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 1. Kubli F, Rungers H, Hailer , Bogdan C, Ramzjn M. Die antepanale fetale H erzfrequenz. 1I. Verhalten von Grundfrequenz, Fluktuarion und Dezelerationen bei anrepartalem Fruchllod. Gebllrrshilfe Peri1/aroI1972; 176: 309-323. 2. Manseau P, Vanquier J, Chavinie J, Sureau C. Le rythme cardiaque foetal sinusoidal. Aspect e\'ocateur de souffranee foerale au cours de la grossesse.] GV1/ecol Obsrer Bioi Reprod (Paris) 1972; 1: 343-352. 3. Gray JH, Cudmore DW, L uther ER, Martin TR, Gardner AJ. Siriusoidal fetal hean rate panern associared with aJphaprodine administration. Obsrec G\'71ecol 1978; 52: 678-681. . 4. Ayromlooi J, Berg P, Tobias M. The significance of sinusoidal feral heart rate pattern during labour and its relation [Q fetal status and neonatal ourcome.llllJ GvmecolObsrer 1979; 16: 341-344. 5. L-ee CY, Drukker B. The nons tress rest for rhe antepartum assessment of fetal reser,·e. Am] Obstel GY1/ecoI1979; 134: 460-468. 6. Young BK, Karz M, Wilson SJ. Sinusoidal feral hearr rate. I. Clinical significance. Am] Obstel GY1/ecol 1980; 136: 5 7-593. 7. Karz M, Wilson SJ, Young BK. Sinusoidal fetal heart rare: I!. Continuous tissue pH srudies. Am] Obslel G)'1lecoI1980; 136: 594-596. 8. Johnson TRB, Compton AA, Rotmensch J, Work BA, Johnson JWc. Significance of the sinusoidal fetal heart rate pallern. Am] Ob,rer Gmecol1981; 139: 446-453. . 9. Rochard F, Schifrin BS, Goupil F, Legrand H, Blolliere J, Sureau C. Nonstressed fetal heart rate monitoring in the antepartum period. Am] Obslet GV1/ecol 1976; 126: 699-706. 10. Cerrulo CL, Schifrin BS. Feral heart rare pallerns preceding dearh i/1 lIlero. ObHer GV1/ecol 1976; 48: 521-527. 11. MOdanlou HO, Freeman RK, Ortiz 0, Hinkes P, Pillsburv G. Sinusoidal fetal heart rate pattern and severe fetal anemia. Obsrer GY1/ecoi 1977; 49: 537-541. 12. Gal 0, Jacobson LM, Ser H, Park SA, Tancer ML. Sinusoidal pallern: an 23 alarming sign of fetal distress. A m] Obstel GY1/ecol 197 ; 132: 903-905. 13. Bask"'t TF, Koh KS. Sinusoidal fetal heart pallern: a sign of fetal hypoxia. Obstel GV1/ecol 1974; 44: 379-382. 14. Krebs HB. Oefmition of sinusoidal fetal heart rare (Letrer). Am] Obstel GY1/PcoI1980; 138: 1231-1232. 15. Birkenfeld A, yarfe H, SadO\' ky E. Sinusoidal feral heart rate pallern wirh severe fetal anaemia Case reporl. Br] ObHer G)'1laecoI1980; 87: 916-919. 16. O'Connor MC, Hassabo MS, McFadven IR. Is the sinusoidal feral heart parrern sinister? ] Ohs"l GY1/ecol 1980; I: 90-95. 17. Jarrell SE, Sokol RJ. Clinical use of stressed and nonstressed monitoring techniques. CIi1/ Obstel GY1/ecol 1979; 22: 617-632. 18. Cherny WB. Sinusoidal pallerns. Ari= Med 1981; 38: 107-108. . 19. Modanlou HO, Freeman RK. Sinusoidal fetal heart rate pallern: its definition and clinical significance. Am] Obsrer GY1/ecol 19 2; 142: 1033-1038. 20. HO""ell OH, Wong YC, Ramam SS. The sinusoidal fetal heart rate parrern. Si1/gapore] ObHer GY1/eco/1982; 13: 65-71. 21. Freeman RK, Garite TJ. Feral Hearl Rare M01/itori1/g. 1st ed. Baltimore: \~'illiams & Wilkins, 1981: 2- 3. 22 . .\\ueller-Heubach E, Caritis SN, Ede!stone 01. Sinusoidal fetal heart rate panern following intrauterine felal transfusion_ Obsrel GY1U'co1197 ; 52, No. I (suppl): 43-46. . 23. Geirsson RT, McFad,'en IR. Sinusoidal fetal heart rate pallern with se,'ere fetal anaemia. Case rePort (Lener :- reply to Birkenfeld er 01.1\). Br] Ob,ter G"naecol 1981; 88: 956-958. 24. Hatjis CG, Mennuti MT, Sacks LM, Schwarz RH. Resolurion of a sinusoidal fetal heart rate pattern following intrauterine transfusion. Am] Obsler Gyt1ecnl 1978; 132: 109-111. 25. Elliot JP, Modanlou HO, O'Keeffe OF, Freeman RK. Significance offetal and neonatal sinusoidal heart rale pattern: furrher clinical obsen-ations in Rh incomparibility. Alii] Obsrer Gynecol 1980; 138: 227-230. 26. Freeman RK, Garite TJ. Feral Heurf Rure Monitoring. Is' ed. Baltimore: Williams & \~'ilkins, 19 I: 110-111. 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.
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