Determinants of Diastolic Dysfunction in Swine with HFpEF Arising From Transient Repetitive Left Ventricular Pressure Overload

Abstract

ObjectiveWe recently demonstrated that swine subjected to 2‐weeks of repetitive pressure overload (RPO) exhibit adaptive myocardial remodeling in the absence of left ventricular (LV) hypertrophy. This remodeling is similar to that arising in many patients with heart failure and a preserved ejection fraction (HFpEF). While LV compliance is markedly reduced, the relative contribution of altered myocardial relaxation vs. passive myocardial properties to this is unclear. Accordingly, the objective of the present study was to determine how RPO affects passive myocardial stiffness and active myocardial relaxation, two key components of LV diastolic function.MethodsSwine (n=14) were subjected to 2‐weeks of RPO via daily infusions of phenylephrine (300 ug/min, 2 hours/day). Invasive measurements of LV performance were collected before and after RPO at rest and during alterations in loading conditions elicited by transient manipulation of venous return. To assess reversibility, a subset of animals (n=6) underwent repeat studies 2‐weeks after cessation of RPO. After the final study, myocardial tissue was collected from the LV free wall for post‐mortem assessment of calcium handling protein expression (western blot; n=8), passive myocardial stiffness (uniaxial tensile testing; n=3), and quantification of interstitial fibrosis (picrosirius red staining).ResultsCompared with baseline measurements, 2‐weeks of RPO did not significantly affect the LV relaxation time constant (Tau) or the rate of LV pressure change during isovolumic relaxation (dP/dtmin; Table ). Consistent with this observation, myocardial expression of calcium handling proteins SERCA (from 0.58±0.24 to 0.52±0.25, p=0.62), ryanodine receptor (from 0.37±0.17 to 0.36±0.14, p=0.99), and phospholamban (from 0.46±0.21 to 0.33±0.15, p=0.17) was not different following RPO vs. normal controls (n=8). However, assessment of LV performance under altered loading conditions revealed a significant increase in the LV stiffness coefficient (β) during IVC occlusion as well as the ΔEDP/ΔEDV ratio during rapid saline loading. These functional changes persisted for 2‐weeks following cessation of RPO and were accompanied by a significant increase in passive myocardial stiffness and interstitial fibrosis.ConclusionsThese results demonstrate that the reduction in LV compliance arising after RPO is not related to delayed active myocardial relaxation at rest or altered expression of sarcoplasmic reticulum calcium handling proteins. However, RPO elicits a persistent increase in passive myocardial stiffness that is likely mediated by interstitial collagen deposition. These passive diastolic properties may explain exercise intolerance in HFpEF patients despite normal resting hemodynamics and the absence of anatomic LV hypertrophy.Support or Funding InformationFunding Sources: The National Heart Lung and Blood Institute (HL‐061610), the American Heart Association (17SDG33660200), the National Center for Advancing Translational Sciences (UL1TR001412), the Department of Veterans Affairs (1IO1BX002659), the Community Foundation for Greater Buffalo, and the Albert and Elizabeth Rekate Fund in Cardiovascular Medicine. Baseline/Control RPO Cessation of RPO Tau (ms) 36.5 ± 1.6 35.9 ± 1.6 34.3 ± 1.7 dP/dtmin (mmHg/s) −2116 ± 369 −2301 ± 133 −2464 ± 272 Diastolic Stiffness Coefficient (β) 0.025 ± 0.003 0.054 ± 0.007 * 0.043 ± 0.009 * ΔEDP/ΔEDV During Saline Loading (mmHg/mL) 0.09 ± 0.02 0.21 ± 0.04 * 0.23 ± 0.03 * Ex Vivo Passive Stiffness (kPa) 77.8 ± 11.0 ‐‐‐ 131.0 ± 6.1 * Interstitial Fibrosis (%) 6.6 ± 0.7 12.9 ± 1.8 * 16.3 ± 1.1 * Values are mean ± SEM. *p<0.05 vs. Baseline/Control