A Perspective on Sheath Selection and Access Sites for Coronary Angiography

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Figure 4. The palmar arch. This illustration is used with permission of the Transradial Center on Angioplasty.Org, online at http://www.angioplasty.org/radial
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Margaret A. Coburn, RT(R)(CI), RCIS, Jefferson School of Health Professions, Philadelphia, Pennsylvania, and Richard J. Merschen, MS, RT(R)(CV), Pennsylvania Hospital, Philadelphia, Pennsylvania

Numerous access and sheath options are available to the interventional cardiologist when performing percutaneous transcatheter procedures. Depending on the procedure, the radial, brachial, or femoral access routes may be used for coronary angiography. Once access is achieved, sheaths offer physicians a safe method for exchange of multiple catheters and wires. Radial artery access is being used more commonly in the United States as results of positive trial data are presented, and operator skill and experience increases. This manuscript will include an overview of access sites and sheath options, as well as a discussion on the practical applications for all access routes that are available for cardiac catheterization.

The advancement in percutaneous coronary angiography techniques and equipment affords many more options to practitioners in securing vascular access. The interventional cardiologist needs to carefully plan the procedure, with the goal of a safe and uncomplicated cannulation of the vessel. Since vascular complications are the most common set of post-catheterization problems, the selection of the best access route maximizes safety and reduces complications. Vascular complications can result in adverse impacts and require additional hospitalizations, transfusions, and surgical procedures to repair the vessel. It is crucial to select the best access route to ensure successful procedural outcomes and improve patient safety. The selection of the most appropriate site of access depends on procedural complexities, operator experience, patient anatomy, and other factors (Table 1). There are devices such as ultrasound guidance, micropuncture systems (Figure 1), and other adjunct devices available to assist physicians in achieving access. These advancements, as well as increased operator skills, have greatly reduced procedure times and complications.

The insertion of a sheath preserves a constant source of arterial access. In addition, the sheath offers the physician a safe method for the exchange of multiple catheters and wires while maintaining hemostasis at the access site via a one-way valve on the sheath. Sheath sizes range from 4 French (Fr) to 24 Fr for percutaneous procedures, with most using 4-6 Fr for diagnostic angiography. Sheath sizes that exceed 10 Fr are usually reserved for special procedures, with the largest used for procedures such as transcatheter valve replacement. Selection of the sheath is based on the size of the catheters employed in the procedure (Figure 2). Catheter size is often determined by operator preference and patient anatomy. Technology has advanced to allow sheath and catheter diameter to become smaller over the years. Contrast media and automatic contrast delivery systems have also improved, and provide better angiographic quality at smaller French sizes. There are some operators who choose to use 4 Fr systems for all diagnostic procedures, barring any patient pathology that may require a larger diameter system. This decision is usually based on the desire for patient comfort, as well as the reduced incidence of procedural complications. These include catheter occlusion of the coronary ostium,(1) vasospasm, and other vascular incidents. Good quality angiography can be achieved in most patients using a 4 Fr system.(2) Generally, the sheath size is kept as small as possible in order to minimize the vascular puncture and therefore, reduce complications. However, there are patients who require larger lumen catheters to visualize the vessel. The current standard is the use of a 5 or 6 Fr sheath for diagnostic angiography, since this provides optimal results in situations when vessels are difficult to access and opacify.(3)

Femoral Access
The femoral artery approach is still the most commonly used route for vascular access in the United States. Some cardiac catheterization procedures require access of both artery and vein. This includes assessment of valvular heart disease, coronary angiography that requires additional right heart hemodynamic measurements, and procedures that require pacemakers or additional venous access. The femoral approach, for these cases, provides access within the same area. Many operators also believe it is the best option for advanced interventional procedures and equipment, and provides higher procedural success rates. In the setting of an emergency or complicated intervention such as the use of the “kissing balloon” technique, complex stenting, complex bifurcation lesions, and/or rotational atherectomy, femoral access gives the operator greater flexibility. In many of these cases, a 7 or 8 Fr sheath and catheter may be required for successful outcomes. Additionally, anomalous takeoff of the coronary artery, complex graft anatomy, transcatheter valvuloplasty, and staged procedures may be better suited for the femoral approach (Table 1). However, according to a meta-analysis by Jolly et al, femoral access bleeding complications are higher (2.3%) compared to the radial approach,(4) and require greater post-procedural nursing care and prolonged bed rest for monitoring complications. This meta-analysis established a standardized major bleeding definition as one of the following: fatal bleeding, intracranial hemorrhage, bleeding with a ≥3 g/dL hemoglobin drop, and bleeding-associated transfusion or surgery,(4) criteria also supported by the American College of Cardiology (ACC). These occurrences have been significantly reduced through the use of closure devices such as Perclose (Abbott Vascular, Redwood City, CA), Starclose (Abbott), and Angio-Seal (St. Jude Medical, Minnetonka, MN). With the use of these devices, patients can ambulate and be discharged within 2-3 hours post-catheterization.

