Fetal radioelectrocardiography: a new method of fetal electrocardiography

Fetal radioelectrocardiography:

a new

method of fetal electrocardiography Preliminary

report

BENJAMIN

KENDALL,

DAVID

M.

FARELL,

HENRY

A.

KANE,

Philadelphia,

M.D M.D. M.D.

Pennsylvania

and Kennedy” in 1942. During the next two decades, reports continued to appear which described rather elaborate techniques and occasionally showed tracings of good quality with demonstrable fetal complexes.3-1f Our knowledge of intrauterine existence has been aided greatly by many of these investigations, but they have not been developed to a point where the methods can conveniently be used wherever obstetrics is practiced. This was due in part to an inability of the systems to develop satisfactory sensitivity without the introduction of significant interfcrence.”

OBSTETRICIANS have long been aware of the need for a practical and reliable method of fetal electrocardiography. To be of the most value, not only must the feta1 electrocardiograph offer an effective way of determining fetal heart rate but also the fetal complex itself should be of clinical significance. With the use of modern electronic advances such as transistors, subminiature components, high-density electronic packaging, and miniaturized broadcasting equipment, a new method has been developed. This paper introduces the system, fetal radioelectrocardiography.”

Equipment

History

The fetal radioelectrocardiograph system permits the remote recording of the combined fetal and maternal electrocardiogram without wires connecting the patient and the recording equipment. The apparatus (Fig. 1) consists of specially designed disposable electrodes, a wallet-sized, battery-powered radio transmitter, and a portable desk-model receiver which is connected to any conventional electrocardiograph machine and, if desired. a cathode ray oscilloscope and a magnetic tape recorder. No sheilded room, special enclosure, or additional grounding provisions are required for either the patient or the apparatus.

The concept of an electrocardiogram of a fetus in utero has excited the interest of many investigators. Although a host of different apparatus were introduced earlier utilizing limb, abdominal, and abdominalvaginal leads, no great improvements were made in the quality of tracings until the reports of Bernstein and Mann1 and Ward From the Department of Obstetrics and Gynecology, and the Department of Pediatrics, Jefferson Medical College Hospital. *The

apparatus used is the RKG 500 radioelectrocardiograph, a product of Telemedics, Inc., Southampton, Pennsylvania (a subsidiary of Vector Manufacturing Company, Inc.). fetal

1629

1630

Kendall,

Farell,

and

Kane

Fig. 1. Entire fetal radioelectrocardiographic unit. A, Electrodes: B, radio transmitter (the electrodes are connected to the transmitter by the patient cable) ; C, radio receiver. Indicated on the radio receiver are I, channel selector switch; 2, calibration switch; 3, electronic filter control; 4, collapsible antenna; 5. skin resistance meter; 6, automatic recharger; 7, power on-off switch and indicator light.

It is well recognized by even recent authors that outside electrical interference offers one of the main problems in eliciting a consistantly accurate recording, even with the most modern apparatus.‘, I27 ‘a Bernstine shows that the magnetic and electrical fields set up by these external sources may cause distortion and interruption of recordings.‘” Fetal radioelectrocardiography has eliminated this difficulty. By the use of a wireless broadcasting system, the unit excludes this significant source of interference. The only signal picked up by the receiver is that being sent by our transmitter on a Federal Communications Commission approved frcqucncy. This Ereqrlt~ncy is much higher than the range employed by all commonly used electrical devices. ‘l’hus, fetal radioelectrocardio,yraphy eliminates one of the main sources of trollble found in other methods. Radio transmitter. The frequency-modu-

June 15, i!W -4111. J. Obst. & Gynec.

