|Year : 2021 | Volume
| Issue : 2 | Page : 46-50
Maternal pulse waveform in second trimester and risk of preeclampsia
Sharan Raj S, Niruby Rasendrakumar, Nidhi Sharma
Department of Obstetrics and Gynaecology, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India
|Date of Submission||05-Jul-2021|
|Date of Acceptance||21-Dec-2021|
|Date of Web Publication||28-Feb-2022|
Department of Obstetrics and Gynaecology, Saveeetha Medical College, Saveetha Institute of Medical and Technical Sciences, No 5 Jayanthi Street, Dr Seethapathi Nagar Velachery, Chennai 600042, Tamil Nadu.
Source of Support: None, Conflict of Interest: None
Background: Preeclampsia is a multisystem heterogeneous disorder occurring in 4%–7% of all pregnancies. Objectives: This study was conducted to define the relation between arterial stiffness and perinatal outcome in a tertiary care center. The relationship between maternal pulse wave augmentation index and adverse perinatal outcome is explored in this study. Materials and Methods: Peripheral pulse waveform of the brachial artery and mean arterial pressure measurement was performed in the second trimester in women with singleton pregnancy. Preeclampsia was recorded in (7%) of all pregnancies. Results: Abnormal peripheral pulse wave augmentation in the second trimester is a good tool for the prediction of preeclampsia (sensitivity 91.23% and specificity 99.06%, P < 0.05). Conclusion: Increased peripheral augmentation index (>2 SD) and mean arterial pressure measurement in combination have better detection rates for early-onset preeclampsia and fetal growth restriction (FGR).
Keywords: Hypertension, mean arterial pressure, preeclampsia pregnancy, pulse waveform
|How to cite this article:|
SharanR, Rasendrakumar N, Sharma N. Maternal pulse waveform in second trimester and risk of preeclampsia. J Cardio Diabetes Metab Disord 2021;1:46-50
| Introduction|| |
The augmentation index (AI) is a measure of arterial stiffness and is calculated as a ratio in the blood pressure (BP) waveform. When arteries are stiff, a reflected wave is formed where arteries split. This reflected wave moves back to the heart and the heart pumps against a higher pressure after receiving this impact. The AI is calculated from the arterial pulse. AI depends on the relationship between augmentation pressure and pulse pressure. The arterial pulse comprises a forward wave generated by left ventricular ejection and a backward wave that depends on elastic properties of the arterial tree, the wave transmission velocity, and the distance from the reflection sites. There are two types of AI based on the reflection site: the central AI and peripheral AI. The peripheral AI is defined as the difference between the second and the first systolic peak and is expressed as a percentage of the central pulse pressure (PP). The AI percentage is calculated as pAI% = [(P2–P1)/PP] × 100.
Preeclampsia can result in high BP and/proteinuria or manifest itself as eclampsia (Greek word eklampsis meaning lightening). These complications are associated with severe complications such as cerebral hemorrhage, lung edema or liver hemorrhage, and rupture.[2
Pregnancy has a superadded fetoplacental circulation. The maternal increase in blood volume and cardiac output is 40% after the first 20 weeks of pregnancy., These changes will result in increased afterload and severe hypertension in nonpregnant women and yet BP falls in pregnancy. This change has been attributed to the decrease in stiffness of blood vessels due to relaxed smooth muscle cells in tunica media under the influence of progesterone secreted by placenta. BP decreases until around 18 weeks of pregnancy and progressively increases toward term. Systolic and diastolic BP both decline early in the first trimester, reaching a nadir by 24–28 weeks; then they gradually rise toward term but never return quite to prepregnancy baseline. Diastolic falls more than systolic, as much as 15 mm Hg. Arterial BP is never normally elevated in pregnancy. This is possible by a steep reduction in systemic vascular arterial resistance and an increase in venous capacitance. The heart rate increases by 20% to compensate for the drop in systemic vascular resistance. Normal pregnancy, therefore, has warm skin, prominent veins, and orthostatic hypotension.
