Purkinje activation precedes myocardial activation following defibrillation after long-duration ventricular fibrillation

Abstract

Background: While reentry within the ventricular myocardium (VM) is responsible for the maintenance of short-duration ventricular fibrillation (SDVF; VF duration <1 minute), Purkinje fibers (PFs) are important in the maintenance of long-duration ventricular fibrillation (LDVF; VF duration >1 minute).

Objective: The purpose of this study was to test the hypothesis that the mechanisms of defibrillation may also be different for SDVF and LDVF.

Methods: A multielectrode basket catheter was deployed in the left ventricle of eight beagles. External defibrillation shocks were delivered with a ramp-up protocol after SDVF (20 seconds) and LDVF (150 seconds). Earliest VM and PF activations were identified after the highest energy shock that failed to terminate VF and the successful shock.

Results: Defibrillation was successful after 36 +/- 12 and 181 +/- 14 seconds for SDVF and LDVF, respectively. The time after shock delivery until earliest activation was detected for failed shocks and was significantly longer after LDVF (138.7 +/- 24.1 ms) than after SDVF (75.6 +/- 8.7 ms). Earliest postshock activation after SDVF typically initiated in the VM (14 of 16 episodes), while it always initiated in the PF (16 of 16 episodes) after LDVF. Sites of earliest activity during sinus rhythm correlated with sites of earliest postshock activation for PF-led cycles but not for VM-led cycles.

Conclusion: Earliest recorded postshock activation is in the Purkinje system after LDVF but not after SDVF. This difference raises the possibility that the optimal defibrillation strategy is different for SDVF and LDVF.

Figure 1

A) Fluoroscopic image of a lateral view of the LV basket catheter and the RV catheter used for VF induction. B) Display of the basket orientation in the LV: 1 = anterior free wall, 3 = lateral free wall, 5 = posterior free wall, 7 = septum. Apical electrodes are towards the center of the display (a) and basal electrodes are towards the periphery (h). C) For statistical analysis, first activation locations during sinus rhythm and during the first postshock activation cycle following shocks were grouped into regions i-viii.

Figure 2

DFTs for the 3 different protocols. Mean values are shown above the standard deviation bars. Brackets indicate paired t-tests performed and the p-values are shown above the brackets.

Figure 3

Electrograms from the site of earliest recorded postshock for A) normal sinus rhythm, B) a SDVF Type A success, C) a SDVF Type B success, D) a LDVF success, E) a SDVF failure, and F) a LDVF failure. In each panel, the top left trace is the unipolar electrogram at the site of earliest activity, and the lower left trace is its temporal derivative. A time-expanded section of the first activation enclosed in the box is shown for an adjacent bipolar electrogram and its derivative. PF activations are marked with black arrows while VM activations are marked with white-filled arrows. Vertical gray lines in Panels B through F mark the timing of the shock and the timing of the gain switch (from low gain to high gain) of the mapping system.

Figure 4

The 64 unipolar basket electrograms for the same shock episodes shown in Fig. 3. The trace order is the same as in Fig. 1B (1a at the top, 8h at the bottom). The spline number for each group of traces is shown in Panel A. Electrograms are shown for the first second following the shock.

Figure 5

Times of PF (red) and VM (blue) activations during the same shock episodes as shown in Fig. 3-4. The trace order is the same as in Fig. 1B (1a at the top, 8h at the bottom). Panels AF are for the same episodes shown in Fig. 3 and 4.

Figure 6

Activation maps showing PF (left diagram in each panel) and VM (right diagram in each panel) activation times of the first postshock cycle for the shock episodes shown in Figures 2-4. Activation times are indicated by the color bar. White indicates that no activation was detected at that electrode. Gray stars indicate the site of earliest activation in each panel.

Figure 7

Locations of earliest recorded postshock activation for all 8 animals in A) PF-led sinus rhythm, B) PF-led first postshock activation cycles, and C) VM-led first postshock activation cycles. For statistical analysis, first postshock activation cycles were grouped as shown in Fig. 1C.