Assessment of left ventricular twist and untwist rate in a rat model of myocardial infarction

Abstract

Purpose: Left ventricular (LV) twist and untwist rate (UR) are known to be strongly related to LV systolic and diastolic function, respectively. Although these parameters are emerging as important tools to evaluate LV function, yet their assessment and physiological significance in small animals remain challenging. The study was designed to investigate how twist and UR, measured by speckle tracking imaging (STI), relate to LV function and extent of fibrosis in a rat model of chronic myocardial infarction (MI).

Methods: 23 Sprague-Dawley rats were subjected to LAD ligation (MI; n=14) or sham surgery (SHAM; n=9). 2D echocardiography at baseline (BL), day 1, day 3 and 2 months post-surgery was used to calculate LV dimensions, volumes (EDV, ESV) and global functional parameters. STI was applied to measure circumferential strain (Scirc), twist and UR. LV fibrosis was estimated from Sirius Red staining at day 1, day 3 and 2 months post-surgery.

Results: Progressive cardiac failure evaluated during 2 months was characterized by a gradual increase in EDV and ESV respectively (0.2±0.04 mL to 0.8±0.2mL, and 0.04±0.02mL to 0.5±0.1 from BL to 2 months post-surgery, p<0.05) along with depressed ejection fraction (76±9 to 32±11%, p<0.05). Peak LV twist and UR progressively decreased over time and were associated respectively with a decreased Scirc (r=-0.58, p<0.001) and an increased myocardial fibrosis (r=-0.70, p<0.001) (fig.1).

Conclusion: Assessment of LV twist and UR is feasible in small animals. Worsening of these parameters is associated with a progressive impairment of LV function in rats with chronic MI and correlates with the amount of fibrosis present in the tissue.