TRIGGERED PROPAGATED CONTRACTIONS IN HUMAN ATRIAL TRABECULAE

Objective: Mechanical stretch and rapid release of locally damaged regions of rat cardiac trabeculae due to contraction of undamaged cells during the regular twitch have been shown to trigger local aftercontractions in the damaged region. These aftercontractions appear to propagate along the length of the trabeculae and to precede triggered arrhythmias. The aim of this study was to determine whether triggered propagated contractions can also be elicited in human cardiac tissue. Methods: Trabeculae were dissected from a biopsy of the fight atrial appendage which was obtained during cardiac surgery. They were mounted horizontally, superfused with a modified Krebs-Henseleit solution, and monitored with a video system. Force was measured with a silicon strain gauge; sarcomere length was measured with laser diffraction techniques. Triggered contractions were elicited in 10 trabeculae following trains of 15 stimuli at a rate of 2 Hz, separated by 15 s rest intervals, at 21-degrees-C and a [Ca2+]o above 5.0 mM. Results: Both video analysis and sarcomere length recordings showed that the contractions started at one end of the trabeculae and travelled from there as a localised contraction along the muscle. Increasing [Ca2+]o or the number of conditioning stimuli increased force of the stimulated twitches up to a maximum; further increase of [Ca2+]o or the number of stimuli was accompanied by a decrease of force. Force of the triggered propagated contractions increased monotonically with increasing [Ca2+]o and number of stimuli, while the interval between last stimulus and the peak of the force transient (or latency) decreased progressively, and propagation velocity increased monotonically. Propagation velocity was calculated from the interval between peak sarcomere shortening at two sites and the distance between these sites, as well as from the ratio between the length of the muscle and the duration of the force transient in the remainder of the trabeculae. With increasing temperature at constant [Ca2+]o twitch force increased while latency, force, and duration of the force transient decreased. At 37-degrees-C, localised contractions travelling along the muscle could still be induced at sufficiently increased [Ca2+]o. For all interventions. propagation velocity varied from 0.8 to 3.9 mm.s-1. Conclusions: Contractions can be elicited in human atrial cardiac trabeculae. These contractions have the same basic characteristics as the triggered propagated contractions that have been described previously in rat ventricular trabeculae.