Quantitative evaluation of a directly depolarized area induced by high-output pacing on the cardiac muscle

Quantitative information is needed on the directly depolarized area (DDA) i nduced by high-output energy during a precise mapping procedure to detect t he origin of a tachycardia. In the present study, a DDA caused by high-outp ut energy was quantitatively evaluated in the exposed canine heart. In 8 do gs, the right atrial and ventricular surfaces were exposed through a right thoracotomy and pacing with various outputs was delivered from the epicardi al surface. A comb-shaped 16 polar electrode array and/or a 224 polar mat e lectrode array were used for recording the epicardial electrograms. The loc al activation time was measured at each electrode site, and the relationshi p of the distance between the electrode location from the pacing site and t he local activation time was plotted and fitted to a primary regression lin e. The intercept of the regression line on the horizontal axis was defined as the radius of the 'DDA' and this was evaluated at each pacing output. Th e radius of the DDA was 0.6+/-0.1 mm with a 2 V and 3.8+/-0.2 mm with a 10 V output when it was evaluated in a direction perpendicular to the fiber or ientation of the pectinate muscle, 0.8+/-0.1 mm with a 2 V and 4.1+/-0.3 mm with a 10 V output in a direction parallel to the pectinate muscle fiber o rientation, and 0.9+/-0.3 mm with a 2 V and 3.6+/-0.5 mm with a 10 V output in the right ventricle. The DDA extended according to the increase in stim ulation outputs at all sites, and there was no significant difference in th e pacing site or the direction of the stimulation propagation. The DDA caus ed by high-output energy is a purely physical phenomenon that depends only on stimulation output and tissue resistance. The diameter of the DDA exceed ed 4 mm (ie, the size of a standard tip electrode for catheter ablation) wh en pacing was delivered with an output greater than 6 V.