Primary T wave abnormalities caused by uniform and regional shortening of ventricular monophasic action potential in dog.

We correlated primary T wave changes with the changes of monophasic action potentials (MAP) recorded with suction electrodes from the ventricular surface of the dog heart following systemic or intracoronary infusions of small doses of isoproterenol (ISP). The portions of the heart perfused with ISP were excised and weighed to determine the mass of perfused tissue. ISP shortened the ventricular MAP by an average of 12-18 msec in the entire ventricular mass following systemic administration, in 34 plus or minus 6 per cent of the ventricular mass after injection into the left circumflex coronary artery (LCA), in 8.5 plus or minus 2.6% of the ventricular mass after injection into a branch of LCA and in 17 plus or minus 8 per cent of the ventricular mass after injection into the right CA. The MAP changes induced by ISP were similar to the transmembrane action potential changes recorded with microelectrodes from papillary muscles excised from the same dogs. The most important results of this study showed that: 1) the early and the late effects of ISP administration produced opposite effects on the T wave polarity. The early T wave change was associated with nonhomogeneous and the late change with homogeneous MAP shortening; 2) the T wave change was greater after infusion into LCA than after systemic administration, 3) the T wave change was greater after infusion into LCA than after infusion into LCA branch apparently because of greater mass of the ISP-perfused myocardium; 4) the T wave change was greater after infusion into LCA branch than after infusion into RCA, apparently due to the unequal regional repolarization contribution to the T wave; 5) the ventricular gradient did not always reflect the magnitude of the primary T wave change. Our study helps to identify factors contributing to high sensitivity and low specificity of T wave abnormalities.