Metabolic acidosis decreases fetal myocardial isovolumic velocities in a chronic sheep model of increased placental vascular resistance

The assessment of fetal cardiac functions in pregnancies with autoimmune diseases: a prospective case-control study

OBJECTIVES

This study aimed to assess the effect of the inflammatory process on fetal cardiac functions in pregnant women with autoimmune diseases (AID).

METHODS

This prospective study included 36 pregnant women with diagnosed AID. Nineteen systemic lupus erythematosus, 12 antiphospholipid syndrome, 5 Sjögren's syndrome, and 72 healthy pregnancies were included. Fetal cardiac functions were evaluated with pulsed-wave, tissue Doppler, and M-mode echocardiography.

RESULTS

Sociodemographic data were similar in both groups. Significant increases were found in tricuspid E (43.5 ± 0.9, p<0.001) and A (59.2 ± 2.2, p<0.001) and E/A (0.74 ± 0.03, p<0.001), E'/A' (0.64 ± 0.15, p<0.001), E/E' (6.5 ± 0.6, p<0.001), and left ventricular myocardial performance index (0.54 ± 0.03, p=0.005). We demonstrated a significant decrease in tricuspid E' (6.7 ± 0.6, p<0.001) and S' (6.9 ± 1, p<0.001) and in TAPSE (7.7 ± 0.5, p=0.002). We also found a significantly prolonged PR interval (130 ± 8, p<0.001). There was a significant increase in E' (6.8, p=0.033) and a significant decrease in E/E' ratio (6.4, p=0.027) in the group using hydroxychloroquine (HCQ) compared to non-users.

CONCLUSIONS

We found that pregnancy with autoimmune diseases affects fetal heart functions. Additionally, hydroxychloroquine may positively affect the heart of AID fetuses. This information might be useful to clinicians in the follow-up of cardiovascular diseases.

Peripheral chemoreflex activation and cardiac function during hypoxemia in near-term fetal sheep without placental compromise

A drop in arterial oxygen content activates fetal chemoreflex including an increase in sympathetic activity leading to peripheral vasoconstriction and redistribution of blood flow to protect the brain, myocardium, and adrenal glands. By using a chronically instrumented fetal sheep model with intact placental circulation at near-term gestation, we investigated the relationship between peripheral chemoreflex activation induced by hypoxemia and central hemodynamics. A total of 17 Åland landrace sheep fetuses at 115-128/145 gestational days were instrumented. Carotid artery was catheterized in 10 fetuses and descending aorta in 7 fetuses. After a 4-day recovery, baseline measurements of fetal arterial blood pressures, blood gas values, and fetal cardiovascular hemodynamics by pulsed Doppler ultrasonography were obtained under isoflurane anesthesia. Comparable data to baseline were collected 10 min (acute hypoxemia) and 60 min (prolonged hypoxemia) after maternal hypo-oxygenation to saturation level of 70%-80% was achieved. During prolonged hypoxemia, pH and base excess (BE) were lower and lactate levels were higher in the descending aorta than in the carotid artery. During hypoxemia mean arterial blood pressure (MAP) in the descending aorta increased, whereas in the carotid artery, MAP decreased. In addition, right pulmonary artery pulsatility index values increased, and the diastolic component in the aortic isthmus blood flow velocity waveform became more retrograde, thus decreasing the aortic isthmus antegrade/retrograde blood flow (AoI Net Flow) ratio. Both fetal ventricular cardiac outputs were maintained even during prolonged hypoxemia when significant fetal metabolic acidemia developed. Fetal chemoreflex activation induced by hypoxemia decreased the perfusion pressure in the cerebral circulation. Fetal weight-indexed left ventricular cardiac output (LVCO) or AoI Net Flow ratio did not correlate with a drop in carotid artery blood pressure.NEW & NOTEWORTHY During fetal hypoxemia with intact placental circulation, peripheral chemoreflex was activated, as demonstrated by an increase in the descending aorta blood pressure, pulmonary vasoconstriction, and an increase in retrograde diastolic AoI blood flow, while both ventricular cardiac outputs remained stable. However, perfusion pressure in the cerebral circulation decreased. These changes were seen even during prolonged hypoxemia when significant metabolic acidosis developed. Weight-indexed LVCO or AoI Net Flow ratio did not correlate with a drop in carotid artery blood pressure.