In preeclampsia due to arterial stiffness, two stages of vascular dysfunction exist. In the first stage, there is a hemodynamic maladaptation to the increased cardiac output and blood volume in pregnancy and suboptimal development of placenta [Figure 1]. This leads to the second stage of placental vascular hypoperfusion and defective placentation. There is acute atherosis and spiral arteries are occluded by fibrinoid material and surrounded by foam cells. Acute atherosis and placental thrombi are also seen in low-birth-weight babies. The functional biochemical changes in placenta are decreased ratio of prostacyclin I2 to thromboxane A2. Furthermore, in preeclampsia, there is impaired vasodilator response to endothelium-dependent agonists such as acetylcholine and bradykinen. Various adaptive mechanisms are employed at the feto-maternal interphase and subsequently after 20 weeks a clinically evident maternal syndrome hypertension, edema, and proteinuria develop. The development of the second stage of systemic and placental inflammation can also happen independently of the first stage. In preeclampsia, there is a latent preclinical stage with impaired vascular resilience, hyperdynamic circulation, and a decreased cardiac output as clinical disease develops. This decreased cardiac output leads to renal and uteroplacental insufficiency. There may also be leaky capillaries leading to pulmonary and cerebral edema. Severe and early-onset preeclampsia has abnormal brachial artery waveform in the preclinical stage and hypertension in the clinical stage. Thus, increased augmentation of the brachial artery may be considered as a local noninvasive imaging of a more generalized systemic vasculopathy. This may mediate further future cardiovascular risks. Women with preeclampsia are also two and a half times likely to die from ischemic heart disease in later life.,, This study was conducted to identify the fetomaternal outcome in high peripheral AI of the brachial artery.
|Figure 1: (B) Conceptual framework of the peripheral augmentation index pAI% = [(P2–P1)/PP] ×100|
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Raised brachial artery impedance is a marker of early endothelial dysfunction. It is associated with an increased aortic pulse wave index and AI in the first trimester of pregnancy. Increased aortic pulse wave index and AI are also a marker of future cardiovascular risk.,, The faster the pulse wave returns from the periphery, the stiffer the arteries are and the higher the AI. Increased homocysteine levels have also been implicated in both cardiovascular risks and preeclampsia. Brachial artery impedance is also associated with adverse perinatal outcomes such as preterm labor, fetal growth restriction (FGR), and abruption placenta., Preterm labor was defined as onset of true labor pains with dilatation of cervix before 37 weeks of pregnancy. FGR was defined as fetal biometry less than 2 SD below that of average of that gestational age. Abruption placenta was defined as premature separation of a normally situated placenta.
The predominant physiological stimulus for endothelial nitric oxide synthesis is flow-induced shear stress., The clinical presentation of preeclampsia, FGR, preterm birth, and abruption placenta are associated with vessel wall stiffness and late endothelial dysfunction. This prospective study was conducted to evaluate the association of increased AI of brachial artery with various disorders of fetomaternal interphase resulting from endothelial dysfunction in the placental insufficiency.
| Materials and Methods|| |
Waveform analysis of the brachial arteries was performed at 20–23 weeks gestation in 141 women with singleton/multiple pregnancies attending a routine target scan. All women with no major fetal anomaly are offered the option of brachial artery evaluation. Written consent was obtained in all cases. Ultrasound was done in all cases in first trimester for correct estimation of gestational age of pregnancy.
Arteriography, popularly known as sphygmocor test, was carried out in the Department of Obstetrics and Gynecology after getting written informed consent from participants in local language. Multiple pregnancies and pregnancies with congenital anomalies are especial considerations and were excluded. Detailed maternal factors like age, gestational age, parity, prepregnancy body mass index, previous low birth weight, hemoglobin levels, chronic hypertension, gestational diabetes, and previous preeclampsia are recorded. Placental problems such as low-lying placenta, infarcts, retro placental calcifications, small placenta, and premature separation are noted. The pregnant women are asked to rest in left lateral position for 10 min. The brachial artery pulse waveforms were recorded with a pressure tonometer. Tonometer machines used for the study were SphygmoCor System; Atcor Medical, Sydney, NSW, Australia (http://www.atcormedical.com/sphygmocor.html). A measurement was considered adequate only the operator index was >80 (as per manufacturer’s instructions, the range of 0–100 was depicted as increasing quality).