lated radio transmitter, including batteries, weighs 10 ounces. Electrocardiographic signals from the electrodes are carried by thr thin flexible wires of a patient cable which snaps onto each electrode and feed the eiectrocardiograph signal to the transmitter located alongside the patient. Here the signal is amplified and transmitted from an antenna built into the transmitter itself. 7’1~ battcrics powering the transistorized circuits arc of a rechargeable type, capable of oporatinK for continuous periods up to 4 hours without recharging. The batteries arc recharged by simply placing the entire transmitter in the automatic battery-charging system located on the receiver. Radio receiver. The desk-model radio reccai\-er meas1ires approximately 12 by 14 inches and is 8 inches high. It weighs 1-k pounds. A collapsible antenna extends to a height of about 3 feet. The receiver console contains these controls and accessories: I. Char1~1 sr’lrctor szeitcll. This connects the recc%ived electrocardiograph signal to any desired recording apparatus or combination of recording apparatus. 2. S/A rc~sistance ntctcr. This permits a cheek on proper electrode application. .‘?. Microrlolt calibration. This provides a mcans of accurately measuring the amplitude of the fetal and maternal complexes, as ~~11 as a reference for comparing the results of \.arious investigators. -h. Filter. An electronic filter which when switched on tends to reduce still further muscle potentials from the tracings. 5. Automatic battery charging syskm. Range of operation. The broadcast range of the RKG 500 fetal radioelectrocardiocraph is several hundred feet. There will he no change in amplitude of the recorded signal when the distance between the transrnittw and receiver is varied. Electrodes. The electrodes each consist of a patch-lype adhcsivc bandage with a unique cblectrocle paste rescxrvoir. a metallic screen, and contact snap fastner (Fig. 2‘1. The electrodes are easily applied to the skin in a manner similar to attaching; most adhesive type handages and with the use of a smafl

Fetal

amount of conductive paste. They measure 1 vZ by If/g inches and are disposable. General

procedure

The following system of electrode placement was found to give optimal results. The patient is placed in the supine position, the abdomen is exposed, and 3 electrodes are positioned as shown in Fig. 3. All 3 electrodes are located on the midline, the lowest one placed just above the symphysis, the middle one 10 cm. above the first, and the upper electrode at the most prominent aspect of the fundus of the uterus. When the uterus is small, only 2 electrodes need be used. In much larger abdomens, where the prospect of multiple pregnancy exists or where polyhydramnios is a factor, two additional lateral electrodes may be placed 10 cm. on either side of the umbilicus. The electrodes are used in pairs. The following system of nomenclature is suggested: Lead I. Where recordings were taken with the use of the upper and middle electrodes. The lower one, therefore, is not utilized. Lead II. Where recordings were taken with the use of the upper and lower electrodes. Lead III. Where recordings were taken with the use of the middle and lower electrodes. This study was conducted using a Lumiscribe KS- 100 electrocardiograph recorder and Tekronix 504 oscilloscope with a long retention tube connected to the radio receiver. Sample tracings from Leads I, II, and III were taken on each patient, and the electrodes were then removed. The entire procedure may take less than 5 minutes. The electrodes can be left in place for up to 24 hours if additional recordings are desired. Tracings have been taken in all stages of labor. Clinical

radioelectrocardiography

1631

problems centering around the presence or absence of fetal life. These, too, are included. Most of the total of 113 tracings were rccorded in the labor room of the Jefferson Ward Obstetric Service, and others were taken in various hospital and clinic locations. Results

Of the 113 cases included, 112 were actually pregnant

the patients in (one case rep-

Fig. 2. Electrodes used in this study. .4 shows the side which comes in contact with the skin. The adhesive surface is protected by paper prior to use. Electrode paste is applied within the metallic area as well as to the patient. B shows the external side of the electrode with the head of the snap fastener visible.

material

One hundred and three unselected patients were studied. Many pregnancies were uncomplicated; others manifested a number of complications. An additional 10 referral cases were evaluated because of specific

Fig.

3. Electrode placement employed in this study indicating the suggested nomenclature for the various leads. All 3 electrodes are in the midline. The lowest is placed just above the symphysis, the middle one 10 cm. above the lowest, and the upper electrode at the most prominent aspect of the fundus.

