Transradial Catheterization: The Road Less Traveled
- Volume 16 - Issue 11 - November, 2004
- Posted on: 8/1/08
- 0 Comments
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Retrograde cannulation of a peripheral artery is a necessary step for current percutaneous coronary procedures. Since the first reported case of coronary angiography via the radial artery by Campeau in 1989, the transradial approach has been well studied. Large randomized clinical trials comparing transradial catheterization to traditional access have demonstrated advantages with respect to patient comfort, cost containment, and greatly reduced local vascular complications.2–4 In one representative study, major entry site complications were absent in the transradial group and present in over 2% of transfemoral and transbrachial groups.4 In another study, a cost savings of almost $300 per procedure along with improved measures of quality of life were found using the transradial approach.5 Length of stay, access complications, and supply costs are likely sources of this cost savings.5,6 And yet remarkably, particularly in the United States, the transradial approach is grossly underutilized. So why is there such a reluctance to travel this safer, more comfortable, and seemingly cheaper path to the coronary circulation? One likely barrier, albeit inaccurate, is the misconception that the procedure will simply take longer and be less effective.
To the contrary, several studies, including a recent large meta-analysis, have demonstrated that after a short initial learning curve, procedure length and success are comparable to the transfemoral approach.7 And, virtually all current interventional devices are compatible with a 6 French system through a radial approach.7–9 The more perverse explanation for the relative infrequency of transradial procedures, and probably the more difficult to overcome, is an engrained inertia to change. Acknowledging these non-medical obstacles, there are certainly legitimate pathophysiologic reasons to take pause before cannulating the radial artery. Beyond patient specific contraindications (i.e. abnormal Allen’s test, upper extremity vascular disease, Buerger’s Disease, severe Raynaud’s, or likely need for intra-aortic balloon counterpulsation), potential short and long-term effects on vessel morphology and function are relevant concerns.
Past study of the local traumatic effects of transradial catheterization have primarily dealt with catheter induced arterial spasm, the most infamous trait of the radial artery. Quantification of spasm using an automatic sheath removal device measuring maximum pullback force has suggested that an intra-arterial spasmolytic cocktail using 5 milligrams of verapamil plus 200 micrograms of nitroglycerin, prior to sheath insertion may reduce the occurrence and severity of radial artery spasm.10,11 Others have found significant reductions in patient discomfort, presumably from less spasm, with the use of hydrophilic-coated catheters, albeit at the cost of local sterile inflammation in about 3% of cases.12,13 In the coronary vasculature, there are limited data supporting a relationship between vasospasm and neointimal hyperplasia.4 However, a similar correlation in the radial circulation has not been defined. Existing reports focus on flow characteristics and suggest that after transradial cannulation, cessation of radial flow, as measured by ultrasound, occurs in anywhere from 5 to 9% of patients in the short term, and between 3 and 5% chronically. Consistent variables which influence the frequency of this asymptomatic complication include artery size at baseline, sheath to artery size ratio, duration of sheath placement, prior procedures, and the presence of diabetes mellitus.15–17 Paralleling the evolution of coronary disease study, more recent investigations have transitioned focus from the vessel lumen to the structure, function, and pathology of the endothelium and the arterial wall. Intravascular ultrasound interrogation has demonstrated significant intima-media thickening and luminal narrowing after prior transradial intervention.18 Unfortunately, more comprehensive study of vessel physiology is lacking.
In this issue of the Journal, Marcelo Sanmartin et al. expand the existing body of literature by exploring the effects of first time radial artery cannulation on arterial vasoreactivity as measured by noninvasive Doppler ultrasonography. Adopting a sophisticated method validated for brachial artery reactivity, the authors conclude that transradial catheterization results in a reversible, short-term impairment in vasoreactivity. Despite a small sample size, a statistically significant impairment of nitroglycerin-induced, non-endothelial mediated vasodilatation was observed at 24 hours after catheter-induced injury as compared with pre-catheterization effects (6.5 +/- 8.4% change vs. 14.1 +/- 7.9% change, p < 0.05). Interestingly, the mean baseline radial artery diameter was significantly increased at 24 hours compared with pre-catheterization measurement (2.86 +/- 0.48 mm vs. 2.56 +/- 0.45 mm), nullifying the effect of impaired vasodilatation on overall maximal diameter.19 Of note was the fact that all differences dissipated at late follow up, a finding contrary to prior studies.
So what, if any, is the clinical relevance of the morphologic and physiologic changes in the radial artery after cannulation? Given the prerequisite dual blood supply of the hand, post-procedural local ischemic complications are rare, even in the setting of complete radial artery occlusion.16 The effects of catheterization induced changes on future clinical uses of the vessel are not nearly as trivial, however. The two main current surgical uses for the non-dominant radial artery are as an additional arterial conduit for aortocoronary bypass surgery complementing the internal mammary arteries, and as the preferred initial artery used in the creation of an arteriovenous fistula for hemodialysis access (i.e. radiocephalic fistula). A fairly consistent body of literature exists to suggest that prior instrumentation of a radial artery destined for service as a bypass graft may result in a significantly higher likelihood of graft closure20,21 And, although less well studied, pre-existing radial intimal hyperplasia is closely associated with failure of radiocephalic arteriovenous fistulas in hemodialysis patients.22
Ultimately, with increased operator experience, miniaturization of devices and increased patient awareness of the alternatives, the non-medical barriers to transradial coronary angiography and intervention will fade. As with most novel advances in medicine however, long term successful implementation will likely hinge on continued study and refinement of technique. Currently, there are sufficient data to support a strategy utilizing radial artery cannulation in patients at low risk for endothelial dysfunction and intimal hyperplasia and in those with a low likelihood of requiring future surgical use of the radial artery. In patients who likely have smaller caliber arteries (e.g. diabetics, smokers, small women), pre-procedural ultrasound may be of benefit. Smaller diameter sheaths should be the norm and repeat procedures should be avoided.17,23 Also, in patients with mild to moderate renal insufficiency or an intermediate risk for requiring surgical revascularization, accessing the dominant radial artery is preferable as it allows for preservation of non-dominant vessel integrity. Ultimately, restrictions on who is an appropriate candidate for radial access will loosen as catheter technology advances and as multivessel drug-eluting stenting becomes a more accepted alternative to surgical revascularization.
Given the current infrastructure in many catheterization laboratories, the femoral artery remains the easy choice for peripheral arterial access. However, in an increasing number of situations, the less traveled transradial road to the coronaries may, in fact, be the right choice. And, for the patient, with respect to cost, comfort and safety, that may make all the difference.