Periods of highly synchronous, non-reentrant endocardial activation cycles occur during long-duration ventricular fibrillation

Abstract

Periods of Highly Organized Activation During VF.

Background: Little is known about long-duration ventricular fibrillation (LDVF), lasting 1-10 minutes when resuscitation is still possible.

Methods and results: To determine global left ventricle (LV) endocardial activation during LDVF, 6 canines (9.5 ± 0.8 kg) received a 64-electrode basket catheter in the LV, a right ventricular (RV) catheter, and a 12-lead electrocardiogram (ECG). Activation sequences of 15 successive cycles after initiation and after 1, 2, 3, 5, 7, and 10 minutes of LDVF were determined. Early during VF, LV endocardial activation was complex and present throughout most (78.0 ± 9.7%) of each cycle consistent with reentry. After 3-7 minutes of LDVF in 5 animals, endocardial activation became highly synchronized and present for only a small percentage of each cycle (18.2 ± 7.7%), indicating that LV endocardial reentry was no longer present. During this synchronization, activations arose focally in Purkinje fibers and spread as large wavefronts to excite the Purkinje system followed by the subendocardial working myocardium. During this synchronization, the ECG continued to appear irregular, consistent with VF, and LV cycle length (183 ± 29 ms) was significantly different than RV cycle length (144 ± 14 ms) and significantly different than the LV cycle length when synchronization was not present (130 ± 11 ms).

Conclusion: After 3-7 minutes of LDVF, a highly organized, synchronous, focal LV endocardial activation pattern frequently occurs that is not consistent with reentry but is consistent with triggered activity or abnormal automaticity in Purkinje fibers. The ECG continues to appear irregular during this period, partially because of differences in LV and RV cycle lengths.

Figure 1

Anterior-posterior chest X-ray showing the basket electrodes in the LV as well as the RV and right atrial catheters in one animal.

Figure 2

Recordings and activation times for 15 cycles soon after the onset of VF (A) and after 5 min of VF (B). The 64 unipolar basket recordings are shown in the top of each panel with an RV unipolar recording and ECG lead II below them. Below the ECG are the V activation times for the 64 basket electrodes during the same time period with each short vertical line representing an activation. At the bottom of each panel the activations for all 64 electrodes are shown on a single line. The 15 cycles are numbered at the top of panel B. In A, endocardial activations are present throughout the cardiac cycles consistent with reentry. In B, however, activation is highly synchronized with activation present during only a small part of the cardiac cycle, so that 14 large temporal gaps are present between the 15 cycles of activation in which no activations are present. This finding is inconsistent with reentry near the LV endocardium. In both panels, RV activation and ECG lead II appear disorganized as expected for VF.

Figure 3

Mean of the 14 largest gaps in activation times during different durations of VF in each animal. The gap is expressed as the percent of the mean VF cycle length during that time interval. Each animal is represented by a different color. VF spontaneously terminated after 3 min in the animal represented by the black line and after 5 min in the animal represented by the blue line. A percent gap >60% (gray line) was considered VES.

Figure 4

VF cycle lengths during the last time interval before VES onset and during VES. Mean RV and LV cycle lengths are shown with the standard deviation indicated by an error bar. The brackets with an asterisk indicate significant differences.

Figure 5

V activation sequences for the 15 VES cycles shown in Figure 2B. Colors represent activation times of the 64 basket electrodes according to the time scale shown to the right. White indicates no activation recorded at that electrode, probably because of poor electrode contact of the basket with the endocardium. Each of the 8 pie-shaped numbered segments represents activation times from a single spline of the basket with the most apical electrode of the spline toward the center and the most basal electrode toward the periphery. The orientation of the basket within the LV is given for the top left activation map. All 15 cycles have a focal origin, but the location of the earliest activation site is not the same for all cycles. The 4 cycles in group 1 had a Spearman correlation ≥0.9 with each other as did the 4 cycles in group 2. The other 7 cycles did not have a Spearman correlation ≥0.9 with any of the other 14 cycles.

Figure 6

Examples of P activations preceding V activations during VES. Unipolar recordings with their temporal derivatives below are shown with P activations indicated by asterisks. In (A), the top tracings are from the electrode recording earliest activation during cycles 6, 7, and 8 shown in Figure 2B after 5 min of VF. In (B), the top tracings are from the electrode recording earliest activation during 3 cycles after 10 min of VF in the same heart. In both (A) and (B), the lower tracings are from electrode 28 in the LV basket.

Figure 7

P and V activation sequences for cycles 7-10 of the VES cycles shown in Figure 2B. P activations lead V activations and earliest P activations are near earliest V activations. Please see Figure 5 for explanation of the activation maps.