Importance of Location and Timing of Electrical Stimuli in Terminating Sustained Functional Reentry in Isolated Swine Ventricular Tissues

BACKGROUND: In excitable chemical media, a spiral wave is formed by reentrant excitation around a core and normal propagation away from the core. Whether or not this applies to cardiac muscle is unknown. METHODS AND RESULTS: In six isolated swine ventricular slices, we induced sustained episodes of functional reentry with a stationary core. A train of stimuli applied away from the core (7- to 8-mm distance) and near the core (within 1.6 mm) terminated 5 of 24 and 14 of 17 episodes of reentry, respectively (P<.001). When the stimulus was applied away from the core, successful terminations occurred when the line connecting the stimulus and the core was along the myocardial fiber orientation and when the coupling interval was 54+/-11% of the reentrant cycle length. Stimulation near the core terminated reentry primarily by propagation of the stimulus-induced wave fronts that closed up the excitable gap. However, in two episodes, the application of a stimulus near the core changed the electrogram morphology in only four bipolar pairs. This was sufficient to cause abrupt termination of reentry. CONCLUSIONS: (1) A thin layer of activation near the core is responsible for the maintenance of functional reentry. (2) Access to the tissue near the core is essential for the termination of functional reentry by a point stimulus. (3) To terminate reentry with a stimulus away from the core, the stimulus must occur at certain critical coupling intervals, and the line connecting the stimulus and the core must be roughly parallel to the fiber orientation.