Key result
Sympathetic stimulation shortened MAPD90 more in the mid-myocardial region (53±4 msec) than in the epicardium (27±3 msec) or endocardium (26±4 msec), reducing transmural dispersion of repolarization.
In a canine model, sympathetic activity reduces the transmural dispersion of ventricular repolarization, providing insight into the autonomic modulation of ventricular arrhythmias.
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No immediate clinical implications; leaves open layer-specific autonomic effects on repolarization for arrhythmia research.
INTRODUCTION: The initiation of ventricular arrhythmias is in part associated with autonomic nervous tone. We investigated the effects of sympathetic and parasympathetic stimulation on the monophasic action potentials (MAPs) of the epicardium (EPi), mid-myocardial (M) region, and endocardium (Endo) in vivo. METHODS AND RESULTS: In 12 mongrel open chest anesthetized dogs, both sides of the cervical vagus nerves and stellate ganglia were crushed with a tight ligature. Right atrial pacing at 600 msec cycle length was begun after the sinus nodal area had been crushed. MAPs from the M region were measured by two needle electrodes that were supported by a W-shaped plastic frame. The epicardial, M region, and endocardial MAP durations at 90% repolarization (MAPD90) were 287+/-7, 315+/-7, and 290+/-8 msec, respectively. The MAPD90 from M cells was longer than that from Epi or Endo. Sympathetic stimulation shortened MAPD90 more in the M region (53+/-4 msec) than that in the Epi (27+/-3 msec) or Endo (26+/-4 msec). The transmural dispersion of repolarization during sympathetic stimulation was shorter than that of the control. Parasympathetic stimulation did not significantly affect any of the MAPD90 values. Simultaneous sympathetic and parasympathetic stimulation produced changes not significantly to those produced by sympathetic stimulation alone. CONCLUSION: Our results suggest that sympathetic activity can reduce transmural dispersion of repolarization under autonomic control in the canine heart under baseline conditions.
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Takei et al. (1999) studied Ventricular repolarization (n=12). Sympathetic and parasympathetic stimulation vs. Baseline control was evaluated on Monophasic action potential duration at 90% repolarization (MAPD90). Sympathetic stimulation shortened MAPD90 more in the mid-myocardial region (53±4 msec) than in the epicardium (27±3 msec) or endocardium (26±4 msec), reducing transmural dispersion of repolarization.
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