Bioinjection treatment: effects of post-injection residual stress on left ventricular wall stress

Abstract

Injection of biomaterials into diseased myocardium has been associated with decreased myofiber stress, restored left ventricular (LV) geometry and improved LV function. However, its exact mechanism(s) of action remained unclear. In this work, we present the first patient-specific computational model of biomaterial injection that accounts for the possibility of residual strain and stress introduced by this treatment. We show that the presence of residual stress can create more heterogeneous regional myofiber stress and strain fields. Our simulation results show that the treatment generates low stress and stretch areas between injection sites, and high stress and stretch areas between the injections and both the endocardium and epicardium. Globally, these local changes are translated into an increase in average myofiber stress and its standard deviation (from 6.9 ± 4.6 to 11.2 ± 48.8 kPa and 30 ± 15 to 35.1 ± 50.9 kPa at end-diastole and end-systole, respectively). We also show that the myofiber stress field is sensitive to the void-to-size ratio. For a constant void size, the myofiber stress field became less heterogeneous with decreasing injection volume. These results suggest that the residual stress and strain possibly generated by biomaterial injection treatment can have large effects on the regional myocardial stress and strain fields, which may be important in the remodeling process.

Keywords: Biomaterial injection; Congestive heart failure; Left ventricular wall stress; Magnetic resonance imaging; Mathematical modeling.

Figure 1

(a): Finite element mesh of the patient-specific LV. (b): Transmural variation of the myofiber orientation. Left ventricular mesh with (c): 12 spherical voids each having a 1mm radius and (d): injections (red) filling up the void spaces. Notice that the injections are no longer spherical and are slightly elongated transmurally.

Figure 2

Comparison of fiber stretch and stress for the baseline, no-residual and residual cases at end-of-diastole. Cutting plane is shown in red at the top picture. Unit of fiber stress is kPa.

Figure 3

Comparison of fiber stretch and stress for the baseline, no-residual and residual cases at end-of-systole Cutting plane is shown in red at the top picture. Arrow in the residual case indicates the reduced mid-wall end-systolic myofiber stress. Unit of fiber stress is kPa.

Figure 4

Effects of injection size (with constant void size) on (a) global myofiber stress and (b) regional myofiber stress near the injection sites. Mean values of myofiber stress are given on top of each bar in (a). Refer to Fig. 2 and 3's legend for ED and ES regional myofiber stress in (b), respectively.