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The effect of posture on cardiac output in late pregnancy complicated by pericardial constriction
Communications in brief 865
Volume 146 Number 7
rings." He concluded, therefore, that these deformities resulted from focal developmental errors in the formation of limb connective tissue. Since then, other histologic studies 1• 3 have confirmed these findings. Additional support for the endogenous theory is the observation that certain other anomalies tend to be associated with amniotic band limb deformities. These anomalies include clubfoot, clubhand, hydrocephalus, and midline facial and scalp defects. 2 The exogenous theory, as espoused by Torpin, 4 was based on early rupture of the membranes leading to a process of mechanical constriction of various parts of the fetus by threads or bands arising from denuded chorion or fragmented amnion. As the affected fetal parts grew in utero, the constricting bands would progressively tighten, causing amputation in its most severe form and shallow depression of the skin in its mildest form. After an extensive review of 400 cases of amniotic band disease, Torpin postulated that the more severe defects, such as clubfoot, were the result of oligohydramnios, which caused the fetus to be overcrowded and compressed by the empty uterus. Furthermore, those defects which seem most difficult to explain as being caused by constriction rings, such as the severe midline facial clefts, resulted when the fetus swallowed amniotic bands early in development. The swallowed bands then caused the fetal head to be drawn into close proximity with the uterine wall and, essentially, "tethered" there. The facial clefts resulted from the indentation produced by the swallowed bands. Attempts have been made to divide amniotic band deformities into two groups according to the timing of rupture of the amnion. If membranes ruptured prior to 45 days' gestational age, more severe defects, such as severe craniofacial malformations, resulted. Later rupture of the membranes resulted only in limb defects. The malformations associated with congenital ring constrictions can be classified into four groups': (1) simple ring constrictions; (2) ring constrictions accompanied by deformity of the distal part with or without lymphedema; (3) ring constrictions accompanied by fusion of distal parts, ranging from fenestrated or terminal syndactyly to "exogenous" syndactyly; (4) intrauterine amputations. Three of the four categories were displayed by the two infants in the present report. The most common finding in the amniotic band syndrome is constriction rings of the fingers and toes. Constriction rings in the lower leg occur up to 46% of the time, with distal syndactyly occurring in 38 ..5% of cases. Lymphedema distal to a band is found in 31% of cases. Torpin has noted that this can rarely be associated with necrosis and gangrene of the extremity. In its most severe form, the limb may require amputation. Fractures and pseudoarthrosis are usually present in this condition as well. The rarest of the limb defects is amputation, stated to occur in only 15.4%. 1 If the etiology of the amniotic band syndrome is genetic or occurs as a result of a "defective germ disk," as proposed by Streeter} monozygotic twins should both
be affected. Thus, our case, in which both twins were affected, lends support to this particular theory. However, in a review of the literature, there have been at least five sets of monozygotic twins where only one twin was affected.L 4 This information would appear to conflict with this theory and support Torpin's theory. 4 Irrespective of which etiology is correct, the clinical management of these cases is unaffected. However, the etiology of this syndrome may have major medicolegal implications. For example, if an infant affected with this syndrome is delivered and either a genetic amniocentesis was done or a therapeutic abortion was attempted during the pregnancy, the question of etiology becomes most important. For these reasons, a more diligent examination of the fetuses, placentas, and membranes of those affected with this entity is required so that the etiology may be more clearly determined. REFERENCES l. Seeds, J. W., Cefalo, R. C., and Herbert, W. N. P.: Amni-
otic band syndrome, AM. J. OBSTET. GYNECOL, 144:243, 1982. 2. Streeter, G. L.: Focal deficiencies in fetal tissues and their relation to intrauterine amputation, Contrib. Embryo!. 22:41, 1930. 3. Stock, R. ]., and Stock, M. E.: Congenital annular constrictions and intrauterine amputations revisited, Obstet. Gynecol. 53:592, 1979. 4. Torpin, R.: Fetal Malformation Caused by Amnion Rupture During Gestation, Springfield, Illinois, 1968, Charles C Thomas, Publisher.
