Distribution of excitation frequencies on the epicardial and endocardial surfaces of fibrillating ventricular wall of the sheep heart

Tissue heterogeneities may play an important role in the mechanism of ventr icular tachycardia (VT) and fibrillation (VF) and can lead to a complex spa tial distribution of excitation frequencies. Here we used optical mapping a nd Fourier analysis to determine the distribution of excitation frequencies in >20 000 sites of fibrillating ventricular tissue. Our objective was to use such a distribution as a tool to quantify the degree of organization du ring VF. Fourteen episodes of VT/VF were induced via rapid pacing in 9 isol ated, coronary perfused, and superfused sheep Ventricular slabs (3x3 cm(2)) . A dual-camera video-imaging system was used for simultaneous optical reco rdings from the entire epi-and endocardial surfaces. The local frequencies of excitation were determined at each pixel and displayed as dominant frequ ency (DF) maps. A typical DF map consisted nf several (8.2+/-3.6) discrete arms (domains) with a uniform DF within each domain. The DFs in adjacent do mains were often in 1:2, 3:4, or 4:5 ratios, which was shown to be a result of an intermittent Wenckebach-like conduction block at the domain boundari es. The domain patterns were relatively stable and could persist from sever al seconds to several minutes. The complexity in the organization of the do mains, the number of domains, and the dispersion of frequencies increased w ith the rate of the arrhythmia. Domain patterns on the epicardial and endoc ardial surfaces were not correlated. Sustained epicardial or endocardial re entry was observed in only 3 episodes. Observed frequency patterns during V T/VF suggest that the underlying mechanism may be a sustained intramural re entrant source interacting with tissue heterogeneities.