Slice-by-Slice Pressure-Volume Loop Analysis Demonstrates Native Differences in Regional Cardiac Contractility and Response to Inotropic Agents

Abstract

Background: Regional changes in diastolic and systolic properties after myocardial infarction contribute to adverse left ventricular (LV) remodeling. Regional function is currently assessed using load-dependent measures such as slice ejection fraction (sEF), wall motion abnormalities, or strain imaging. However, load-independent measures of cardiac function may be useful in the study of the infarction-induced remodeling.

Methods: In this study, we used a recently validated 2-dimensional (2D) real-time magnetic resonance imaging (MRI) technique to evaluate regional variations in load-independent slice-by-slice measures of systolic and diastolic function and compared the values to a load-dependent measure in 11 sheep at rest and during inotropic agent infusion.

Results: Slice-derived ejection fraction (sEF) was greater in the apex relative to the midventricular and basal regions, and inotropic infusion increased sEF in the base more than in the apex and midventricle. Slice-derived ESPVR (sESPVR) in the apex was significantly lower than in the midventricle and the base, and inotropic infusion increased sESPVR in the apical slices more than in the midventricle. Similarly, slice-derived volume-axis intercept V0 (sV0) was higher in the base relative to the midventricle and apex. sEDPVR did not demonstrate significant regional variations, but inotropic infusion resulted in a small increase in the apex.

Conclusions: In conclusion, acquisition of slice-derived load-independent measures demonstrated variations that contradict those observed with load-dependent sEF. The approach may provide advanced slice-based measures of function during the LV remodeling process and aid in the development of therapies.

Figure 1

Example of Slice Derived Pressure-Volume Recordings across 5 slices from the apex (top) to base (bottom) of the LV. The first and second column demonstrate changes in end-diastolic (first) and end-systolic (second) images as the slice location varies. The third column illustrates the differences in PV Loops obtained by imaging different slice locations. As the slices move from the apex to the base, there is an increase in volume corresponding to a rightward shift of the PV loop. The load-independent measures obtained from preload occlusions at each slice location are shown in the rightmost column with a noticeable shift rightward and upward of the ESPVR relationship.

Figure 2

Regional differences in measured sEF (A), sESPVR (B), sV0 (C) and sEDVPR (D) across the LV at rest and during inotropic infusion.