Modulation of synchrony of left ventricular contraction by regional adrenergic stimulation in conscious dogs

The sympathetic innervation of the left ventricle provides a potential mechanism for modulation of synchrony of myocardial contraction. Dogs were instrumented to measure left ventricular pressure and segment length in the posterior region of the left ventricle perfused by the circumflex artery (PSL) and in an anterior region perfused by the anterior descending artery (ASL). Norepinephrine (NE) was injected into the circumflex artery using an indwelling catheter in bolus doses sufficient to produce no direct systemic effects. Intracoronary injection of NE resulted in significant increases in percent segment shortening and mean shortening velocity in the PSL. Duration of shortening in the PSL was significantly reduced. Percent shortening, velocity of shortening, and shortening duration in the ASL were unchanged. While there was no change in left ventricular systolic pressure, +dP/dt(max) and -dP/dt(min) increased with intracoronary NE. These results demonstrate alterations in the synchrony of myocardial contraction following regional myocardial stimulation with intracoronary injections of NE at doses within the expected physiological range and suggest that activation of localized sympathetic neural pathways may result in problems involving mechanical performance of the heart.