What is the pathophysiology of Patent Ductus Arteriosus (PDA) in adults?

Pathophysiology of Patent Ductus Arteriosus in Adulthood

Fundamental Hemodynamic Mechanism

In adults with PDA, the pathophysiology centers on persistent left-to-right shunting from the aorta to the pulmonary artery through a ductus that failed to close after birth, leading to left ventricular volume overload and/or progressive pulmonary arterial hypertension, with eventual shunt reversal (Eisenmenger physiology) in untreated large defects. 1

The ductus arteriosus normally connects the pulmonary artery to the descending aorta just distal to the left subclavian artery and should close after birth with the commencement of pulmonary blood flow and transition to a 2-ventricle circulation. 2 When this closure fails and the defect persists into adulthood, the pathophysiological consequences depend entirely on the size of the ductus and the resulting hemodynamic burden. 1

Hemodynamic Profiles in Adult PDA

The European Society of Cardiology classifies adult PDA into three distinct pathophysiological patterns based on hemodynamic consequences rather than absolute measurements: 1, 3

Small PDA

• No left ventricular volume overload with normal LV size and function 1, 3
• Normal pulmonary artery pressures throughout the disease course 1, 3
• Patients remain asymptomatic, though a continuous machinery murmur may be audible 1, 3

Moderate PDA with Two Distinct Pathways

Pathway 1: Predominant LV Volume Overload

• Chronic left-to-right shunting causes progressive left ventricular and left atrial dilatation from volume overload 1, 3
• The left ventricle may develop normal or reduced systolic function over time 1, 3
• Patients present with left heart failure symptoms including dyspnea and fatigue 1, 3
• Pulmonary pressures may be elevated but not yet at systemic levels 1

Pathway 2: Predominant Pulmonary Arterial Hypertension

• Some patients develop disproportionate elevation in pulmonary artery pressure relative to the degree of shunting, likely due to genetic predisposition 1
• The right ventricle becomes pressure-overloaded rather than the left ventricle being volume-overloaded 1, 3
• Patients may present with right heart failure symptoms 1

Large PDA with Eisenmenger Physiology

The most severe pathophysiological consequence occurs when chronic exposure to high pulmonary blood flow and pressure causes irreversible pulmonary vascular remodeling: 1, 3

• Severe, irreversible pulmonary vascular disease develops with markedly elevated pulmonary vascular resistance 1, 3
• When pulmonary vascular resistance exceeds systemic vascular resistance, shunt reversal occurs (right-to-left shunting) 1, 3
• This creates the pathognomonic finding of differential cyanosis and clubbing, affecting the lower extremities and sometimes the left arm, because deoxygenated blood from the pulmonary artery enters the descending aorta distal to the left subclavian artery 1, 3
• Differential hypoxemia manifests with lower oxygen saturation in the feet compared to the right hand 1, 3
• The continuous murmur disappears as the shunt reverses, leaving only a systolic component or no murmur at all 1

Critical Anatomical Considerations in Adults

Adults who reach adulthood with unrepaired PDA develop specific anatomical changes that complicate management: 4

• Calcification of the ductus occurs with aging, making surgical closure potentially hazardous due to tissue fragility 1, 4
• Aneurysm formation of the duct is a rare but serious complication that may compress the left main coronary artery 1
• These histologic alterations increase surgical risk, making transcatheter closure the preferred approach when technically feasible 1, 4

Unique Assessment Requirements

Because of the anatomical location of the PDA connecting to the descending aorta, accurate assessment requires checking oxygen saturation in both feet and both hands, not just standard finger oximetry, to detect differential cyanosis from right-to-left shunting. 1, 3 Additionally, pulse oximetry should be performed both at rest and with ambulation, as some patients with resting systemic oxygen saturation >90% will desaturate to <90% with activity, revealing dynamic shunt reversal induced by exercise. 1

Progression and Natural History

The pathophysiology in adults reflects either: 1

1. Survival with a small defect that never caused significant hemodynamic consequences
2. Moderate defects where either LV volume overload or PAH predominates based on individual patient factors including genetic predisposition
3. Large defects where Eisenmenger physiology has already developed, representing end-stage disease with irreversible pulmonary vascular changes

The risk of endarteritis exists but appears to be low in adult patients. 1 However, when Eisenmenger physiology develops, morbidity and mortality are high, and closure of the shunt is contraindicated as it would eliminate the only pathway for right ventricular decompression. 1