How do you differentiate between Patent Ductus Arteriosus (PDA) and Deep Vein Thrombosis (DVT)?

Differentiating Patent Ductus Arteriosus (PDA) from Deep Vein Thrombosis (DVT)

PDA and DVT are completely different cardiovascular conditions affecting entirely different anatomical structures and patient populations—PDA is a congenital heart defect involving a persistent connection between the aorta and pulmonary artery, while DVT is an acquired thrombotic condition of the deep venous system, typically in the lower extremities. 1, 2

Fundamental Anatomical and Pathophysiological Differences

Patent Ductus Arteriosus

• Location: Persistent communication between the proximal left pulmonary artery and descending aorta just distal to the left subclavian artery 1
• Pathophysiology: Creates a left-to-right shunt causing left ventricular volume overload and potentially pulmonary arterial hypertension 1
• Nature: Congenital cardiovascular malformation present from birth, though may be diagnosed later in life 1

Deep Vein Thrombosis

• Location: Blood clot formation in deep veins, most commonly in lower extremities 1, 2
• Pathophysiology: Venous stasis and thrombosis leading to venous obstruction and potential pulmonary embolism 1, 2
• Nature: Acquired condition related to predisposing factors like immobility, surgery, trauma, or hypercoagulable states 1, 3

Clinical Presentation Differences

PDA Clinical Features

• Cardiac auscultation: Continuous "machinery-type" murmur heard best at left infraclavicular area (in moderate-large PDA without severe pulmonary hypertension) 1, 4
• Pulse examination: Bounding peripheral pulses with wide pulse pressure due to left-to-right shunting 1, 4
• Symptoms: Dyspnea, easy fatigability from left heart failure (moderate PDA), or differential cyanosis affecting lower extremities more than upper body (large PDA with Eisenmenger physiology) 1, 4
• Age presentation: Often diagnosed in infancy/childhood, but can present in adults if previously undetected 1, 5

DVT Clinical Features

• Limb examination: Unilateral leg pain, swelling, erythema, and dilated superficial veins in affected extremity 3
• Cardiac auscultation: No characteristic murmurs 3
• Pulse examination: Normal arterial pulses (venous, not arterial pathology) 3
• Symptoms: Localized limb symptoms rather than cardiac symptoms; risk of pulmonary embolism if clot embolizes 1, 2

Diagnostic Approach Differences

PDA Diagnosis

• Primary imaging: Echocardiography with color Doppler in parasternal short-axis view directly visualizes the duct and demonstrates shunting 1, 4
• ECG findings: May show left atrial enlargement, LV hypertrophy (moderate shunt), or RV hypertrophy (if pulmonary hypertension present) 1, 4
• Chest X-ray: Cardiomegaly, increased pulmonary vascular markings, prominent pulmonary artery segment 1, 4
• Cardiac catheterization: Reserved for cases with elevated pulmonary artery pressure to assess pulmonary vascular resistance 1

DVT Diagnosis

• Clinical decision rule: Wells score or similar to stratify pre-test probability as "unlikely" or "likely" 3
• D-dimer testing: If DVT "unlikely" and D-dimer normal, DVT excluded; if elevated, proceed to imaging 3
• Primary imaging: Compression ultrasonography of affected limb is diagnostic test of choice 2, 3
• No cardiac imaging needed: DVT diagnosis does not require echocardiography or cardiac catheterization 3

Key Distinguishing Features in Practice

When to Suspect PDA

• Continuous cardiac murmur on auscultation 1, 4
• Bounding pulses with wide pulse pressure 1, 4
• Evidence of left ventricular volume overload on echocardiography 1, 4
• Differential cyanosis (lower extremities more cyanotic than upper) in severe cases 1, 4

When to Suspect DVT

• Unilateral limb swelling and pain without cardiac murmur 3
• Recent surgery, trauma, immobilization, or known thrombophilia 1
• Elevated D-dimer with appropriate clinical context 3
• Positive compression ultrasound showing non-compressible vein 3

Common Pitfalls to Avoid

Do not confuse PDA with other causes of continuous murmur: Aortopulmonary collaterals, coronary arteriovenous fistula, ruptured sinus of Valsalva, or VSD with aortic regurgitation can mimic PDA on examination 1

Do not assume all leg swelling is DVT: Consider alternative diagnoses like cellulitis, lymphedema, or musculoskeletal injury, which require different management than anticoagulation 3

Recognize that PDA and DVT can theoretically coexist: While extremely rare, a patient with congenital heart disease could develop DVT as a separate acquired condition, requiring evaluation and treatment of both conditions independently 1, 2