The T Deflection of Isolated Mammalian Heart Muscle Electrogram

Both bipolar and unipolar electrograms recorded from well-oxygenated isolated papillary muscle preparations consist of R and T deflections in the same direction. The T is inverted by anoxia, rapid late, and injury. When cut linear strips of ventricular muscle are observed for many hours, during which time they presumably recover from the initial injury, the T deflection becomes upright in most cases, and then can be depressed and inverted by anoxia or rapid rates of stimulation. Since, in the absence of modifying factors, the T is in the same direction as the R deflection in a simple linear .strip, it probably cannot be adequately explained on the basis of membrane repolarization. Since the nerve after-potentials are believed to represent processes involving oxidative metabolism, the T deflection may also be produced by metabolic processes, although the possibility cannot be ex- cluded that it represents a combination of membrane repolarization and other processes. A CCORDING to the commonly accepted /jL theory of the genesis of the electro- / m cardiogram, the R and T deflections are due to changes in polarization of the myo- cardial cell membrane. The R deflection is considered the result of depolarization, and the T is ascribed to repolarization. This con- cept is based to a large extent on experiments on heart muscle strips from various species. 1 Preliminary studies on the papillary muscle preparation of Cattell and Gold 2 yielded