the use of transradial coronary angiography and intervention ( tri ) is increasing because of its low rates of major vascular access - related complications and the potential for early mobilization.1)2 ) a large - bore guiding catheter ( gc ) with a large - bore introducer sheath is needed in patients with complex lesions , but they can not be used in patients with a small radial artery ( ra ) because they can cause forearm discomfort and ra spasm and occlusion,3 ) which are significant limitations to the transradial approach . to conquer this limitation , gc that does not require the sheathless gc system ( sheathless eaucath , asahi intecc , japan ) consists of a hydrophilic gc and a central dilator . this system can be used to insert the gc into the ra without the use of an introducer sheath . the outer diameter of the 6.5 french ( fr . ) sheathless gc ( 2.16 mm ) is smaller than a 5 fr . sheathless gc ( 2.49 mm ) is also less than that of a 6 fr . 1 ) . with this feature , the sheathless gc system enables performance of tri even in patients with small ras . furthermore , the hydrophilic coating that is present along the entire length of the gc may be helpful in reducing radial pain and ra spasm . here , we evaluated the feasibility of coronary intervention using the sheathless gc in patients with small ras . all patients underwent diagnostic coronary angiography using a 5 fr . conventional catheter through a 5 fr . patients who required primary percutaneous coronary intervention ( pci ) were excluded because preparation of a sheathless gc that is composed of two pieces ( a catheter and a central dilator ) requires more time than a conventional one - piece gc . all procedures were performed in the left ra unless the patient had a history of previous angiography through the right ra . a loading dose of 600 mg clopidogrel and 300 mg aspirin was given to all patients at least three hours before the procedure . we administered 5,000 units of heparin through the ra after insertion of the 5 fr . introducer sheath . an additional dose of 5,000 units heparin was given through the same route before pci the ra was punctured using a 20-g venous needle at a point 5 - 10 mm proximal to the styloid process after subcutaneous infiltration with 0.6 ml of 2% lidocaine . a 5 fr . normal saline ( 10 ml ) with 200 g of nitroglycerine was injected into the ra through the introducer sheath to prevent ra spasm . angiography of the ra was performed after injection of normal saline ( 10 ml ) with 200 g of nitroglycerine . a 30- to 40-mm long segment of ra from the tip of the introducer sheath was selected for the determination of the mean diameter . the mean of the maximal and minimal diameter of the selected segment of ra was used to determine the size of the ra using a computer - assisted quantification method ( ge , us ) . because the outer diameter of the 5 fr . introducer sheath was approximately 2.3 mm in diameter , a small ra was defined as a diameter 2.3 mm . after the diagnostic angiography , the sheath was exchanged for the sheathless catheter over a standard 150 cm j - tipped 0.035-inch ( terumo , japan ) wire . the shape and size of the sheathless gc the sheathless gc was composed of two parts : a hydrophilic catheter and a central dilator . the sheathless gc with the central dilator was advanced along the 0.035-inch wire to the proximal ascending thoracic aorta . the ostium of the selected coronary artery was engaged by the gc and pci was performed . we defined procedural success as the successful implantation of stent(s ) with final thrombolysis in myocardial infarction flow grade 3 and residual stenosis < 30% , despite the selection of the gc . all patients underwent diagnostic coronary angiography using a 5 fr . conventional catheter through a 5 fr . patients who required primary percutaneous coronary intervention ( pci ) were excluded because preparation of a sheathless gc that is composed of two pieces ( a catheter and a central dilator ) requires more time than a conventional one - piece gc . all procedures were performed in the left ra unless the patient had a history of previous angiography through the right ra . a loading dose of 600 mg clopidogrel and 300 mg aspirin was given to all patients at least three hours before the procedure . we administered 5,000 units of heparin through the ra after insertion of the 5 fr . introducer sheath . an additional dose of 5,000 units heparin was given through the same route before pci . the ra was punctured using a 20-g venous needle at a point 5 - 10 mm proximal to the styloid process after subcutaneous infiltration with 0.6 ml of 2% lidocaine . a 5 fr . normal saline ( 10 ml ) with 200 g of nitroglycerine was injected into the ra through the introducer sheath to prevent ra spasm . angiography of the ra was performed after injection of normal saline ( 10 ml ) with 200 g of nitroglycerine . a 30- to 40-mm long segment of ra from the tip of the introducer sheath was selected for the determination of the mean diameter . the mean of the maximal and minimal diameter of the selected segment of ra was used to determine the size of the ra using a computer - assisted quantification