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New Echocardiographic Protocol for the Assessment of Experimental Myocardial Infarction in Rats
Background: The rat infarct model was used extensively to study the pathophysiology of myocardial infarction and to evaluate different therapies. Transthoracic echocardiography is used in rats in order to assess cardiac anatomy and function, being a safe and reliable non-invasive technique. However, studies combining conventional with new echo techniques, such as tissue Doppler imaging (TDI) and speckletracking echocardiography (STE), are lacking.
Objectives: To validate a protocol using the available conventional and new echocardiographic techniques (TDI and STE) for a comprehensive assessment of cardiac remodelling and function, after myocardial infarction in rats.
Methods: Ten Wistar (W) and five Sprague Dawley (SD) male rats (aged 21±2 weeks, mean weight 355±43 g) were evaluated by echocardiography, before and 24 hours post-ligation of the left coronary artery, with previous anaesthesia. Left ventricular (LV) structure was assessed by end-diastolic and endsystolic anterior wall thickness and LV diameters (from the SAX view), while LV function by fractional shortening (FS) and ejection fraction (EF) (by area-length formula), septal mitral annular plane systolic excursion (MAPSE), cardiac output (CO), myocardial performance index (MPI), septal mitral annular systolic velocity (S’, by TDI), and global circumferential and radial systolic strain (GCS, GRS) and strain rate (GCSr, GRSr) by STE, from the SAX view at the level of papillary muscles.
Results: Feasibility of measuring the above mentioned parameters was 100%. Twenty-four hours after myocardial infarction, rats had lower heart rate (373±44 vs. 351±32 bpm, p<0.05) and thinner LV anterior wall, while LV diameters and volumes were significantly higher. FS (54±7 vs. 33±9%), EF (72±9vs. 47±10%), septal MAPSE (2.02±0.17 vs. 1.44±0.22 mm), CO (76±15 vs. 48±12 ml/min), MPI (0.33±0.11 vs. 0.50±0.14), S’ (5.58±1.20 vs. 3.84±1.06 cm/s), and LV strain and strain rate (GCS: -23.52±2.44 vs. -13.33±1.51% and GRS: 50.45±13.11 vs. 17.27±5.2%, GCSr: -8.42±0.85 vs. -4.68±0.53; and GRSr: 11.93±2.39 vs. 4.89±1.18 1/s) were significantly lower, all p<0.01.
Conclusion: Our echocardiographic protocol of experimental myocardial infarction in rats is feasible. The impact of myocardial infarction in rats could be more extensively assessed using a comprehensive echocardiographic protocol of conventional and specific myocardial parameters, measured by TDI and STE, in order to quantify better the LV structure and function. Therefore, we suggest that this protocol may be used in order to assess the effect of different regenerative therapies in experimental myocardial infarction in rats.
Keywords: Wistar, Sprague Dawley, myocardial infarction, echocardiography, speckle tracking