How do you size a patent ductus arteriosus (PDA) as small, moderate, or large?

PDA Sizing Classification

Patent ductus arteriosus is classified as small, moderate, or large based on hemodynamic consequences rather than absolute measurements, with small PDAs showing no left ventricular volume overload and normal pulmonary artery pressures, moderate PDAs demonstrating either predominant LV volume overload or pulmonary arterial hypertension, and large PDAs presenting with Eisenmenger physiology. 1

Small PDA

A small PDA is defined by the absence of hemodynamic consequences:

• No left ventricular volume overload with normal LV size and function 1
• Normal pulmonary artery pressure (PAP) 1
• Patients are generally asymptomatic 1
• Continuous machinery murmur may be present at the left infraclavicular area 1
• Normal ECG findings 1, 2
• Normal chest radiograph without cardiomegaly or increased pulmonary vascular markings 1

Moderate PDA

Moderate PDAs present with two distinct hemodynamic profiles, either of which defines the moderate category:

Profile 1: Predominant LV Volume Overload

• Large/dilated left ventricle with normal or reduced function 1
• May present with left heart failure symptoms including dyspnea and fatigue 1
• Left atrial enlargement and LV hypertrophy on ECG 1, 2
• Cardiomegaly and increased pulmonary vascular markings on chest x-ray 1
• Wide pulse pressure and bounding pulses 1

Profile 2: Predominant Pulmonary Arterial Hypertension

• Pressure-overloaded right ventricle 1
• May present with right heart failure 1
• Elevated pulmonary artery pressure but not yet Eisenmenger physiology 1
• RV hypertrophy on ECG 1, 2
• Continuous murmur may be replaced by systolic murmur only when PAH develops 1, 2

Large PDA

Large PDAs are characterized by severe, irreversible pulmonary vascular disease:

• Eisenmenger physiology with shunt reversal 1
• Differential cyanosis and clubbing affecting lower extremities (and sometimes left arm) 1
• Differential hypoxemia with lower oxygen saturation in feet compared to right hand 1
• Continuous murmur disappears with development of Eisenmenger syndrome 1
• Prominent proximal pulmonary artery segment on chest x-ray indicating elevated PAP 1

Key Diagnostic Approach

The classification relies on echocardiographic assessment of:

• LV chamber size and function to assess volume overload 1, 2
• Pulmonary artery pressure estimation via transpulmonary gradient with continuous-wave Doppler 1, 2
• Right ventricular size and function to evaluate pressure overload 1
• Shunt direction and magnitude using color Doppler 1, 2

Cardiac catheterization is indicated when:

• PAP appears high on echocardiography to measure pulmonary vascular resistance (PVR) 1
• Determining operability in patients with PAH and PAP >2/3 systemic pressure or PVR >2/3 SVR 1

Clinical Pitfall

The critical distinction is that PDA size classification is functional/hemodynamic rather than anatomic. A physically small ductus by diameter measurement may still cause significant hemodynamic consequences if non-restrictive, while a larger ductus may be restrictive and hemodynamically insignificant. 1, 3 The presence or absence of LV volume overload, pulmonary hypertension, and shunt direction determines the clinical category and guides management decisions. 1