1632

Kendall,

Farell,

and Kane

‘: .c f

f

f

Fig. 4. Fixre representative in 81.1 per cent of the fetal life. E shows the taken with the elrctronic

f

f

f

f

f

f

f

f

tracings, A, B, and C demonstrate good quality cases. D represents a tracing of the poorest quality presence of two Cetal hearts. indicating twins. All filter and at a paper speed of 25 mm. per second.

resented pseudocyesis). There were 4 cases of twins. This brings the total number of fetuses in this report to 116. Of these, 10 were felt to be dead at the time the tracings were taken. Therefore, the total number of fetuses that probably were viable at the time of the recording was 106 (Table I). In 105 of the 106 cases in which a viable infant was probably present, the fetal radioelectrocardiogram indicated the presence of

f

f

recordings demonstrating these tracings

f

f

f

f

as seen only were

fetal life. This 99.1 per cent accuracy indicates the extreme sensitivity of the allparatus (Table II). Readable fetal complexes were observed in 86 cases or 81.1 per cent (Table III). The significance of these complexes will be discussed later. The cases include all periods of gestation, the earliest being 14 weeks. Several sample tracings can be seen in Fig. 4. Tracings of various quality are included.

Fetal

Table

I. Breakdown

of cases according

to length

First trimester (under 12 weeks) No. of cases Twins Total No. of fetuses No. of fetuses known to be dead at time of tracing? No. of fetuses probably viable at time of tracing ‘One $A rzaciyq

case

01 pscudocycsis

total of 12 of these were taken becauw

Table

II. Kesults

I

Second trimester (13-26 weeks)

the

116 fetuses fetal heart

I

trimester

weeks

/

35-40

weeks

Total

23 2 25

76 2 78

112” 4 116

0

2

2

6

10

72

106

11 to 113.

were delivered sounds were

A negative

23 tracing:

as stillbwn, audible.

the presence

j “~~~~“’ of fetuses probably viable at time of tracing Evidence of fetal life seen on FECG ‘lo of cases showing fetal life

27-34

13 0 13

total

in determining

in weeks Last

*

1633

0 0 0

0

brings

of gestation

radioelectrocardiography

was obtainrd

but

2 of

the

I?

in

this

case.

breeze felt

to

bt:

alive

at

the

time

thy

of fetal life

1 ,,:;i~e~t&

1 27-34 :;;I

“;“‘;;y;o

weeks (

Total

No.

‘If this

the 2 cases of stillbirths, in which total, our accu~-acy far the IO4 live

Table

III.

Results in obtaining

0

11

0 0

11 100

fetal hi&s

23 22 95.7

heart sounds were bead would be 100 per cent.

a readable

72

at

tbc

106” 105 99.1

72 100

time

of

the

tracings,

H~IC

eliminated

from

fetal complex -

I

First trimester (under 12 weeks)

of fetuses probably viable at time of tracing Evidence of readable fetal complex seen on FECG %I of cases showing complex

Second trimester 1 (13-26 weeks)

Last trimester /

27-34

weeks

1 35-40

weeks

I (

Total

No.

0

11

23

72

106

0 0

8 72.1

13 56.5

65 90.2

fffffffffffffffffff Fig.

5. Case

14. Tracing

demonstrating

definite

evidence

of fetal

life.

ffffffffffffffffffff Fig. 6. Case 49. Tracing obtained life felt. Fetal radioelectrocardiography

when no fetal demonstrates

heart fetal

sounds life.

could

be heard

and

no fetal

86 81.1

-

1634

Kendall,

Farell,

and

Kane

,,

“_

kf

f

f

Fig. 7. Case 90. Tracinq complex can be seen.

