The contractility and performance of the preterm left ventricle before and after early patent ductus arteriosus occlusion in surfactant-treated lambs

High-sensitivity troponin T in preterm infants with a hemodynamically significant patent ductus arteriosus

OBJECTIVE

To investigate if a hemodynamically significant patent ductus arteriosus (hsPDA) leads to elevated high-sensitivity troponin T (hsTnT) and NTproBNP levels in serum.

STUDY DESIGN

Infants <34 weeks and <1500 g were prospectively enrolled, except those with major congenital or chromosomal anomalies. An echocardiogram (ECHO) was performed and hsTnT and NTproBNP were measured within 5 days of life and repeated after treatment of hsPDA. Clinical, ECHO, and hsTnT data were analyzed using Student t-test, two proportion z-test, and regression analysis.

RESULTS

Seventy infants were enrolled. Infants in the hsPDA group had lower gestation and birth weight. Mean hsTnT and NTproBNP levels in the hsPDA group were higher compared to the group without an hsPDA, with levels being 251.54 vs 161.6 pg/ml, p < 0.01 for hsTnT and 18181.02 vs 3149.23 pg/ml, p < 0.001 for NTproBNP.

CONCLUSION

HsPDA leads to increased hsTnT and NTproBNP levels in preterm infants without affecting cardiac function.

Measurement of the ductal L-R shunt during extracorporeal membrane oxygenation in the lamb

OBJECTIVE

In neonates, initially a ductal shunt is often observed during veno-arterial extracorporeal membrane oxygenation (ECMO). Depending on the degree of pulmonary hypertension in these patients, the ductal shunt will be right to left (R-L), left to right (L-R), or bidirectional. A ductal L-R shunt will possibly lead to pulmonary hyperperfusion and interact with ECMO weaning. The aim of this study was to give more insight in this ductal L-R shunt during ECMO by quantification of this shunt in relation to cardiac output and ECMO flow.

METHODS

In 7 lambs, closure of the duct was prevented by infiltration of the ductal wall with 10% formaline. This patent duct could be closed using a vesselloop around the duct. Ultrasound flowprobes were installed around the pulmonary artery, ascending aorta, and around the ECMO circulation tube. Right and left ventricular output and ECMO flow were measured. Ductus flow was defined as ductal left to right shunt (Qduct L-R) = flow in ascending aorta (Qao) - flow in central pulmonary artery (Qpa) and Qduct R-L = Qpa = Qao.

RESULTS

In 6 of 7 lambs a ductal L-R shunt was observed with a mean shunt of 44% (range, 11 to 79) of left ventricular output (Qduct L-R/Qao). Comparison with ECMO flow (Qduct L-R/Qecmo) showed a mean shunt of 76% (range 15 to 230). When compared with the total systemic circulating volume (Qpa + flow in the ECMO circuit [Qecmo]), the mean ductal L-R shunt showed a percentage of 51% (range, 7% to 142%).

CONCLUSIONS

During ECMO, mostly a ductal L-R shunt is observed in this lamb model. This ductal shunt is hemodynamically important. The percentages of this shunt in comparison with left ventricular output, and total circulating volume will support the idea that a ductal L-R shunt during ECMO could be another deteriorating factor in the often critical circulation of the neonate on veno-arterial ECMO.

Changes in left ventricular volume and systolic function before and after the closure of ductus arteriosus in full-term infants

Using echocardiographic techniques, the change in left ventricular (LV) volume and its effect on systolic function were studied before and after the closure of ductus arteriosus in 18 full-term infants. Examinations were performed twice in each infant, within 6 h after birth and on day 5, and the patency of the ductus with left-to-right shunt was confirmed at the first examination by Doppler echocardiography. A biplane Simpson's rule method was used for volume measurements. The LV end-diastolic volume, stroke volume, and cardiac output were more than 1.3-fold before the ductal closure, and the ejection fraction showed the similar change. However, the mean normalized systolic ejection rate, an index of contractility, and heart rate showed no significant difference. The Frank-Starling curve was obtained from the relationship between the LV end-diastolic and stroke volumes, and the LV performance was operated at a higher level on that curve when the ductus was open. Our data indicated that LV cardiac output was significantly higher during the patency of the ductus arteriosus and that this high cardiac performance might depend more on the Frank-Starling response to the volume load through the ductus arteriosus than on the increase of LV contractility and heart rate.