Nifedipine disturbs fetal cardiac function during hypoxemia in a chronic sheep model at near term gestation

BACKGROUND

Nifedipine is a widely used drug in pregnancies complicated by maternal hypertensive disorders that can be associated with placental insufficiency and fetal hypoxemia. The evidence regarding fetal myocardial responses to nifedipine in hypoxemia is limited.

OBJECTIVE

We hypothesized that nifedipine would not impair fetal sheep cardiac function under hypoxemic environment. In particular, we investigated the effects of nifedipine on fetal ventricular functional parameters and cardiac output.

STUDY DESIGN

A total of 21 chronically instrumented fetal sheep at 122 to 134 gestational days (term, 145 days) were included in this study. Fetal cardiac function was evaluated by measuring global longitudinal strain, indices describing ventricular systolic and diastolic function, and cardiac outputs using two-dimensional speckle tracking and tissue and spectral pulsed-wave Doppler echocardiography. Fetal carotid artery blood pressure and blood gas values were invasively monitored. After baseline data collection, fetal hypoxemia was induced by maternal hyperoxygenation. After hypoxemia phase data collection, 9 fetuses received nifedipine infusion, and 12 fetuses received saline infusion. Data were collected 30 and 120 minutes after the infusion was started. After 120 minutes of data collection, maternal and fetal oxygenation were normalized, and normoxemia phase data were collected, while infusion was continued.

RESULTS

Hypoxemia decreased fetal carotid artery mean arterial pressure from 40 (8) mm Hg to 35 (8) mm Hg (P<.007), and left ventricular global longitudinal strain showed less deformation than at baseline (P=.001). Under hypoxemia, nifedipine caused a reduction in right ventricular global longitudinal strain (P<.05), a decrease in right ventricular isovolumic relaxation velocity and its deceleration (P<.01) indicating diastolic dysfunction, and a drop in right ventricular cardiac output (P<.05). Nifedipine did not alter fetal left ventricular functional parameters or cardiac output. When normoxemia was restored, fetal right ventricular functional parameters and cardiac output returned to baseline level.

CONCLUSION

In hypoxemic fetus, nifedipine impaired right ventricular function and reduced its cardiac output. The detrimental effects of nifedipine on fetal right ventricular function were abolished, when normoxemia was restored. Our findings suggest that in a hypoxemic environment nifedipine triggers detrimental effects on fetal right ventricular function.

Feasibility of ventricular volumetry by cardiovascular MRI to assess cardiac function in the fetal sheep

KEY POINTS

The application of fetal cardiovascular magnetic resonance imaging (CMR) to assess fetal cardiovascular physiology and cardiac function through the quantification of ventricular volumes has previously been investigated, but the approach has not yet been fully validated. Ventricular output measurements calculated from heart rate and stroke volumes (SV) of the right and left ventricles measured by ventricular volumetry (VV) exhibited a high level of agreement with phase-contrast (PC) blood flow measurements in the main pulmonary artery and ascending aorta, respectively. Ejection fraction of the right ventricle, which is lower than that of the left ventricle in postnatal subjects, was similar to the left ventricular ejection fraction in the fetus; probably due to the different loading conditions present in the fetal circulation. This study provides evidence to support the reliability of VV in the sheep fetus, providing evidence for its use in animal models of human diseases affecting the fetal circulation.

