The slope of the segmental stretch-strain relationship as a noninvasive index of LV inotropy

Abstract

Objectives: The aim of this study was to test the hypothesis that the noninvasively constructed slope of the relationship between left ventricular (LV) regional systolic strain and stretch during atrial contraction represents LV inotropic state.

Background: LV systolic response to a changing preload depends on its inotropic state. Changing the preload has allowed constructing the slope of the end-systolic pressure-volume relationship that is used as an invasive measurement of LV inotropy. We assumed that the slope of the relationship between regional systolic LV strain (total_S) and stretch during atrial contraction (preS) depends on the LV inotropic state as well and can thus be used as a LV inotropy index.

Methods: Strain curves (tissue Doppler) were extracted from 27 healthy individuals to determine the normal stretch-strain relationship at rest, during a low-dose dobutamine (LD) challenge and during passive leg-lift (LL). The method was also applied in 7 patients with breast cancer before and after chemotherapy with anthracyclines.

Results: PreS and total_S correlated closely in all subjects (r = 0.82). Total_S values increased (p < 0.05) with LD (-20.44 ± 3.89% vs. -24.24 ± 5.55%) and LL (-19.65 ± 3.77% vs. -24.05 ± 3.67%), whereas preS increased only with LL (5.96 ± 1.72% vs. 8.61 ± 2.18%), but not with LD (6.83 ± 2.34% vs. 7.29 ± 2.24%). No changes of total_S or preS were observed after the exposure to chemotherapy (-21.23 ± 2.93% vs. -21.49 ± 2.89% and 8.11 ± 1.03% vs. 8.59 ± 1.73%, respectively). The slope of stretch-strain relationship got steeper with LD (-1.47 ± 0.36 vs. -2.34 ± 0.36, p < 0.05), declined after the chemotherapy (-1.68 ± 0.15 to -0.86 ± 0.23, p < 0.05) and did not change with LL (-1.39 ± 0.57 vs. -1.51 ± 0.38, p = NS).

Conclusions: The slope of the regional stretch-strain relationship can be regarded as a noninvasive index of myocardial inotropic state. It gets steeper with increasing inotropy, does not change with preload induced changes of LV systolic function, and flattens after the exposure to a cardiotoxic drug.