The utility of the small rodent electrocardiogram in toxicology

Extensive research has lead to a growing appreciation that the heart is acutely sensitive to a broad array of toxicants via multiple routes of exposure. These agents are as diverse as the antineoplastic drug doxorubicin and environmental agents including ambient air pollution. Adverse effects in the heart often manifest as a change in the electrocardiogram (ECG). The ECG has long been used in the clinic to assess human cardiovascular health. Surface electrocardiographic recordings (i.e., those made from the skin) in humans often help to detect abnormal myocardial impulse formation, conduction, cardiac rhythm disturbances, and altered autonomic regulation of the heart. In toxicology, the ECG provides a collection of end points that may be used to assess both the quality and magnitude of cardiac toxicity. Increasingly over the last two decades, the cardiotoxicity of agents have been characterized using small rodent electrocardiography. Additionally, tremendous insight into possible mechanisms of action of known human cardiotoxicants has been gained. Rat and mouse models offer a number of advantages relative to larger animals including lower cost, less variability, the availability of transgenic models, and a plethora of research tools. Modern day advances in small rodent electrocardiography have enabled assessments in conscious unrestrained animals and improved ECG interpretation. Thus, the incorporation of small rodent electrocardiographic assessments into toxicology studies may facilitate the screening of cardiotoxic potential and the elucidation of mechanisms of action. This review will discuss the utility of the small rodent ECG, various methodologies used to derive ECG data in rats and mice, and various applications in toxicology.