ABSTRACT

The application of ventricular volumetry (VV) by cardiovascular magnetic resonance imaging (CMR) in the fetus remains challenging due to the small size of the fetal heart and high heart rate. The reliability of this technique in utero has not yet been established. The aim of this study was to assess the feasibility and reliability of VV in a fetal sheep model of human pregnancy. Right and left ventricular outputs by stroke volume (SV) measured using VV were compared with 2D phase-contrast (PC) CMR measurements of blood flow in the main pulmonary artery (MPA) and ascending aorta (AAo). At 124-140 days (d) gestation, singleton bearing Merino ewes underwent CMR under general anaesthesia using fetal femoral artery catheters, implanted at 109-117d, to trigger cine steady state free precession acquisitions of ventricular short-axis stacks. The short-axis cine stacks were segmented at end-systole and end-diastole, yielding right and left ventricular SV, ejection fraction, and cardiac outputs (SV × heart rate). PC cine acquisitions of MPA and AAo were analysed to measure blood flow, which served as comparators for the right and left cardiac outputs by VV. There was good correlation and agreement between VV and PC measures of ventricular outputs with no significant bias (r²  = 0.926; P < 0.0001; Bias = -4.7 ± 10.5 ml min^-1  kg^-1 ; 95% limits of agreement: -15.9 to 25.2 ml min^-1  kg^-1 ). This study validates fetal VV by CMR in a large animal model of human pregnancy and provides preliminary reference values of fetal sheep right and left ventricles in late gestation.

Foramen ovale blood flow and cardiac function after main pulmonary artery occlusion in fetal sheep

NEW FINDINGS

What is the central question of this study? At near-term gestation, foramen ovale blood flow accounts for a significant proportion of fetal left ventricular output. Can the foramen ovale increase its volume blood flow when right ventricular afterload is increased by main pulmonary artery occlusion? What is the main finding and its importance? Foramen ovale volume blood flow increased during main pulmonary artery occlusion. However, this increase was attributable to an increase in fetal heart rate, because left ventricular stroke volume remained unchanged. These findings suggest that the foramen ovale has a limited capacity to increase its volume blood flow.

ABSTRACT

The foramen ovale (FO) accounts for the majority of fetal left ventricular (LV) output. Increased right ventricular afterload can cause a redistribution of combined cardiac output between the ventricles. To understand the capability of the FO to increase its volume blood flow and thus LV output, we mechanically occluded the main pulmonary artery in seven chronically instrumented near-term sheep fetuses. We hypothesized that FO volume blood flow and LV output would increase during main pulmonary artery occlusion. Fetal cardiac function and haemodynamics were assessed by pulsed and tissue Doppler at baseline, 15 and 60 min after occlusion of the main pulmonary artery and 15 min after occlusion was released. Fetal ascending aorta and central venous pressures and blood gas values were monitored. Main pulmonary artery occlusion initially increased fetal heart rate (P < 0.05) from [mean (SD)] 158 (7) to 188 (23) beats min^-1 and LV cardiac output (P < 0.0001) from 629 (198) to 776 (283) ml min^-1 . Combined cardiac output fell (P < 0.0001) from 1524 (341) to 720 (273) ml min^-1 . During main pulmonary artery occlusion, FO volume blood flow increased (P < 0.001) from 507 (181) to 776 (283) ml min^-1 . This increase was related to fetal tachycardia, because LV stroke volume did not change. Fetal ascending aortic blood pressure remained stable. Central venous pressure was higher (P < 0.05) during the occlusion than after it was released. During the occlusion, fetal pH decreased and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>P</mml:mi> <mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:math> increased. Left ventricular systolic dysfunction developed while LV diastolic function was preserved. Right ventricular systolic and diastolic function deteriorated after the occlusion. In conclusion, the FO has a limited capacity to increase its volume blood flow at near-term gestation.

Effect of Sildenafil on Pulmonary Circulation and Cardiovascular Function in Near-Term Fetal Sheep During Hypoxemia

Sildenafil is a potential new treatment for placental insufficiency in human pregnancies as it reduces the breakdown of vasodilator nitric oxide. Pulmonary vasodilatation is observed in normoxemic fetuses following sildenafil administration. Placental insufficiency often leads to fetal hypoxemia that can cause pulmonary vasoconstriction and fetal cardiac dysfunction as evidenced by reduced isovolumic myocardial velocities. We tested the hypotheses that sildenafil, when given directly to the hypoxemic fetus, reverses reactive pulmonary vasoconstriction, increases left ventricular cardiac output by increasing pulmonary venous return, and ameliorates hypoxemic myocardial dysfunction. We used an instrumented sheep model. Fetuses were made hypoxemic over a mean (standard deviation) duration of 41.3 (9.5) minutes and then given intravenous sildenafil or saline infusion. Volume blood flow through ductus arteriosus was measured with an ultrasonic transit-time flow probe. Fetal left and right ventricular outputs and lung volume blood flow were calculated, and ventricular function was examined using echocardiography. Lung volume blood flow decreased and the ductus arteriosus volume blood flow increased with hypoxemia. There was a significant reduction in left ventricular and combined cardiac outputs during hypoxemia in both groups. Hypoxemia led to a reduction in myocardial isovolumic velocities, increased ductus venosus pulsatility, and reduced left ventricular myocardial deformation. Direct administration of sildenafil to hypoxemic fetus did not reverse the redistribution of cardiac output. Furthermore, fetal cardiac systolic and diastolic dysfunction was observed during hypoxemia, which was not improved by fetal sildenafil treatment. In conclusion, sildenafil did not improve pulmonary blood flow or cardiac function in hypoxemic sheep fetuses.

