Mechanical restitution curves reflect post-ischemic stunning in pigs

Objectives The time constant of mechanical restitution (T_(MRC)), proposed to reflect changes in calcium release and uptake, has been shown to increase in left ventriculariz (LV) failure. In this study, we tested the hypothesis that T_(MRC) also can identify post-ischemic, reversible LV dysfunction (stunning).

Design Stunning was induced by a series of left main coronary artery occlusions in eight anesthetized open chest pigs. Left ventricular pressure–volume relations were assessed using a pressure–volume catheter during right atrial pacing. Mechanical restitution curves (MRCs) were constructed using two different measures of contractile response: maximal first derivative of pressure (CR_(dP/dtmax)) and stroke work (CR_(SW)).

Results Mean arterial pressure, stroke volume and dP/dt_max were decreased 30 min after stunning. Slopes of end-systolic pressure volume relation and preload recruitable stroke work, however, showed no significant changes after stunning. For MRCs based on CR_(dP/dtmax), T_(MRC) increased in all eight animals. Using CR_(SW), T_(MRC) increased in seven out of eight pigs.

Conclusions Ischemia–reperfusion induce changes in MRCs based on CR_(dP/dtmax) and CR_(SW). The MRC concept may have potential as a clinical left ventricular performance index.