Indications and Preparation for Angiography
Angiography is the direct intravascular administration of radiographically visible dye in order to gain anatomic information about a particular blood vessel or group of blood vessels. Arteriography is defined as angiography of the arterial system, and venography is angiographic imaging of the veins. Historically, angiography has mostly served a diagnostic purpose, providing a road map to guide appropriate surgical intervention. The past two decades, however, have witnessed considerable growth in minimally invasive techniques to treat disease and injury from within the vessel lumen—the so-called endovascular procedures. As many of these procedures are performed using small wires and catheters, another commonly used term is catheter-based procedures. Common endovascular procedures are angioplasty, stenting, stent-graft repair of aneurysms, embolization, and catheter-directed thrombolysis. A number of vascular specialists are trained in angiography and endovascular procedures, from the disciplines of interventional radiology, cardiology, and vascular surgery. Perhaps a more encompassing term for a physician performing endovascular procedures is the “vascular interventionalist” or “endovascular specialist.”
I. Indications.
Nearly every vessel in the human body can be imaged with angiography by a motivated and skilled vascular interventionalist. However, the indications for angiography are just as important as the skills required to perform it. Even the simplest angiographic procedures carry risk to the vessel(s) being imaged and to the patient as a whole. Therefore angiography should not be undertaken without clear and appropriate indications. History, physical exam, and noninvasive tests are nearly always sufficient to make the diagnosis of peripheral arterial disease (PAD). The specific indications for lower-extremity, cerebrovascular, and renal and mesenteric arteriography are discussed in detail in their respective chapters. In general, angiography should only be employed when the additional anatomic information will clearly affect the sound clinical management of the patient.
Informed consent for angiography includes an explanation of the indications, alternative methods of diagnosis, and potential
complications. Patients should understand that angiography can be either diagnostic or therapeutic and that, in general, solely diagnostic angiograms are becoming less common given the imaging capability of noninvasive modalities (duplex, computed tomography angiogram [CTA], and magnetic resonance arteriography [MRA]). Additionally, endovascular treatments are often possible in the same setting as the diagnostic angiogram following the diagnostic phase. The vascular interventionalist may plan a solely diagnostic angiogram under certain circumstances, such as determining suitability for complex endovascular interventions such as carotid stenting or aortic endografting. Angiography is the best test for the rapid diagnosis of some specific vascular emergencies, such as acute mesenteric or limb ischemia and can also help solve certain diagnostic dilemmas— for example, vasospastic disorders versus occlusive disease of the hands, Buerger’s disease, temporal arteritis, and periarteritis nodosa.
complications. Patients should understand that angiography can be either diagnostic or therapeutic and that, in general, solely diagnostic angiograms are becoming less common given the imaging capability of noninvasive modalities (duplex, computed tomography angiogram [CTA], and magnetic resonance arteriography [MRA]). Additionally, endovascular treatments are often possible in the same setting as the diagnostic angiogram following the diagnostic phase. The vascular interventionalist may plan a solely diagnostic angiogram under certain circumstances, such as determining suitability for complex endovascular interventions such as carotid stenting or aortic endografting. Angiography is the best test for the rapid diagnosis of some specific vascular emergencies, such as acute mesenteric or limb ischemia and can also help solve certain diagnostic dilemmas— for example, vasospastic disorders versus occlusive disease of the hands, Buerger’s disease, temporal arteritis, and periarteritis nodosa.
The objective and potential outcomes of the angiogram should be understood from the outset and explained to the patient. The patient should understand that attempts at diagnosing and/or treating the condition with noninvasive modalities have been exhausted and that angiography is necessary for clinical decision making. We inform patients undergoing a lower-extremity arteriogram for chronic limb ischemia of three possible outcomes of the procedure:
Diagnostic information leading to an endovascular therapy at that setting or at a later date
Diagnostic information leading to an open treatment at a later date
Diagnostic information leading to no intervention due to disease pattern or severity
The decision to proceed with endovascular or surgical treatment depends on the patient’s anatomy, medical comorbidities, and clinical presentation. In many cases, either endovascular or open surgical therapy may be appropriate. It is important that the patient be presented with balanced and realistic expectations about any procedure, its durability, the need for future interventions, and potential complications.
Endovascular procedures are attractive to both patients and clinicians. As an example, endovascular aortic aneurysm repair has reduced mortality and morbidity compared with open aneurysm repair, and has allowed treatment in patients who would not be suitable for open repair (Chapter 15). However, the dizzying angiographic success and rapid recovery that patients often experience with endovascular procedures should be viewed in the context of evidence supporting longer term outcomes both of the procedure and the patient (i.e., will they last and will the patient have good mid- to long-term survival?). Vascular specialists should be cautious not to lower the threshold for the treatment of vascular diseases simply because of the availability of endovascular techniques. The potential benefits of intervention should be tempered with an understanding of the natural history of the disease and life expectancy of the patient. The majority of patients with claudication, for example, can be treated medically and will experience no worsening in their disease.
Treatment, whether endovascular or surgical, should be limited to the minority of patients with progressive, lifestyle-limiting claudication.
Treatment, whether endovascular or surgical, should be limited to the minority of patients with progressive, lifestyle-limiting claudication.