f obtained

f

f after

f an x-ray

In all 1 cases of twin pregnancy, an indication of fetal life of both fetuses was observed. Only in 5 of the 8 fetuses represented could readable complexes be demonstrated. The 4 patients were at the following stages of ,eestation: 32, 34. 36, and 40 weeks. It can be seen from our results that frorn the twenty-seventh to the thirty-fourth week of gestation. the yield of readable fetal complexes is somewhat reduced. This phenomenon has been reported previously.lf 7 Case

reports

The value of the fetal radioelectrocardiographic system can be emphasized by the following 3 case reports: Case 14. A 25-year-old

white

,.:

f

f’f report

f of “f&+1

to he present.

performed

death.”

f

f

f

A definite

An emergency

and a sluggish

f

f

fetal

crsarean

edematous

section

was

7 pound,

6 ounce male infant was delivered. The inf;ult survived and was discharged with the mother. Case 90. A 27-year-old Negro woman, gravida vii, para v, was admitted to the gynecology ward with a history of 41 weeks of amenorrhea. The patient gave a history of spotting for thp past month, with no symptoms of pregnancy. The fundus was at the level of the umbilicus, and no fetal heart sounds were heard. An x-ray fihn of abdomen taken one week prior to adnlisGon KS read as “fetal death.” Electrocardiocrraphic tracirlgs taken on admission obviously ~ldicated fetal life (Fig. 7). The diagnosis. thercforc, was thrcatcned late abortion. At the time of this writing this patient was still undclivcrcd and the uterus was growing normally.

female, gravida

i, para 0, was referred by a private obstetrician. ‘7 Tht > patrcnt had had 28 weeks of amenorrhea. but the funduc was only 15 cm. in height. No fetal movcmrnts were felt by the patient and no fetal heart sounds wrre heard. Her physician questioned the possibility of an abnormal prrgnancy. The tracing in Fig. 5 was obtained. Thus we knew that a normal fetus, probably of 18 weeks’ gestation, was present. At the time of this writing the patient was still undelivered, good fetal heart sounds were present, and normal uterine growth was occurring. Case 49. A 23-year-old Negro woman, gravida i. para 0, at 36 weeks’ gestation with polyhydramnios and controlled diabetes was admitted for delivery, not in labor. Heart sounds were difficult to hear and after the third day in the hospital could not be heard at all. The only signs of fetal life were the tracings shown in Fig. 6. The patient did not experience fetal movement. Oxytocin induction of labor was instituted but, because of marked variations of fetal heart rate, as shown in the recordings (still no sounds heard), fetal distress was considered

The

fetal

complex

In all cases in which fetal life was positively determined, the fetal heart rate could accurately be measured. In 81.1 per cent of the cases, significant and easily recognizable fetal complexes could be seen. So that fullest meaning from these complexes may be obtained, recordings should be made without the use of the electronic filter which ma>’ eliminate some of the finer qualities of the fetal complex. Most information can be obtain& when the recorder paper speed is ri0 mm. per second and where the base lint on the recording is the flattest. Fetal P waves are infrequently seen, but fetal ‘I’ waves are usually present. The fetal QKS complex is always prominent and can be accurateIy measured in both amplitude and duration. The amplitude of the QRS complex varies greatly from patient to patient, but its duration is usually between 0.02 and 0.04 second in normal cases.

Fetal

Possibly the most significant part of the fetal complex appears to be the S-T segment. In all cases in which a healthy living infant was delivered, the fetal S-T segment was not depressed. However, in the one case in which a markedly depressed infant was delivered which after 2 hours of resuscitation had a respiratory rate of 9 and a heart rate of 90, there was a marked depression and notching of the S-T segment. The infant died 24 hours after birth. The tracing (Fig. 8) was taken 5 hours prior to abrupt cessation of the fetal heart sounds and an emerqcncy midforceps delivery. Although the fetal heart rate was 114 prior to its disappearance, it was regular and steady and there appeared to be no evidence of distress. The S-T segment depression in this case may have been an early sign of fetal anoxia and impending disaster 5 hours prior to its clinical recognition. Additional cases of fetal anosia, distress, and S-T depression must be evaluated before this finding can be placed in its proper perspective. Southern’”

