M.R. Akhmetshina1, E.V. Ivanov2, A.K. Erdiakov3, A.R. Gizatulina4, D.Yu. Izmailov5, S.V. Buravkov6, S.A. Gavrilova7

1–7 Lomonosov Moscow State University (Moscow, Russia)

1 akhmetshinamar@gmail.com, 2 ivanovev101@gmail.com, 3 erdiakovak@my.msu.ru, 4 albina.giz@yandex.ru, 5 dizm@mail.ru, 6 sergey@wolf.ru, 7 sgavrilova@mail.ru

The article investigates heart rate variability (HRV) in rats with experimental myocardial infarction followed by reperfusion, focusing on changes in autonomic regulation. Based on clinical evidence that reduced HRV after myocardial infarction and in chronic heart failure is associated with increased mortality, we evaluated the applicability of time‑domain HRV parameters in an ischemia/reperfusion rodent model and introduced the cold test as a useful sympathetic nervous system activator trigger.

A total of 58 rats with induced myocardial infarction (reperfusion after 2,5 hours) were studied, followed up for 24 hours after ischemia. Electrocardiograms were recorded in freely moving animals, and HRV analysis was performed with standard time‑domain indices: mean RR intervals and heart rate (RR‑Avg, HR‑Avg), their standard deviations (RR‑SD, HR‑SD), short‑term variability markers with parasympathetic nervous system activity predisposition RMSSD and pNN3, as well as two integral indices with sympathetic nervous system activity predisposition RR‑Avg‑SD and HR‑Avg‑SD.

Statistical analysis was carried out in JASP 0.96.0; distribution normality was evaluated using QQ‑plots and Shapiro-Wilk test; repeated measures t-test or Wilcoxon test were used for repeated measurements assessment, results with p<0.05 were considered statistically significant.

In intact rats, the cold test induced a clear sympathetic response, with 28% increase in heart rate and a marked rise in the sympathetic-associated HRV indices RR-Avg-SD and HR-Avg-SD by 526% and 753%, respectively, while parasympathetic markers decreased moderately (RMSSD by 15.8% and pNN3 by 54.1%). Twenty-four hours after myocardial ischemia/reperfusion, mortality reached 34.5%, leaving 38 animals for paired analysis. At rest, post-ischemic animals showed significantly increased heart rate, reduced overall HRV (RR-SD, HR-SD), and decreased vagal-associated pNN3, indicating impaired autonomic regulation. In response to the cold test after ischemia/reperfusion, the increase in sympathetic-associated parameters was substantially blunted: RR-Avg-SD rose by only 91.7% and HR-Avg-SD by 121.3%, which was 5-6 times lower than in intact animals. Morphological examination confirmed severe myocardial injury, including necrosis spanning at least 50% of the free wall of the left ventricle, hemorrhages, neutrophil-monocyte infiltration, and cardiomyocyte contractures.

These findings show that the cold test is an effective functional probe for revealing sympathetic reactivity in rats under physiological conditions and after myocardial infarction. While resting HRV parameters already indicated autonomic imbalance 24 hours after ischemia/reperfusion, stress testing exposed a more pronounced reduction in regulatory reserve, reflected by the weakened sympathetic response to cold stimulation. The combination of functional HRV analysis with histological verification strengthens the interpretation of autonomic disturbances by linking them to structurally confirmed myocardial damage.

Myocardial ischemia/reperfusion in rats leads to reduced HRV, depressed vagal influence, and a marked loss of autonomic regulatory reserve. The cold test combined with time-domain HRV analysis provides a sensitive approach for detecting these abnormalities and may be useful for experimental assessment of post-infarction cardiac dysfunction.

Akhmetshina M.R., Ivanov E.V., Erdiakov A.K., Gizatulina A.R., Izmailov D.Yu., Buravkov S.V., Gavrilova S.A. Cold probe as a tool to assess functional response of heart rate variability indices in rats before and after myocardial ischemia\reperfusion. Technologies of Living Systems. 2026. V. 23. № 3. Р. 97-106. DOI: https://doi.org/10.18127/j20700997-202603-10 (In Russian).

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