Venous access for either diagnostic or interventional procedures can be readily accomplished in a fashion complimentary to the techniques used for radial arterial access. Although peripheral access from the arm to the central venous system was reported in the first heart catheterization by Werner Forssmann in 1929,1 it was generally forgotten as a technique until several recent reports from the transradial literature2- 4 resurrected its utility. Routine right heart catheterization has been supplanted in many cases by noninvasive technology; however, the need for access to the central venous system still exists in approximately 10% of cardiac catheterization laboratory procedures (Penn State Hershey Medical Center, unpublished data, February 2010). Understanding the basics of venous access from the forearm empowers the invasive operator to further expand the usefulness of transradial techniques and minimize the potential iatrogenic complications inherent in other similarly invasive techniques using nonradial access.

This article is an overview of the technique to achieve central venous access from a forearm vein in the setting of transradial cardiac catheterization. It is meant to be a primer on the technique and focuses on how to get from skin entry to the central venous system. It is assumed that once central access is established, the operator will then be able to navigate the final path through the central venous and cardiac structures in a fashion consistent with standard catheterization techniques.

ANATOMICAL CONSIDERATIONS
The arm is a rich source of venous access. Although there is a general tendency for veins to accompany most arteries in the body, the region of interest during transradial procedures includes not only the area immediate to the radial artery but essentially the entire forearm from the antecubital fossa down to the wrist. Figure 1 is a schematic of the forearm venous system. There is great variability among individuals in the actual course and number of these veins, but they are all potential sources of access to the central venous system.

Functionally, veins that originate on the ulnar (medial) side of the forearm tend to drain in a relatively straight course into the basilic vein that then joins with the brachial vein to form the axillary vein and ultimately the subclavian vein (Figure 2). When advancing up by this approach, little fluoroscopic guidance may be required, and it may be possible to pass equipment to the pulmonary artery under only hemodynamic guidance. In addition, the veins in the upper forearm tend to be large (> 10 mm in diameter) and can tolerate larger-sized devices easily if needed.

Veins that originate on the radial (lateral) side of the forearm tend to drain either into the cephalic or basilic vein with an even distribution.6 The cephalic vein passes up laterally over the upper arm and enters the axillary vein at a junction referred to as a “T-junction.” This intersection can result in a right-angle turn that must be considered and negotiated if using this lateral venous approach to the central system. Historically, the use of a cephalic approach was considered a relative contraindication for right heart access due to this sharply angled intersection and the potential for traumatic injury. Before introduction of soft balloon-tipped catheters in the late 1970s, typical right heart catheters were on the order of 8 F in size and were very stiff compared to present day equipment.

Although both arteries and veins can dilate and increase in diameter, the capacity for venous enlargement significantly exceeds that of the arterial system. This compliance on the part of the venous system allows passage of equipment that, at first glance, may not seem possible based on arterial experience. Unfortunately, veins are not as resilient as arteries with respect to vessel wall strength, and overzealous forced dilation of these structures can result in rupture or tearing of their walls.

FUNCTIONAL CONSIDERATIONS
Early operators using stiff, large-bore equipment reported problems with spasm, including reports of resistant venospasm. This does not appear to represent a significant concern with present day, soft, small-caliber catheters. Nevertheless, veins have a muscular component that can contract and respond to vasoactive agents.

The primary venodilating agent is nitroglycerin. Nitroglycerin can be delivered via many routes, including intravenously or topically over the course of the vein. Although routine use of vasodilators is recommended in the radial artery system, routine nitrates are not needed for venous catheterization. Likewise, both arteries and veins respond to nitrates; however, only arteries effectively respond to calcium-channel blockers, and therefore, calcium- channel blockers, such as verapamil or nicardipine, are not useful vasodilating agents in the venous system. Using hydrophilic sheaths that reduce arterial spasm may also provide some further protection against functional spasm when used in the venous system. In general, the risk of significant venospasm when using small-diameter equipment (5-F range) appears to be low and is rarely a clinical cause of procedural failure.

