Studying semblances of a true killer: experimental model of human ventricular fibrillation

Abstract

It is unknown whether ventricular fibrillation (VF) studied in experimental models represents in vivo human VF. First, we examined closed chest in vivo VF induced at defibrillation threshold testing (DFT) in four patients with ischemic cardiomyopathy pretransplantation. We examined VF in these same four hearts in an ex vivo human Langendorff posttransplantation. VF from DFT was compared with VF from the electrodes from a similar region in the right ventricular endocardium in the Langendorff using two parameters: the scale distribution width (extracted from continuous wavelet transform) and VF mean cycle length (CL). In a second substudy group where multielectrode phase mapping could be performed, we examined early VF intraoperatively (in vivo open chest condition) in three patients with left ventricular cardiomyopathy. We investigated early VF in the hearts of three patients in an ex vivo Langendorff and compared findings with intraoperative VF using two metrics: dominant frequency (DF) assessed by the Welch periodogram and the number of phase singularities (lasting >480 ms). Wavelet analysis (P = 0.9) and VF CL were similar between the Langendorff and the DFT groups (225 ± 13, 218 ± 24 ms; P = 0.9), indicating that wave characteristics and activation rate of VF was comparable between the two models. Intraoperative DF was slower but comparable with the Langendorff DF over the endocardium (4.6 ± 0.1, 5.0 ± 0.4 Hz; P = 0.9) and the epicardium (4.5 ± 0.2, 5.2 ± 0.4 Hz; P = 0.9). Endocardial phase singularity number (9.6 ± 5, 12.1 ± 1; P = 0.6) was lesser in number but comparable between in vivo and ex vivo VF. VF dynamics in the limited experimental human studies approximates human in vivo VF.

Fig. 1.

A: image of endocardial electrode arrays for the left ventricle. The endocardial array is made of 112 bipolar electrodes stitched on the exterior surface of an extensible balloon. Each endocardial electrode consists of two silver beads (2 mm diameter) separated by 2.1 mm center to center. B: image of the epicardial sock electrode array made of 112 bipolar electrodes organized in 14 rows of 8 electrodes each, mounted on an extensible mesh.

Fig. 2.

Top: typical human ventricular fibrillation (VF) electrograms and different scaled versions of a mother wavelet. These different scaled versions of the mother wavelet are combined in different proportions to model the signal. The resulting wavelet decomposition will distribute the signal energy proportionately to different wavelet scales depending upon their contribution in modeling the signal. Bottom: an example of energy distribution over scale and the measurement of scale distribution width (SDW).