Angiography

Anatomy and Physiology

The complete anatomy of the vascular system is beyond the scope of this article. Key anatomical structures relevant to angiography will be discussed.

The aorta starts at the aortic root, which in healthy individuals measures up to 4.3 cm.[3] The aorta gives off the left and right main coronary arteries at the level of the sinus of Valsalva. It then continues as the ascending aorta, before turning into the aortic arch. Three important branches originate from the arch:

• The brachiocephalic trunk divides to form the right common carotid and right subclavian arteries.
• The left common carotid artery further divides to form the internal and external carotid arteries. The internal carotid artery, together with the vertebral artery, will form the circle of Wilis, while the external carotid artery gives off the superior thyroid artery, the ascending pharyngeal artery, and the lingual artery. Other branches of the external carotid artery include the facial artery, the occipital artery, the posterior auricular artery, the maxillary artery, and the superficial temporal artery
• The left subclavian artery

The subclavian artery is divided into three sections by the scalenus anterior muscle. The first part gives off the vertebral artery, which supplies blood to the vertebrobasilar system and the circle of Willis. The other arteries that originate from the first part are the internal mammary artery and the thyrocervical trunk. The costocervical trunk arises from the second part of the subclavian and the dorsal scapular artery from the third part. The subclavian artery changes its name to the axillary artery after passing over the first rib and supplies the upper extremity.

The abdominal aorta has three anterior unpaired branches to the viscera: coeliac axis (giving off the hepatic artery, splenic artery, and left gastric artery); the superior mesenteric artery; and the inferior mesenteric artery. The abdominal aorta also has three important lateral paired branches to the viscera: the suprarenal artery, the renal artery, and the testicular or ovarian artery. The abdominal aorta terminates as common iliac arteries, which further bifurcates to form internal and external iliac arteries. The internal iliac artery divides into the anterior and posterior divisions to supply the pelvic and perineal organs, while the external iliac artery courses below the inguinal ligament to form the femoral artery. The femoral artery supplies the lower extremity. The femoral and radial arteries are common sites of angiography catheter insertion.

A limitation of angiography is its inherent limitations of obtaining images that are a lumenogram compared with intravascular imaging modalities such as intravascular ultrasound, particularly in regard to the identification of arterial calcification.[4]

Indications

Indications for Angiography Based on Systems

Neuroangiography

• Extracranial disease indications include cavernous-carotid fistula, extracranial carotid stenosis, epistaxis, and subclavian steal syndrome.
• Intracranial disease indications are subarachnoid hemorrhage without a history of trauma, cerebral arteriovenous malformations and aneurysms, cerebral vasospasm, acute stroke, and WADA test.[5]

Cardiovascular

• Thoracic and abdominal aortic aneurysm and dissection
• Diagnosis and treatment of coronary artery disease
• Coronary artery aneurysms
• Peripheral vascular disease including intermittent claudication and limb-threatening ischemia
• Vascular malformations

Pulmonary

• Pulmonary hemorrhage

Gastrointestinal system

• Mesenteric ischemia
• Arterial embolization in critical gastrointestinal bleeding

Renal

• Renovascular hypertension
• Dialysis fistula mapping and maintenance angioplasty

Reproductive system

• Embolization of varicoceles
• Embolization of ovarian veins in patients with pelvic congestion syndrome
• Fibroids embolization

Oncology

• Transarterial cancer therapy (e.g., chemotherapy and radiofrequency ablation)
• Hepatoma
• Colorectal liver metastases
• Carcinoid tumors
• Renal cell carcinoma

Trauma

• Torn extremity arteryIntractable internal bleeding from visceral injury and pelvic trauma

Contraindications

Absolute Contraindications

Some conventional angiography tables in North America have a labeled weight limit of 350 pounds. Morbidly obese patients with weights exceeding this limit may not have angiography for technical safety concerns.

Relative Contraindications

Pregnancy, except in the presence of intractable hemorrhage with a risk of maternal death

History of severe iodinated contrast medium allergy manifesting as bronchospasm, laryngospasm, angioedema, and cardiovascular collapse. Carbon dioxide angiography could be done on these patients when available. 

Patients with a history of mild allergic reactions can be pretreated with steroids and antihistamines.

Patients with underlying renal impairment or dehydration are at high risk of developing renal function following exposure to contrast medium. Ultra-low contrast or zero contrast techniques have been proposed for this subset of patients.[6][7] 

Patients with coagulopathy, INR > 2, and platelet count < 50,000/microliter are at higher risk of bleeding. However, with the advent of vascular closure devices, the risk of bleeding is now minimal.

Patients with diabetes on metformin are at risk of deterioration in renal function and lactic acidosis, especially if they have underlying renal impairment. 

Patients with excessive anxiety or who are unable to lie still may require conscious sedation.

Equipment

The procedure room for angiography and angiography related interventions should be spacious enough to accommodate all of the machinery as well as staff.

• The essential equipment needed for conventional angiography include:
• Set of catheters and guide wires
• Autoinjector
• Image intensifying screen
• Sliding table
• Remote computerized equipment
• Biplane C-arm digital imaging
• Generator

Personnel

Angiography teams are usually led by clinicians who possess highly specialized critical care and technical skills and maybe specialized in interventional radiology, vascular surgery, interventional neuroradiology, or interventional cardiology, depending on the specific study or procedure.

