The distribution of refractory periods influences the dynamics of ventricular fibrillation

The spatial and dynamic properties of ventricular fibrillation (VF) may be random or related to cellular electrical properties of the normal heart. Lo cal activation intervals (AIs) in VF may depend on the local refractory per iod (RP). and sustained VF may require a steep action potential (AP) restit ution curve. In guinea pig hearts, AP durations (APDs) and RPs on the epica rdium are shorter at the apex and progressively longer toward the base, pro ducing gradients of RPs that may influence the spatial organization of VF. In the present study, the influence of APDs on VF dynamics is investigated in perfused guinea pig hearts stained with a voltage-sensitive dye by compa ring APD gradients to the dynamics of VF elicited by burst pacing. In VF, A Is had no clear periodicity, but average AIs were shorter at the apex (57.5 +/-8.1 ms) than the base (76.1+/-1.5 ms, n=6, P<0.05) and had gradients sim ilar to APD gradients (correlation coefficient 0.71+/-0.04). Analysis of lo cal velocity vectors showed no preferential directions, and fast Fourier tr ansform (FFT) power spectra were broad (10 to 24 Hz) with multiple peaks (n =6). However, the selective inhibition of delayed K+ rectifying currents, I -Kr (EA031; 0.5 <mu>mol/L, n=3), shifted FFT spectra from complex to a lowe r dominant frequency (10 Hz) and altered repolarization but retained the co rrelation between mean AIs and RPs. Thus, VF dynamics are consistent with a multiple wave-make and wave-break mechanism, and the local RP influences V F dynamics by limiting the range of VF frequencies and AIs at each site. Th e full text of this article is available at http://www.circresaha.org.