Comparison of different methods to measure experimental chronic infarction size in the rat model.

Objective: To evaluate the differences between three methods for the measurement of experimental infarction in rats in comparison to the traditional method.

Methods: Histological analysis of the infarction area (AREA), histological analysis of the internal cavity perimeter (PER) and echocardiogram analysis of the internal perimeter (ECHO) were compared to the traditional method (histological analysis of the epicardial and endocardial circumferences of the infarction region - CIR). Repeated ANOVA measurements were used in conjunction with the Dunn multiple comparison test, the Bland and Altman concordance method and the Spearman correlation test. Significance was established as p < 0.05.

Results: The data of 122 animals were analyzed, 3 to 6 months after the infarction. Infarction size assessments revealed differences between CIR and the other three methods (p < 0.001): CIR = 42.4% (35.9-48.8), PER = 50.3% (39.1-57.0), AREA = 27.3% (20.2-34.3), ECHO = 46.1% (39.9-52.6). Therefore, measurement by area underestimated the infarct size by 15%, whereas the echocardiogram and histological internal perimeter measurements overestimated the infarct size by 4% and 5%, respectively. In relation to ECHO and PER, even though the difference between the methods was only 1.27%, the concordance interval ranged from 24.1% to -26.7%, suggesting a low level of concordance between the methods. In relation to associations, statistically significant correlations were found between: CIR and PER (r = 0.88 and p < 0.0001); CIR and AREA (r = 0.87 and p < 0.0001) and CIR and ECHO (r = 0.42 and p < 0.0001).

Conclusion: Despite the high level of correlation, there was a low level of concordance between the methods to define infarct size.