Effect of ligation of patent ductus arteriosus on left ventricular performance and its determinants in premature neonates

OBJECTIVES

The purpose of this study was to determine in preterm newborn infants the effects of ductal ligation on ventricular performance and its determinants: preload, afterload and contractility.

BACKGROUND

Neonatal ventricular performance is highly sensitive to afterload. Therefore, the increase in systemic vascular resistance associated with ligation of a patent ductus arteriosus might worsen ventricular performance in the preterm infant.

METHODS

All 14 premature infants undergoing patent ductus arteriosus ligation in a 1-year period at our institution underwent echocardiography at three times: before, immediately after and 24 h after ligation. Indexes studied included ventricular performance (fractional area change), preload (left ventricular end-diastolic dimension), afterload (end-systolic wall stress) and contractility (the difference between the measured and predicted velocity of circumferential fiber shortening). Blood pressure was measured; systemic resistance was calculated. These data were compared with those of 14 preterm infants without patent ductus arteriosus.

RESULTS

The infants with patent ductus arteriosus had higher values for ventricular performance (mean +/- SD fractional area change 60 +/- 9% vs. 52 +/- 11%, p < 0.05) and lower values for wall stress (22 +/- 6 vs. 44 +/- 17 g/cm2, p < 0.05) before ligation than did the control group. At 24 h after ligation, ventricular performance was not significantly changed (fractional area change 60 +/- 9% to 57 +/- 12%). There were significant increases in blood pressure and systemic vascular resistance but no changes in wall stress or contractility.

CONCLUSIONS

Ventricular performance is higher in premature infants with than in those without patent ductus arteriosus because afterload is lower in the former group. Although ductal ligation increases blood pressure and systemic resistance, wall stress and ventricular performance are maintained. Our results suggest that the premature newborn maintains ventricular performance during stress, at least in part, by manipulating afterload.

Effect of ductal patency on organ blood flow and pulmonary function in the preterm baboon with hyaline membrane disease

OBJECTIVE

To examine the effect of early ductal ligation vs. maintenance of ductal patency on vital organ perfusion and pulmonary function in premature baboons with hyaline membrane disease.

DESIGN

Randomized, controlled interventional study to compare early ligation with formalin infiltration of the ductus arteriosus.

SETTING

Animal care facility at a dedicated research foundation.

SUBJECTS

Eighteen premature baboons delivered by hysterotomy at 140 +/- 2 day gestation.

INTERVENTION

Nine premature baboons underwent formalin infiltration of the ductus arteriosus (group 1), and nine underwent ductal ligation (group 2). Surgical ligation or formalin infiltration was performed at 2 to 4 hrs of age. Animals were maintained on mechanical ventilation and ventilator parameters were adjusted to maintain PaO2 and PaCO2 within the physiologic range.

MAIN OUTCOME MEASURES

Left ventricular output indexed to body weight and vital organ perfusion were measured at 24 hrs of age by the radiolabeled microsphere method. Lung mechanics, including lung wet/dry weight ratio, total lung water, static compliance and functional residual capacity were measured immediately following euthanasia.

RESULTS

Total pulmonary blood flow was significantly lower (p = .0001) in group 2 (mean = 94 mL/min/kg), compared with group 1 (mean = 287 mL/min/kg). Systemic blood flow and effective pulmonary blood flow were higher in group 1 (p = .07). No significant difference between groups in absolute organ blood flow was noted, although flow as a percent of left ventricular index was significantly higher in all organs except the kidney in group 2. There was no difference in arterial blood gas values, parameters of mechanical ventilation, percent lung water, or postmortem measurement of lung mechanics between groups.