The correlation of morphological and thrombotic villous arterial lesions with fetal Doppler echocardiographic measurements in the placentas of low-risk term pregnancies

OBJECTIVE

Few studies have correlated the placental vasculature with fetal cardiac function other than umbilical artery Doppler assessment in low-risk pregnancies. We assessed the contribution of the placental vasculature to fetal echocardiographic parameters using histopathological and morphometric analyses of placental resistance arteries.

STUDY DESIGN

Thirty-four low-risk singleton term pregnancies were assessed, including 24 thrombosis-negative cases (no/minimal gross and histological placental abnormalities) and 10 thrombosis-positive cases (histologically identified chorionic plate/stem vessel thrombosis). Fetal ventricular Doppler inflow velocities (E and A waves) and myocardial systolic (S'), early (E'), and late diastolic (A') tissue Doppler velocities were measured within three days before birth. The myocardial performance index (MPI') was calculated. Morphometric variables of placental stem villi arterioles (external diameter 10-150 μm) were examined, including the mean arteriolar density, total cross-sectional lumen area, and wall area/total vessel area (WA/TVA) ratio.

RESULTS

The thrombosis-positive group had a higher umbilical artery pulsatility index and a lower tricuspid E'/A' ratio compared to the thrombosis-negative group. The WA/TVA ratio of stem villi arterioles was negatively correlated with tricuspid E, A, and S' velocities as well as the E/E' ratio (n = 34). The tricuspid MPI' was positively correlated with the total cross-sectional lumen area of stem villi arterioles (n = 34).

CONCLUSION

We conclude that changes in several fetal echocardiographic parameters are associated with placental vascular histopathological and morphological characteristics in a low-risk population. Further studies are needed to assess whether fetal echocardiographic assessment is a promising prenatal predictor of placental vascular histopathological and morphological characteristics in the general population.

Effect of Hypoxemia on Fetal Ventricular Deformation in a Chronically Instrumented Sheep Model

We hypothesized that in near-term sheep fetuses, hypoxemia changes myocardial function as reflected in altered ventricular deformation on speckle-tracking echocardiography. Fetuses in 21 pregnant sheep were instrumented. After 4 d of recovery, fetal cardiac function was assessed by echocardiography at baseline, after 30 and 120 min of induced fetal hypoxemia and after its reversal. Left (LV) and right (RV) ventricular cardiac output and myocardial strain were measured. Baseline mean (standard deviation [SD]) LV and RV global longitudinal strains were -18.7% (3.8) and -14.3% (5.3). Baseline RV global longitudinal and circumferential deformations were less compared with those of the left ventricle (p = 0.016 and p < 0.005). LV, but not RV, global longitudinal strain was decreased (p = 0.003) compared with baseline with hypoxemia. Circumferential and radial strains did not exhibit significant changes. In the near-term sheep fetus, LV global longitudinal and circumferential strains are more negative than RV strains. Acute hypoxemia leads to LV rather than RV dysfunction as reflected by decreased deformation.

