Medical imaging has benefitted from a boom in innovation in the past 50 years, which has allowed for rapid development in the field of interventional radiology. Angiography is used to image anatomical and structural details of the vascular system by detecting contrast injected into a blood vessel and projecting this on a series of x-rays to outline the inner vessel wall and show flow through the lumen. Starting as a diagnostic tool, angiography underwent a technological transformation over the last century and became a basis for interventional therapy as well. Angiography, initially a static two-dimensional record of the vasculature on screen-films, has evolved to a real-time two-dimensional display of the vasculature on television screens, and three-dimensional reconstruction from computed tomographic scans. Angiography has many advantages as it achieves real-time, dynamic imaging using a traditional imaging device - such as x-rays or computed tomography (CT), and it also offers therapeutic options at the time of initial diagnosis. Conventional angiography is invasive. In addition to providing therapeutic options, invasive angiography remains the gold standard in diagnosing most intravascular pathologies. Advances in imaging technology in the last three decades have expanded the scope of angiography to include non-invasive techniques using CT and magnetic resonance imaging technologies.
In CT angiography (CTA), intravenous contrast is administered via a peripheral vein, and triple-phase CT is usually acquired. CTA is based on high-resolution CT data acquisition, with subsequent angiographic two or three-dimensional reconstruction. Advances and adaptations of CTA principles have been of immense benefit to patients with cardiovascular diseases. Whereas this is an excellent first-line investigation and offers information regarding the surrounding soft tissues, it is less useful in investigating blood flow to the extremities due to the small diameter. Interventional angiography provides higher resolution imaging and can detect changes in the small vessels.
Magnetic resonance angiography (MRA): Clinical applications of MRA have become more salient for the patient and the clinician, especially in this era of rapid advances in imaging techniques. Magnetic resonance imaging (MRI) relies on the intrinsic magnetic trait of body tissues in an external magnetic field. It does not require ionizing radiation. The details of CTA and MRA are beyond the scope of this review.
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. 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 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.
Indications for Angiography Based on Systems
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.
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.
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.
The procedure room for angiography and angiography related interventions should be spacious enough to accommodate all of the machinery as well as staff.
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.
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.
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.
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.
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.
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. 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. 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.
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. 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.
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.
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