Assessment and quantification of foetal electrocardiography and heart rate variability of normal foetuses from early to late gestational periods 3

Clinical application of non-invasive foetal ECG 128 CHAPTER CLINICAL APPLICATION OF NON-INVASIVE FOETAL ECG Clinical application of non-invasive foetal ECG 129 Introduction Cardiac arrhythmias arise as a result of abnormal cardiac electrical conduction. The gold standard for the diagnosis of arrhythmias has always been via the ECG. Foetal arrhythmias occur in to percent of pregnancies. These range from benign premature atrial or ventricular contractions to life-threatening supraventricular and ventricular tachycardia. Foetal arrhythmias are currently being diagnosed by Mmode echocardiography, which is labour-intensive and indirectly detects the cardiac mechanical rather than electrical activity. Non-invasive abdominal foetal ECG (fECG) is a convenient, inexpensive and effective technique for the detection of the foetal heart’s intrinsic electrical activity. Although it has not yet been integrated into clinical practice, it seems promising for future clinical application in the diagnosis and management of foetal arrhythmias. Case report of a foetus with premature ventricular contractions The following is a case report that illustrates the clinical application of non- invasive fECG in a foetus with premature ventricular contractions (PVCs), which was missed by cardiotocography (CTG) monitoring. Using non-invasive fECG, the true foetal heart rate was determined. This led to the probability of avoiding unnecessary operative intervention to deliver the foetus under emergency conditions. 2.1 Antenatal foetal ECG A young and healthy 17-year-old primigravida at 37 weeks’ gestation underwent a routine CTG monitoring during an antenatal visit. The pregnancy had Clinical application of non-invasive foetal ECG 130 thus far been uneventful. However, the baseline foetal heart rate (fHR) on the CTG measured 60-70 beats per minute (bpm), with occasional, sudden “jumps” to 120 bpm (Figure 8-1). The foetus is otherwise well with active movements noted. The mother had no history of Systemic Lupus Erythematosus (SLE), which is known to be associated with heart blocks in the foetus. With the mother’s consent, the fHR was determined using the FEMO fECG monitoring system (Medco Electronics Limited, Israel). The method of measurement of fECG has been described in Chapter 6. Using FEMO, baseline fHR was reflected as 130 bpm (Figure 8-2). Since the FEMO monitor documented a stable fHR tracing, the decision was not to intervene unless the foetus started to show signs of compromise. Doppler and M-mode echocardiography revealed the presence of frequent PVCs, mainly occurring in bigeminy (Figure 8-3). During follow-up assessment in the following weeks, fHR was still recorded as 60-70 bpm and 120-140 bpm by the CTG and FEMO, respectively. Upon closer examination of the raw abdominal ECG trace of FEMO, it was discovered that PVCs could be observed. Figure 8-4 shows an abdominal strip with PVCs occurring in bigeminy. In addition, measurement of the averaged fECG complex revealed a prolonged QRS duration (mean QRS duration = 76 ms) when compared to the cohort of healthy foetuses of the same gestational age in this study (mean QRS duration = 53 ms) (Figure 8-5). A widened QRS is one of the characteristic ECG findings of PVCs in adults and children. PVC indicates depolarization that arises in either ventricle before the next expected sinus beat. In such circumstances, the normal sequence of ventricular depolarization is altered, and the two ventricles depolarize sequentially Clinical application of non-invasive foetal ECG 131 FM= foetal movement; Toco= uterine activity Figure 8-1: The CTG at 38th week of gestation showed the baseline foetal heart rate (fHR) as 60-70 bpm. Clinical application of non-invasive foetal ECG 132 Figure 8-2: The foetal heart rate (fHR) and maternal heart rate (mHR) as displayed by FEMO at 38th week of gestation. The baseline fHR is about 130 bpm with good beat to beat variability. Clinical application of non-invasive foetal ECG NB – normal beat; PVC – premature ventricular contraction Figure 8-3: Ventricular bigeminy as demonstrated by Doppler echocardiography. 