method ( ge , us ) . because the outer diameter of the 5 fr . introducer sheath was approximately 2.3 mm in diameter , a small ra was defined as a diameter 2.3 mm . after the diagnostic angiography , the sheath was exchanged for the sheathless catheter over a standard 150 cm j - tipped 0.035-inch ( terumo , japan ) wire . the shape and size of the sheathless gc the sheathless gc was composed of two parts : a hydrophilic catheter and a central dilator . the sheathless gc with the central dilator was advanced along the 0.035-inch wire to the proximal ascending thoracic aorta . the ostium of the selected coronary artery was engaged by the gc and pci was performed . we defined procedural success as the successful implantation of stent(s ) with final thrombolysis in myocardial infarction flow grade 3 and residual stenosis < 30% , despite the selection of the gc . a total of 25 patients ( 29 lesions ) with a small ra who underwent pci using a sheathless gc were included in this study . the mean age was 66.110.2 years , and nine ( 36.0% ) patients were men . approximately half of the patients had a history of hypertension ( 52.0% ) and diabetes mellitus ( 52.0% ) . eleven ( 44.0% ) patients had stable angina , 12 ( 48.0% ) had acute coronary syndrome , and two ( 8.0% ) had ischemic heart failure . twenty ( 69.0% ) lesions were located in the left anterior descending ( lad ) coronary artery . according to the modified american college of cardiology / american heart association criteria , most of the lesions were type b2 ( 27.6% ) or c ( 37.9% ) . a 6.5 fr . power backup ( pb ) 3 cm sheathless gc was used in approximately half of the cases ( 51.7% ) . most of the lesions were implanted with a zotarolimus - eluting stent(s ) ( 48.2% ) or everolimus - eluting stent(s ) ( 37.9% ) . one lesion consisting of restenosis of a previously implanted drug - eluting stent was treated using balloon angioplasty with a cutting balloon . the mean total length of the stents was 36.819.9 mm and the mean diameter was 2.960.43 mm . two of three bifurcated lesions were treated with a kissing balloon technique and one lesion was treated with two stents by using a modified t - stenting technique . two of the successfully treated lesions required conversion to a conventional gc after insertion of the 6 fr . amplatz left ( al ) 0.75 sheathless gc in the right coronary artery ( rca ) was treated by conversion to 6 fr . these two sheathless gcs did not engage the coronary arteries and provided poor guiding support ; however , the main reason for conversion to a conventional gc was a limitation in gc shape selection . the two failed lesions were chronic total occlusions ( cto ) in the lad that could not be crossed with a guidewire supported by a microcatheter . only one patient , who developed ra spasm during coronary angiography using a conventional 5 fr catheter , complained of forearm pain during pci . although there was no immediate access site complication including hematoma and bleeding , two patients lost pulse in the ra used as the access site without hand ischemia during a median 357 ( 140 - 432 ) days of follow - up . our study shows the feasibility of tri using a sheathless gc in 25 consecutive patients ( 29 lesions ) with small ras ( diameter 2.3 mm ) . the procedural success rate of tri is comparable to that of transfemoral coronary intervention with the benefit of lower rates of bleeding and fewer vascular complications.1)2 ) however , a larger gc and introducer sheath can not be used in some patients because of the small diameter of their ra . saito et al.3 ) demonstrated that the ras were smaller than the outer diameter of a 6 fr . they also reported that when the ratio of the ra inner diameter to the cannulated sheath outer diameter was less than 1.0 , the incidence of flow reduction was increased . they therefore suggested that smaller catheters should be considered to prevent ra occlusions or narrowing . with the sheathless gc system , one can use the larger - bore gc in patients with a small ra without using an introducer sheath and thereby minimizing radial discomfort.4 ) yoo et al.5 ) have shown that the mean ra diameter measured by ultrasound was 2.660.44 mm ( male : 2.690.40 mm , female : 2.430.38 mm ) in korean patients . although direct comparison is difficult because we did not use ultrasound to measure ra diameter , the mean diameter of the ra in our study was 1.820.27 mm , which is smaller than the mean ra diameter in korean patients and smaller than the outer diameter of the sheathless gc . despite this finding this patient developed severe ra spasm before using the sheathless gc and the operator has difficulty in performing diagnostic coronary angiography with the conventional 5 fr . however , the operator did not experience any difficulty in manipulating the catheter during pci . despite the above - mentioned results , a disadvantage in using a sheathless gc was noted . because sheathless gcs slide easily within vessels due to the hydrophilic coating , disengagement of the catheter could happen in cases requiring good guiding support . in our study , the sheathless gc frequently slipped away from the ostium