OPTICAL MAPPING OF REPOLARIZATION AND REFRACTORINESS FROM INTACT HEARTS

Background Heterogeneities of repolarization (R) across the myocardium have been invoked to explain most reentrant arrhythmias. The measurem ent of refractory periods (RPs) has been widely used to assess R, but conventional electrode and extrastimulus mapping techniques have not p rovided reliable maps of RPs. Methods and Results Guinea pig hearts we re stained with a voltage-sensitive dye to measure fluorescence (F) ac tion potentials (APs) from 124 sites with a photodiode array. AP durat ion (APD) was defined as the time between depolarization (dF/dt)(max) and R time points (ie, the time when AP returns to baseline or some pe rcent thereof). However, R time points are difficult to determine beca use AP downstrokes are often encumbered by drifting baselines and moti on artifacts, which make this definition ambiguous. In optical and mic roelectrode recordings, the second derivative of AP downstrokes is sho wn to contain an easily detected, unique local maximum. The correlatio n between the position of this maximum (d(2)F/dt(2))(max) and R has be en tested during altered AP characteristics induced by changes in cycl e length, ischemia, and hypoxia. Under these various modifications of the AP, the time points of (d(2)F/dt(2))(max) fell at 97.0+/-2.1% of r ecovery to baseline. Extrastimulus techniques applied to (1) isolated myocytes, (2) intact hearts, and (3) mathematical simulations indicate d that (d(2)V/dt(2))(max) coincided with the effective RPs of APs. The coincidence of RPs and (d(2)V/dt(2))(max) was valid within 5 millisec onds, for resting potentials of -75 to -90 mV and extrastimuli three t imes threshold voltage. Conclusions Thus, optical APs and (d(2)F/dt(2) )(max) can be used to map activation, R, and RPs with AP recordings fr om a single heartbeat.