How a patent ductus arteriosus effects the premature lamb's ability to handle additional volume loads

Effects of Early Myocardial Postnatal Maturation on Tolerance to Atrial Tachycardia With Altered Loading Conditions: An in vivo Swine Model

Post-natal maturation of the myocardium starts shortly after birth and could affect how clinicians should provide hemodynamic support during this transition. Our aim was to assess the impact of post-natal maturation on tolerance to tachycardia with altered loading condition in a piglet model. Methods: We report three series of experimentations. Six groups of landrace cross neonatal piglets (NP) (1-3 days) and young piglets (YP) (14-17 days) were assigned to tachycardia (NP, YP), tachycardia and hypervolemia (NPV, YPV) or tachycardia and increased afterload (NPA, YPA) groups (n = 7/group). Under anesthesia, a pressure catheter was placed in the left ventricle and pacing wire in the right atrium. NPV and YPV groups had 60 ml/kg of normal saline infused over 20 min. NPA and YPA had balloon sub-occlusion of the descending aorta. Heart rate was increased by 10 bpm increments to 300 bpm. Left ventricular output was measured by echocardiography. Results: NP maintained left ventricular output throughout the pacing protocol but it decreased in the YP (p < 0.001). With volume loading both NPV and YPV maintained their output with tachycardia. Although increased afterload resulted in reduced output during tachycardia in NPA (p = 0.005), there was no added impact on output in YPA. Interestingly, 4 of 7 NPV had significant desaturation at 300 bpm (baseline 99.7% vs. 300 bpm 87.9%, p = 0.04), associated with a right to left shunt through the patent foramen ovale which resolved immediately on cessation of pacing. Conclusions: Early post-natal maturation is associated with improved myocardial tolerance to increased afterload and poor tolerance of tachycardia, the latter of which may be alleviated by increasing intravascular volume. These data could translate into the development of better strategies to optimize cardiac output at these early development ages.

The ductus arteriosus: physiology, regulation, and functional and congenital anomalies

Over the last three decades, knowledge about fundamental and clinical aspects of the ductus arteriosus has substantially improved, leading to considerable progress in the management of various cardiac diseases involving the ductus. The identification of the mechanisms regulating ductal patency led to design pharmacological drugs to achieve medical closure of PDA in premature infants, or inversely to maintain patency in neonates with duct-dependent congenital heart diseases. Concurrently, widespread availability of echocardiography has improved the detection of congenital PDA, resulting in earlier treatment. Closure of PDA, by either surgery or transcatheter techniques, can now be achieved safely, resulting in a decrease in the incidence of severe complications of PDA.

Does retrograde diastolic flow in the descending aorta signify impaired systemic perfusion in preterm infants?

High-volume systemic-to-pulmonary ductal shunting occurs frequently in preterm infants and is indicated by diastolic flow reversal in the descending aorta (DAo). We studied the relationship between ductal diameter, diastolic DAo reversal, and left ventricular output (LVO); and superior vena caval (SVC) flow (upper body perfusion) and DAo flow (lower body perfusion) in preterm (<31 wk) infants. Echocardiographic assessments were performed at 5, 12, 24, and 48 h postnatal age (80 infants, median gestation 28 wk, 1060 g). Incidence of ductal patency fell from 100% at 5 h to 72% at 48 h; incidence of pure systemic-to-pulmonary shunting increased from 66% to 95% of infants with patent ducts. In infants with duct diameter greater than the median, 35-48% of infants had DAo flow reversal. In infants with duct diameter greater than median, DAo reversal was associated with 23-29% increases in LVO at 5-48 h, and 35% decreases in DAo flow volume at 24-48 h, but no differences in SVC flow. In conclusion, a large duct with left-to-right shunting is common in preterm infants. Retrograde DAo flow is a marker of high-volume shunt, evidenced by increased LVO. Preterm infants with high-volume ductal shunt may have preserved upper body perfusion but reduced lower body perfusion.

The hemodynamically significant ductus arteriosus in critically ill full-term neonates. Two case reports?

In premature infants, the clinical effects and management of a hemodynamically significant patent ductus arteriosus (HSDA) are well-described. In full-term neonates the ductus arteriosus (DA) is rarely monitored except in cases of concomitant pulmonary hypertension or duct dependent congenital heart disease. Although systemic-pulmonary shunting commonly occurs in mature infants, coinciding with the normal postnatal fall in pulmonary vascular resistance, cardiac failure in the neonatal period is rarely attributed directly to the DA. In this case series, we report two full-term infants who were initially treated for pulmonary hypertension and myocardial dysfunction but developed clinical, radiographic and two-dimensional echocardiographic evidence of cardiac failure secondary to a large unrestrictive patent DA (PDA). One patient was treated with indomethacin, and, although transductal diameter decreased, there was no clinical benefit. Cardiac failure resolved and myocardial function improved in both cases after PDA ligation. We suggest that PDA be monitored closely in neonates recovering from PPHN who have ongoing oxygenation difficulties or myocardial failure. PDA ligation should be considered an option for full term neonates with cardiac failure secondary to a HSDA when other therapeutic options fail.

Left ventricular systolic and diastolic function during early neonatal period using transthoracic echocardiography

To examine the effects of ductal closure on left ventricular (LV) systolic and diastolic function during the early neonatal periods, 45 normal term neonates delivered after uncomplicated pregnancies (mean 39 weeks) were studied using two-dimensional and Doppler echocardiography. We measured ductus arteriosus size, arterial blood pressures, ascending aortic size, LV dimensions, and transmitral flow velocity patterns and calculated LV output and rate-corrected fiber shortening fraction (mVcfc) at 2, 12, 24, and 120 hours after birth. The inner diameter of the ductus arteriosus was 4.3 +/- 0.7mm at 2 hours, 2.1 +/- 0.6 mm at 12 hours, and had closed in 42 of 45 neonates at 24 hours. LV output and LV end-diastolic dimension showed the highest level at 2 hours of age. However, the mVcfc did not change from 2 to 120 hours of age. The peak velocity during early diastole (peak E) was significantly greater at 2 hours than at 12 hours. The peak velocity during atrial contraction (peak A) remained unchanged during this period. The normalized peak filling rate at isovolumic relaxation time did not change over 120 hours. The present study demonstrated changes in LV systolic function and LV diastolic filling during the early neonatal period. LV systolic and diastolic function was preserved under the hemodynamic changes associated with the early neonatal period.

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.

Changes in the volume and performance of the left ventricle in the early neonatal period

To evaluate the effect of changes in preload on left ventricular (LV) performance, we used echocardiography to measure end-diastolic dimension, end-systolic dimension, and stroke volume in newborns at 2, 12, 24, and 120 h of age. The stroke volume was calculated by the pulsed Doppler technique. The stroke volume showed the highest level at 2 h of age. The size of the ductus arteriosus correlated with the stroke volume. These results indicated that the increase in stroke volume was related to the increase in LV preload due to the shunt flow volume through the patent ductus arteriosus. M-mode echocardiographic indexes such as end-diastolic dimension, LV end-diastolic volume, and LV ejection fraction did not show any significant changes from 2 to 120 h of age. We conclude that M-mode echocardiographic evaluation of LV performance is unreliable in the early neonatal period. Our data also provide a useful basis for the interpretation of abnormal left ventricular systolic function in the early neonatal period.

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.

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.