The effect of posture on cardiac output in late pregnancy complicated by pericardia! constriction Sean Blake, Fiona Bonar, Conor McCarthy, and Dermot McDonald Mater Misericordia£ Hospital and National Maternity Hospital, Dublin, Ireland
A patient, aged 31, presented for cardiac assessment during her first pregnancy. A tentative diagnosis of noncalcified pericardia! constriction was made, and for confirmation cardiac catheterization without x-irradiation was performed at 33 weeks. Advantage was taken of the opportunity to study the behavior of the cardiac output during pregnancy as part of a more general study on the control of cardiac output in pericardia! constriction. A Swan-Ganz catheter was introduced into the pulmonary artery, and cardiac outputs were measured by thermodilution on an Edwards cardiac output computer. All results represent the mean of three mea-
Reprint requests: Prof. Sean Blake, Mater Misericordiae Hospital, Dublin 7, Ireland.
866 Communications in brief
August l, 1983
Am.
J. Obstet. Gynecol.
Table I. Results of measurement of cardiac output Time (min) 0 3
6 17 25 35
Position
Supine Side Side Side Side Side
RAP (mmHg)
LAP (mmHg)
Heart rate (bpm)
(Limin)
co
RA02 (ml/100 ml)
24
27
108
6.3 7.4 10.8 8.0 7.7 6.9
67 68
17 18 21
114
ll2 106 110 110
72
Time: Minutes after turning on side; RAP: right atrial mean pressure; LAP: left atrial mean pressure; CO: cardiac output; RA0 2 : right atrial oxygen saturation. surements. Blood oxygen was determined by a reflectometer (American Optical) and pressures were measured by a Hewlett-Packard photographic recorder, transducer, and pressure amplifier (Model 8805 C). In the supine position the baseline for pressure measurements was taken as being a vertical distance below the sternal angle equal to one third of the anteroposterior diameter of the chest at that point. In the left lateral position the baseline was taken as being 2 em vertically above the thorack spines. The mean right atrial pressure was 24 mm Hg, indicating severe constriction (Table 1). The resting supine cardiac output was 6.3 L/min. The patient was then turned to the left lateral position, and during the next 35 minutes further estimations of cardiac output were made. Other measurements (incomplete because their value had not been anticipated) are also included in Table I. At 6 minutes the cardiac output had risen by 70% and at 17 minutes, with the patient remaining on her left side, it had begun to fall back again, finally reaching the supine level after 35 minutes. Mixed venous samples obtained for oxygen saturation determination were too few to confirm the magnitude of the increase in cardiac output, but they support the conclusion that in spite of severe pericardia! constriction the cardiac output did increase. It is noteworthy that the mean right atrial pressure changed in a direction opposite to that of the cardiac output. Where there is a normal venous filling pressure, an increase in heart rate alone will produce relatively little increase in cardiac output 1; the high cardiac output in normal pregnancy is due mainly to an increase in stroke volume. 2 On the other hand, where the venous pressure is high, 3 especially in the particular circumstances of pericardia! constriction, an increase in heart rate will significantly augment cardiac output. Thus, in pregnancy associated with pericardial constriction, where an increase in venous pressure will not augment stroke volume, cardiac output will be highly rate dependent. During cardiac catheterization in this case, the pulse rate was approximately 50% above the normal nonpregnant level (see Table 1), and this may well have been the essential mechanism of the elevated output found initially in the supine position. On turning the patient on her side, as is the expected finding in normal pregnant women in the third trimes-
ter, the cardiac output increased as uterine pressure on the inferior vena cava was relieved. Initially this was a surprising finding because of the tight pericardia! constriction. It cannot have been due to the insignificant simultaneous alteration in heart rate (see Table 1). It is noteworthy that in the normal pregnant woman the increase in cardiac output on turning from the supine to the lateral position is not due merely to a venous transfusion effect from the sudden removal of caval compression. This is a m,Yor factor but there is also an important element of diminution in total systemic vascular resistance. With uterine compression of the inferior vena cava, the total systemic vascular resistance is in two main parts, the arteriolar and the venous. The venous part is not trivial; in the supine hypotensive syndrome, it approaches the infinite. It is this venous part which is ameliorated by removal of caval compression. In constrictive pericarditis the augmented venous return cannot per se increase the cardiac output, but a diminution in vascular resistance can do so. This is probably the explanation of the increase found here. The only surprise is its magnitude (see Table I). This may be related to the very high venous pressure. The cardiac output, having reached a peak, gradually declined again to reach the supine level at 35 minutes. This was not anticipated but perhaps should have been. Presumably the systemic arteriolar resistance gradually increased to compensate for the fall in venous resistance. This is to be expected3 since there seems no reason to suppose that cardiovascular reflexes are not functioning normally in pregnancy, albeit geared to a higher level of cardiac output. The changes in the right atrial pressures would support this suggestion in that they moved in a direction opposite to that of the cardiac output; a fall in impedance to ventricular ejection would be expected to diminish ventricular filling pressure. However, the more helpful measurement would have been the left atrial pressure change but this was not followed. Clearly the behavior of cardiac output with changes of posture may not be similar in normal pregnancy and in pregnancy complicated by pericardia! constriction. However, the findings reported here do raise questions about the normal. The mechanisms involved may well be fundamentally similar. If cardiovascular reflexes are functional in pregnancy, then variations in posture
Communications in brief
Volume 146 Number 7
during the third trimester, while undoubtedly causing acute changes in cardiac output, would be expected to cause these changes only transiently. Short-term studies may detect only transient changes and in the literature, when the information is provided, all studies to date have been short term (less than 20 minutes). 4 Even then there has not been a complete consensus about the behavior of the cardiac output in relation to posture during the third trimester. The general opinion is that it does not fall except as a result of uterine pressure, but the work of Ueland and associates 4 would suggest that it does. 4 It is an important point for the management of heart disease in pregnancy and requires further studv.
867
REFERENCES 1. Ross, J., Jr., Linhart, J. W., and Braunwald, E.: Effects of changing heart rate in man by electrical stimulation of the right atrium, Circulation !42:549, 1965. 2. Perloff, j. K.: Pregnancy and cardiovascular disease, in Braunwald, E., editor: Heart Disease: Textbook of Cardiovascular Medicine, Philadelphia, 1980. W. B. Saunders Company, p. 1873. 3. Guyton, A. C.: The relationship of cardiac output and arterial pressure control, Circulation 64:1079, I 981. 4. Ueland, K., Novy, M. J., Peterson, E. N., and Metcalfe, J.: Maternal cardiovascular dynamics. IV. The influence of gestational age on the maternal cardiovascular response to posture and exercise, AM. J. 0BSTET. GY!IIECOL. 104:856, 1969.
Volume 146 Number 7
rings." He concluded, therefore, that these deformities resulted from focal developmental errors in the formation of limb connective tissue. Since then, other histologic studies 1• 3 have confirmed these findings. Additional support for the endogenous theory is the observation that certain other anomalies tend to be associated with amniotic band limb deformities. These anomalies include clubfoot, clubhand, hydrocephalus, and midline facial and scalp defects. 2 The exogenous theory, as espoused by Torpin, 4 was based on early rupture of the membranes leading to a process of mechanical constriction of various parts of the fetus by threads or bands arising from denuded chorion or fragmented amnion. As the affected fetal parts grew in utero, the constricting bands would progressively tighten, causing amputation in its most severe form and shallow depression of the skin in its mildest form. After an extensive review of 400 cases of amniotic band disease, Torpin postulated that the more severe defects, such as clubfoot, were the result of oligohydramnios, which caused the fetus to be overcrowded and compressed by the empty uterus. Furthermore, those defects which seem most difficult to explain as being caused by constriction rings, such as the severe midline facial clefts, resulted when the fetus swallowed amniotic bands early in development. The swallowed bands then caused the fetal head to be drawn into close proximity with the uterine wall and, essentially, "tethered" there. The facial clefts resulted from the indentation produced by the swallowed bands. Attempts have been made to divide amniotic band deformities into two groups according to the timing of rupture of the amnion. If membranes ruptured prior to 45 days' gestational age, more severe defects, such as severe craniofacial malformations, resulted. Later rupture of the membranes resulted only in limb defects. The malformations associated with congenital ring constrictions can be classified into four groups': (1) simple ring constrictions; (2) ring constrictions accompanied by deformity of the distal part with or without lymphedema; (3) ring constrictions accompanied by fusion of distal parts, ranging from fenestrated or terminal syndactyly to "exogenous" syndactyly; (4) intrauterine amputations. Three of the four categories were displayed by the two infants in the present report. The most common finding in the amniotic band syndrome is constriction rings of the fingers and toes. Constriction rings in the lower leg occur up to 46% of the time, with distal syndactyly occurring in 38 ..5% of cases. Lymphedema distal to a band is found in 31% of cases. Torpin has noted that this can rarely be associated with necrosis and gangrene of the extremity. In its most severe form, the limb may require amputation. Fractures and pseudoarthrosis are usually present in this condition as well. The rarest of the limb defects is amputation, stated to occur in only 15.4%. 