Arteriography of brachial artery in longitudinal scan was used to obtain 10 similar consecutive waveforms. A corresponding central aortic waveform is projected with the help of a validated computerized inbuilt mathematical function. The same is repeated for the contralateral brachial artery and the mean of the two vessels is calculated. Recordings for measurements are obtained in the absence of fetal breathing movement and maternal heart rate between 70 and 80 and fetal heart rate between 120 and 160 beats per minute. The arteriography cuff covered more than three-fourths circumference of the arm. Patients were called for antenatal visits every 2 weeks till 36 weeks and weekly thereafter. BP was measured in the right arm in the sitting posture and koratkoff 5 sound as taken as the diastolic BP. Urine albumin was measured at each visit.
If hypertension and/or proteinuria developed before 34 weeks, the gestation was classified as early-onset preeclampsia. If hypertension and/or proteinuria developed after 34 weeks, the pregnancy was diagnosed as late-onset preeclampsia.
Preeclampsia was defined according to the guidelines of the International Society for the Study of Hypertension in Pregnancy. This requires two recordings of diastolic BP of ≥90 mm Hg at least 4 h apart in previously normotensive women after 20 weeks of pregnancy, and proteinuria of 300 mg or more in 24 h, or two readings of at least + + on dipstick analysis of midstream or catheter urine specimens if no 24-h collection is available. FGR was defined as a fetal weight below the expected weight in the customized population fetal growth charts. Preterm Labor is defined as a regular uterine activity before 37 completed weeks of gestation associated with dilatation of cervix. Abruption of placenta is identified as presence of retro placental clots in ultrasound or placental examination after delivery. Descriptive and inferential statistics were used to analyze the data. Differences were considered significant when P < 0.05. Logistic regression was used to obtain the odds ratio (OR) and 95% confidence interval (CI).
| Results|| |
After waveform examination of brachial arteries, satisfactory waveforms were obtained in 99% (138) of all pregnancies. All the recruited pregnancies were followed up during the antenatal and postnatal period. Brachial artery AI is not normally distributed but is found skewed to the right. [Table 1] summarizes the maternal history variables and demographic characteristics of mothers associated with preeclampsia.
|Table 1: Maternal demographic variables associated with high pulse wave augmentation index in first trimester|
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[Table 2] brings up the fact that the presence of high pulsatility is a significant risk factor for early-onset preeclampsia as compared to late-onset preeclampsia. Approximately 8.18% pregnancies resulted in preeclampsia. There were no intrauterine deaths in this study. Out of hypertensive pregnancies, approximately 30% were early onset (<34 weeks) and 70% were late onset (>34 weeks).
|Table 2: High pulse wave augmentation index (>2 SD) of brachial artery in second trimester and prediction of preeclampsia, fetal growth restriction (FGR), preterm labor and Abruption placenta|
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Gestational age rather than weight was a predictor of neonatal mortality, as all FGR babies beyond 34 weeks had no neonatal mortality. In few neonates, sometimes no maternal cause of FGR can be identified. [Table 2] brings up the fact that the presence of high pulse wave AI as compared to low pulsatility confers a significant risk (31.58% vs. 2.19%) for FGR (P < 0.05).
It also brings up the fact that the presence of high peripheral pulse wave AI as compared to low peripheral pulse wave AI is a significant risk factor for preterm labor and abruption placenta. There were cases of grade one abruption, grade 2 abruption, and grade three abruption. There can also be grade 0 abruption. Out of FGR newborns, almost all survived beyond four weeks of life, as there is a catch-up growth after delivery.
