Background: In the fields of cardiac regeneration and cardioprotection,
robust quantification of the cardiac function is paramount for the
assessment of the effects of experimental interventions on the
heart. We hypothesized the feasibility of performing cardiac MRI strain
imaging and assessed its superiority to ejection fraction (EF) in I/R
MI rats.
Methods: Lewis rats (normal versus 24–48-hour post I/R MI, each n =
6) were imaged using cine FLASH and high-frame rate IntraGate cine
(Bruker BioSpec 9.4T MRI, Ettlingen) conforming to AHA's planes recommendations. MI was confirmed using multi-slice IR LGE. Segment
(Medviso AB, Lund) and 2D CPA MR (Tomtec) were used respectively
for volumes measurements and strain analysis.
Results: Normal rat versus MI rats: EF (mean 64.0%, SD 2.3% versus mean
59.5%, SD 5.1%), p = 0.089; endo peak GLS (global longitudinal strain)
(mean -21.9.0%, SD 1.1% vs. -14.1%, SD 5.5%), p = 0.017; endo
peak GCS (global circumferential strain) (mean -34.0%, SD 1.4% versus
mean -26.1%, SD 6.4%), p = 0.028; myo peak GCS (mean -23.5%,
SD 1.7% vs -17.0%, SD 5.4%), p = 0.032; GRS (global radial strain)
(mean 45.8%, SD 5.3% versus mean 33.7%, SD 9.8%), p = 0.029.
Conclusion: Strain imaging indices show statistically significant
changes after MI where EF does not. A small change in EF was observed
despite large infarct sizes. Increase in heart rate and alterations of
remote regional strain and tissue velocities (data not shown) are suggested to be compensatory mechanisms which preserve EF.