Pulmonary Angiography Technique

The pulmonary vasculature may be evaluated with various invasive and noninvasive methods. Historically, catheter-directed pulmonary angiography has been used most commonly for the diagnosis of suspected pulmonary embolism (PE). Over the past two decades, however, catheter angiography has become almost entirely supplanted by CT angiography (CTA), which is now the accepted standard of care for diagnosis of suspected PE, in part owing to its superior sensitivity and specificity.[1, 2, 3, 4, 5, 6, 7] Other noninvasive methods, such as MRI/A and V/Q scans, are also used to evaluate the anatomy and hemodynamics of the pulmonary vasculature.[8]

Multislice computed tomography (MSCTA) has been shown to have a sensitivity of 82-97% and a specificity of 78-96% in the diagnosis of pulmonary embolism.[9, 10, 11, 12, 13, 14]  Multidector CT (MDCT) technology has the potential to further enhance the ability of CTPA to determine the presence and clinical significance of pulmonary thromboembolism.[15]

Currently, the main clinical utility of conventional pulmonary angiography is for therapeutic intervention and, in selected cases, preoperative evaluation of the pulmonary arteries.

Selected examples of abnormalities identified with pulmonary angiography are shown below.

According to American College of Radiology (ACR) and Society of Interventional Radiology (SIR) guidelines,[16]  there are no absolute contraindications to catheter pulmonary angiography. As with any interventional procedure, evaluation of the patient’s clinical and renal status, any allergies to intravenous contrast, and anticipated hemodynamic or cardiac issues should be carefully weighed.

If the catheter does not easily advance into the RV, the coronary sinus may have been entered inadvertently. Gently inject contrast material under fluoroscopy to check for this if the catheter does not advance.

Be cognizant of left bundle branch block (LBBB) before starting the procedure. To avoid complete heart block, a transvenous pacemaker or external pacing leads should be in place prior to starting the procedure.

With the use of modern equipment and nonionic low osmolar contrast agents, complications in conventional pulmonary angiography are rare and usually minor. They include the following[17] :

• Transient arrhythmia (be aware of preexisting arrhythmia, particularly LBBB)

• Entry-site hematoma

• Contrast reaction

• Respiratory distress

• Pulmonary edema[18]

• Rarely, injury to pulmonary artery (PA), cardiac perforation, cardiac arrest

• Rare case report of stroke in a patient with PFO[19]

Catheter pulmonary angiography is indicated for diagnosis and treatment of PE in certain circumstances. Pulmonary angiography can be used in a diagnostic dilemma, although CTA is the clinically preferred method. In chronic PE, pulmonary angiography is used for surgical planning prior to pulmonary endarterectomy.[20] As for treatment indications, thrombectomy and catheter-directed thrombolysis are used for acute massive or submassive PE.[21, 22, 23, 24, 25] Indications include hemodynamic instability, right heart strain/failure, severe hypoxemia, free-floating right ventricular (RV) thrombus, patent foramen ovale (PFO), and failed systemic thrombolysis.[26, 27]

Pulmonary angiography is indicated in the treatment of pulmonary arteriovenous malformations or fistulas. Endovascular coiling is indicated when the feeding artery is greater than 3 mm in diameter.[28]

Treatment of iatrogenic or postinfectious pseudoaneurysm is an indication, particularly in the presence of significant hemoptysis.[29, 30]

Pulmonary angiography is indicated as part of a complete embolization for severe cavitary or inflammatory lung lesions.

It is indicated in the evaluation of the pulmonary arteries for tumor encasement.

Catheter pulmonary angiography is also used in the retrieval of foreign objects, such as an embolized catheter fragments or even inferior vena cava (IVC) filters.[31]

Before the procedure, the interventionalist should review the following patient information in addition to a complete history and physical examination:

• Vital signs and hemodynamic parameters

• Allergies, particularly to intravenous contrast material or other procedural medications such as sedatives

• Medications, including anticoagulants, antiplatelet agents, and metformin

• ECG abnormalities: Look specifically for LBBB[32] ; potentially fatal complete heart block is a risk during manipulation of the catheter through the right heart by induction of a right bundle branch block; if LBBB is present, a transvenous pacemaker or external pacing leads should be in place prior to starting the procedure possibly in consultation with the cardiology service

• Laboratory studies: Blood urea nitrogen/creatinine, coagulation parameters (PT, PTT, INR, platelets), pregnancy test (if appropriate)

• Imaging: CT scanning (to evaluate anatomic abnormalities and to plan approach), ultrasonography (to check for location of deep venous thrombosis, if present), echocardiography (may show right heart dysfunction in a patient with PE; PFO increases the risk of periprocedural stroke in rare circumstances)

The patient is placed on nothing by mouth (NPO) status according to the institution’s requirements for patients undergoing monitored moderate conscious sedation.

Anesthetize the skin using appropriate anesthetic agent. Conscious sedation may be used depending on the clinical status of the patient.

Be alert for airway issues when giving respiratory depressants. Avoid excessive sedation, since breath-holding during imaging is crucial in obtaining diagnostic-quality imaging.

The patient is placed in the supine position on the angiographic table.

Periprocedural observation includes puncture site checks to evaluate for hematoma, in addition to frequent vital sign monitoring for the first 4 hours postprocedure.

Using ultrasonography, evaluate the common femoral (or, if required, the right internal jugular) vein for patency and compressibility. If there is any thrombus or indwelling catheter, the approach may need to be altered. Clean and drape the site. Anesthetize the skin using appropriate anesthetic agent. Conscious sedation may be utilized depending on the clinical status of the patient. Avoid oversedation since patient cooperation and breath holding are imperative for good quality imaging.

