Predictive Value of Allen's Test Result in Elective Patients Undergoing Coronary Catheterization Through Radial Approach (RADAR)

The transfemoral access (TFA), through the percutaneous Seldinger technique, is the preferred approach in most catheterization laboratories worldwide due to its long history of use, the large availability of several dedicated preformed Judkins-type catheters and the possibility to exploit relatively large diameter catheters and sheaths, should these be necessary for complex percutaneous coronary intervention (PCI). Being a relatively deep and terminal vessel however, the femoral artery as percutaneous access site may expose to rare ischemic but frequent bleeding complications which occurs between 3-7% of patients undergoing interventional procedures, especially with modern anti-thrombotic drugs, including glycoprotein IIb/IIIa receptor blockers and clopidogrel. The difficulties in obtaining a stable and definitive local haemostasis, even when dedicated arterial vascular closure devices (VCD) are employed, make prolonged bed rest after TFA necessary in the majority of cases which result in patient discomfort and overall increase in medical expenditure.

In the last fifteen years, after Campeau's report of successful coronary angiography by transradial approach (TRA), the radial artery has been increasingly employed as an alternative access site both for diagnostic and interventional procedures.

The main advantage offered by percutaneous TRA is represented by the very low incidence of relevant vascular access site complications and bleeding and allows for early mobilization of the patient and thus to early discharge. As bleeding complications are increasingly recognized as strong and independent predictors of short and long-term outcomes following PCI, TRA may be the preferred access site by experienced teams. Radial artery (RA) cannulation, however, carries a risk of RA occlusion with an incidence of 4.8% to 19%. This is usually of no consequence, because the hand receives blood from both the radial and ulnar arteries (UA) with extensive collateral channels; however, some patients have incomplete palmar arches and might not have adequate communications between the ulnar and radial arteries. In these patients, there is a potential risk of hand ischemia in the event of RA occlusion.

A simple bedside test to check for communications between the ulnar and radial arteries is the modified Allen's test (AT). Patients with an abnormal test will usually have their cardiac catheterization performed via the femoral artery, thus denying them the potential advantages of transradial cardiac catheterization. In patients undergoing coronary angiography, the incidence of an abnormal AT ranges from 6.4% to 27%. Whether the AT can predict ischemic complications after RA cannulation is controversial, and some centers no longer exclude patients with an abnormal AT.

However, In 50 patients undergoing coronary angiography were screened for AT time. Circulation in the RA, UA, principal artery of the thumb (PAT), and thumb capillary lactate were measured before and after 30 min of RA occlusion. patients with an abnormal AT showed significantly reduced blood flow to the thumb and increased thumb capillary lactate (compared with patients with a normal AT) suggestive of ischemia. Based on these findings, Authors concluded that Transradial cardiac catheterization should not be performed in patients with an abnormal AT.

Aim of the RADAR study is to evaluate whether results of Allen's test in consecutive patients undergoing transradial coronary catheterization predict the occurrence of ischemic complications defined primarily as an increase of thumb capillary lactate and secondarily as a composite of local discomfort during and/or after the procedure, disability of the instrumented arm defined as perceived (subjective) or objective muscular weakness, need for surgical intervention or RA occlusion at any time within 30 days after catheterisation. Bleeding complications will be also monitored.