Key Points
- To assess early and late alterations in left ventricular dynamic geometry and contractile function following changes in contraction frequency in conscious subjects.
- Studied 10 conscious dogs instrumented with chronically implanted pulse-transit ultrasonic dimension transducers and high-fidelity left ventricular micromanometers.
- Applied atrial pacing and introduced an extrasystole and postextrasystole after every 20th regular baseline beat to evaluate rapid and steady-state responses.
- Postextrasystolic inotropic potentiation exhibited a direct linear relationship with the change in contraction frequency induced by the extrasystole (r² = 0.97) when end-diastolic geometry was matched.
- Steady-state increases in contraction frequency did not significantly alter maximum contractile velocity (P > 0.20), while end-diastolic volume decreased significantly (P < 0.05).
Structured PICO
PPopulation10 conscious dogs with chronically implanted pulse-transit ultrasonic dimension transducers and a high-fidelity micromanometer
IInterventionAtrial pacing with an extrasystole and a postextrasystole introduced after every 20th regular beat
CComparatorControl beat (basic pacing rhythm)
OOutcomeDegree of postextrasystolic potentiation of ventricular function (ratio of the maximum derivative of left ventricular pressure of the postextrasystolic beat to the control beat)surrogate
In conscious dogs, postextrasystolic inotropic potentiation is directly related to the change in contraction frequency induced by the extrasystole, highlighting the need to control end-diastolic geometry and frequency perturbation when evaluating left ventricular function.