Effects of pregnancy on electrocardiographic, vasovagal tonus index, and echocardiographic variables in horses

Research (Published online: 28-08-2023)

25. Effects of pregnancy on electrocardiographic, vasovagal tonus index, and echocardiographic variables in horses

Chayanon Chompoosan, Pongphol Pongthaisong, Wootichai Kenchaiwong, Theerapong Pontaema, and Wichaporn Lerdweeraphon

Veterinary World, 16(8): 1765-1771

Chayanon Chompoosan: Applied Animal Physiology Research Unit, Faculty of Veterinary Sciences, Mahasarakham University Mahasarakham 44000, Thailand.

Pongphol Pongthaisong: Applied Animal Physiology Research Unit, Faculty of Veterinary Sciences, Mahasarakham University Mahasarakham 44000, Thailand; Small Ruminant Research Unit, Faculty of Veterinary Sciences, Mahasarakham University, Mahasarakham 44000,Thailand.

Wootichai Kenchaiwong: Applied Animal Physiology Research Unit, Faculty of Veterinary Sciences, Mahasarakham University Mahasarakham 44000, Thailand; Small Ruminant Research Unit, Faculty of Veterinary Sciences, Mahasarakham University, Mahasarakham 44000,Thailand; Network Center for Animal Breeding and Omics Research, Khon Kaen University, Khon Kaen 40002, Thailand.

Theerapong Pontaema: Applied Animal Physiology Research Unit, Faculty of Veterinary Sciences, Mahasarakham University Mahasarakham 44000, Thailand.

Wichaporn Lerdweeraphon: Applied Animal Physiology Research Unit, Faculty of Veterinary Sciences, Mahasarakham University Mahasarakham 44000, Thailand; Small Ruminant Research Unit, Faculty of Veterinary Sciences, Mahasarakham University, Mahasarakham 44000,Thailand.

Background and Aim: Pregnancy affects maternal hemodynamics. The changes in autonomic nervous system activity for hemodynamics adaptation in pregnant horses are still unclear. Thus, this study aimed to examine the effect of pregnancy on electrocardiographic, vasovagal tonus index, and echocardiographic variables in horses.

Materials and Methods: A total of 23 Thai native crossbred mares without any cardiac abnormalities were included in this study. The animals were assigned into two groups, a non-pregnant mare group (n =12) and a pregnant mare group (n = 11). Electrocardiogram recordings (paper speed = 25 mm/s and calibration = 10 mm/mV) were performed to obtain six limb leads (leads I, II, III, aVR, aVL, and aVF). The vasovagal tonus index (VVTI) was calculated to assess variability in heart rate over short periods using just 20 consecutive beats. Cardiac structure and function were evaluated by echocardiography.

Results: Heart rate, P wave duration, PR interval, QRS duration, QT interval, and T wave duration were significantly different between non-pregnant and pregnant horses (p < 0.05). Pregnant horses had significantly lower VVTI than non-pregnant (p < 0.05). There were no significant differences in cardiac structures including % interventricular septum (IVS), % left ventricular posterior wall (LVPW), IVS in diastole, left ventricular internal diameter at end-diastole, LVPW thickness at end-diastole, IVS in systole, left ventricular internal diameter at end-systole, LVPW thickness at end-systole, and left atrium/aortic roots ratio between the two groups. However, the pregnant horses had a significantly higher cardiac output and % ejection fraction than non-pregnant horses (p < 0.05).

Conclusion: This study provided the first evidence that hemodynamic adaptations during pregnancy modified cardiac conduction, vasovagal tonus index, and echocardiographic variables in horses.

Keywords: echocardiography, electrocardiogram, horses, pregnancy, vasovagal tonus index.