Fetal ventricular interactions and wall mechanics during ductus arteriosus occlusion in a sheep model

We investigated the effect of fetal sheep ductus arteriosus occlusion (DO) on the distribution of cardiac output and left and right ventricular function by tissue and pulsed Doppler at baseline; after 15 and 60 min of DO induced with a vascular occluder; and 15 min after release of DO. Ductal occlusion decreased fetal pO2. Mean left ventricular output increased (p < 0.001) from 725 to 1013 mL/min, and right ventricular (1185 mL/min vs. 552 mL/min) and systemic (1757 mL/min vs. 1013 mL/min) cardiac outputs fell (p < 0.001) after 15 min of DO, compared with baseline. Pulmonary vascular impedance decreased and volume blood flow increased more than threefold during DO, whereas foramen ovale volume blood flow remained unchanged. Left ventricular systolic function was unaffected, whereas isovolumic relaxation velocity deceleration decreased. Right ventricular functional indices remained unchanged. We conclude that DO increased pulmonary volume blood flow, not foramen ovale volume blood flow. Left ventricular output increased, although not as much as right ventricular output fell, resulting in decreased systemic cardiac output. During DO, left ventricular function exhibited diminished relaxation.

The cardiac state diagram as a novel approach for the evaluation of pre- and post-ejection phases of the cardiac cycle in asphyxiated fetal lambs

The aim of this study was to investigate myocardial wall motion using echocardiography and color-coded tissue velocity imaging and to generate a cardiac state diagram for evaluation of the duration of the pre- and post-ejection phases in asphyxiated fetal lambs. Six near-term lambs were partly exteriorized and brought to cardiac arrest through asphyxia. Echocardiography measurements were recorded simultaneously with arterial blood sampling for lactate and blood gases. All fetal lambs exhibited prolongation of the pre- and post-ejection phases at the time when the most pronounced changes in lactate concentration and pH occurred. The mean change in duration of the pre- and post-ejection phases for all fetal lambs was 36 ± 7 ms (p < 0.002) and 77 ± 17 ms (p < 0.019), respectively, and the percentage change was 50% (p < 0.001) and 38% (p < 0.049), respectively. As asphyxia progressed in fetal lambs, the duration of the pre- and post-ejection phases increased. The cardiac state diagram has the potential to be a comprehensible tool for detecting fetal asphyxia.

Anesthetic Techniques for Fetal Surgery

Background:

Use of high-dose inhalational anesthesia during open fetal surgery may induce maternal–fetal hemodynamic instability and fetal myocardial depression. The authors’ preliminary human retrospective study demonstrated less fetal bradycardia and left ventricular systolic dysfunction with lower dose desflurane supplemented with propofol and remifentanil IV anesthesia (SIVA). In this animal study, the authors compare maternal–fetal effects of high-dose desflurane anesthesia (HD-DES) and SIVA.

Methods:

Of 26 instrumented midgestational ewes, data from 11 animals exposed to both SIVA and HD-DES in random sequences and six animals exposed to HD-DES while maternal normotension was maintained were analyzed. Maternal electroencephalography was used to guide comparable depths of anesthesia in both techniques. Hemodynamic parameters, blood gas, and fetal cardiac function from echocardiography were recorded.

Results:

Compared with SIVA, HD-DES resulted in significant maternal hypotension (mean arterial pressure difference, 19.53 mmHg; 95% CI, 17.6–21.4; P &lt; 0.0001), fetal acidosis (pH 7.11 vs. 7.24 at 150 min, P &lt; 0.001), and decreased uterine blood flow. In the HD-DES group with maternal normotension, uterine blood flow still declined and fetal acidosis persisted, with no statistically significant difference from the group exposed to HD-DES that had maternal hypotension. There was no statistically significant difference in fetal cardiac function.

Conclusion:

In sheep, SIVA affects maternal hemodynamics less and provides better fetal acid/base status than high-dose desflurane. Fetal echocardiography did not reflect myocardial dysfunction in this model.

The fetal cardiovascular response to increased placental vascular impedance to flow determined with 4-dimensional ultrasound using spatiotemporal image correlation and virtual organ computer-aided analysis

OBJECTIVE

We sought to determine if increased placental vascular impedance to flow is associated with changes in fetal cardiac function using spatiotemporal image correlation and virtual organ computer-aided analysis.

STUDY DESIGN

A cross-sectional study was performed in fetuses with umbilical artery pulsatility index >95th percentile (abnormal [ABN]). Ventricular volume (end-systole, end-diastole), stroke volume, cardiac output (CO), adjusted CO, and ejection fraction were compared to those of 184 normal fetuses.