CONCLUSION

Early ductal ligation did not result in improved cardiac output, increased organ blood flow, or improved pulmonary function. We postulate that gradual constriction of the ductus arteriosus may play an important role in successful cardiovascular adaptation in the premature infant. While it is clear that premature infants with symptomatic patent ductus arteriosus often benefit from ductal closure, we question the practice of prophylactic early ductal closure.

Left ventricular preload reserve in preterm infants with patent ductus arteriosus

The left ventricular Frank-Starling response was studied in 15 preterm infants, less than 1500 g birth weight, and in 16 fullterm infants with patent ductus arteriosus. Left ventricular end diastolic volume (LVEDV), stroke volume, and cardiac output were calculated from biplane echocardiographic images with a modified Simpson's rule, and the left ventricular function curve was obtained by standardising with birth weight and body length. In the relationship between LVEDV and stroke volume, the slope of the regression line was significantly milder in preterm than in fullterm infants; however, there was no significant difference in the relationship between LVEDV and cardiac output. The heart rate was significantly higher in preterm than in fullterm infants. Our data indicated that the premature infants had less left ventricular reserve capacity to respond to the increased preload through the left-to-right ductal shunting than the mature ones, and that the high pulse rate made it possible to generate adequate cardiac output in premature infants.

Effects of patent ductus arteriosus on left ventricular output and organ blood flows in preterm infants with respiratory distress syndrome treated with surfactant

Thirty preterm infants (birth weight < 1500 gm) treated with Surfactant TA for the respiratory distress syndrome, who had no complicating clinical problems other than ductal patency, were studied by serial Doppler flow examinations to determine the effects of early left-to-right shunt through the patent ductus arteriosus on the left ventricular output and organ blood flows. Doppler flow variables in 15 infants with a hemodynamically significant patent ductus arteriosus (hsPDA) were compared with those in 15 subjects without hsPDA matched for age, body weight, and gestational age. Infants with hsPDA had significantly higher left ventricular output and significantly lower blood flow volume in the abdominal aorta, and lower temporal mean blood flow velocities, with concomitant increases in the relative vascular resistance in the celiac artery, superior mesenteric artery, and renal artery. Pulsatility indexes of these vessels and the anterior cerebral artery were significantly higher in the hsPDA group, but the temporal mean blood flow velocities in the anterior cerebral artery and its vascular resistance were not significantly different between the two groups. After closure of the patent ductus arterious was achieved with mefenamic acid therapy, alterations in Doppler flow variables in the hsPDA group reverted to the levels seen in the group without hsPDA. These results suggest that despite large left-to-right ductal shunting, the heart of the preterm infant is capable of mounting a compensatory increase of cardiac output sufficient to maintain unchanged cerebral blood flow, but is unable to maintain postductal organ blood flows because of decreased perfusion pressure (ductal steal) and localized increase in vascular resistance.

Effect of patency of the ductus arteriosus on blood pressure in very preterm infants

Forty one preterm infants (birth weight < 1500 g) were studied by daily Doppler echocardiography for the first week of life to examine the effect of a haemodynamically significant ductus arteriosus (HSDA) on systemic blood pressure. Hourly records of blood pressure were averaged for each infant to produce a 24 hour mean value and the infants were then allocated to groups according to whether, by echocardiographic criteria, there was a HSDA on that day. In infants from 1000 to 1500 g the differences in all parameters of blood pressure between those with and without a HSDA were not significant. In infants < 1000 g the mean blood pressure was significantly less in the infants with a HSDA throughout the first week of life. Systolic blood pressure was reduced by as much as diastolic blood pressure and as a result the pulse pressure did not differ. Infants < 1000 g with a HSDA were given more plasma and a greater number received inotropic support. Gestational age, respiratory disease severity, and complication rates did not differ between those with and without a HSDA. The possibility of a clinically silent HSDA should be considered before large amounts of plasma volume expanders are given to treat hypotension in infants < 1000 g.

