Selecting the transthoracic defibrillation shock directional vector based on VF amplitude improves shock success.

Introduction: Termination of ventricular fibrillation (VF) by a defibrillating shock is more likely to occur when the VF amplitude is larger. We hypothesized that a defibrillation shock would achieve higher success if the shock vector was oriented along the largest of the VF amplitudes measured simultaneously in 3 orthogonal ECG leads, and that this axis could be determined near-instantaneously in real time.

Methods And Results: In 9 closed-chest anesthetized swine, a new directional defibrillation (DD) device was used to simultaneously measure the VF peak amplitudes displayed by 3 orthogonal pairs of defibrillation electrodes: anterior-posterior, lateral-lateral, and superior-inferior. Four shocks at each of 3 energy levels (30 Joules [J], 50 J, and 100 J) were delivered through the electrode pair measuring the largest (LA) and smallest (SA) VF peak amplitude at the time of the shock. The odds of shock success (VF termination followed by a perfusing rhythm) were 5 times more likely when shocks were delivered from the LA electrodes than the SA electrodes (odds ratio 5.10, 95% CI: 1.39, 18.79). At the intermediate energy level of 50 J, shocks delivered through the LA electrode pairs had an almost 9 times higher odds of shock success than 50 J shocks delivered through the SA electrode pairs (68.3% vs 18.9%, P = 0.002) (odds ratio 8.94, 95% CI: 2.59, 30.82). Transthoracic impedance and current did not differ for shocks delivered in the LA versus SA groups.

Conclusion: Choosing the defibrillation directional vector based on the largest VF amplitude improved shock success.