in two cases of rca intervention , despite the small size of the ra . mamas et al.6 ) fixed the sheathless gc to the forearm at the point of entry to the ra using a tegaderm adhesive dressing to avoid slippage during the procedure . even if this solution could be helpful in preventing the slippage of gc , it could also be very dangerous if the patient were to move unconsciously as it may result in an aortic or coronary dissection . two studies have reported successful use of a sheathless gc in complex interventions with large bore catheters including rotablation , crush stent bifurcation lesions , 7 fr . proximal protection , thrombectomy devices , and simultaneous kissing stenting.7)8 ) in our study , we successfully performed three complex procedures including two in which the kissing balloon technique was used and one in which the modified t - stenting technique was used . most recently , mamas et al.6 ) reported a 100% procedural success using the sheathless gc in 100 patients . the primary difference in our study is that we enrolled only patients with small radial arteries , because the use of a sheathless gc is more beneficial for these patients . although we failed to treat two cases of cto lesions which required catheter conversion from sheathless to conventional , these results were not due to the gc itself but to limitations in gc selection with different shapes . only al , pb , hotkey stick , and judkins left gcs were available at our institute , and the shapes of catheters were slightly different from those of conventional catheters . during a median 357 days of follow - up , two patients ( 8% ) developed ra occlusion , and this is consistent with a previous report of an asymptomatic ra occlusion rate of 5 - 10%.9 ) because the outer diameter of the sheathless gc is smaller than that of the conventional gc , we expected a lower incidence of ra occlusion , and our results may be related to the fact that we included only patients with small ras and some of the patients had a ra with a diameter smaller than the outer diameter of sheathless gcs . even though the sheathless gc could be beneficial in forearm pain , the risk of ra occlusion should be considered in treating patients with small ras . although the use of the sheathless gc is feasible in cases of primary pci , this system requires more time to assemble because it is composed of two parts , and the introducer sheath must be removed before inserting it . first , although we measured the diameter of the ra by angiography after using a vasodilator , this intervention could not completely prevent vasospasm . this fact could result in a smaller ra diameter than the diameter measured by non - invasive methods such as ultrasound . second , we documented the presence of forearm pain only when the patient complained of forearm pain and did not use a pain scale such as the visual analogue scale or the 4-category verbal rating scale . finally , this was not a randomized trial to compare the sheathless gc with the conventional gc . the use of a sheathless gc was feasible in almost clinical settings for patients with small ras regardless of complexity or severity of the lesion . however , disengagement of the gc and limitations in the setting of primary pci should be taken into account . the use of a sheathless gc was feasible in almost clinical settings for patients with small ras regardless of complexity or severity of the lesion . however , disengagement of the gc and limitations in the setting of primary pci should be taken into account .
background and objectivestransradial coronary angiography and intervention are increasing in frequency due to lower major vascular access site complications and the potential for early mobilization . 
 however , the small size of the radial artery ( ra ) is a major limitation of this technique . a sheathless guiding catheter ( gc ) has recently been introduced that has a 1 - 2 french smaller diameter compared with the corresponding introducer sheath . 
 this catheter also has a hydrophilic coating along its entire length . 
 we evaluated the feasibility of using a sheathless gc in patients who have small radial arteries.subjects and methodsthe procedural results were evaluated in patients with small radial arteries ( diameter < 2.3 mm ) who underwent transradial coronary intervention using a sheathless gc.resultsa total of 25 ( male : 9 ) patients with 29 lesions were enrolled . 
 the mean ra diameter was 1.810.26 mm . 
 44% of the patients had stable angina and 50.0% had acute coronary syndrome . 
 the procedural success rate was 93.1% . 
 two patients ( 6.9% ) had chronic total occlusive lesions that could not be crossed with a guide - wire despite good guiding support . 
 an intravascular ultrasound could be used for all of the treated lesions . 
 multi - vessel intervention was performed in 29.2% of the patients . 
 two bifurcated lesions were treated with a kissing balloon technique , and one with a modified t - stenting technique . 
 no catheter related complications were reported.conclusionthe use of a sheathless gc is feasible in patients with small radial arteries without catheter related complications .