Left ventricular mechanics in the preterm infant and their effect on the measurement of cardiac performance

The effects of the transition from fetal to postnatal circulation on left ventricular geometry, wall motion, and echocardiographic measurements of function in the human preterm infant are largely unknown. To determine whether abnormalities in left ventricular geometry are present in the normal preterm infant after birth and, if so, for how long, and to examine possible contributing factors and their effect on the measurement of cardiac performance, we obtained serial echocardiograms of 14 healthy preterm infants (gestational age, 33 +/- 2 weeks; birth weight, 1940 +/- 470 gm) at 9.5 +/- 3.5 days of age (time 1) and again at 51 +/- 16 days (time 2). Left ventricular shape and wall motion were measured and estimates of wall stress and mass were made. Performance was assessed by standard M-mode shortening fraction and by transverse two-dimensional area shortening. At time 1 septal flattening caused distortion of left ventricular shape. As the patients grew older, septal flattening resolved and the left ventricle tended to assume a circular cross-sectional shape. Wall-motion analysis demonstrated poor motion of the midseptum and anterior free wall at time 1, which improved at time 2 (p = 0.06). Left ventricular mass increased from 24 +/- 5 to 41 +/- 7 gm/m2 (p = 0.0001) and wall stress decreased from 49 +/- 21 to 38 +/- 13 gm/cm2 (p = 0.005) between time 1 and time 2. Shortening fraction was lower at time 1 than at time 2 (18% +/- 7% vs 28% +/- 8%; p = 0.001; normal limit = 28% to 45%); however, there was no significant difference in area shortening between time 1 and time 2 (49% +/- 10% vs 53% +/- 8%; normal limit = 45% to 65%). We conclude that the preterm newborn infant has distorted left ventricular shape and abnormal wall motion, which alter measurements of shortening fraction and persist for the first weeks of life. Area shortening may be necessary to assess left ventricular performance during the first weeks of life in the premature infant.

Left ventricular dysfunction following ligation of the ductus arteriosus in the preterm baboon

We evaluated the effect of early closure of the patent ductus arteriosus (PDA) on cardiac performance in a preterm baboon model of hyaline membrane disease. Eleven baboon fetuses were delivered at 75% gestation, resuscitated, and treated with conventional ventilation. The animals were divided into two groups, and underwent left thoracotomy at 2 hr of age. Group 1 (N = 5) had ductal infiltration with formalin to maintain ductal patency. Group 2 (N = 6) had ductal ligation. Hemodynamic parameters were compared between groups before and after surgical intervention. Examination of cardiovascular function was performed at intervals over a 24-hr period using two-dimensional, M-mode, and pulsed Doppler echocardiography. Ventricular performance was significantly worse in the ligation animals as demonstrated by reduced left and right ventricular outputs and reduced left ventricular shortening. However, pulmonary disease and arterial blood gases were not different. Early ligation was also associated with significantly increased systemic vascular resistance. We conclude that early ductal ligation leads to impaired ventricular performance in the premature primate. We hypothesize that the PDA may protect the immature ventricle by preventing pressure overload during adaptation to postnatal life.

Effects of left-to-right ductus shunting on left ventricular output and cerebral blood flow velocity in 3-day-old preterm infants with and without severe lung disease

The effects of early left-to-right ductus shunting on left ventricular output (LVO) and cerebral blood flow velocity (CBV) were investigated in 3-day-old preterm infants by means of two-dimensional Doppler and M-mode echocardiography. Nineteen infants required mechanical ventilation because of severe lung disease (group A), and 19 had mild or no lung disease (group B). Six infants in each group had predetermined Doppler and M-mode criteria of a hemodynamically significant left-to-right ductus shunt (hsPDA). In group A the LVO was similar in infants with and without hsPDA, but those with hsPDA had lower mean arterial pressure (p = 0.006) and lower mean systolic-diastolic CBV (p = 0.001) than those without hsPDA. In group B the presence of hsPDA was associated with a higher LVO (p = 0.002), whereas neither mean arterial pressure nor mean systolic-diastolic CBV differed significantly in infants with and without hsPDA. In infants without hsPDA, those in group A had higher LVO (p = 0.012), lower mean arterial pressure (p = 0.003), and lower estimated systemic vascular resistance (p = 0.004) than those in group B. These results indicate that severely ill preterm infants receiving mechanical ventilation are less able than spontaneously breathing infants to defend systemic pressures and cerebral perfusion through an increase of LVO when a large ductus shunt develops. Possible reasons include an elevated baseline LVO, caused by systemic vasodilation, and hence a low preload reserve.