TECHNIQUE
The first step in venous access is deciding where access will be initially achieved and by whom. An efficient technique involves the nurse's first achieving venous access outside of the catheterization laboratory, with the procedure finished within the laboratory. In essence, initial venous access is achieved by the nursing staff or intravenous (IV) team and saves valuable catheterization laboratory time otherwise spent finding a vein. The vein is cannulated with a standard, peripheral IV catheter, and the access is capped with a rubber or latex end that is typically referred to as a “heparin lock” in many hospitals. The antecubital fossa is the easiest target for large veins; however, there are advantages to using more peripheral veins along the forearm all the way out to the radial access site region. One advantage in using distal venous access involves the logic of moving away from the antecubital region because it has nerves and arteries in close proximity and is at increased risk for collateral damage if a complication occurs. Also, peripheral locations that are away from the joint lines provide easier and more comfortable anatomical locations for hemostasis. In general, if the equivalent of a 21-gauge IV catheter can be placed in a vein, it is usually adequate for subsequent placement of a 5-F micropuncture introducer and passage of a venous cardiac catheter. Although just about any vein can be used, the most common entry sites tend to be either just proximal to the wrist in a radial or ulnar vein or in the antecubital fossa when peripheral veins are sparse.

Setup in the cardiac catheterization laboratory includes sterile preparation of the venous entry site, with care not to dislodge the heparin lock/venous catheter. Depending on its anatomical location, the skin preparation may be performed through the same opening required for radial artery access or through a separate location. If venous access has been achieved outside of the laboratory, there is no need for a tourniquet, and no laboratory time is wasted looking for veins.

Before exchanging the heparin lock for a vascular sheath, the venous entry site should receive some subcutaneous anesthesia to prevent pain at the skin entry site. If the operator uses a surgical blade to nick the skin, care must be taken not to lacerate the superficial vein that may lie directly under the skin layer. After anesthesia, the access needle from a micropuncture access kit is pushed through the stopper at the end of the heparin lock, and the access kit's wire is then passed through the needle and up the IV catheter into the arm vein. The wire should be passed without resistance far enough to allow the exchange of the heparin lock system for the access sheath. When exchanging out the IV catheter equipment that was placed before entering the laboratory with the vascular sheath, the operator can handle the foreign catheter with a gauze and remove the needle, rubber stopper, and IV catheter together over the vascular wire without having physical contact with your gloves. This may further ensure the sterility of the field.

For routine diagnostic right heart catheterization, there are commercially available 5-F balloon-tipped catheters and thermodilution catheters. Larger sheaths may be used depending on the vein location, size, and if venous access indicates that a larger introducer sheath is required. If larger sheaths are being used, it is important to consider whether the access is in the distribution that will drain medially up the arm and avoid the T-junction at the cephalic/axillary intersection, potentially impeding the passage of a large or stiff catheter.

If venous access is not possible outside of the laboratory due to a lack of superficial veins, it may still be possible to find venous access. Many laboratories now have vascular ultrasound equipment for identifying vascular structures. By examining the deeper arteries, or even the radial and ulnar arteries, often a coexisting vein can be identified and its position can be localized relative to the artery. Palpating the artery and placing the needle at the estimated location of the deep vein will often provide venous access in patients in whom peripheral access was not initially deemed feasible.

Once the vascular sheath is in place, it should be flushed with saline, but routine addition of a vasodilator is not needed. It is quite possible that attempts to withdraw fluid from the side arm will be unsuccessful because the vein easily collapses under the vacuum of drawback and may occlude the sheath. As long as the initial wire passed up the vein without resistance, the patient expressed no significant discomfort during sheath placement, and fluid flushes in the sheath easily, the sheath is most likely located in the venous system. Heparin or antithrombin therapy used for radial artery access should be administered as usual, although there are no data to support or deny the utility of anticoagulation for isolated venous puncture. Short-term venous catheterization with relatively small catheters has not been reported to produce acute thrombosis, so it is suspected that anticoagulation for isolate venous catheterization is probably not warranted. Long-term central venous catheterization for monitoring from peripheral access has been associated with venous thrombus, and anticoagulation may be needed under those conditions.