RESULTS

A total of 34 fetuses were evaluated at a median gestational age of 28.3 (range, 20.6-36.9) weeks. Mean ventricular volumes were lower for ABN than normal cases (end-systole, end-diastole) with a proportionally greater decrease for left ventricular volume (vs right). Mean left and right stroke volume, CO, and adjusted CO were lower for ABN (vs normal) cases. Right ventricular volume, stroke volume, CO, and adjusted CO exceeded the left in ABN fetuses. Mean ejection fraction was greater for ABN than normal cases. Median left ejection fraction was greater (vs right) in ABN fetuses.

CONCLUSION

Increased placental vascular impedance to flow is associated with changes in fetal cardiac function.

Fetal sheep left ventricle is more sensitive than right ventricle to progressively worsening hypoxemia and acidemia

OBJECTIVE

In a sheep model we tested the hypothesis that the fetal left ventricle is less tolerant to worsening acidemia than the right ventricle.

STUDY DESIGN

At 106-124/145 days of gestation, 12 fetuses were instrumented. After a 4-day recovery, placental vascular resistance was increased by fetal angiotensin (AT) II infusion. After a 2h ATII infusion, to further deteriorate fetal oxygenation, maternal hypoxemia was induced. Fetal cardiac function and hemodynamics were assessed by tissue Doppler imaging (TDI) and pulsed Doppler imaging. Ultrasonography was performed at baseline, at 1 and 2h after the beginning of ATII infusion and during the ATII+hypoxemia phase.

RESULTS

Fetal pH and pO₂ decreased significantly and progressively during the experiment. Left ventricular TDI-derived isovolumic relaxation velocity (IVRV) was lower during ATII 2h and ATII+hypoxemia phases than at baseline. The IVRV deceleration was significantly less during the ATII+hypoxemia phase than at baseline. Right ventricular IVRV was significantly lower during the ATII+hypoxemia phase than at baseline. IVRV deceleration did not change. Only left ventricular IVRV deceleration correlated with fetal pO₂ (R=0.36, p<0.05). Fetal right and left ventricular cardiac outputs, as well as umbilical artery, aortic isthmus and ductus venosus pulsatility indices remained unchanged during the experiment.

CONCLUSION

Our results show that signs of cardiac dysfunction develop earlier in the left ventricle than in the right ventricle. The fetal left ventricle seems to be more sensitive to progressively worsening hypoxemia and acidemia than the right ventricle.

Myocardial performance and its acute response to angiotensin II infusion in fetal sheep adapted to chronic anemia

Fetal chronic anemia causes lengthening of cardiomyocytes. In adults, severe left ventricular overload may lead to irreversible ventricular dysfunction. We hypothesized that in sheep fetuses with chronic anemia, remodeled myocardium would less successfully respond to angiotensin II (AT II) infusion than in fetuses without anemia. A total of 14 ewes with twin pregnancy underwent surgery at 113 ± 1 days of gestation. After a recovery period, anemia was induced by isovolumic hemorrhage in 1 fetus of each pair. At 126 ± 1 days of gestation, longitudinal myocardial velocities of the right (RV) and left (LV) ventricles were assessed at the level of the atrioventricular valve annuli via tissue Doppler imaging. Cardiac outputs were calculated by pulsed Doppler ultrasound. All measurements were performed at baseline and during fetal AT II infusion. Fetal serum cardiac natriuretic peptide (N-terminal peptide of proatrial natriuretic peptide [NT-proANP] and B-type natriuretic peptide [BNP]) concentrations were determined. Nine ewes successfully completed the experiment. At baseline, ventricular free wall thicknesses, cardiac outputs, and NT-proANP levels were significantly greater in the anemic fetuses than in the controls. The LV isovolumic contraction velocity (IVCV) acceleration and isovolumic relaxation velocity (IVRV) deceleration were lower (P < .05) in the anemic fetuses than in the controls. In the anemic fetuses, there was a positive correlation (R = .93, P < .01) between RV IVRV deceleration and NT-proANP concentration. Angiotensin II infusion increased (P < .05) LV IVCV acceleration in the anemic fetuses. We conclude that in anemic sheep fetuses, myocardial adaptation is associated with impaired LV early contraction and relaxation. However, the LV can improve its contractility with an inotropic stimulus, even in the presence of increased afterload.

