Fig. 6.

Cryoablation of mid- and endocardial structures in an aged rat heart and the effect of 0.1 mM H₂O₂. A: simultaneous microelectrode (top) and ECG (bottom) recordings in a heart subjected to cryoablation of the endo- and midmyocardial structures (whitish area in D). EADs, TA causing VF, are still present after the cryoablation procedure. C: optical snapshots of two EADs (1 and 2 in B) causing focal activation that arises from the base of the surviving thin LV epicardial rim. Snapshots in C show activation time starting with 0 ms (arbitrary) with the second EAD (EAD2) arising 68 ms after the first EAD (EAD1). Only a thin rim of epicardial tissue survives the ablation procedure as indicated by the reddish area in this triphenyltetrazolium chloride-stained cross-sectional view of the LV (D). Me, the site of microelectrode recording shown in A and B; Ant, Sep, Lat, and Post, anterior, septal, lateral, and posterior wall of the LV, respectively. Notice that the VF in this cryoablated heart terminates spontaneously within 1 min of initiation consistent with tissue mass reduction (Ref. 13).