Patent Ductus Arteriosus

The Controversy Surrounding PDA in Prematurity

Despite countless trials conducted in various forms (and a lot of money invested in running these trials), reflecting real-world neonatal practice, none have shown a meaningful improvement in outcomes. In fact, they have highlighted the potential harm associated with these interventions. We cannot conduct research solely to "prove" what we wish to be true and then disregard the results when they do not align with our expectations. Science demands that we remain objective, follow the evidence wherever it leads, and adapt our practices accordingly. This is a recording of a talk I gave to our neonatal hemodynamics fellows. Perhaps I can persuade you to reconsider practices that do not appear to benefit some of the most vulnerable babies we care for and instead advocate for evidence-based approaches rooted in science. More importantly, this is also a call to pursue research and explore new strategies to continuously improve outcomes for these fragile newborns. Hope you enjoy it!

Left to Right Patent Ductus Arteriosus

Diameter of the PDA

It is good practice to have the ECG and the B-Mode and Colour box in order to clearly identify the ductus at its narrowest point during systole. 

Small restrictive PDA by 2D ultrasound and restrictive profile (high-velocity) obtained by CW-Doppler. 

Another example of a small PDA left to right, restrictive. The peak systolic gradient is estimated at 80 mmHg. Indicating that the systolic pulmonary arterial pressure is at least 80 mmHg below the systolic blood pressure at the time of the image acquisition. 

LA/Ao ratio

Doppler Profile in Aorta, Cerebral Artery and Celiac Artery

Various degree of holo-diastolic retrograde flow in the descending abdominal aorta in the context of diastolic steal in patients with left to right PDA.

Examples of transcranial Doppler when one may appreciate the Circle of Willis. The middle cerebral artery is seen coming towards the probe. 

Restrictive Left to Right PDA

Sweep without a PDA

Two examples of the modified high (left) parasternal short axis view. This sweep is important to rule out the presence of a PDA connecting the pulmonary artery and the aorta. In these examples, there is no evidence of a PDA (one must be careful not to miss a Right to Left ductus, which will be "blue" - flow away from the probe).

3D Echocardiography and Navigation for a Left to Right Large PDA

Stead Family Children’s Hospital, Iowa City - PDA screening and management guideline for ELBW infants - Available from the NHRC website

Left to Right ductus is considered significant if: 

• Ductal diameter is > 1.5mm AND 

• Predominant (>90%) left-to-right transductal flow AND 

• PDA shunt volume score is ≧ 6

E wave, IVRT, LVO - see example here.

In a large left-to-right patent ductus arteriosus (PDA), increased pulmonary venous return and left atrial (LA) volume overload significantly impact mitral inflow dynamics, particularly the E-wave (early passive filling phase of the left ventricle). During ventricular systole, the mitral valve remains closed, while continuous pulmonary venous return leads to progressive LA filling. In the presence of a large PDA, excess pulmonary blood flow results in elevated LA pressure, reducing the LV-LA pressure gradient needed for mitral valve opening. When the mitral valve opens, the E-wave velocity increases, reflecting a rapid "gush" of blood into the LV due to high preload (high LA pressure). This augmented early diastolic filling can mimic restrictive physiology in severe cases, characterized by shortened IVRT, increased E/A ratio, and shortened deceleration time due to elevated LA pressures.

Other considerations:

• E/A Ratio: Often increased due to the disproportionately higher E-wave compared to A-wave. 

• Deceleration Time (DT): May be shortened due to elevated left atrial pressures, resulting in rapid equilibration of LA-LV pressures. 

With a large left-to-right patent ductus arteriosus (PDA), the increased pulmonary venous return and left atrial (LA) volume overload have notable effects on isovolumic relaxation time (IVRT). The IVRT (Isovolumic Relaxation Time) shortens due to increased left atrial pressure and higher left ventricular (LV) preload. Elevated left atrial pressure reduces the pressure gradient required for the LV to relax to below LA pressure, thereby shortening IVRT. The rapid diastolic filling from the increased pulmonary venous return contributes to early LV filling.