133 Clinical application of non-invasive foetal ECG M M F F (PVC) F F (PVC) 134 M M F F (PVC) M F F (PVC) M= maternal QRS complex F= foetal QRS complex PVC= premature ventricular contractions Figure 8-4: Raw abdominal ECG strip showing PVCs occurring in bigeminy. Clinical application of non-invasive foetal ECG 135 (a) (b) Figure 8-5: Average foetal ECG waveform of a healthy term foetus (a) with average QRS duration of 53 ms and that of the foetus with PVC with an average QRS duration of 76 ms (b). Clinical application of non-invasive foetal ECG 136 rather than simultaneously, thus resulting in a wide QRS complex. This is in contrast to premature atrial contractions (PACs), where the QRS durations are not prolonged and the P waves have a configuration different from the normal P wave. In this case study, the abnormally wide QRS duration and normal P wave suggest that the ectopics were ventricular (and not supraventricular) in origin. 2.2 Intrapartum foetal ECG During labour, it was noted that the CTG tracing during labour remained at 70 bpm and was not recordable most of the time. Foetal scalp ECG monitoring was performed but it failed to record either the fECG or the fHR. The fHR of a healthy foetus is generally in the range of 110-150 bpm. A fHR27-32 49 139.5 (12.1) 136.1142.9 433.3 (37.0) 422.9443.7 26.7 (10.2) 23.829.6 17.0 (8.5) 14.619.4 8.7 (6.2) 6.910.4 >32-22-27 wks ] ] 25 SDNN (ms) 420 mNN (ms) ] ] 405 390 375 20 15 360 10 18-22 wks >22-27 wks >27-32 wks >32-=37 wks >27-32 wks >32-=37 wks ] ] ] ] 14 12 10 18-22 wks 18-22 wks >22-27 wks >27-32 wks >32-=37 wks >22-27 wks >27-32 wks >32-=37 wks Gestational age Gestational age Figure 10-1: Time-domain parameters (mNN, SDNN, rMSSD, and pNN27) at various gestational ages. Heart rate variability of healthy foetuses 160 (p=0.011). Another time domain parameter of short-term variability, pNN27, also increased significantly from 7.9% at 18-22 weeks to 11.4% at ≥ 37 weeks (p=0.003). Figure 10-1 depicts graphically the increases in rMSSD and pNN27 with respect to foetal gestational age. 4.2 Foetal HRV (frequency-domain analysis) at different gestational ages Visual inspection of the foetal spectrograms to evaluate the changes in power or variability over gestational age revealed a LF peak that centered around 0.1 Hz. Another peak was observed occurring in the HF range, widely-dispersed and centered around 0.6-0.8 Hz. However, this HF peak was only observed in the spectrograms of mature foetuses, especially in those aged 37 weeks and above (Figure 10-2). Table 10-2 shows frequency-domain parameters where absolute power contained in the LF component decreased as gestational age increases (403 ± 257 ms2 in young foetuses to 248 ± 181 ms2 in mature foetuses, p27-32 week-old foetuses and then decreased to 279 ± 155 ms2 in ≥ 37 weeks (p=0.001). The total power was observed to increase minimally in the period from 18 weeks (1127 ± 614 ms2) to before 37 weeks (1176 ± 732 ms2) after which it fell to 907 ± 557 ms2 (p=0.018). Figure 10-3 shows how the total power, as well as absolute LF and HF power changed with foetal gestational age. 161 Heart rate variability of healthy foetuses Patient’s name and identification number Date; Gestational week= 20 LF (a) Patient’s name and identification number Date; Gestational week= 37 LF HF (b) LF-Low Frequency; HF- High Frequency Figure 10-2: The HRV power spectra of a foetus at 20 weeks (a) and 37 weeks (b), showing the presence of an additional HF peak at 37 weeks. 162 Heart rate variability of healthy foetuses Table 10-2: Frequency-domain variables in relation to gestational age GA (weeks) LF power (ms2) LF power norm HF power (ms2) (n.u.) HF power norm (n.u.) LF/HF Total power (ms2) N Mean (SD) 95% CI Mean (SD) 95% CI Mean (SD) 95% CI Mean (SD) 95% CI Mean (SD) 95% CI Mean (SD) 95% CI 18-22 88 403 (257) 351456 60.1 (17.3) 56.663.6 217 (125) 192242 36.9 (13.8) 34.139.7 2.1 (1.7) 1.82.5 1127 (614) 10031252 >22-27 59 344 (194) 296392 54.3 (15.5) 50.458.1 256 (153) 218294 41.7 (12.7) 38.544.8 1.6 (1.3) 1.31.9 1123 (629) 9671279 >27-32 49 386 (173) 338435 54.4 (10.2) 51.557.2 311 (143) 271351 43.8 (9.1) 41.346.4 1.3 (0.5) 1.21.5 1141 (524) 9941289 >32-27-32 wks >32-=37 wks Gestational age 350 55 300 HF power (ms2) ] ] ] 250 ] 200 150 Normalized HF power (n.u.) ] ] 100 50 ] 45 ] ] 40 ] 35 30 18-22 wks >22-27 wks >27-32 wks >32-=37 wks 18-22 wks Gestational age >22-27 wks >27-32 wks >32-=37 wks Gestational age 2.5 1250 ] Total power (ms2) LF/HF ratio 2.0 ] 1.5 ] ] 1.0 ] ] ] ] 1000 ] 750 ] 0.5 500 18-22 wks >22-27 wks >27-32 wks >32-=37 wks 18-22 wks >22-27 wks >27-32 wks >32-=37 wks Gestational age Figure 10-3: Absolute and normalized HF and LF power, total power and LF/HF ratio at various gestational ages. Heart rate variability of healthy foetuses 164 Since there was a significant change in total power, the evaluation of normalized LF and HF power, which eliminates the contribution of total power, was especially necessary for a more accurate evaluation of the relative activity between the sympathetic and parasympathetic systems. There was a steady reduction in normalized LF power as with increasing gestation, from the initial 60.1 ± 17.3 n.u. from the 18th –22nd week of gestation to 42.1 ± 15.6 n.u. after the 37th week of gestation (p32-0.05 (not significant) for all HRV parameters. 166 Heart rate variability of healthy foetuses 42 480 38 34 SDNN (ms) mNN (ms) 460 440 420 30 26 22 18 400 female female 14 380 10 male 18-22 wks >27-32 wks >22-27 wks male 18-22 wks >=37 wks >27-32 wks >22-27 wks >32-=37 wks >32-27-32 wks >22-27 wks >=37 wks >32-27-32 wks >22-27 wks >=37 wks >32-27-32 wks >22-27 wks 50 40 female 30 male 18-22 wks 60 20 >=37 wks male 18-22 wks >32-27-32 wks >22-27 wks Gestational age >32-=37 wks 300 200 100 female >27-32 wks >22-27 wks 50 40 30 female 20 male 18-22 wks 60 male 18-22 wks >=37 wks >27-32 wks >22-27 wks >32-=37 wks >32-27-32 wks >22-27 wks >32-=37 wks 200 male 18-22 wks >27-32 wks >22-27 wks >=37 wks >32-[...]... 18-22 88 4 03 (257) 35 1456 60.1 (17 .3) 56.6 63. 6 217 (125) 192242 36 .9 ( 13. 8) 34 . 139 .7 2.1 (1.7) 1.82.5 1127 (614) 10 031 252 >22-27 59 34 4 (194) 29 639 2 54 .3 (15.5) 50.458.1 256 (1 53) 218294 41.7 (12.7) 38 .544.8 1.6 (1 .3) 1 .31 .9 11 23 (629) 9671279 >27 -32 49 38 6 (1 73) 33 8 435 54.4 (10.2) 51.557.2 31 1 (1 43) 27 135 1 43. 8 (9.1) 41 .34 6.4 1 .3 (0.5) 1.21.5 1141 (524) 9941289 >32 - 22-27 59 141.9 (9.4) 139 .6144 .3 424.6 (29.7) 417 .34 32.0 25.8 (8.7) 23. 628.0 17.5 (7.7) 15.619.4 9.9 (7.8) 7.911.8 >27 -32 49 139 .5 (12.1) 136 .1142.9 433 .3 (37 .0) 422.94 43. 7 26.7 (10.2) 23. 829.6 17.0 (8.5) 14.619.4 8.7 (6.2) 6.910.4 >32 - 22-27 wks ] ] 25 SDNN (ms) 420 mNN (ms) ] ] ] 405 39 0 37 5 20 15 36 0 10 18-22 wks >22-27 wks >27 -32 wks >32 - 22-27 wks >27 -32 wks >32 - =37 wks 18-22 wks Gestational age >22-27 wks >27 -32 wks >32 - =37 wks Gestational age 35 0 55 30 0 HF power (ms2) ] ] ] 250 ] 200 150 Normalized HF power (n.u.) ] ] 100 50 ] 45 ] ] 40 ] 35 30 18-22 wks >22-27 wks >27 -32 wks >32 - =37 wks 18-22 wks Gestational age >22-27 wks >27 -32 wks >32 - =37 wks Gestational age 2.5 1250 ] Total power (ms2)... > =37 wks >27 -32 wks >32 - =37 wks ] ] ] 8 ] 14 6 12 4 10 18-22 wks 18-22 wks >22-27 wks >27 -32 wks >32 - =37 wks >22-27 wks >27 -32 wks >32 - =37 wks Gestational age Gestational age Figure 10-1: Time-domain parameters (mNN, SDNN, rMSSD, and pNN27) at various gestational ages Heart rate variability of. .. Development of a novel HRV software 142 The objectives of F-EXTRACT were primarily to automate the extraction of RR-interval data from foetal ECG recorded from FEMO, and to display the power spectra of foetal HRV so as to provide insightful visualization of the data An automated computation of time- and frequency-domain parameters of foetal HRV was necessary because manual measurement of RR-intervals from. .. 2 533 19 46.5 (12.6) 43. 649.5 1.2 (0.7) 1.11.4 1176 ( 732 ) 1005 134 7 ≥ 37 107 248 (181) 214282 42.1 (15.6) 39 .245.0 279 (155) 25 030 8 53. 5 ( 13. 5) 51.056.0 0.9 (0.6) 0.81.0 907 (557) 8 031 011 p value for ANOVA GA- Gestational age . recorded from FEMO, and to display the power spectra of foetal HRV so as to provide insightful visualization of the data. An automated computation of time- and frequency-domain parameters of foetal. foetal heart rate variability (HRV) from the RR-interval data obtained from FEMO abdominal foetal ECG monitor. The development of F-EXTRACT arose from the growing interest in HRV and the lack of. CTG at 38 th week of gestation showed the baseline foetal heart rate (fHR) as 60-70 bpm. Clinical application of non-invasive foetal ECG 132 Figure 8-2: The foetal heart rate