Access the femoral (or right internal jugular) vein using the standard venous puncture protocol. Ultrasonography may be used as an adjunct, if needed. Sheath placement depends on operator preference.

Studies have shown high success rates with ultrasound-directed catheter pulmonary angiography for thrombolysis in massive and submassive pulmonary embolism.[22, 24]

 

Numerous articles have described a multitude of techniques for accessing the pulmonary arteries, some using specialized catheters and guidewires.[33, 34, 35, 36, 37]

The Grollman catheter, for example, is a preformed pigtail catheter that has a gentle rightward curve with a second 90° leftward curve at the distal aspect of the catheter; its distal tip is in a pigtail configuration (see the image below). This shape was designed for access from the right femoral vein and allows for easier maneuvering through the right heart and pulmonary arteries.[38]

Multiple variations on this design have been produced, such as the St. Charles catheter. More standard catheters, such as the Omni-flush, may be used along with a malleable hydrophilic wire to shape the catheter. There is also a specialized C-shaped Hunter catheter for a brachiocephalic approach.[35] A Swan-Ganz catheter can also be used to flow directly into the pulmonary arterial circulation by inflating the balloon.

The Berman catheter is a balloon-tipped, end-capped, pressure-rated catheter that can be advanced through the right heart into the pulmonary artery. The end cap protects the distal pulmonary vasculature from injury during high-pressure injections. Multiple fenestrations along the catheter tip allow for pressure diffusion and rapid exit of contrast solution.[39]

The main principles for catheter and guidewire selection

Use a catheter that has side-holes, such as a pigtail, to decrease the risk of damaging the vasculature

Have some means of creating a 90° or near 90° angle within several centimeters of the distal portion of the catheter to improve maneuverability through the right heart. Use a preformed specialized catheter or gently bend the stiff end (back end) of a guidewire to create an angle in an otherwise straight catheter (make sure the guidewire always stays inside the catheter; otherwise, it will damage the vessel/mediastinal structures.)

Use a soft-tipped or tip-deflecting wire (eg, Reuter tip-deflecting wire) and protect the tissues from a regular-tip wire.

After gaining central venous access, advance a 6-7F catheter into the right atrium under fluoroscopic guidance (see the image below). Continuous cardiac monitoring is imperative to assess for arrhythmia as the catheter traverses the heart.

Rotate the catheter such that the pigtail lies facing the tricuspid valve. Advance the catheter tip into the RV. Turn the catheter counterclockwise while advancing the catheter, and the pigtail should approach the main pulmonary artery (see the images below).

The left pulmonary artery is the continuation of the main pulmonary artery and is easily accessed by advancing the catheter placed in the main pulmonary artery.

Accessing the right pulmonary artery requires a sharp turn, and using a J-tipped guidewire may assist in accessing this vessel. Alternatively, a hydrophilic wire may sometimes be necessary to access the right pulmonary artery (see the image below).

For selective catheterization of segmental pulmonary arteries, a straight-tipped catheter, such as the Berenstein, may be used (see the image below).

Measuring pressures in the heart and pulmonary arteries may be necessary, especially when evaluating a patient with chronic thromboembolic disease. Typically, pressures in the right atrium, RV, and main pulmonary artery are measured.[40]  When interpreting the images, evaluate for aberrant vessels, such as scimitar vein or anomalous coronary artery, particularly in the pediatric population.[41]  Also assess the caliber and contour of vessels. Vessels should be free of filling defects and should taper gradually. Flow dynamics are also assessed. Finally, evaluate the timing of arterial, parenchymal, and pulmonary venous opacification.

Normal pressure values are as follows:

• Right atrium or central venous pressure, 3-5 mm Hg

• RV, 20-25 mm Hg

• Pulmonary artery, 20-25 mm Hg/10-15 mm Hg

• Pulmonary capillary wedge, 10-15 mm Hg

To obtain a diagnostic pulmonary angiogram, have the patient suspend respiration after a full inspiration during the injection of contrast material to minimize motion artifact. For most studies, it is recommended to obtain 3-4 images per second for the first 5 seconds and then 1-2 images per second for the remainder. The following views should be obtained for a complete study:

• Anteroposterior of each side (see the image below)

  Normal right (A) and left (B) pulmonary angiograms showing gradual tapering of the pulmonary arteries, normal caliber vessels, and no filling defects.

• Posterior oblique projections of the lower lobes (see the image below)

  (A) Anteroposterior angiogram of the right pulmonary artery shows no abnormality. (B) On the oblique view, a filling defect is visible posteriorly (arrow).

• Use magnification to interrogate any specific regions of interest (see the image below)

  (A) Left pulmonary angiogram shows faint subsegmental filling defect in the lateral basal pulmonary artery that is imaged more clearly (arrow) on the magnified view (B).

To minimize the risk of adverse reactions, low osmolar nonionic contrast should be used. Typical injections rates are listed below. To help determine the rate of injection, evaluate the rate of flow through the selected artery using hand-delivered test injections; if contrast dissipates quickly, a higher rate should be used. Although the authors list injection rates for the main pulmonary artery to be complete, images from such injections are typically of poor quality, and injection here is therefore not advised. Selective right and left lung arteriograms yield better diagnostic images.

For patients with renal failure or other contraindications to iodinated contrast material, CO2 may safely be used as a contrast agent[42] ; however, imaging of the distal vasculature may be of poor quality.[43]

Injection rates

Injection rates are as follows:

• Main pulmonary artery, 25-30 mL/s for 2 seconds

• Left pulmonary artery or right pulmonary artery, 15-20 mL/s for 2 seconds

• Lobar or segmental, 5-10 mL/s for 2 seconds