Phase plane analysis of post extra-systolic potentiation

Improved cardiac function after a spontaneous extrasystole in an anesthetized mongrel dog preparation was analyzed based on left ventricular pressure measurement only. Experiments were performed on open-chest anesthetized dogs. Left ventricular pressure (LVP) was measured with a Millar type catheter-tip pressure transducer inserted through an isolated femoral artery and advanced to the left ventricular chamber. In addition, a standard electrocardiogram was recorded continuously. An extrasystole in this study was defined as a spontaneous premature ventricular contraction beat (PVC) such that the premature contraction did not generate enough pressure to open the aortic valve. Phase planes were constructed from left ventricular pressure (abscissa) and its first time derivative (ordinate). Results from the phase plane analysis show that the potentiation is indeed a systolic event, with little alteration in left ventricular relaxation and diastolic function