1 If the etiology of the amniotic band syndrome is genetic or occurs as a result of a "defective germ disk," as proposed by Streeter} monozygotic twins should both
be affected. Thus, our case, in which both twins were affected, lends support to this particular theory. However, in a review of the literature, there have been at least five sets of monozygotic twins where only one twin was affected.L 4 This information would appear to conflict with this theory and support Torpin's theory. 4 Irrespective of which etiology is correct, the clinical management of these cases is unaffected. However, the etiology of this syndrome may have major medicolegal implications. For example, if an infant affected with this syndrome is delivered and either a genetic amniocentesis was done or a therapeutic abortion was attempted during the pregnancy, the question of etiology becomes most important. For these reasons, a more diligent examination of the fetuses, placentas, and membranes of those affected with this entity is required so that the etiology may be more clearly determined. REFERENCES l. Seeds, J. W., Cefalo, R. C., and Herbert, W. N. P.: Amni-
otic band syndrome, AM. J. OBSTET. GYNECOL, 144:243, 1982. 2. Streeter, G. L.: Focal deficiencies in fetal tissues and their relation to intrauterine amputation, Contrib. Embryo!. 22:41, 1930. 3. Stock, R. ]., and Stock, M. E.: Congenital annular constrictions and intrauterine amputations revisited, Obstet. Gynecol. 53:592, 1979. 4. Torpin, R.: Fetal Malformation Caused by Amnion Rupture During Gestation, Springfield, Illinois, 1968, Charles C Thomas, Publisher.
The effect of posture on cardiac output in late pregnancy complicated by pericardia! constriction Sean Blake, Fiona Bonar, Conor McCarthy, and Dermot McDonald Mater Misericordia£ Hospital and National Maternity Hospital, Dublin, Ireland
A patient, aged 31, presented for cardiac assessment during her first pregnancy. A tentative diagnosis of noncalcified pericardia! constriction was made, and for confirmation cardiac catheterization without x-irradiation was performed at 33 weeks. Advantage was taken of the opportunity to study the behavior of the cardiac output during pregnancy as part of a more general study on the control of cardiac output in pericardia! constriction. A Swan-Ganz catheter was introduced into the pulmonary artery, and cardiac outputs were measured by thermodilution on an Edwards cardiac output computer. All results represent the mean of three mea-
Reprint requests: Prof. Sean Blake, Mater Misericordiae Hospital, Dublin 7, Ireland.
866 Communications in brief
August l, 1983
Am.
J. Obstet. Gynecol.
Table I. Results of measurement of cardiac output Time (min) 0 3
6 17 25 35
Position
Supine Side Side Side Side Side
RAP (mmHg)
LAP (mmHg)
Heart rate (bpm)
(Limin)
co
RA02 (ml/100 ml)
24
27
108
6.3 7.4 10.8 8.0 7.7 6.9
67 68
17 18 21
114
ll2 106 110 110
72
Time: Minutes after turning on side; RAP: right atrial mean pressure; LAP: left atrial mean pressure; CO: cardiac output; RA0 2 : right atrial oxygen saturation. surements. Blood oxygen was determined by a reflectometer (American Optical) and pressures were measured by a Hewlett-Packard photographic recorder, transducer, and pressure amplifier (Model 8805 C). In the supine position the baseline for pressure measurements was taken as being a vertical distance below the sternal angle equal to one third of the anteroposterior diameter of the chest at that point. In the left lateral position the baseline was taken as being 2 em vertically above the thorack spines. The mean right atrial pressure was 24 mm Hg, indicating severe constriction (Table 1). The resting supine cardiac output was 6.3 L/min. The patient was then turned to the left lateral position, and during the next 35 minutes further estimations of cardiac output were made. Other measurements (incomplete because their value had not been anticipated) are also included in Table I. At 6 minutes the cardiac output had risen by 70% and at 17 minutes, with the patient remaining on her left side, it had begun to fall back again, finally reaching the supine level after 35 minutes. Mixed venous samples obtained for oxygen saturation determination were too few to confirm the magnitude of the increase in cardiac output, but they support the conclusion that in spite of severe pericardia! constriction the cardiac output did increase. It is noteworthy that the mean right atrial pressure changed in a direction opposite to that of the cardiac output. Where there is a normal venous filling pressure, an increase in heart rate alone will produce relatively little increase in cardiac output 1; the high cardiac output in normal pregnancy is due mainly to an increase in stroke volume. 