Other considerations for the femoral artery approach include patients on hemodialysis and patients who have failed the Allen’s test. Patients who have undergone radial artery harvesting for bypass surgery, those who have previously had multiple radial procedures or a-lines, patients with breast cancer, and patients who have undergone a mastectomy are probably better candidates for the femoral approach. Patients with long-standing hypertension may have extremely tortuous vessels, making upper extremity angiography much more complex due to tortuosity of the vessels coming off the aortic arch.

It is our opinion that acute myocardial infarctions (MIs) should always be done via the femoral approach, because of the potential for intra-aortic balloon pump (IABP) insertion, transvenous pacemaker, and Swan-Ganz placement. In an emergency situation, using the groin allows easy access to two femoral arteries and two femoral veins for central line placement. The limited sheath size in the upper extremity can severely restrict the interventional cardiologist in emergency situations.

Upper Extremity Access
Upper extremity access is being performed with greater frequency in the United States as results of randomized trials are presented, and practitioner training and expertise have increased.(4) Many studies have concluded that lower bleeding complications (Figure 3), better patient outcomes, and lower hospital costs are associated with access of the radial artery compared to the femoral artery. The radial artery approach, however, requires considerable operator skill and experience due to the susceptible nature of the smaller vessels to irritation, spasm, and tortuosity. This technique provides several advantages to the patient when performed by a skilled operator, including earlier ambulation and reduced hemostasis complications. Radial access serves as an alternative to the femoral technique in obese patients (Table 1). Since the average radial artery lumen is approximately 2mm, the operator is limited in sheath size. As a result, a rule of thumb for radial artery access is to not go above 6 Fr due to the increased risk of vasospasm.(5) Aggressive use of vasodilators like verapamil or nitroglycerin are required to aid in catheter manipulation and prevent vascular injury. The dominant hand of the patient should be considered in radial cases when both radial arteries are patent, and if possible, the contralateral side should be accessed. Often, a micropuncture needle (Figure 1) is used for initial access, as it produces less trauma, irritation and spasm to the vessel. Radial artery occlusion is rare and likely related to the ratio of the arterial diameter to the sheath.(6) The incidence of radial artery occlusion is approximately 1-3% due to intima-media thickening, which may be a result of acute inflammatory reaction and endothelial dysfunction post procedure, as reported by Yan.(7) Most of these occlusions tend to be benign, but can limit future access via the radial approach. Moreover, Yonetsu reports in a study that assessed 73 radial arteries post-intervention that significant acute injuries and chronic intimal thickening of the radial artery occurred after transradial coronary intervention.

This trauma and narrowing of the vessel was significantly greater in the proximal and distal areas of the radial artery in patients who underwent repeat transradial interventions. Therefore, the use of the radial artery as a conduit in coronary bypass surgery post-transradial intervention should be avoided until long-term patency of the artery can be demonstrated(8) (Figure 4 - please note this illustration is used with permission of the Transradial Center on Angioplasty.Org, online at http://www.angioplasty.org/radial). Performing an Allen’s test is critical in determining the availability of the radial artery for cardiac catheterization and is used to ensure patency of the ulnar artery distally if thrombus occurs. A study conducted by Kohonen in 2007 with 145 patients who underwent the Allen’s test showed that 77% of patients had a normal Allen’s test, allowing for a safe transradial approach.(9) Other literature states that the rate is closer to 90%. Either way, the Allen’s test is a significant indicator for radial access.

The brachial artery approach can be used when there are known lower extremity vascular issues such as peripheral vascular disease, vessel tortuosity, or obesity. However, brachial artery access is often associated with higher risk of thrombotic complications than the radial artery (Table 1). Patients are also vulnerable to compartment syndrome via the brachial route, because of the complex network of muscle compartments and nerves located at the puncture site. It is important to carefully monitor the brachial artery to quickly identify potential hematomas. The best way to observe the arm is to do 15-minute checks post-cath for at least 2 hours, and regularly assess radial and ulnar pulses. The use of a paper tape to measure the circumference of the arm allows the post-cath team to monitor the development of a hematoma. The brachial approach does not have the structural hemostasis support that the femoral and radial approaches have, making it necessary for a vigilant staff to observe the patient post-procedurally.

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