Background: Paired electrical stimulation and postextrasystolic potentiation (PESP) of contractility has been extensively studied in ventricular myocardium, but less is known about PESP of atrial contractility. Our aim was to determine whether PESP of atrial contractility could augment left ventricular (LV) preload and improve LV systolic performance.
Methods and results: A paired electrical stimulus closely following the pacing stimulus was applied to isolated atrial and ventricular myocardium from 4 dog hearts, and the interval dependent force potentiation was examined. In isolated atrial myocardium, paired pacing increased the active tension from a baseline of 1.36 +/- 0.23 to 2.60 +/- 0.57 g/mm(2); in ventricular myocardium active tension increased from 2.58 +/- 0.42 to 3.81 +/- 0.27 g/mm(2) (both P <.01). Then, LV pressure (micromanometer) and segment length (ultrasonic crystals) were measured in the intact hearts of 7 anesthetized dogs in which premature stimuli were applied to the atrium. In intact hearts, paired pacing of the atrium (coupling interval 200 ms) increased LV end-diastolic pressure from 3.8 +/- 1.0 to 6.4 +/- 1.0 mm Hg; systolic pressure increased from 105 +/- 6 to 112 +/- 7 mm Hg (both P <.05). LV pressure-length loop area (regional stroke work) increased 10.5 +/- 0.2%.
Conclusions: Isolated atrial myocardium exhibits substantial PESP of contractility, which is similar to ventricular myocardium. In the intact heart, atrial PESP augments LV systolic performance by effecting an increase in LV preload. This technique may provide a means of improving cardiac performance in patients with heart failure.