2 On the other hand, where the venous pressure is high, 3 especially in the particular circumstances of pericardia! constriction, an increase in heart rate will significantly augment cardiac output. Thus, in pregnancy associated with pericardial constriction, where an increase in venous pressure will not augment stroke volume, cardiac output will be highly rate dependent. During cardiac catheterization in this case, the pulse rate was approximately 50% above the normal nonpregnant level (see Table 1), and this may well have been the essential mechanism of the elevated output found initially in the supine position. On turning the patient on her side, as is the expected finding in normal pregnant women in the third trimes-
ter, the cardiac output increased as uterine pressure on the inferior vena cava was relieved. Initially this was a surprising finding because of the tight pericardia! constriction. It cannot have been due to the insignificant simultaneous alteration in heart rate (see Table 1). It is noteworthy that in the normal pregnant woman the increase in cardiac output on turning from the supine to the lateral position is not due merely to a venous transfusion effect from the sudden removal of caval compression. This is a m,Yor factor but there is also an important element of diminution in total systemic vascular resistance. With uterine compression of the inferior vena cava, the total systemic vascular resistance is in two main parts, the arteriolar and the venous. The venous part is not trivial; in the supine hypotensive syndrome, it approaches the infinite. It is this venous part which is ameliorated by removal of caval compression. In constrictive pericarditis the augmented venous return cannot per se increase the cardiac output, but a diminution in vascular resistance can do so. This is probably the explanation of the increase found here. The only surprise is its magnitude (see Table I). This may be related to the very high venous pressure. The cardiac output, having reached a peak, gradually declined again to reach the supine level at 35 minutes. This was not anticipated but perhaps should have been. Presumably the systemic arteriolar resistance gradually increased to compensate for the fall in venous resistance. This is to be expected3 since there seems no reason to suppose that cardiovascular reflexes are not functioning normally in pregnancy, albeit geared to a higher level of cardiac output. The changes in the right atrial pressures would support this suggestion in that they moved in a direction opposite to that of the cardiac output; a fall in impedance to ventricular ejection would be expected to diminish ventricular filling pressure. However, the more helpful measurement would have been the left atrial pressure change but this was not followed. Clearly the behavior of cardiac output with changes of posture may not be similar in normal pregnancy and in pregnancy complicated by pericardia! constriction. However, the findings reported here do raise questions about the normal. The mechanisms involved may well be fundamentally similar. If cardiovascular reflexes are functional in pregnancy, then variations in posture
Communications in brief
Volume 146 Number 7
during the third trimester, while undoubtedly causing acute changes in cardiac output, would be expected to cause these changes only transiently. Short-term studies may detect only transient changes and in the literature, when the information is provided, all studies to date have been short term (less than 20 minutes). 4 Even then there has not been a complete consensus about the behavior of the cardiac output in relation to posture during the third trimester. The general opinion is that it does not fall except as a result of uterine pressure, but the work of Ueland and associates 4 would suggest that it does. 4 It is an important point for the management of heart disease in pregnancy and requires further studv.
867
REFERENCES 1. Ross, J., Jr., Linhart, J. W., and Braunwald, E.: Effects of changing heart rate in man by electrical stimulation of the right atrium, Circulation !42:549, 1965. 2. Perloff, j. K.: Pregnancy and cardiovascular disease, in Braunwald, E., editor: Heart Disease: Textbook of Cardiovascular Medicine, Philadelphia, 1980. W. B. Saunders Company, p. 1873. 3. Guyton, A. C.: The relationship of cardiac output and arterial pressure control, Circulation 64:1079, I 981. 4. Ueland, K., Novy, M. J., Peterson, E. N., and Metcalfe, J.: Maternal cardiovascular dynamics. IV. The influence of gestational age on the maternal cardiovascular response to posture and exercise, AM. J. 0BSTET. GY!IIECOL. 104:856, 1969.