Effect of angiotensin II on the left ventricular function in a near-term fetal sheep with metabolic acidemia

We tested the hypothesis that, in acute metabolic acidemia, the fetal left ventricle (LV) has the capacity to increase its contractility in response to angiotensin II infusion. Eleven ewes and their fetuses were instrumented at 127–138/145 days of gestation. The effect of angiotensin II on fetal LV function was assessed using intraventricular pressure catheter and tissue Doppler imaging (TDI). Angiotensin II increased fetal arterial blood pressure, whereas pH and pO₂ decreased. The heart rate and systemic venous pressure were not affected significantly. The LV end-diastolic and end-systolic pressures, as well as dP/dt_max, increased. The TDI-derived LV longitudinal myocardial isovolumic contraction velocity and its acceleration and velocity during early filling were higher than those at baseline. The incidence of absent isovolumic relaxation velocity was greater during angiotensin II infusion. In summary, during acute metabolic acidemia, the fetal left ventricle could increase its contractility in response to inotropic stimulus even in the presence of increased afterload. The diastolic LV function parameters were altered by angiotensin II.

Regional myocardial function and response to acute afterload increase in chronically anemic fetal sheep: evaluation by two-dimensional strain echocardiography

We hypothesized that in chronic fetal anemia, remodeling of the myocardium is related to abnormalities in regional wall motion and acutely increased afterload further disturbs myocardial strain. Chronic anemia was induced in one fetus of each of seven sheep twin pregnancies. The fetuses were studied by two-dimensional (2-D) strain echocardiography at baseline and during increased afterload via angiotensin II (AT II) infusion. At baseline, the peak systolic longitudinal, radial and circumferential strains in the left ventricular lateral wall in anemic fetuses were lower than those in the controls (all p<0.05). During AT II, the circumferential strain of right ventricular free wall decreased significantly both in the control and anemic fetuses. Left ventricular free wall systolic strains were not affected by AT II. Fetal myocardial remodeling in chronic anemia decreases left ventricular systolic free wall strains. The myocardial adaptation does not change ventricular responses to acutely increased afterload.

Ductus venosus velocimetry in acute fetal acidemia and impending fetal death in a sheep model of increased placental vascular resistance

We investigated whether hypoxemia without acidemia affects ductus venosus (DV) blood velocity waveform pattern in sheep fetuses with intact placenta and whether worsening acidemia and impending fetal death are related to changes in DV velocimetry in fetuses with increased placental vascular resistance. A total of 34 fetuses were instrumented at 115–136/145 days of gestation. Placental embolization was performed in 22 fetuses on the fourth postoperative day, 24 h before the experiment. The control group was comprised of 12 fetuses with intact placenta. The experimental protocol consisted of fetal hypoxemia that was induced by replacing maternal inhaled oxygen with medical air. To further deteriorate fetal oxygenation and blood-gas status, uterine artery volume blood flow was reduced by maternal hypotension. Fetuses that underwent placental embolization were divided into two groups according to fetal outcome. Group 1 consisted of 12 fetuses that completed the experiment, and group 2 comprised 10 fetuses that died during the experiment. DV pulsatility index for veins (PIV) and fetal cardiac outputs (COs) were calculated. Placental volume blood flow, fetal blood pressures, and acid base and lactate values were monitored invasively. On the experimental day, the mean gestational age did not differ significantly between the groups. In groups 1 and 2, the baseline mean DV PIV and fetal COs were not statistically significantly different from the control group. In the control group, the DV PIV values increased significantly with hypoxemia. In groups 1 and 2, the DV PIV values did not change significantly, even with worsening acidemia and imminent fetal death in group 2. During the experiment, the fetal COs remained unchanged. We conclude that fetal hypoxemia increases the pulsatility of DV blood velocity waveform pattern. In fetuses with elevated placental vascular resistance, DV pulsatility does not increase further in the presence of severe and worsening fetal acidemia and impending fetal death.