Periodic variation in R-R intervals and cardiovascular autonomic regulation in young adult Syrian hamsters

Several hamster strains are commonly used as models for cardiomyopathic phenotypes evolving toward heart failure. However, little is known about heart rate variability (HRV) in this species. Prolonged surface ECG recording, a prerequisite to HRV studies, can be obtained either by telemetry or by restraints. Here, we performed long time ECG recording using telemetry on young adult Syrian hamsters and we analyzed time series of interbeat intervals. Standard statistics showed that the mean of normal R-R intervals slightly increased with age, with standard deviation of normal R-R intervals remaining stable over time. However, time domain analysis using Poincaré plots revealed dynamic changes in the HRV. Analysis of frequency domains revealed that the ratio of spectral components (low frequency/high frequency) exhibited a maturation pattern. Thus refined analysis of HRV revealed a more complex pattern than common statistical analysis would translate. Unlike other rodents, hamsters display a great spontaneous variability of their heart rate. As the complexity canvas of HRV might be the consequence of extracardiac regulation factors, we assessed the sympathovagal balance in both time and frequency domain of heart rate. Pharmacological tests revealed that both sympathetic and vagal tones contribute to HRV in Syrian hamsters. Thus Syrian hamsters have a broad intrinsic HRV with large influences of the neurovegetative system. However, the influence of the previous beat seems to prevail over the autonomic oscillators. These animals present a high sensitivity to artificially altered cardiac regulation and might be great models for the diagnosis of early alterations in the HRV related to pathology. Therefore, Syrian hamsters represent a unique model for HRV studies.

Non-invasive restrained ECG recording in conscious small rodents: a new tool for cardiac electrical activity investigation

In vivo electrophysiology remains a suitable method to monitor cardiac activity; however, surface electrocardiogram (ECG) monitoring remains complicated in the case of small animals. Sedation has helped to maintain the animal still; however, it is known that anesthetic drugs impair the regulation of the cardiac electrical activity. To circumvent this problem, ECG monitoring using telemetry or restraints has been developed. This study reports a new methodology, based on a restraining system without further sedation, for recording ECGs on small animal models. We investigated its efficacy in Syrian hamsters and in several strains of mice, and we compared these data to those obtained with telemetry devices. We show that this new system can easily be used in animals of different sizes ranging from adult hamsters to newborn mice. When compared to telemetry, this restrained ECG monitoring method shows a very good yield, as 65% of total beats can be used for further analysis. When recorded in the same animals, RR intervals distributions are identical for both techniques. In conclusion, this restrained ECG monitoring technique is a well-suited tool for exploring various aspects of cardiac electrophysiology in a wide variety of small animals including very young mice.