Angiography lab nurses and nurse managers ensure the safety of patients before, during, and after the procedure, and they must possess critical care and cardiovascular monitoring skills. Radiology technicians in the angiography room possess the technical skills for vascular imaging and cardiovascular monitoring to ensure the safety of patients.

Preparation

Patients' preparations before conventional angiography are individualized based on the patients' characteristics, type of angiography that is planned, and the indication. All patients undergoing conventional angiography should be well hydrated to minimize the risk of contrast medium-induced nephrotoxicity. Fasting for 6 t 8 hours may be required in certain circumstances. Patients with impaired renal function, diabetic patients on metformin, patients on antiplatelet or anticoagulant agents, and those with prior history of allergy to iodinated contrast should be appropriately evaluated before angiography to ensure the safety of the procedure.

Technique or Treatment

Access for angiography is gained via a large or medium-sized artery, and location varies according to the procedure. The femoral route is usually used as a retrograde approach for procedures involving the iliac vessels, the abdominal and thoracic aorta, the upper limbs, and the head and neck. Due to its large caliber, it allows for larger devices such as stents or occlusive aortic balloons. The radial approach is now commonly used in coronary angiography, as it comes with a lower risk of complications compared to the previous femoral or brachial routes. Larger size sheaths are easily accommodated via the femoral route, and often percutaneous suture devices and collagen plugs are used.  For angiography of the lower limbs, an antegrade femoral approach or a popliteal approach is used.

An appropriate catheter is introduced via the access site, using a system of guide wires, and advanced to the appropriate vessel depending on the particular procedure. A contrast medium is introduced to outline the vasculature distal to the catheter tip. The X-ray images taken may be still or fluoroscopic, using digital subtraction angiography (DSA) technique, which is obtained by taking the images at 2 to 3 frames per second. The degree of stenosis or other abnormalities is identified by visual assessment.

Imaging of the thoracic aorta begins by looking at the aortic root, the ascending aorta, the aortic arch, and the proximal descending aorta. The patient's head is tilted to the right and in the chin-up position for better access to the branches. An image of the arch at 40° LAO (left anterior oblique) is commonly acquired at the start of the procedure as it allows to describe the type of aortic arch which predicts the difficulty of the procedure, as type II and III arches make cannulation of the common carotid more difficult.[8]

In imaging of the abdominal aorta, the patient lies in the supine position, and PA and 90° lateral views are used. The field of view includes the top of the diaphragm to the border of the iliac wings, and the first angiogram run is acquired with the pigtail catheter positioned at the level of the first lumbar vertebra (L1). Following this, the catheter is traditionally advanced to the level of the aortic bifurcation (L4), and the iliac vessels are imaged using anterior oblique projections.

Complications

Though overall complications related to angiography remain low, the risk of complications following conventional angiography is higher in the elderly, patients with reduced cardiac reserve, calcified non-compliant arteries, renal disease, and multiple comorbidities.

Minor Complications

• Bruising
• Nausea
• Pain at the puncture site
• Minor allergic reactions like rash, itch, or hives
• Transient deterioration in renal function
• Transient hot flushes or burning sensation

Major Complications

• Significant bleeding, hematoma, or false aneurysm occur in <5% of angiograms, and 1 in 100 patients require overnight admission in the observation unit, while 1 in 500–1000 patients will require a second intervention or blood transfusion to correct the bleeding.[9]
• Significant allergic reaction (anaphylactoid reaction)
• Acute renal failure

Contrast-induced nephropathy (CIN) is a substantial source of morbidity, which might require a brief period of renal replacement therapy. The essential preventive measures for contrast related complications include adequate peri-procedural hydration and use of minimal contrast volume.[9] Cigarroa et al. estimated the maximal acceptable contrast dose (MACD) using the following equation: (5 x bodyweight in Kg) divided by serum creatinine in mg/dl; up to a maximum volume of 300ml.[10] However, this formula is less useful in high-risk patients such as those with anemia, diabetes, heart failure, and cardiogenic shock, and it is infrequently used in clinical settings. Gurm et al. concluded that the ratio of contrast volume (CV) to the calculated creatinine clearance (CCC) of less than two is associated with a low incidence of CIN. In contrast, the risk of CIN is markedly increased when the ratio exceeds three.[11]

Clinical Significance

Noninvasive CTA and MRA have replaced most of the diagnostic uses of conventional invasive angiography. Beyond anatomic diagnosis, CTA and MRA can provide a functional assessment of vascular lesions that is comparable to conventional angiography. A systematic review showed the overall diagnostic accuracy of computed tomography fractional flow reserve (CT-FFR), compared with invasive FFR to be 81.9%; however, this drops to 46.1% if in CT-FFR value is between 0.70 and 0.80, and this is where invasive FFR is essential.[12][13] Conventional invasive angiography remains invaluable in the era of fast-expanding therapeutic percutaneous interventions including percutaneous coronary intervention (PCI), mechanical thrombectomy for cerebrovascular accidents, peripheral vascular stenting, renal artery stenting, transarterial chemoembolization. Angiographic-derived physiology metrics have recently been introduced and demonstrated to have high accuracy when compared with invasive pressure wire-derived FFR.[14]

Enhancing Healthcare Team Outcomes

Successful angiography requires a collaborative interprofessional effort by the entire healthcare team. Registered nurses, nurse managers, and radiologic technologists with specialized critical care and technical skills are essential components of the angiography team. In the post-procedural period, case managers and social workers address the social circumstances peculiar to each patient and coordinate patients’ care with the clinicians.