Factors influencing baseline electrocardiographic parameters in rats: A systematic review of experimental studies published from 1960 to the present.

Experimental studies in rats use baseline or control values as a reference against which changes after experimental interventions are assessed. However, baseline or control ECG parameters may already be influenced by several factors before the experiment begins, complicating interpretation of the results. Therefore, this review summarizes baseline or control ECG parameters (heart rate, PR (or PQ) interval, QRS complex, QT and QTc intervals, P-wave duration and amplitude, R- and T-wave amplitudes, and ST-segment) from 285 in vivo rat studies published from 1960 to the present, identified through searches of Web of Science, Scopus, and PubMed. The aim of this review was not to assess the quality of the included studies, but to help researchers navigate the data and identify potential biological and methodological sources of variability or confounding affecting baseline or control ECG parameters. Our findings should be interpreted with caution due to limitations including variability and small datasets in some groups, unequal sample sizes, aggregation of study-level mean values into a single mean, grouping of different anesthetic agents into a category, underrepresentation of females, incomplete reporting of anesthesia and measurement time, and inconsistent QTc correction methods. These limitations highlight the need for standardized experimental protocols and reporting practices.