End-systolic pressure length relations of stunned right and left ventricles after inotropic stimulation

Regional end-systolic pressure-segment length relationships (ESPSLR) were 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 above intrinsic heart rate) without and with dobutamine (2 μg · 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) and the total area of the pressure-length relationship (PLA) were determined. From the latter, the distribution into external work (EW) and potential energy (PE) as well as the efficiency of energy transfer (EET = EW/PLA) were calculated. In both the stunned left and right ventricular myocardium E(es) and EW were reduced according to the same linear regression equations (ΔE(es) = 0.7 E(es,baseline) - 11.4, r² = 0.86 and ΔEW = 0.4 EW(baseline) + 2.3, r² = 0.67), where E(es,baseline) and EW(baseline) are E(es) and EW at baseline, respectively. EET of the stunned left and right ventricular segments decreased as PLA remained 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 segment 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 respect to stunning levels, whereas the additional infusion of dobutamine restored E(es), EW, and PE and consequently EET to baseline values. In conclusion, the right ventricle is susceptible to stunning. During atrial 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 volume). Dobutamine not only increased E(es), EW, and EET but also restored the relationship between E(es) and EET in both ventricular stunned segments.