Developmental changes in left and right ventricular diastolic filling patterns were determined noninvasively in isoflurane-anesthetized outbred ICR mice. Blood velocities in the mitral and tricuspid orifices were recorded in 16 embryos at days 14.5 (E14.5) and 17.5 of gestation (E17.5) using an ultrasound biomicroscope and also serially in three groups of postnatal mice aged 1-7 days (n = 23), 1-4 wk (n = 18), and 4-12 wk (n = 27) using 20-MHz pulsed Doppler. Postnatal body weight increased rapidly to 8 wk. Heart rate increased rapidly from approximately 180 beats/min at E14.5 to approximately 380 beats/min at 1 wk after birth and then more gradually to plateau at approximately 450 beats/min after 4 wk. Ventricular filling was quantified using the ratio of peak velocity of early ventricular filling due to active relaxation (E wave) to that of the late ventricular filling caused by atrial contraction (A wave) (peak E/A ratio) and the ratio of the peak E velocity to total time-velocity integral of E and A waves (peak E/total TVI ratio). Both ventricles had similar diastolic filling patterns in embryos (peak E/A ratio of 0.28 +/- 0.02 for mitral flow and 0.27 +/- 0.02 for tricuspid flow at E14.5). After birth, mitral peak E/A increased to >1 between the third and fifth day, continued to increase to 2.25 +/- 0.25 at approximately 3 wk, and then remained stable. The tricuspid peak E/A ratio increased much less but stabilized at the same age (increased to 0.79 +/- 0.03 at 3 wk). The peak E/total TVI ratio showed similar left-right differences and changes with development. Age-related changes were largely due to increases in peak E velocity. The results suggest that diastolic function matures approximately 3 wk postnatally, presumably in association with maturation of ventricular recoil and relaxation mechanisms.

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...