II. Preparation.
A.
Prior to angiography, the endovascular specialist should review the patient’s history, lab work, and indications for the procedure. The informed consent forms are also reviewed and the patient should have the opportunity to ask “last minute” questions.
B.
An abbreviated physical exam should be performed just prior to the procedure to confirm previous findings and assure no interval change.
1. An evaluation of the planned access vessel is critical in the pre-procedure holding area. The absence of or change in a pulse should prompt reconsideration of the access site except in cases of access distal to known disease that is the target of intervention (e.g., femoral access distal to iliac disease that is target of intervention).
2. Distal pulses or Doppler signals should be confirmed prior to lower-extremity angiography and ABIs recorded if an intervention is likely. The absence of a pulse or Doppler signal after intervention implies embolization, vessel dissection, or poor technical result. Ankle-brachial indices should be recorded after any lower-extremity endovascular intervention and compared with pre-procedure values.
3. Newly recognized or poorly treated medical conditions such as severe hypertension, arrhythmia, or renal insufficiency generally contraindicate angiography.
4. Patients with foot ulcers or gangrene should have their wounds reassessed, as they may benefit from debridement prior to or just following the endovascular procedure.
C.
Previous open surgical or endovascular procedures are particularly relevant and should be reviewed as part of this pre-procedure routine. Vessels that have been accessed multiple times in the past or the presence of an extremity bypass may affect the location and method of access for angiography. For example, previous aortobifemoral bypass will present specific challenges related to scar and number of patent lumens at the femoral level (e.g., prosthetic bypass limb and native femoral/iliac lumen). In this same scenario the bypass graft presents a narrow bifurcation at the aortic position that generally prevents placement of a sheath into the contralateral limb of the graft. The locations of prior endovascular interventions, along with balloon and/or stent sizes, and complications from prior procedures should be recorded, noting access problems.
D.
Allergy to iodinated contrast material should be ascertained and can occur in 2-5% of patients. These reactions are usually mild, with itching and urticaria. Rarely, more severe anaphylactic reactions occur, manifested by wheezing, bradycardia, and hypotension. Patients with prior contrast reactions are at higher risk for recurrent allergic complications with repeat angiography. Although the benefits of some type of pretreatment in this high-risk group are controversial, it is generally recommend that a “prep” consisting of steroids and diphenhydramine (Benadryl, Johnson and Johnson, New Brunswick, NJ, U.S.A.) be administered prior to the
angio gram. One such regimen includes 50 mg of prednisone by mouth 13, 7, and then 1 hour prior to the procedure. A single dose of 25 to 50 mg of diphenhydramine may also be given 1 hour prior to the administration of contrast. When an urgent angiogram or CTA is obtained, an emergency prep can be administered with 50 mg diphenhydramine intravenously and 100 mg hydrocortisone intravenously.
angio gram. One such regimen includes 50 mg of prednisone by mouth 13, 7, and then 1 hour prior to the procedure. A single dose of 25 to 50 mg of diphenhydramine may also be given 1 hour prior to the administration of contrast. When an urgent angiogram or CTA is obtained, an emergency prep can be administered with 50 mg diphenhydramine intravenously and 100 mg hydrocortisone intravenously.
E.
The patient should be questioned as to his or her current medications.
1. Care must be exercised in the use of iodinated contrast in patients taking metformin (Glucophage, Bristol-Myers Squibb, New York, NY, U.S.A.). This oral agent used to treat non-insulin-dependent diabetes mellitus can cause a severe lactic acidosis that can be precipitated by contrast agents. The risk is especially high in patients with renal dysfunction. In general, patients should not take metformin for 48 to 72 hours after the use of iodinated contrast agents. This is especially true in patients who have a baseline creatinine of greater than 1.5 mg/dL.
2. Anticoagulants such as warfarin should be stopped before procedures that involve arterial access. This usually means stopping warfarin for 2 to 4 days and allowing the international normalized ratio to fall below 1.5. Of course, the indications for anticoagulation must be noted because some patients, such as those with mechanical heart valves or known pulmonary emboli, should not be off of anticoagulation. A heparin “window” can be used in patients at high risk for stopping anticoagulation. The patient is kept fully anticoagulated on intravenous unfractionated heparin (UFH) while the warfarin is held. UFH has a short half-life (90 minutes) compared to warfarin (36 hours), so that it can be held for several hours prior to and after the angiogram. The development of low molecular weight heparins now allows a number of patients at moderate risk for holding anticoagulation to “bridge” at home with subcutaneous injections. Antiplatelet agents such as aspirin and/or clopidogrel (Plavix) are commonly taken by patients with peripheral vascular disease. Some interventionalists insist these drugs are held prior to angiography, while others do not. Prior to some interventions such as carotid or renal stenting, many physicians ensure that antiplatelet agents are “on board” or even administer high doses on the day of the procedure. There is no consensus on the use of antiplatelet agents and angiography. At present, each case must be assessed individually, balancing the risk of bleeding with thrombosis. Patients with a personal or family history of bleeding problems should be carefully evaluated with a platelet count and coagulation studies (prothrombin time and partial prothrombin time). A hematology consultation should be sought if heritable bleeding disorder is suspected.
