Quatrefoil reentry in myocardium: An optical imaging study of the induction mechanism

Quatrefoil Reentry in Myocardium. Introduction: The "critical point hypothe sis" for induction of ventricular fibrillation has previously been extended to infer the coexistence of four critical points, and hence four simultane ous spiral reentries or a quatrefoil reentry, resulting from only one prema ture stimulus delivered to the same location as the pacing stimulus, An opt ical imaging technique was used to explore its existence and to study the i nduction mechanism of this peculiar reentry pattern. Methods ana Results : In 16 isolated, Langendorff-perfused rabbit hearts, h igh-speed optical imaging at 133 or 267 frames/sec was performed to observe the induced response with a unipolar point electrode, A novel quatrefoil-s haped reentry pattern consisting of two pairs of opposing rotors was create d by delivering long stimuli during the vulnerable phase. Successful induct ion occurred in a narrow range of coupling intervals. A dogbone pattern of virtual electrodes was established during the premature stimulus. Propagati ng wavefronts launched from the virtual anodes immediately after the termin ation of S2, The alternating blocking and conducting effects of the virtual electrodes, as well as the boundary between virtual cathode and virtual an ode, provided the necessary pathways for quatrefoil reentry. Propagation di rections of the reentrant spiral wavefronts reversed with a reversal in S2 polarity. Quatrefoil reentries were not sustained and lasted 1 to 4 complet e cycles. Conclusion : The initiation of quatrefoil reentry followed anodal or cathod al-break stimulation as a result of local symmetrical enhancement of the di spersion of tissue excitability, The "critical point hypothesis" provides t he minimum topology required for this type of reentry; the "graded response hypothesis" can be viewed as providing a more detailed explanation of how this topology is actually realized. Triggering mechanisms due to the "break " mode of stimulation also posits a new mechanism for defibrillation.