19
SA MEDICAL JOURNAL VOLUME 64 2 JULY 1983
Review Article
Sinusoidal versus pseudosinusoidal fetal
heart rate patterns
G.J.HOFMEYR, E.W.W.SONNENDECKER
Summary
Reports on fluctuating fetal heart rate (FHR)
patterns, which have been called sinusoidal FHR
patterns in the literature, have been critically
reviewed. Based on this analysis, stricter criteria are
presented whereby the true sinusoidal pattern can
be diagnosed and distinguished from the
pseudosinusoidal pattern. A practical approach to
the interpretation and management of fluctuating
FHR patterns is presented.
sinusoidal FHR panern. Their example shows a peak-to-peak
frequency of only 3 cycles per minute, which suggests that they
counted both the upward and the downward deflections. We
advocate adherence to the strict mathematical definition of
cycles per minute in which these are counted from one peak to
the next peak. We are also opposed to the use of the term
'periodicit1s' to describe frequency in sinusoidal FHR
panerns,6, 8 as this term is employed in cardiotocographic
terminology to describe events occurring in relation to uterine
contractions.
Definitive characteristics
S AfT Med J 1983; M: 19 - 23.
Although the sinusoidal fetal heart rate (FHR) pattern has been
generally recognized' since 1972,1,2 confusion regarding its
nomenclature and definition persists a decade later. Moreover,
recent publications3' 8 which contradict the ominous significance
attached to the sinusoidal FHR pattern by other authors 1,2,9-12
have caused uncertainty as to its interpretation and appropriate
management.
We have therefore critically reviewed the literature and
examined the published tracings of such patterns to formulate
practical guidelines for clarification of so-called sinusoidal
patterns. On the basis of this analysis we present strict criteria
whereby true sinusoidal patterns are distinguished from
pseudosinusoidal patterns.
.
The sinusoidal FHR panern has generally been dermed as a
FHR fluctuation with a frequency of 2 - S cycles per minute and
an amplitude of greater than S beats per minute. Uncritical
application of this definition has resulted in the reporting of
numerous cases with 'sinusoidal' FHR panerns in which the
ominous prognosis, as already mentioned, previously ascribed to
this pattern is contradicted. Attention has been drawn to the
misinterpretation of FHR panerns, usually occurring during
labour, which resemble the sinusoidal panern. Representative
examples illustrating the differences are shown in Figs I - 3.
.L-"--'--'---r---r--.. +-j-----,~_____t-.;...-_:_-----;---r--__t_-·l+r- ~
-li--,-+---,--+-_+-I-+-+--+-'60~:'--1'-+--l-+----t-:
I
+-..;J.·-+-----,-,-+i-o----"--'.:...-.....::--4.--+----1-+-+~:
, - - '_I -':+_1- --,::;;i _'
+
"",""""'_+," .+.---,+,---,-c----ri----t\, -t1\'-l:,Hr'f'r 2'~---+''''r--1'\___,f':_1i'r-A~,f-i
,,"v:-F'tl'y
I " '"
' "
"" I
--+-----l--.,: \} \
',',J.t-t' ,"'" --,'ilo-_Vl~r::.-=-c,._+l;-=-~i-=--=-i--...,----j+~----:+~---__;_
-----+-,,-.'
+----L--+~
I
"cr'
I
Nomenclature
The description of the sinusoidal FHR panern is confused
because of a lack of uniformity of nomenclature between authors.
Amplitude is measured br some as the 'peak-to-nadir'
difference9,13-16 and by others ,17,18 as the displacement above or
below the so-called baseline. As the baseline in the sinusoidal
panern is an arbitrary level midway between the peak and nadir,
we prefer using the peak-to-nadir difference as a more definitive
measurement of amplitude.
Frequency is counted as the number of peak-to-peak periods
per minute, referred to as cycles6,8,9,16,19 or as oscillations. 3,15,;j)
Oscillations have been counted as the number of deflections both
above and below the 'baseline' .14 Freeman and Garite 21 utilized a
cycliciry of 'above 4 - 8 per minute' in their definition of the
Department of Obstetrics and Gynaecology, University of
the Witwatersrand and Johannesburg Hospital,
Johannesburg
G. J. HOFMEYR, M.B. B.CH., M.R.C.O.G., LeClurer and Consulcanc
E. W. W. SONNENDECKER, M.MED. (0. ET G.l, F.RC.o.G.,Senior
Lecturer and Principal Consulranc
Date received: 10 Sep[ember 1982.