Changes of the cardiovascular system during the perinatal period

After describing the particular features of the fetal circulation, changes in the pattern of blood flow at the time of birth and during early neonatal life are explained. From animal studies it is wellknown that during the first hours and weeks after birth newborns are characterized by an extremely high cardiac output due to high metabolic demands. In order to meet this marked volume loading, already under resting conditions the neonatal heart appears to be operating nearly at its full capacity without reserves in contractility, preload and afterload. Consequently the newborn heart has less ability to cope with additional acute afterload and/or preload stress. Few investigations on cardiac output and myocardial performance in healthy human newborns provide presumptive evidence that the postnatal human heart performs probably as well as the heart of other species. These observations may influence the therapeutic approach in clinical situations with additional alterations in loading conditions.

Cardiovascular effects of patent ductus arteriosus in preterm lambs with respiratory distress

We created a model for studying the cardiovascular and pulmonary effects of patent ductus arteriosus (PDA) in premature lambs with respiratory distress. In 47 fetal lambs at 129 to 133 days gestation (term, 145 days), we infiltrated the ductus arteriosus with formalin and placed a mechanical occluder about it so that its patency could be regulated. Two days later the lambs were delivered, given sheep surfactant, paralyzed, and their lungs mechanically ventilated. These premature lambs could more than double their left ventricular output when challenged with increasing degrees of left-to-right shunts through the PDA. This was accomplished by an increase in stroke volume, not by an increase in heart rate. During the 40-minute observation period, there was no change in dynamic compliance or functional residual capacity while the ductus was patent. When the ductus was patent, there was a significant increase in arterial PaO2 (even with small left-to-right shunts) and a decrease in PaCO2 (with large shunts). Despite the heart's ability to handle the increased volume load of a PDA, there were significant alterations in individual organ blood flows, resulting from a combination of decreased perfusion pressure and localized vasoconstriction. The abdominal organs had significant reductions in blood flow even with small PDA shunts. This decrease in organ blood flow may explain some of the pathophysiologic manifestations of PDA in preterm infants.

Left ventricular performance and contractility before and after volume infusion: a comparative study of preterm and full-term newborn lambs

We studied left ventricular performance and contractility after volume loading in lambs at 122 days (group I, n = 9) and 139 days gestational age (group II, n = 9) and in 8-day-old full-term lambs (group III, n = 7). All were mechanically ventilated; each preterm lamb was treated with surfactant to stabilize pulmonary function and the ductus arteriosus was occluded with an inflated catheter balloon. Cineangiograms, left ventricular and vascular pressures, and the isovolumetric index of contractility, first derivative of left ventricular pressure (dP/dt), were recorded before and after three successive whole blood volume infusions of 10 ml/kg (total 30 ml/kg). The left ventricular end-diastolic volume per kilogram and stroke volume per kilogram increased significantly in all groups after volume infusion; these measurements and heart rate and systemic vascular resistance did not differ significantly between the groups either before or after the infusions. The left ventricular peak dP/dt did not change significantly within the groups during the volume infusions. The left ventricular stroke work was greatest in full-term animals and increased significantly in all groups after volume infusion. Thus, the left ventricles of the preterm and full-term lambs had quantitatively similar Frank-Starling responses and there was no increase in contractility during the infusions of whole blood. However, the left ventricle of the full-term lamb is capable of generating greater stroke work than that of the preterm lamb. These findings may contribute to the understanding of development aspects of postnatal circulatory adaptation.