END-SYSTOLIC PRESSURE LENGTH RELATIONS OF STUNNED RIGHT-AND-LEFT-VENTRICLES AFTER INOTROPIC STIMULATION

Regional end-systolic pressure-segment length relationships (ESPSLR) w ere used to compare the degree of right and left ventricular stunning induced by a 10-min occlusion of the left anterior descending coronary artery and the response to subsequent atrial pacing (50 beats/min abo ve intrinsic heart rate) without and with dobutamine (2 mug.kg-1.min-1 ) in nine anesthetized open-chest pigs. From the ESPSLR, the slope (E( es)) (at 100 mmHg for the left and 25 mmHg for the right ventricle) an d the total area of the pressure-length relationship (PLA) were determ ined. From the latter, the distribution into external work (EW) and po tential energy (PE) as well as the efficiency of energy transfer (EET = EW/PLA) were calculated. In both the stunned left and right ventricu lar myocardium E(es) and EW were reduced according to the same linear regression equations (DELTAE(es) = 0.7 E(es,baseline) - 11.4, r2 = 0.8 6 and DELTAEW = 0.4 EW(baseline) + 2.3, r2 = 0.67), where E(es,baselin e) and EW(baseline) are E(es) and EW at baseline, respectively. EET of the stunned left and right ventricular segments decreased as PLA rema ined unchanged, due to an increase in PE. EET decreased from 0.84 +/- 0.02 to 0.71 +/- 0.03 (P < 0.05) in the stunned right ventricular segm ent and from 0.71 +/- 0.02 to 0.44 +/- 0.03 (P < 0.05) in the stunned left ventricular segment. Atrial pacing did not affect EET with respec t to stunning levels, whereas the additional infusion of dobutamine re stored E(es), EW, and PE and consequently EET to baseline values. In c onclusion, the right ventricle is susceptible to stunning. During atri al pacing the EET was lower than expected from the E(es), which could, in agreement with the time-varying elastance concept, be explained by an increase in afterload (a consequence of the decrease in stroke vol ume). Dobutamine not only increased E(es), EW, and EET but also restor ed the relationship between E(es) and EET in both ventricular stunned segments.