[Table 2] also tells us the sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratio positive and likelihood ratio negative of early- and late-onset preeclampsia, FGR, preterm birth, and abruption placenta when there is a high peripheral pulse AI percentage.
| Discussion|| |
Brachial artery is a continuation of subclavian artery and the main artery entering the forearm and hand, whose anterior division gives of the radial artery. Endothelial dysfunction and arterial stiffness might show two varied aspects of vessel wall. The arterial stiffness is determined by elastin to collagen ratio in the vessel wall muscle. On the contrary, the endothelium responds to nitric oxide, and other cytokines and inflammatory mediators such as vascular endothelial growth factor (VEGF), transforming growth factor (TGF), placental growth factor (PLGF), and soluble endoglin (sENG).
Generalized vasodilatation starts during the luteal phase after conception and peripheral resistance falls substantially after 5 weeks gestation until reaching values 34% lower than the prepregnant state at 20 weeks gestation., Arterial pulse wave velocity and AI are consistent with vessel wall dysfunction in vivo and in vitro studies. The likely cause is deranged nitric oxide availability, although the precise underlying pathophysiology is unclear. Numerous clinical studies have shown the efficacy of nitric oxide donors to suppress hypertension and improve umbilical cord flow to fetus., Ischemic placenta may secrete sFLT (soluble fms like tyrosine kinase) and sENG. These decoy molecules trap the available growth factors. The decoy molecule sFLT binds to VEGF and PLGF, sENG binds to TGF-β and thus there is an imbalance of proangiogenic and antiangiogenic factors leading to preeclampsia and fetoplacental complications. The molecule sFLT is a free-floating variant of FLT-1. FLT-1 is a receptor––a docking point of VEGF and PLGF in the vessel wall. This binding process is necessary for vessels to remain healthy. sFLT-1 binds the available VEGF and PLGF and the vessel walls deprived of VEGF and PLGF remain stiff and inelastic and deteriorate. Endoglin receptor on the vessel wall is a docking point of TGF-β. The free circulating levels of sENG act as a decoy diverting TGF-β away from vessels. Deprived of TGF-β the vessel wall becomes less elastic. However, the effect of these molecules on vessel wall stiffness is still to be correlated.
The maternal increase in blood volume and cardiac output is 40% to supply an added fetoplacental circulation. These changes will result in severe hypertension in nonpregnant women but still BP falls in pregnancy. This adaptation to pregnancy is the result of a steep reduction in systemic vascular arterial resistance and an increase in venous capacitance. Normal pregnancy therefore has warm skin, prominent veins, and orthostatic hypotension. There is an increased flow to skin, kidneys, and uterine arteries. Severe and early-onset preeclampsia is characterized by hypertension and abnormal brachial artery waveform. Thus, pulse waveform analysis of brachial artery may be considered as a local noninvasive imaging of a more generalized systemic vasculopathy.,, This may be a common factor of cardiovascular risks. Further studies to resolve the maternal cardiovascular maladaptation will involve the echocardiography of maternal heart and mediators of atherosclerosis and oxidative stress in preeclampsia. The plausible explanation of early-onset preeclampsia is reduced nitric oxide from vascular endothelium as a result of shear stress that subsequently leads to noncompliant and stiff vessels., High brachial artery AI is an impaired ability of vasculature to respond to the profound changes required for normal pregnancy. The decreased AI as happens in normal pregnancy has a protective role and will tend to dampen the increased pulse pressure., This will reduce the transmission of pulsatile energy to the delicate fetal tertiary stem villi floating in the intervillous space. Future research can identify how VEGF165-dependent mitogenic activity, tube formation, and receptor phosphorylation regulate the elasticity and augmentation pressure index in vessel wall.
| Conclusion|| |
Brachial artery AI identifies a subset of pregnant women with a nonresilient and nonelastic cardiovascular system that fails the hemodynamic stress imposed by the superadded fetoplacental circulation. The women manifest as increased peripheral BP, damage of fetal villi, and premature separation of the placenta. Vascular inelasticity and increased AI in pregnancy can be useful in identifying adverse perinatal outcomes. High peripheral pulses AI may be used in further long-term follow-up studies in pregnant women to predict future cardiovascular risk.
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Institutional ethical committee approval is obtained and preserved by authors.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]