.
T-~' -
'8'0.-'----,--+-- +-__ ---,-_L
I.
-.~.-+----r--,----I:------,....~----r--.:...
r - - - :
- ,
- - : - ' - ,
-60
!
I
I
~_:....
~-_.:..--.:.-.---L-_...J...-L_...J...-L.-....:....-LII~;i~ot---"'----_-_--t,-------t-T,~-_-~.~- 8
i
6
------r--- -
:
~ ..
------r-
'
I
----I-·-:=l-===±= ~-4-----,--+------r-.l"-1
::-:r-r- ,
I' ,
"
!
---r-T-r
I _
Fig. 1. True sinusoidal FHR pattern with frequency 2 cycles per
minute, amplitude 15-35/min, diminished short-term baseline
variability and rounded peaks.
Krebs'4 refers to the patterns which resemble the sinusoidal
panern as 'sinuslike' or 'sinuform' variability. Freeman and
Garite 21 use the term 'pseudosinusoidal', which we prefer. They
distinguish these benign patterns by the lack of uniformi ry of the
sine wave panern, nnequal distribution of variability above and
below the baseline, and presence of short-term variability.
Modanlou and Freeman 19 found the following features to be
associated with ominous outcome and administration of
alphaprodine: (z) a stable baseline heart rate of 120-l60/min with
regular oscillations; (iz) an amplitude of S - IS/min, rarely
20
SA MEDIESE TYDSKRIF DEEL 64 2 JULlE 1983
I
. 140--
',-
I
-+-~~I-~J=r-+----t-"':-+
Fig. 2. Pseudosinusoidal FHR pattern recorded during labour.
Frequency 4 cycles per minute, amplitude 20-25/min. Note
pointing of peaks with 'saw-tooth' appearance.
greater; (iiz) frequency of 2 - S cycles per minute (as long-term
variability); (iv) fixed or flat short-term variability; (v) oscillation
of the sinusoidal wave form above and below a baseline; and (VI)
no areas of normal FHR variability or reactivity. Our critical
application of the above criteria (Table I) showed that at least 9 of
the tracings interpreted by Modanlou and Freeman as true
sinusoidal patterns did not meet all their stated criteria.
However, we agree that the first 7 cases tabulated are true
sinusoidal patterns. Accordingly, we have reservations about the
usefulness of certain oftheir criteria as outlined below: (a) the socalled baseline, a hypothetical line midway between the peaks
and nadirs, is not invariably between 120 and 160/min;
adherence to these limits does not improve the accuracy of
diagnosis; Cb) their stated upper limit of IS/min for amplitude,
with the concession that this may rarely be greater, does not
facilitate the interpretation of individual tracings; we found S
tracings in their series which exceeded this limit; (c) 'oscillation
of the sinusoidal wave form above and below a baseline' we
interpret to mean that the peaks as well as the nadirs must
conform to the smooth, rounded configuration of the
mathematical sine wave. We found rounding of the peaks to be a
consistent finding in true sinusoidal patterns, whereas the nadirs
were frequently pointed or irregular, as seen in 9 of the cases
interpreted as sinusoidal by Modanlou and Freeman, 19 who have
evaluated available tracings3.9.11-13.15.22 in the literature to
determine whether their predetermined criteria would
distinguish the significant from the less significant so-called
sinusoidal patterns. Our approach to the problem differed in that
we analysed the available published tracings in terms of
individual characteristics and fetal outcome in order to identify
thecriteria which most reliably distinguished between ominous
Fig. 3. A - pseudosinllsoidal pattern recorded during labour 50
minutes alter intravenous administration of 50 mg pethidine HCI
and 100 mg hydrc)xY"zin~. Frequency 5 cycles per minute;
amplitUde 5-10/min. Note presence of short-term variability,
pointing of peaks and single early deceleration. B pseudosinusoidal F:tlR pattern recorded antenatally. Frequency
4 cycles per minute; amplitude 6·7/min. Short-term variability
retained and fetalll1~yementspresent, but no FHR accelerations.
and benign patterU:5. Ac ordingly, t:he following features were
critically evaluared: amplitude of fluctuations, short-term
variability, shape of peaks and nadirs, and fetal movements (if
mentioned). The =~ were then classified according to the
TABLE I. CHARACTERISTICS OF TRACINGS INTERPRETED BY MODANLOU At.;IO FREEMAN 19 AS SINUSOIDAL,
IN RELATION TO THREE OF THEIR STATED eRITE RIA
Criteria of Modanlo u al1d Freeman 19
Authors
Rochard et al. 9
Modanlou et al. 11
Gal et al. '2
Mueller-Heubach et a/. 22
Birkenfeld et a/. 15
Baskett and Koh '3
Gray et aJ.3
"Interpreted by us as pseudosinusoidal.
