Pulmonary Artery Dissection

Pulmonary artery dissection is a tear in the intima of a pulmonary artery that lets blood enter and split the wall, forming a false lumen. It is very rare, with fewer than 100 cases reported, and is usually found in the main pulmonary artery or its proximal branches.

Over 70% occur with long standing pulmonary hypertension, from Eisenmenger syndrome (patent ductus arteriosus or septal defects), idiopathic pulmonary arterial hypertension, or chronic thromboembolic disease. Other causes are catheter injury (pulmonary artery catheter, balloon pulmonary angioplasty), trauma, cardiac or thoracic surgery, connective tissue disease (Marfan syndrome), arteritis (Takayasu) and infection. Some cases have no clear cause.

Pathophysiology. Chronic high pressure and pulsatile stress degenerates the elastic media, with cystic medial change and intimal weakening. A tear allows blood in at systemic like pressure, extending the dissection along the wall. The false lumen can rupture into the pericardium (tamponade), pleura or lung, or compress the airway and coronary arteries.

Sudden chest pain (often mimicking aortic dissection or pulmonary embolism), worsening dyspnoea, syncope, haemoptysis and hypotension, or sudden death. Signs of pulmonary hypertension and right heart failure are present in most. Many are diagnosed at autopsy. Tamponade shows raised jugular venous pressure, hypotension and muffled heart sounds.

Sudden chest pain with haemodynamic instability in a patient with pulmonary hypertension needs immediate imaging and resuscitation.

• CT pulmonary angiography: the key test, showing an intimal flap, a false lumen with differential enhancement, mural thrombus in the false lumen, a double lumen, and pulmonary artery dilatation (main trunk often over 4 cm). ECG-gated CT clarifies the aortic root and coronary arteries.
• Echocardiography (transthoracic or transoesophageal): a flap in a dilated pulmonary artery, pericardial effusion, right ventricular strain and the associated defects.
• MR angiography when stable and CT is not conclusive.
• Right heart catheterisation only if essential, since the catheter may extend the dissection.
• Differentiation from pulmonary embolism (a thrombus filling defect without a flap) and aortic dissection.
• Blood tests: troponin, D-dimer (raised), full blood count, lactate, and group and crossmatch.

Differential diagnosis.

• Acute pulmonary embolism
• Aortic dissection (Type A)
• Acute coronary syndrome
• Pulmonary artery aneurysm rupture
• Pericarditis and tamponade of other cause

• Resuscitation: oxygen, analgesia (morphine 2.5 to 5 mg intravenously), avoid fluid overload and anticoagulation or thrombolysis, which are dangerous because of rupture.
• Urgent pericardiocentesis or surgical drainage for tamponade.
• Pulmonary hypertension therapy to reduce pulmonary pressure and wall stress: sildenafil 20 mg three times daily, bosentan 62.5 mg twice daily increasing to 125 mg twice daily, or inhaled or intravenous prostanoid (treprostinil subcutaneous or intravenous 1.25 ng/kg/min, titrated) under specialist care. Use caution with vasodilators in hypotension.
• Conservative management with close surveillance is reported for stable patients with a short or non-expanding dissection, and mortality is high.
• Surgery in unstable or enlarging dissection, or when compression or rupture occurs: dissection repair with graft replacement of the pulmonary trunk, correction of the shunt, or heart lung or lung transplantation in end stage Eisenmenger syndrome. Endovascular stent grafting is reported in a few cases.
• Treat the cause: repair of the defect (if operable before irreversible hypertension), immunosuppression for Takayasu arteritis (prednisolone 0.5 to 1 mg/kg daily), and antibiotics for infection.
• Avoid pregnancy and strenuous exertion, and follow with a pulmonary hypertension centre.

Complications and prognosis. Cardiac tamponade, rupture, airway or coronary compression, thromboembolism and death. In hospital mortality is about 50% or more, and the outcome is better with prompt diagnosis and repair.

Monitoring. Repeat CT or MRI at 1, 3 and 6 months, then yearly, echocardiography at each visit, and haemodynamic review in the pulmonary hypertension clinic.

Referral and escalation. Refer immediately to cardiothoracic surgery and a pulmonary hypertension centre, with intensive care.