Stimulus-induced critical point. Mechanism for electrical initiation of reentry in normal canine myocardium.

Abstract

The hypothesis was tested that the field of a premature (S2) stimulus, interacting with relatively refractory tissue, can create unidirectional block and reentry in the absence of nonuniform dispersion of recovery. Simultaneous recordings from a small region of normal right ventricular (RV) myocardium were made from 117 to 120 transmural or epicardial electrodes in 14 dogs. SI pacing from a row of electrodes on one side of the mapped area generated parallel activation isochrones followed by uniform parallel isorecovery lines. Cathodal S2 shocks of 25 to 250 V lasting 3 ms were delivered from a mesh electrode along one side of the mapped area to scan the recovery period, creating isogradient electric field lines perpendicular to the isorecovery lines. Circus reentry was created following S2 stimulation; initial conduction was distant from the S2 site and spread towards more refractory tissue. Reentry was clockwise for right S1 (near the septum) with top S2 (near the pulmonary valve) and for left SI with bottom S2; and counterclockwise for right S1 with bottom S2 and left SI with top S2. The center of the reentrant circuit for all S2 voltages and coupling intervals occurred at potential gradients of 5.1±0.6 V/cm (mean±standard deviation) and at preshock intervals 1±3 ms longer than refractory periods determined locally for a 2 mA stimulus. Thus, when S2 field strengths and tissue refractoriness are uniformally dispersed at an angle to each other, circus reentry occurs around a "critical point" where an S2 field of -

Vulnerability to ventricular fibrillation

“…This ''reentrant'' activity was possible because of the inhomogeneity in excitability that existed for a brief moment and was ''unmasked'' by the special stimulation protocol. Similar results have later been obtained ͑but with a single very strong stimulus͒ in intact hearts 12 and in isolated thin preparations of dog and sheep cardiac muscle, 13 where unidirectional block and reentry were induced by a similar stimulation pattern. ͑For an excellent description of the basic characteristics of reentry the reader is referred to the article by Gray and Jalife, appearing in this volume.͒ 14 A key requirement for the induction of reentry is the presence of unidirectional block.…”

Mechanisms of defibrillation

“…These considerations led to the ULV hypothesis, which states that for a shock to successfully terminate VF, it must alter the transmembrane potential throughout the myocardium in such a way that the wavefronts of VF are halted, yet new wavefronts that can reinitiate VF are not induced (69). These realizations led to the development of the critical point theory of defibrillation, which suggested that reentry was initiated at the intersection of critical points of local field strength and tissue with critical levels of recovery (68,71).…”

“…In many of the optical and electrical mapping studies that have attempted to determine the mechanism by which shocks give rise to action potentials that reinitiate VF, the shocks were not given during VF but during phase 2 or phase 3 of the action potential of paced rhythm (54,(71)(72)(73)(74). These shocks were observed to induce reentry that degenerated into VF by the creation of a critical point (Figure 12).…”

Meandering Spiral Waves in the 1,4-Cyclohexanedione Belousov−Zhabotinsky System Catalyzed by Fe[batho(SO3)2]34-/3-

“…11,12 Different meandering spiral patterns are also found in a RD model of flames. 13 Although some deviations from circular cores have been reported for yeast extracts 14 and neural tissue, 15,16 systematic experiments on noncircular tip trajectories are limited to the BZ reaction. In this system, tip trajectories can follow circles, hypocycles (outwardly pointing petals), epicycles (inwardly pointing petals), or a special kind of trochoid called prolate cycloid with lobes along a straight line.…”

“…23 Experimental evidence for this behavior is meager and limited to investigations of highly anisotropic heart muscles using multiple electrode mapping techniques. 15,16 However, these experiments lacked the necessary resolution to yield detailed tip trajectories.…”