Fig. No.
Baseline
120-160/min
3
1
2
Amplitude
5-15/min rarely::::>
10-25
35-90
10-35
1b
2b
1
1-2
3"
1b"
110-105
185-170
30-50
10-20
Sinusoidal wave form
above and below baseline
Poi nted nadirs
Occasional pointed nadirs
Poi nted nadirs
Poi nted nadirs
Poi nted nadirs
Poi nted nadirs
Pointed and irregular nadirs
Pointed peaks and nadirs
Pointed peaks and nadirs
SA MEDICAL JOURNAL VOLUME 64 2 JULY 1983
reported fetal outcome into either an 'ominous' group, which
included cases of severe fetal anaemia and asphyxia, or a 'benign'
group in which there was no fetal compromise in terms of scalp
pH or condition at birth (Table 11). The recorded FHR
characteristics were individually assessed to determine which of
these correlated with poor and which with good fetal outcome.
Contrary to the fmdings of previous authors 13 ,16,23 we found
measurement of amplitude to be unhelpful as there was a wide
and overlapping range in both ominous (7-90/min) and benign
(5-40/min) tracings. Furthermore, variation in amplitude within
a single tracing was not inconsistent with the true sinusoidal
pattern, as seen in cases reported by Modanlou er al. 11 and
Freeman and Garite. 21 The shape ofthe nadirs was not specific to
either group, pointed and irregular nadirs occurring in both
ominous and benign patterns. The criteria which we found to be
reliable in distinguishing the ominous from the benign tracings
are shown in Table 11. The tracings associated with fetal
compromise were found to have diminished short-term
variability and rounded peaks. Fetal movements were absent in
the 2 cases where mentioned. With the exception of Figs 2 and 4
of Johnson eT al. ,8 all the tracings not associated with fetal
compromise showed either retention of short-term variability,
presence of fetal movements, or pointing or irregularity of the
21
peaks. In accordance with these findings we propose the
following comprehensive definition of the sinusoidal FHR
pattern (Table Ill): (I) a fluctuating FHR pattern; (il) frequency
2 - 5 cycles per minute, counted from peak to peak; (iil)
amplitude> 5/min (measured from peak to nadir); (iv) markedly
reduced short-term variability « 5); (v) rounded peaks; and (VI)
reduced or absent fetal movements. Although the last criterion is
based on fetal movements, which have been mentioned in very
few papers, it is consistent with our clinical experience.
We would stress that the sinusoidal FHR pattern as defined
above is not a complete diagnosis but represents the
morphological description of a FHR pattern which is usually
associated with severe fetal compromise. This association is
clearly demonstrated by the data in Table IV.
The rare cases of transient FHR fluctuation after sedation
which do meet the above criteria must be called sinusoidal in
spite of the fact that they revert to a normal pattern. Reversion to
a normal pattern is also seen after intra-uterine transfusion. 24
It is mandatory to emphasize that persistent sinusoidal
patterns indicate intervention. Fluctuating FHR patterns which
do not meet our stated criteria should, however, be termed
pseudosinusoidal and necessitate further evaluation of feral
wellbeing.
TABLE 11. CHARACTERISTICS OF FHR PATTERNS REPORTED AS SINUSOIDAL
Fetal
condition
Antepartum
severe anaemia
Intrapartum
severe asphyxia
Authors
Fig. No.
FM
Rochard et al. 9
Modanlou et al. '1
Hatjis et al. 24
3
1
1
?
Nil
?
Mueller-Heubach et al. 22
Birkenfeld et al. 15
Elliot et a/. 25
O'Connor et al. 16
Horwell et al. 2o
Modanlou and Freeman '9
1b and 2b
1
2c
2
1
1
?
?
Nil
?
?
?
