Foetal Electrocardiography in the Mare

Abstract

SUMMARY The paper is based on 595 foetal electrocardiograph traces, made from 33 mares. Foetal electrocardiography is a simple technique for the detection of singleton and twin pregnancies. It is also of value for monitoring foetuses in difficult or induced parturitions, and in circumstances where positive evidence of a live foetus is required. Although the foetal heart rate shows periods of intermittent tachycardia, the mean foetal heart rate decreases and mean maternal heart rate increases gradually from 150 days gestation to term. The foetal heart rate in the first stage of induced parturition is found to be related to the duration of first stage labour. Foetal cardiac arrhythmia is most common in abnormal pregnancies. Tachycardia, followed by bradycardia, with slurring of the foetal QRS complex has been seen in a dying foetus. The amplitude of the foetal electrocardiograph (FECG) may vary considerably and rapidly, with the mean amplitude increasing from 150 days to term. Between 220 and 280 days a period of increased variance above and below the mean occurs, lasting for about 3 weeks for any individual animal. Changes in polarity of the foetal deflection are frequent, and may be due to vector changes arising in the myocardium, as well as to differences in foetal position. No positive deflections were recorded from mule foetuses before 300 days. RÉSUMÉ 595 ECG foetaux ont été enregistrés sur 33 juments. L'ECG foetal offre une méthode simple de diagnostic des gémelliparités avancées. II est également utile pour surveiller les foetus en difficulté ou lors de mises bas provoquées et dans les circonstances où l'on souhaite vérifier la présence d'un foetus en vie. Le rythme cardiaque foetal peut montrer des périodes de tachycardie transitoire. Mais d'une manière plus générale on constate qu'à partir de 150 jours de gestation jusqu'au terme, le rythme foetal moyen décroit comme celui de la poulinière s'accélère. Le rythme cardiaque foetal lors de mise bas provoquée parait être en relation avec la durée de la première phase du poulinage. Des arythmies cardiaques foetales sont fréquentes lors des gestations anormales. On a rencontré chez un foetus agonisant une tachycardie suivie par une bradycardie avec étalement du complexe QRS. L'amplitude de l'ECG foetal peut varier considérablement et rapidement. L'amplitude moyenne s'accroit de 150 jours au terme. Entre 220 et 280 jours une période de variations marquées au dessous et au dessus de la moyenne a été constatée: elle dure environ 3 semaines pour chaque individu. Les changements de polarité des déflexions foetales sont fréquentes, dûs sans douteà des modifications du vecteur myocardique età des variations dans la position du foetus. Aucune déflexion positive n'a pu être enregistrée sur le mulet foetal avant 300 jours de gestation. ZUSAMMENFASSUNG Dieser Artikel bezieht sich auf 595 Aufnahmen foetaler Elektrocardiogramme bei 35 Stuten. Die foetale Elektrocardiographie ist eine einfache Methode zur Erkennung von Einlings‐ oder Zwillingsträchtigkeiten. Sie ist auch wert...

Ultrasonographic assessment of fetal well‐being during late gestation: development of an equine biophysical profile

“…Fetal heart rate accelerations of 2 5 4 0 beatdmin for approximately 30 s (average of 10 cardiac accelerations in 10 min) are frequently detected in association with fetal movement in normal equine fetuses. A markedly elevated fetal heart rate or large range of fetal heart rates may indicate excess fetal stress, has been documented in the equine fetus during parturition (Colles et al 1978;Yamamoto et al 1991) and could be brought on by painful maternal systemic problems, e.g. colic.…”

“…Cardiac decelerations have been associated with a poor outcome in pregnant mares (Adams-Brendemuehl 1987) and in man (Grubb and Paul 1992). An abnormally low heart rate or lack of heart rate variation suggests CNS depression, probably due to hypoxia and possible impending fetal demise (Colles et al 1978). Tachycardia inappropriate for the gestational age of the equine fetus has been detected with transabdominal ultrasonography (Adams-Brendemuehl and Pipers 1987) and fetal electrocardiography (Colles et al 1978) and was associated with a negative outcome.…”

“…from the previously determined normal control mean (x>104 beatshin; Reef et al 1995) were considered abnormal. Fetuses were split into 2 groups based on gestational age (c330 days and 2330 days) to determine low fetal heart rate because fetal heart rate is correlated with gestational age in the equine fetus (Colles et al 1978;Matsui et al 1984;Pipers and Adams-Brendemuehl 1984). Fetal heart rates lower than 2 s.d.…”

Sonographic parameters for assessment of fetal well-being in mid-gestation in german Thoroughbred mares

“…We did not observe significant differences between abortion rates of mares with normal and abnormal FHRs. Colles et al (1978) reported that persistent tachycardia serves as an indication to continue monitoring, although it not necessarily indicates fetal distress. Marked or progressive bradycardia, however, may have a more serious prognosis.…”

Some aspects of equine placental exchange and foetal physiology

“…Apart from determinations of umbilical blood flow in chronically catheterised animals (Silver and Comline 1975 ; Silver et a1 1982) and measurements of foetal heart rates by non-invasive techniques over the latter part of gestation (Colles, Parkes and May 1978), few studies on the foetal cardiovascular system have been carried out on the pregnant mare. By contrast, a comparatively detailed picture of circulatory development and homeostasis has been provided by investigations on chronically instrumented foetal sheep (Rudolph and Heymann 1973).…”