In a swine model, chest compressions cause ventricular capture and, by means of a long-short sequence, ventricular fibrillation

Abstract

Background: During resuscitation, fibrillation often recurs. In swine, we studied refibrillation after long-duration ventricular fibrillation, investigating an association with chest compressions (CCs).

Methods and results: In protocol A, 47 episodes of long-duration ventricular fibrillation lasting at least 2.5 minutes were induced in 8 animals. After defibrillation, CCs were required for 35 episodes and delivered with a pneumatic device (Lucas cardiopulmonary resuscitation). In 9 episodes, refibrillation occurred within 2 seconds of CC initiation (group 1) and in 26 episodes, CCs were delivered without refibrillation (group 2). From the ECG and intracardiac electrodes, the RR interval preceding CCs, the shortest cycle length during the first 2 CCs (short), and the preceding cycle length (long) were measured. A similar study was conducted in 3 more animals without intracardiac catheters (protocol B). In protocol A, the mean RR before CC was 665+/-292 ms in group 1 and 769+/-316 in group 2. CCs stimulated ventricular beats in all 35 episodes. The short and long intervals were shorter in group 1 (215+/-31 and 552+/-210 ms) than in group 2 (402+/-153 and 699+/-147 ms) (P=0.009 and P=0.04, respectively). The prematurity index (short/RR) was lower in group 1 than in group 2 (0.35+/-0.09 vs 0.58+/-0.21; P<0.01). A short interval <231 ms predicted refibrillation with 88% sensitivity and 91% specificity. In protocol B, CCs were required in 11 episodes, causing ventricular stimulation in all of them and ventricular fibrillation within the first 2 CCs in 3.

Conclusions: Under some conditions, CC during resuscitation can stimulate the ventricles and initiate ventricular fibrillation by a long-short sequence.

Keywords: Chest Compressions; Refibrillation; Ventricular Capture.

Figure 1

Study Design. In Protocols A and B, only the episodes of Long-Duration VF that required CCs to achieve ROSC were used in this analysis. The episodes in Protocol A were divided into Groups 1 and 2 depending on the occurrence or not of refibrillation within the first two chest Compressions. CCs: Chest Compressions; ROSC: Return of Spontaneous Circulation; VF: Ventricular Fibrillation.

Figure 2

Cardiac stimulation and VF induction by initiation of mechanical chest compressions. Panel A shows ventricular capture in a 1:1 ratio beginning with the first CC (Group 2). Panel B shows ventricular capture for the first two compressions with an interposed spontaneous depolarization associated with long and short intervals that is immediatelly followed by VF (*) (Group 1). The Short, Long and RR intervals are identified. Arrows mark each chest compression. Panels A and B show 8 s of data.

Figure 3

Intermittent ventricular capture by CCs. Panel A shows ventricular depolarizations recorded by the MAP electrode and also seen on the surface ECG closely following CCs (arrowheads) for the first 6 cycles, while no stimulation is seen with the following 5 CCs. In panel B, intermittent capture is seen in animal with no intracardiac electrodes during CCs (Protocol B); the 2^nd, 9^th, 10^th and 11^th CCs do not stimulate the ventricles, while capture is seen with the other compressions on the ECG and bipolar lead recording. The tracing labeled “Lucas device” corresponds to each CC delivered, with the ascending limb of the tracing marking compressions. Panels A and B show 8 s of data.

Figure 4

Receiver-operating-characteristic (ROC) curve for various cutoff levels of the Short interval. The cutoff level with maximum diagnostic accuracy is in bold. (CI = confidence interval)

Figure 5

Episode of refibrillation seen in animal that did not have intracardiac electrodes during CCs (Protocol B). Ventricular capture is seen with the first CCs and VF arises after the second CC is delivered. The tracing labeled “Lucas device” corresponds to each CC delivered, with the ascending limb of the tracing marking compressions. Figure shows 8 s of data.

Figure 6

Refibrillation arising 42 seconds after initiation of chest compression. Figure shows 8 s of data.