Basket! and Koh '3
Cetrulo and Schifrin lO
Gal et al. 12
1
4 and 5
1
2
1
8,25
?
?
?
?
?
?
3
1b
?
?
?
O'Connor et al. 16
Freeman and Garite 26
Intrapartum;
no fetal
compromise
Basket! and Koh '3
Gray et al. 3
Jarrell and SOkOP7
Lee and Drukker 5
Katz et aJ.7
Johnson et al. 8
O'Connor et al. ,6
Young et al. 6
Horwell et al. 2o
FM
= fetal
movement, ?
= not mentioned, + =
Short-term
variability
Shape of
peaks
1
Rounded
Rounded
Rounded
I
I
Rounded
Rounded
Rounded
Rounded
Rounded
Rounded
I
I
±
1
1
I
Rounded
Equivocal
Equivocal
Rounded
Equivocal
Rounded
5
1
1
2
+
?
?
?
Pointed
Pointed
Most pointed
Rounded
Irregular
IrregUlar
Rounded
3
4
?
?
Irregular
Rounded
5
3-4
5
3
4
4
?
?
?
?
?
?
9
present. 1 = decreased, ± = eqUivocal.
+
I
I
1
+
I
Pointed
Pointed
Irregular
Irregular
Irregular
Irregular
Comments
Resolved after
intra-uterine
transfusion
Post-transfusion
Poor tracing
Persisted after
delivery
Reduced scale
Poor tracing
Reduced scale
Post-a1phaprodine
Transient
Transient postsedation
Paracervical
block
Post-alphaprodine
pH 7,38
Meconium aspiration
22
SA MEDIESE TYDSKRIF DEEL 64 2 JULlE 1983
TABLE Ill. COMPARISON OF SINUSOIDAL AND PSEUDOSINUSOIDAL FHR PATTERNS
Common
Sinusoidal
characteristics
Pseudosinusoidal
Fluctuating FHR pattern
2-5 cycles/m in (peak-to-peak)
> 5/min (peak-to-nadir)
Description
Frequency
Amplitude
Distinguishing
characteristics
Short-term variability
Wave form
Fetal movements
Other associations
Clinical situations
Relation to sedation
Duration
Prognosis
Management
Markedly reduced"
Rounded peaks"
Reduced"
Retainedt
Pointed or irregular peakst
Normalt
Usually antepartum
with anaemia or intrapartum with asphyxia
Rare
Usually persistent
Usually ominous
Occasionally benign
when occurs transiently
after sedation
If persistent, delivery
or intra-uterine transfusion
Usually intrapartum
Frequent
Usually transient
Usually benign
Further evaluation
·AII present.
t One or more present.
TABLE IV. CORRELATION OF FETAL OUTCOME WITH PUBLISHED FHR TRACINGS CLASSIFIED ACCORDING TO
OUR CRITERIA
FHR pattern
Authors
Fig. No.
Fetal condition and outcome
Sinusoidal
(Antepartum)
Rochard et a/. 9
Modanlou et al. 11
Hatjis et al. 24
Mueller-Heubach et al. 22
3
1
1
1b
2b
1
2c
2
1
1
Severe anaemia. 50"10" stillborn or NND
Severe anaemia. Apgar 1. Fetomaternal transfusion
Severe anaemia. Resolved after IUT
Severe anaemia. Apgar 5-6.t NND
Severe anaemia. IUT
Severe anaemia. Cord Hb 2g/dl; NND
Severe anaemia. Apgar 5-7.t Cord Hb 5,7 g/dl
Severe anaemia. IUD
Severe anaemia. Apgar 6-6.t Cord Hb 4,0 g/dl
Severe anaemia. Exchange transfusion
1
Hypoxia. Apgar O. NND
Postmaturity. Apgar 2-6.t pH 7,11
Nuchal cord. Meconium. Apgar 3-7t
Following epidural. Apgar 8. Gastroschisis
Following paracervical block. Excellent outcome"
Birkenfeld et al. 15
Elliot et al. 25
O'Connor et al. 16
Horwell et a/. 2o
Modanlou and Freeman 19
Sinusoidal
(Intrapartum)
Pseudosinusoidal
Baskett and Koh 13
Gal et al. 12
Freeman and Garite 26
Johnson et al. 6
Baskett and Koh 13
Gray et af.3
Jarrell and SokoP7
Lee and Drukker 5
Katz et al. 7
Johnson et al. 8.