The pattern of shortened IVRT and increased E-wave velocity is a hallmark of significant left heart volume overload, commonly seen in large left to right PDAs with significant shunt volume.

With a large left-to-right patent ductus arteriosus (PDA), left ventricular output (LVO) is typically increased due to the significant volume overload on the left heart. Here’s why:

1. Increased Pulmonary Blood Flow → Increased Pulmonary Venous Return

   • The left-to-right shunt directs a portion of the systemic output back into the pulmonary circulation, leading to excessive pulmonary venous return to the left atrium (LA).

   • This results in elevated left atrial pressures and increased preload for the left ventricle (LV).

2. Increased LV Stroke Volume and Cardiac Output

   • Due to the increased preload, the LV must accommodate a higher volume of blood, leading to increased stroke volume and, consequently, an elevated left ventricular output (LVO).

   • The Frank-Starling mechanism contributes to increased contractility, maintaining a high cardiac output.

Key Echocardiographic Findings:

• Increased LVO (measured via LVOT VTI and diameter)

• Elevated E-wave velocity due to high preload

• Shortened IVRT and deceleration time

• Increased left atrial and LV dimensions (LA dilation, LVEDD increase)

Application of NPE in the assessment of a patent ductus arteriosus (van Laere D et al.). Pediatric Research (2018) 84:S46 – S56

PDA score by El-Khuffash A. et al.

PDA risk score = (Gestation in weeks × −1.304) + (PDA diameter in mm × 0.781) + (Left ventricular output in mL/kg/min × 0.008) + (maximum PDA velocity in m/s × −1.065) + (left ventricular a' wave in cm/s × −0.470) + 41.

Score ranges between 0 (low risk) and 13 (high risk).

References:

• El-Khuffash A, James AT, Corcoran JD, Dicker P, Franklin O, Elsayed YN, Ting JY, Sehgal A, Malikiwi A, Harabor A, Soraisham AS, McNamara PJ. A Patent Ductus Arteriosus Severity Score Predicts Chronic Lung Disease or Death before Discharge. J Pediatr. 2015 Dec;167(6):1354-1361.e2. doi: 10.1016/j.jpeds.2015.09.028. Epub 2015 Oct 21. PMID: 26474706.

  • Narrowest PDA diameter (mm) by 2D at pulmonary end 

  • Max velocity across PDA ( in m/s); 

  • LV output (in mL/kg/min); 

  • Tissue Doppler imaging was obtained at apical 4-chamber view. Late diastolic (a′) velocities used at the level of the lateral mitral valve annulus. If the e′ and a′ waves were fused, they measured the single wave as an a′ wave.

• El-Khuffash A, Bussmann N, Breatnach CR, Smith A, Tully E, Griffin J, McCallion N, Corcoran JD, Fernandez E, Looi C, Cleary B, Franklin O, McNamara PJ. A Pilot Randomized Controlled Trial of Early Targeted Patent Ductus Arteriosus Treatment Using a Risk Based Severity Score (The PDA RCT). J Pediatr. 2021 Feb;229:127-133. doi: 10.1016/j.jpeds.2020.10.024. Epub 2020 Oct 16. PMID: 33069668.

  • <29 weeks: echo at 36 to 48 hours of life.

  •  In RCT, infants with risk score of ≥5.0 deemed at high risk for chronic lung disease or death and were randomized

Examples of bidirectional flow via the ductus. This profile may be seen in the context of iso-systemic PA pressures. This could be secondary to high pulmonary pressures, low systemic pressures, a mix, or a large PDA with rapid equalization of pressure on both side of the PDA.

Examples of large PDA with bidirectional shunts. On the first clip, one may appreciate the retrograde flow in diastole within the descending aorta.

Pathological example from the Maude Abbott Medical Museum