Clinical significance of short-term variability computed from heart-rate waveforms

The significance of short-term variability (STV) of the baseline fetal heart rate (FHR) as a prime indicator of fetal well-being is well recognized. It is obvious that for consistently reliable assessment of short-term variability, objective quantification is a necessity. This paper presents a retrospective clinical evaluation of a new technique of STV quantification in terms of beats per minute derived from the slowly varying instantaneous FHR waveform rather than from the relatively rapidly varying fetal ECG. FHR signals from 45 patients, internally monitored during labor, were digitized onto IBM-compatible 9-track digital magnetic tape using a PERKIN-ELMER model 7/32 minicomputer at a sampling rate of 240 milliseconds. The digitized signals were then analyzed off-line for STV and FHR. For each patient about 600 clinical variables were entered into the computer and these data were utilized to comprehensively evaluate the neonatal outcome according to HOBEL's neonatal risk assessment system. The values of mean STV ranged from 1.21 b.p.m. to 6.47 b.p.m. with a median value of 2.75 b.p.m., which was used to divide the patient population into a low-variability (less than or equal to 2.75 b.p.m.) and a high-variability (greater than 2.75 b.p.m.) group. This was found to be justified as the STUDENTS's t-test on mean baseline STV values for these two populations showed them to differ significantly (P less than 0.001). Analysis of the results (Fig. 1) showed that 28.7% of the low-variability population were associated with a poor outcome compared with 4.3% in the high-variability group.(ABSTRACT TRUNCATED AT 250 WORDS)