Mapping of refractory periods with voltage-sensitive dyes

Spatial heterogeneities in refractory period (RP) have been invoked to explain the genesis of re-entrant a arrhythmias. Numerous studies have demonstrated that a conduction block can arise in regions with spatial heterogeneities of RPs, which can lead to wavefront fractionation and reentry. However, conventional techniques do not provide maps of repolarization and/or RPs with sufficient spatial and temporal resolution. RPs measured by extra-stimuli (S₁-S₂) and multiple surface electrograms require that the extra-stimulus be applied at the recording site and this must be repeated for every site on the map (ie., poor temporal resolution). Suction electrodes damage the tissue and as with intracellular microelectrodes are not practical for mapping. Signal processing techniques have been used to estimate RPs using unipolar electrograms by correlating (dV/dt)_max near the peak of T-wave to repolarization of the local AP. It has been suggested that RPs correlate with (dV/dt)_max of T-waves. However, this empirical correlation was not reliable because it was strongly dependent on the polarity of the T-wave and failed for multiphasic T-waves. In addition, it is still difficult to obtain T-waves with sufficiently reliable amplitudes and kinetics to predict RPs.