O'Connor et al. 16
2
8,25
2
4
3
1b
9
5
1
1
3
.5
3 and 4
5
Young et a/. 6
Technically
unsatisfactory
Horwell et al. 2o
3
4
4
Cetrulo and Schifrin lO
Gal et al. 12
O'Connor et al. 16
4 and 5
1
1
No fetal compromise
Good outcome"
'Normal at birth'
Temporary pattern. No compromise
Mild acidosis. Apgar 9-10.t Occult cord prolapse
I
No details.
Following meperidine
Excellent outcome
Following alphaprodine
pH 7,38. Subsequent poor outcome"
Apgar 8-1 Ot
~
No details
Good outcome"
No details
Apgar 6-7.t Meconium aspiration
Postmaturity. Stillborn
IUD during OCT in hypertensive patient
Antepartum haemorrhage. IUD; unexplained asphyxia
·Outcome given for whole group of which the tracing is representative.
[h~~~i~:~ef~~~~~Sw~:(~ve':t~~~ Apgar score these refer to the 1-minute and the 5-minute values respectiVely, where one figure is given for the Apgar score only
NND = neonata! death;
IU~::;: intra-uterine transfusion;
IUD = intra-uterine death; aCT::;: oxytocin challenge test.
SA MEDICAL JOURNAL VOLUME 64 2 JULY 1983
REFERENCES
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H erzfrequenz. 1I. Verhalten von Grundfrequenz, Fluktuarion und
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GV1/ecol Obsrer Bioi Reprod (Paris) 1972; 1: 343-352.
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.
4. Ayromlooi J, Berg P, Tobias M. The significance of sinusoidal feral heart rate
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.
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23
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.
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Heart rate changes after acute fetal
haemorrhage - a basis for the
pathophysiology of the sinusoidal pattern
G. J. HOFMEYR,
E.W.W.SONNENDECKER
Summary
The sequence of fetal heart rate (FHR) changes
recorded in a case of acute fetal haemorrhage is
reported. Initial bradycardia progressed through an
undulatory phase to tachycardia. Analysis of these
patterns in the context of experimental data on intrinsic heart rate control suggests that the FHR was
limited by availability of local myocardial energy,
which at a critical level produced low-frequency FHR
fluctuations. Extrapolation of this hypothesis to the
pathophysiology of the true sinusoidal FHR pattern
is discussed.
S Afr Med J 1983; 64: 23 - 25.
Department ofObstetrics and Gynaecology, University of the
Witwatersrand and Johannesburg Hospital, Johannesburg
G. J. HOFMEYR, .\I.B. B.CH., .\\R.c.o.G.,LeclUrer and ConSllham
E. W. W. SONNENDECKER, .\\MED. (0. ET G.I, F.R c.O.G., Senior
LeclUrer and Principal Consuham
Date recei\·ed: 10 September 1982.
The exact pathophysiology of the sinusoidal fetal heart rate
(FHR) pattern remains uncertain. I - 3 Sinusoidal FHR has been
ascribed to loss of autonomic nervous system control of the heart
rate4 - 6 as a result of tissue hypoxia,7,8 which may well account for
the loss of short-term variability, but which does not explain the
lo.w-frequency FHR fluctuations characteristic of the sinusoidal
pattern, its striking association with fetal anaemia, or its absence
in most cases of fetal asphyxia unassociated with anaemia. 9
Modanlou er al. 9have suggested that the common factor underlying the sinusoidal FHR pattern is high-output cardiac failure.
The evidence supporting the role of haemodynamic factors in the
pathogenesis of the sinusoidal FHR pattern is as follows: (i) Elliot
er al. 8 reported that it persisted for 3 hours in an anaemic neonate
despite normal arterial oxygen pressure and resolved only during
exchange transfusion; (ii) Hatjis er al. l reported its disappearance
following intra-uterine transfu ion; (iii) sinusoidal FHR has not
been observed in hypoxic neonates without anaemia;9 and (iv) it
has been reported in a fetus which was found to be in cardiogenic
shock after delivery. IQ
The need for further research in this field has recently been
emphasized by Johnson er at. II Since few relevant data have been
reported, we document a case which allows postulation of an
hypothesis on the pathophy iology of the sinusoidal FHR pattern.