EUROPEAN-COMMUNITY MULTICENTER TRIAL FETAL ECG ANALYSIS DURING LABOR - THE P-R INTERVAL

The aim of the European Community Multicentre Trial on Fetal ECG Analy sis During Labour was to collect a clinical database of electrocardiog rams on which the different patterns of ST waveform and time interval changes, so far identified, could be studied The aim of this paper was to study the PR-RR relationship and the P wave patterns during normal labour. One thousand three hundred fifty accelerations and 350 decele rations were analysed in 618 labours, ail with normal fetal outcome. A ll ECGs were recorded with the STAN recorder and linked to a PC system for data acquisition and analysis. A positive relationship between P- R and R-R intervals was identified in all reactive fetal heart rate tr aces. A P-R shortening was identified also with all decelerations of m ore than 40 bpm from the baseline, resulting in a negative PR-RR relat ionship. Experimental works have described a P-R shortening concurrent with the maximal R-R lengthening during acutely induced hypoxemia in fetal lambs. In our study normal cord acid-base status indicated that the majority of bradycardia episodes recorded were not related to acut e hypoxemia: PR-RR relationship changes seem therefore to indicate an intact physiological fetal heart adaptive response to rapid change in the environment of either hypoxemic or haemodynamic origin. A negative PR-RR relationship by itself seems to be nothing more than an indicat or of decelerations during labour and seems unable to discriminate bet ween decelerations of different origin. Finally the P wave was no long er detectable during decelerations of more than 800 msec: in this situ ation the P-R interval can not be reliably measured.