Prolonged Asynchronous Left Ventricular Isovolumic Relaxation Constant in Ascending Compared to Descending Thoracic Aortic Stenosis for Chronic Early Left Ventricular Afterload and Late Left Ventricular Afterload Increase.

Background: In arterial hypertension, left ventricular relaxation is affected early on in relation to a chronic difference in peak left ventricular afterload with early development of HF. Objective: in ascending compares to descending thoracic aortic stenosis, resulting in chronic late and early LV afterload increase, to assess the left ventricular isovolumic relaxation pressure decay constant through regression analysis, a parameter of left ventricular relaxation on the 4th and 8th week period from invasive left ventricular pressure measurements. Methods: fourteen pigs underwent posterolateral thoracotomy for ascending aortic stenosis, resulting in chronic early left ventricular afterload increase (EL = 6], or descending thoracic aortic stenosis creating chronic late systolic left ventricular load (LL = 8]. Exponential regression with nonzero asymptote for τ assessment, with linear and nonlinear regression were performed on isovolumic relaxation pressure decay from the left ventricular invasive pressure measurements on 4th and 8th week. Two-way repeated measurement ANOVA, post-hoc Tukey test and linear regression were performed for statistical analysis. Results presented are mean ± SEM or median (quartiles], with significance is at p < 0.05. Results: The ascending aortic stenosis associated with prolonged biexponential asynchronous τ, compared to the descending thoracic aorta stenosis, resulted in data that were different at the 8th week in presence of respirations (interaction p < 0.05]. Monoexponential and linear τ were not different in either respiration being preserved or suspended transitionally and in preload reduction. Preload sensitive response of τ was found in ascending compared to descending thoracic aortic banding that reduced in EL and in LL it increased with load reduction (p < 0.05]. These results indicated that τ is not different in and between LV afterloading conditions in a chronic setting, although it indicates that myocardial ischemia is present and that it is greater in ascending aortic banding, compared to descending thoracic aorta banding at the 8th week. Conclusion: In different sequence of the left ventricular afterload, ventricular relaxation is affected early on, having in EL compared to LL prolonged biexponential asynchronous left ventricular relaxation constant, thus indicating the development left ventricular myocardial ischemia and different elastic recoil in an invasive left ventricular hemodynamic assessment.