VENOUS ACCESS TO THE CENTRAL VENOUS SYSTEM
With vascular venous access in place, the catheter to be used in the central venous system can then be advanced. The venous system should offer no resistance. Forceful advancement can cause vein perforation as demonstrated in Figure 3. Balloons used for flow direction should not be inflated until after they enter the subclavian vein or else forward movement may be impaired by balloon entrapment. Advancing up medially into the basilic and axillary vein is a very direct route to the central/subclavian system, and fluoroscopy is rarely needed except for troubleshooting. Entering the central venous system from the lateral aspect of the arm through the cephalic vein may require an evaluation at the level of the T-junction under fluoroscopy to ensure proper passage of the catheter toward the central system and not back down the axillary vein into the arm. Again, the balloon-tipped catheter should not be inflated until this T-junction is properly traversed. Deep breaths by the patient or use of a flexible wire placed through the lumen of the catheter may be needed to negotiate this junction.

Force should never be applied to a catheter that is failing to transverse the T-junction or if it is held up along the way. Veins are more fragile than arteries and can tear or perforate if mishandled. Similar to techniques used to troubleshoot in the arterial system, a limited venogram can be very helpful in understanding why a catheter may not be progressing. A venogram may also demonstrate a variety of other channels that may be taken to the central system because the venous system is characterized by redundant interconnections, unlike the arterial tree, which has far fewer connections.

Once the subclavian level is reached with the right heart catheter or device, manipulation is similar to any other access to the central system, be it from the subclavian or jugular veins. When the procedure is concluded, the catheter is withdrawn with its balloon deflated, and the vascular sheath can be removed from the venous system in the laboratory. Analogous to arterial access, venous access can be removed immediately, regardless of the anticoagulation status. Unlike in the arterial system, a firm hemostatic device is not needed, and the venous puncture site in the low-pressure venous system can be controlled for hemostasis with a simple compression bandage.

CHALLENGES
The most likely cause of difficulty in passing catheters from the peripheral veins of the forearm into the central system usually stems from trauma, either medically induced or from a previous accident resulting in venous occlusion. Occlusion of the proximal veins is usually asymptomatic, and clinical findings are usually absent. Obtaining a clinical history usually reveals the potential for difficulty and may prompt the operator to consider using the contralateral side or other sites of access. Previous trauma that resulted in humerus or shoulder fracture can produce collateral damage to the venous system that may prevent smooth passage to the central system. Damage induced by radiation therapy or central venous vascular ports for chemotherapy to treat malignancies can also sclerose veins so that they no longer easily allow catheters to pass. Finally, electrophysiology devices infrequently develop overlying organized thrombus that can also present a challenge in passing catheters. Figure 4 shows one example of pacemaker-associated venous thrombosis that prevented passage into the central venous system.

If it is difficult to pass a catheter, a limited venogram, as mentioned previously, can be very instructive. The operator can determine if there is a solution for overcoming the challenge and easily entering the central system. Often, especially around pacing leads, a channel is seen, and efforts can then focus on passing through that particular region of the venous system. Likewise, the demonstration of only microvascular channels or bridging collaterals should probably result in a prompt re-evaluation for another site of venous access.

CONCLUSION
The need for central venous access, be it a right heart catheterization, temporary pacing wire, or even a larger device for a right ventricular biopsy, should not be an excuse to avoid the transradial arterial approach. The eloquence and safety of transradial cardiac interventions can be extended by becoming familiar with the techniques of central vein access from the arm. These procedures can be accomplished, as noted in Table 1, with results that are at least as good or better than similar procedures performed by more traditional approaches.7 The addition of venous access to the basic transradial artery approaches can be useful in many situations, including anticoagulated patients, and adds further flexibility to the radialist's tool box.

Ian C. Gilchrist, MD, FACC, FSCAI, is Professor of Medicine at Penn State's Heart and Vascular Institute, Hershey Medical Center in Hershey, Pennsylvania. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Gilchrist may be reached at (717) 531- 5888; icg1@psu.edu.

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