed-chest, anesthetized, swine (22.0 ± SE0.8 kg, n=9), a new directional defibrillation device was used to simultaneously measure the VF amplitude through three orthogonal pairs of defibrillation electrodes: anterior-posterior, lateral-lateral, and superior-inferior. VF was electrically induced and persisted for 15 seconds. During defibrillation, the device identified the electrode pair that measured the largest or smallest peak amplitudes (+ or −) within the previous 100msec through which to deliver the shock. Defibrillation success for the electrodes measuring the largest or smallest VF amplitude was evaluated by delivering four 50J shocks for VF through each of these electrode pairs (in random order). The electrode pair measuring the largest VF signal amplitude was considered to be most closely aligned with the functional VF vector.
Results: Fifty J shocks (n=37) delivered through the electrode pair measuring the largest VF signal amplitude had higher defibrillation success than 50J shocks (n=37) delivered through the electrodes measuring the smallest VF signal amplitude (62 ± 10% vs.19 ± 8%, p<0.05). Impedance and current were not different.
Conclusions: By using a directional defibrillation device which instantaneously measures the peak VF signal amplitude in three pairs of orthogonally oriented defibrillation electrodes, it is feasible to determine which set of electrodes is oriented more favorably to the functional VF vector and to direct the shock through that set of electrodes. Matching the defibrillation vector to the fibrillation vector improves shock success.