Shorten τ<sub>1</sub> in Chronic Early vs. Late Systolic LV Load for Systolic Dysfunction in Ascending vs. Descending Thoracic Aortic Stenosis

Abstract

<i>Background:</i> Arterial hypertension (HTA) results with diastolic LV dysfunction (DD), important to develop systolic LV dysfunction and exercise intolerance with HF. Separating between chronic late (LL) to early LV load (EL) during systole, impaired LV relaxation is present earlier in chronic LL vs. EL, having early HF, as result of myocardial ischemia and systolic LV dysfunction in HTA. <i>Objective and Methods:</i> to assess early systolic in diastolic LV dysfunction from biexponential τ regression assessment, using single beat and mono-exponential regression analysis, with nonzero asymptote with special software in LL and EL, between 4<sup>th</sup> and 8<sup>th</sup> week in a porcine model. This assesses early HF and systolic LV pump dysfunction, from fast_τ (τ<sub>1</sub>), for early systolic LV dysfunction, in LVH remodeling in moderate LV afterload increase. Fourteen domestic male pigs, underwent LV pressure measurements with conductance Millar 5F catheter having moderate ascending aortic banding (EL=6), and in descending thoracic aortic stenosis, as in hypertension (LL=8). τ<sub>1</sub> (τ_fast) and τ<sub>2</sub> (for τ_slow) component of bi-exponential τ analyzed LV dysfunction at 4<sup>th</sup> vs. 8<sup>th</sup> week. Under reduced LV load (m3), during ventilation preserved (m1) or suspended transitionally (m2), fast τ assess early systolic dysfunction in LL vs. EL. Associated murmurs were assessed to detect LV valves dysfunction. Data was compared statistically, using two-way repeated measurement ANOVA, after Leven normality test. Results are means±SEM or medians (quartiles), for significant p<0.05. <i>Results:</i> mono-exponential τ was not different, neither changed in LL vs. EL at 4<sup>th</sup> and 8<sup>th</sup> week in m1, m2 or m3, that reduced in both groups with mechanical LV load reduction at 4<sup>th</sup> and 8<sup>th</sup> week (p<0.05). Prolonged bi-exponential asynchronous τ<sub>2</sub>/τ<sub>1</sub> ratio in EL was different from LL at 8<sup>th</sup> week, resulted from LV afterload (τ<sub>2</sub>τ<sub>1</sub> interaction p<0.05). τ_fast was different, being shorten in EL vs. LL at 4<sup>th</sup> and 8<sup>th</sup> week. Reduced bi-exponential τ<sub>2</sub>τ<sub>1</sub> ratio in EL and increased in LL, with mechanical load reduction, improved LV ischemia with DD in EL at 4<sup>th</sup> and 8<sup>th</sup> week of moderate LV afterload increase, but did not respond in LL. There was predominant systolic murmur in EL and diastolic murmur in LL, pronounced with load reduction. <i>Conclusion:</i> Prolonged bi-exponential τ<sub>1</sub> in LL shows early systolic LV dysfunction within DD. LV ischemia and systolic with diastolic LV pump dysfunction in EL presents shorten fast_τ, being unresponsive to mechanical LV load reduction in LL.