Diagnosis of the Preterm Patent Ductus Arteriosus: Clinical Signs, Biomarkers, or Ultrasound?

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The current uncertainty in relation to treatment of the preterm patent ductus arteriosus reflects limitations to our understanding of the pathophysiology of ductal shunting, most particularly which ducts matter to which babies and when they matter. Doppler ultrasound offers a pragmatic tool with which to assess ductal patency and shunt significance and to allow prediction of spontaneous and therapeutic closure. Biomarkers, such as B-type natriuretic peptide, and clinical signs may have a diagnostic role where ultrasound is not available and also possibly as an adjunct to echocardiography in determining the pathophysiological impact of a ductal shunt in an individual baby.

Section snippets

Doppler Ultrasound and the Ductus Arteriosus

Doppler ultrasound provides accurate information on ductal patency and can give us some information in an individual baby of the size of a ductal shunt and the clinical impact of that shunt. Doppler ultrasound allows the direct imaging of the ductus to determine patency and degree of constriction. This is aided by color Doppler mapping that confirms the presence and direction of any shunt and the degree of constriction. Pulsed Doppler can be used to more accurately measure the pattern and

Is the Ductus Arteriosus Patent?

The resolution of modern ultrasound is such that indirect echocardiographic methods for assessing ductal patency have been rendered largely obsolete, though as described below, they may add information on the significance of a ductal shunt. Determining patency should involve direct imaging of the duct. The ductus leaves the main pulmonary artery (MPA) at its junction with the left pulmonary artery (LPA) and continues in the same posterior direction as the MPA to describe an arch into the

How Well Has the Ductus Arteriosus Constricted?

The fetal ductus arteriosus is a large vessel, not much smaller than the MPA, reflecting the fact that it carries 90-95% of the cardiac output. In the early postnatal period, almost all babies will show some degree of constriction from this fetal size. In healthy term babies, this constriction is universal and powerful.8 In preterm babies it is more variable.9 These differences in ductal constriction are readily apparent on color Doppler and 2D imaging, (Fig. 3). Measurement of the degree of

What Are the Direction and Velocity of the Ductal Shunt?

The direction and velocity of the shunt through the patent duct are direct products of the relative pressures at each end of the duct. These waves are not synchronous, with the pressure wave from the right heart arriving at the duct slightly earlier than the left, mainly owing to closer proximity to the heart. When the pulmonary pressures are clearly lower than systemic or clearly higher, the shunt will be left-to-right or right-to-left, respectively. However, as the pulmonary pressures

What Is the Volume of the Ductal Shunt?

Doppler ultrasound assessments of volume of ductal shunt are divided into direct and indirect assessments of this flow volume. The direct assessments are derived from the laws of fluid dynamics, which dictate that flow must be the product of the size (or cross-sectional area) of the vessel and the pressure gradient across that vessel. The size can be estimated as described above from direct 2D imaging together with color Doppler, and the pressure gradient can be estimated from the Doppler

Overload of the Pulmonary Circulation

The increase in PBF is essentially a passive process limited only by ductal size and the pulmonary vascular resistance. True primary pulmonary hypertension is rare in the preterm infant and even in the early postnatal hours; the dominant direction of shunting is left to right. Large PBFs can result when the ductal constriction fails.9

Echocardiographic measures of PBF are made complicated by the intracardiac shunts. The LV output may not represent PBF because the volume load on the left atrium

Drainage From the Systemic Circulation

A left-to-right ductal shunt drains more blood from the systemic circulation in systole than it does in diastole; the term “diastolic steal” is one of the great misnomers in neonatology. Although the amount drained is passive, the cardiac compensation for the drainage is not and depends on the ability of the left ventricle to increase its output to compensate for this continuous sump of blood out of the systemic circulation. This is complex, and ultrasound approaches to this depend on your bias

Clinical Signs and Symptoms of a PDA

Much harder in defining vulnerability is predicting or defining the clinical or symptomatic impact in an individual baby. Despite the limitations to our understanding, ultrasound remains the gold standard in PDA diagnosis, although not all neonatal intensive care units can access this modality in a timely manner. Ultrasound machines are expensive; the skills take time to acquire; and there are often political barriers to the implementation of neonatologist-performed point-of-care ultrasound.

Biomarkers and the PDA

About 10 years ago, biomarkers were introduced into this uncertain mix. There are essentially 3 biomarkers that have been studied in the recent literature; cardiac troponin T (TnT), atrial natriuretic peptide (ANP), and BNP. TnT is a marker of myocardial injury and so probably reflects pathologic consequences of the preterm transitional circulation, including failure of ductal constriction.9 ANP is released by atrial myocytes, whereas BNP is released from the ventricles of the heart in response

BNP and the Preterm Duct

BNP is produced by the ventricles, in response to stress, in the form of pro-BNP. This inactive precursor is cleaved into BNP and the inactive N-terminal pro-BNP (NTpBNP). Both have a limited half-life: BNP, about 20 minutes, and NTpBNP, about an hour. BNP reduces intravascular volume (and so ventricular loads) by causing diuresis and vasodilatation.28 With the introduction of a bedside testing kit, this measure developed to potential for real clinical utility. The research that recognized the

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