Classifications of Patent Ductus Arteriosus by Anatomic Shape and Size
Primary Classification System (Krichenko Classification)
PDA morphology is traditionally classified into five main anatomic types (A through E) based on angiographic appearance, with a sixth type (F) recently proposed for premature infants. 1
Standard Krichenko Types (A-E)
The classification system categorizes PDAs according to the degree of ductal tapering and the presence, absence, or location of abrupt ductal narrowing: 2
- Type A: Conical shape with gradual tapering from aorta to pulmonary artery
- Type B: Window-like or short, broad connection
- Type C: Tubular shape with minimal tapering
- Type D: Complex or multiple fenestrations
- Type E: Elongated, tortuous configuration
Type F (Fetal-Type PDA)
Type F PDA represents a distinct morphology seen predominantly in premature infants that does not fit the traditional Krichenko classification. 1
- Characteristics: Relatively larger and longer compared to other types, with mean length-to-descending aorta ratio of 1.88 (versus 0.9-1.21 for other types) 1
- Population: Children born prematurely (median 27.5 weeks gestation) 1
- Device requirements: Requires relatively large devices for occlusion (mean device-to-descending aorta ratio of 1.04 versus 0.34-0.87 for other types) 1
- Preferred closure method: Amplatzer vascular plug-II is effective in 85% of Type F PDAs 1
Size Classification
By Hemodynamic Significance
PDAs are functionally classified based on shunt magnitude and cardiac effects, though standardized size cut-offs remain controversial: 3
- Small PDA: No left ventricular volume overload, normal pulmonary artery pressure, normal cardiac chamber dimensions 3
- Moderate PDA: Evidence of left ventricular volume overload OR predominant pulmonary arterial hypertension 3
- Large PDA: Nonrestrictive with Eisenmenger physiology, differential cyanosis and clubbing 3
Important Clinical Caveat
Fixed diameter cut-offs are inadequate for pediatric patients because defect size must be considered relative to body size and cardiac chamber dimensions. 3 Two-dimensional measurements may be inaccurate for complex geometry; three-dimensional echocardiography demonstrates that the majority of PDAs (71% of pulmonary ostia, 79% of ampullae) are oval rather than circular. 4
Anatomic Measurement Parameters
Key Dimensions for Device Selection
Critical measurements include: 1, 5
- Minimal ductal diameter (MDD): The narrowest point of the ductus, typically at the pulmonary end 5
- Aortic ostium diameter: Opening at the aortic end 5
- Ampulla diameter: Measured 3mm above the MDD or pulmonary ostium 4
- Ductal length: Distance from aortic to pulmonary ostium 1
Echocardiographic measurements of minimal diameter and aortic ostium diameter correlate well with angiography (R² = 0.88 and 0.72 respectively), supporting their use for assessing transcatheter closure suitability. 5
Special Morphologic Variants
Ductal Aneurysm
A rare variant characterized by focal dilation of the ductus, which may compress adjacent structures including the left main coronary artery. 3, 6
Calcified Ductus
Calcification is particularly important in adult patients, as it increases surgical risk of rupture during repair and influences the choice between surgical approaches (ligation/division versus patch closure). 3, 7 Calcified PDAs should prompt consideration of catheter intervention as first-line therapy when anatomically suitable. 3, 7
Associated with Vascular Ring
The PDA or its ligamentous remnant can form part of a vascular ring when associated with abnormal aortic arch formation. 6
Clinical Implications of Classification
Accurate morphologic assessment is essential because PDA type determines optimal closure strategy—device selection for transcatheter closure or surgical approach. 1, 2 Type IIA is the most frequently encountered variant (54.4% of cases), while Type III PDAs are significantly wider than other phenotypes and may require larger devices or surgical intervention. 2