A

radioelectrocardiography

1635

also placed great significance on the fetal S-T segment, although Hon’s15 work has failed to confirm this. Comment

Although fetal electrocardiography is more than fifty years old, no method yet developed displays all the advantages of fetal radioelectrocardiography with its unique wireless system. With its precise determination of fetal heart rate and rhythm and its high yield of probably significant readable complexes, this method offers a new tool to evaluate the environment of the unborn infant. We now have an opportunity to see what changes occur in the fetal heart under ( 1) normal the following circumstances: labor, (2) labor induced or stimulated by oxytocin, (3) operative delivery, (4) obstetric analgesia and anesthesia, (5) an? and all medication administered to the pregnant patient, (6) vaginal bleeding from any cause, (7) fetal distress manifested by decreased or irregular fetal heart sounds, meconium-stained amniotic fluid, or delivery of a distressed infant, (8) prolapsed cord. and (9) any pregnancy complications. These uses of the apparatus are in addition to such established uses as determining the presence or absence of fetal death, diagnosis of fetal cardiac abnormalities, and detection of multiple pregnancy. Summary

f

i

f

t3 f

f

f

f

Fig. 8. A, Tracing taken from a fetus delivered 5 hours later in extreme distress. Note the marked depression and notching of the S-T segment (see arrow). B, The usual complex seen in a normal fetus from another patient. Both tracings were taken without the electronic filter and at a paper speed of 50 mm. per second.

Fetal radioelectrocardiography, a new approach to the science of fetal electrocardiography, has been introduced. The advantages of this system are as follows: 1. Its accuracy is excellent (99.1 pet cent). False negative results are rare. 2. To date, no false positive results have been obtained. 3. A high percentage of readable fetal complexes can be obtained. The si,+ficance of these complexes was discussed. 4. This procedure can be used in all pregnant patients, with no special preparations, and at any location. 5. The system is almost completely free of electrical interference.

1636

Kendall,

6. The cordings. be mol,ed receiver stationary. Practical

Farell,

and

Kane

wireless system enables remote reThus, only the transmitter need to the patient’s room, whereas the and recording apparatus remain

tool

has

been outlined.

LYc \vish application

of this new obstetric

Additional

work

is in

progress.

Ri&rd

to expr~s

M.

Berman

our appreciation for

his

technical

to hlr. assistance.

REFERENCES

Bernstein, P., and Mann, H.: AM. J. OBST. & GYNEC. 43: 21, 1942. J. W., and Kennedy, J. A.: .4m. Heart 2. Ward, J. 23: 64, 1942. 3. Vara, P., and Niemineva, K.: Medizinische, pp. 375-77, March 21, 1953. ‘l. \‘ara. P., and Hahn&n, E.: Acta obst. et gyn~. scandinav. 31: 179, 1952. C. N.: Lancet 1: 1124, 1953. 5. Smyth, 6. Bergman, P., and Hall, P.: Acta obst. et gyncc. scandinav. 37: 348, 1958. 7. Swartwout, J. R., and Walter, E. P.: AM. J. OBST. & GYNEC. 77: 1100, 1959. 8. Han, E. H.: Connecticut M. J. 24: 289, 1960. 1.

9. IO. 11. 12.

13. 14. 15.

Hon.

E.

OHST.

&

H., and Hess, 0. W.: Ax. GYNEC. 79: 1012, 1960. Larks, S. D.: AM. J. OBST. & GYNEC:. 1109, 1959. Shubeck, F.: GP 23: 98, 1961. Bernstine, R. L.: Fetal Electrocardiography and Electroencephalography, Springfield, 1961, Charles C Thomas, Publisher. Caughey, A. F.: Obst. & Gynec. 17: 1961. Southern, E. M.: AM. J. OBST. & GYNEC. 233, 1957. Hon. E. H.: AM. J. OBST. PC GYNEC. 78: 1959.

J. 77:

Ill.. 382. 73: 47.