Effect of autonomic nervous system on the transmural dispersion of ventricular repolarization in intact canine

The effect of the autonomic nerves on the transmural dispersion of ventricular repolarization in intact canine was investigated. By using the monophasic action potential (MAP) recording technique, monophasic action potentials (MAPs) of the epicardium (Epi), midmyocardium (Mid) and endocardium (Endo) were recorded simultaneously by specially designed plunge-needle electrodes at the left ventricular free wall in 12 open-chest dogs. MAPD90 and transmural dispersion of repolarization among three myocardial layers as well as the incidence of the EAD before autonomic nervous stimulation and during autonomic nervous stimulation were compared. The results showed that the MAPD90 of Epi, Mid and Endo before autonomic nervous stimulation were 278 +/- 11 ms, 316 +/- 16 ms and 270 +/- 12 ms respectively, the MAPD90 of Mid was significantly longer than that of Epi or Endo (P<0.01). MAPD90 of Epi, Mid and Endo were shortened by 19 +/- 4 ms, 45 +/- 6 ms, 18 +/- 3 ms respectively during sympathetic stimulation. Compared with that of the control, the transmural dispersion of repolarization during sympathetic stimulation was shortened from 44 +/- 4 ms to 15 +/- 3 ms (P<0.01), but early afterdepolarizations were elicited in the Mid of 5 dogs (41%) during sympathetic stimulation. Parasympathetic stimulation did not significantly affect the MAPD90 in the three layers. It is concluded that there is the transmural dispersion of ventricular repolarization in intact canine. Sympathetic stimulation can reduce transmural dispersion of repolarization, but it can produce early afterdepolarizations in the Mid. Parasympathetic stimulation does not significantly affect the transmural dispersion of ventricular repolarization.