EFFECT OF SUBENDOCARDIAL RESECTION ON SINUS RHYTHM ENDOCARDIAL ELECTROGRAM ABNORMALITIES

Background Patients with sustained ventricular tachycardia after acute myocardial infarction frequently have characteristic abnormalities of left ventricular endocardial electrical activity, including fractiona ted (prolonged, multicomponent, low-amplitude), split (having discrete widely separated deflections), and late (extending after the end of t he QRS complex) electrograms. The exact cause and source of these elec trograms are not clear. Methods and Results In this study, endocardial electrograms from 18 patients were recorded with a 20-electrode array from the same area immediately before and immediately after resection of subendocardial tissue at the time of surgery for ventricular tachy cardia, Electrograms could be compared before and after resection from 298 of 360 (83%) of the electrodes, Before resection, split electrogr ams were present in 130 (44%) and late components in 81 (27%) of the r ecordings. Recordings made after resection showed fewer abnormalities, including complete absence of split electrograms as well as all previ ously recorded late components (P<.02). Mean electrogram amplitude inc reased from 0.5+/-0.8 to 1.0+/-1.6 mV (P<.0001) because of removal of the attenuating effect of endocardial scar; mean duration decreased fr om 112+/-38 to 65+/-27 ms (P<.0001) mainly because of loss of late and split components. Overall electrogram contour was very similar aside from these changes. Conclusions These data show that (1) some of the s ignal recorded on the endocardial surface is derived from deeper tissu e layers and (2) split and late electrogram components appear to be ge nerated by cells in the superficial endocardial layers, since they are eradicated by removal of this tissue. These findings correspond well with previous histological studies of resection specimens that show bu ndles of surviving muscle cells separated by layers of dense scar that act as an insulator.