A pulmonary angiogram (PA-gram) is an invasive radiological procedure most commonly performed for the diagnosis of pulmonary emboli (PE). As this examination enables the visualization of the entire pulmonary circulation, it remains the gold standard test for determining the presence of a vascular occlusion in this organ system.
If a patient presents with the symptoms of a PE, the first examination that will be performed after the chest x-ray will most likely be a V/Q scan, a nuclear medicine study that assesses the ventilation and perfusion of the lungs. If the results of the V/Q scan are equivocal, and if the patient doesn't have any absolute contraindications (e.g. severe pulmonary hypertension or congestive heart failure in an unstable patient), a PA-gram should be performed if there is a high suspicion of the presence of emboli. In some cases, a vascular ultrasound of the veins of the leg will be performed prior to the PA-gram to confirm the presence of thrombus that may be dislodged and captured in the pulmonary arterial system.
Making the correct diagnosis of PE is crucial for several reasons, the most pressing being the viability of the pulmonary parenchyma distal to the occlusion; in cases of severe occlusion, an embolectomy might need to be performed. Furthermore, a diagnosis of PE essentially commits a patient to a lifetime of anticoagulation. If anticoagulation is contraindicated, a filter may need to be placed in the inferior vena cava (IVC) to catch medium and large emboli and prevent them from getting lodged in the pulmonary circulation.
The skin around the groin is shaved and sterilized and local anaesthesia is injected into the subcutaneous tissue over the region of the right common femoral vein. A small incision is made with a scalpel and a specialized needle (one with a hollow external barrel, a sharp and beveled internal mandril, and small, wing-like handles that allow for control and stabilization of the device) is inserted percutaneously into the femoral vein. The mandril is removed and once it has been confirmed that the correct vessel has been punctured (venous blood is darker than arterial blood), a guide wire is threaded through the barrel of the needle. The needle is removed over the guide wire and, while maintaining firm pressure on the vein to reduce the bleeding, a catheter is inserted over the guide wire and into the IVC. Fluoroscopy and the hand-injection of a small amount of contrast material are used to confirm proper placement. Then, using fluoroscopic guidance, the catheter is floated up the IVC, through the right side of the heart, and into the pulmonary trunk. The specialized catheter has been designed to respond to small chages in torque so that the tip may be placed in the lumen of both pulmonary arteries.
The catheter will then be attached to a contrast injection machine and series of radiographs will be taken concurrent with the injection of the contrast. Images of the arterial and venous phases of both lungs are obtained and initially reviewed; oblique views may be necessary to properly visualize the entire vasculature. Once the images have been obtained, the catheter is removed and firm, steady pressure is applied to the puncture area (usually by a resident or medical student.)
The pulmonary arterial vasculature looks like a tree with a complex branching structure. Each vessel should taper down gradually and have a smooth contour. An embolus will appear as an abrupt cut-off in a vessel with no evidence of filling distally. Sometimes multiple emboli may be present; some may not occlude the vessel, but will show up as filling defects within the lumen.