Effect of short-duration electrically induced tachycardia on regional myocardial contractility.

Abstract

BACKGROUND: Tachycardia is a physiological mechanism for adapting cardiac output to modifications in energy consumption in the organism. The repercussions that short-duration tachycardia has on myocardial contractility have not been sufficiently studied.<br /> To study the effects of short-duration tachycardia on regional myocardial function in the anterior face of the left ventricle depending on the rate, duration, and origin of the electrical stimulation producing the tachycardia. MATERIAL/METHODS: Two series were studied in an in vivo canine experimental model. Stimulation was performed in the right atrium and in the base of the left ventricle at a frequency 20 and 40% above the basal rate. The duration of each pacing episode was 10, 20, and 40 minutes followed by a recovery period of 40 minutes. ECG, left ventricular pressure, and regional function curves of a myocardial segment were studied. RESULTS: During atrial pacing there was a similar decrease in both regional segment lengths (end-systolic and end-diastolic lengths) and no variation in the shortening fraction or in hemodynamic parameters. During ventricular pacing, systolic pressure in the left ventricle decreased, end-diastolic pressure increased, end-diastolic length shortened (meaning less ventricular filling), and the end-systolic length increased, leading to a reduced shortening fraction or regional contractility alteration which was temporarily maintained once pacing ceased. CONCLUSIONS: The transient persistence of segment dysfunction after induced ventricular tachycardia ceases indicates the activation of a different, unknown mechanism.