Impact of radial compression protocols on radial artery occlusion and hemostasis time in coronary angiography.

Protocols for hemostasis after trans-radial approach (TRA) vary depending on the institute as there is no established evidence-based protocol. This study aimed to investigate the clinical implications of radial compression protocols. Consecutive patients who underwent outpatient invasive catheter angiography before and after April 2018 were treated with traditional and new protocols, respectively. Using the same hemostasis band, in the conventional protocol, fixed amount of air was removed soon after the procedure, 2 h later, and 3 h later, whereas the air was removed as much as possible every 30 min in the new protocol. A total of 1842 patients (71 ± 10 years old, 77% male) were included. Compared with the traditional protocol group (n = 1001), the new protocol group (n = 841) had a significantly lower rate of dual antiplatelet therapy (35% and 24% in the traditional and new groups, respectively, p < 0.001). The time required for complete hemostasis was approximately one-third with the new protocol (190 ± 16 and 66 ± 32 min, p < 0.001) with no clinically relevant bleeding. The incidence of radial artery occlusion (RAO) was 9.8% and 0.9% in the traditional and new protocol groups, respectively (p < 0.001). After adjusting for covariates, the new protocol was associated with a reduced risk of RAO (odds ratio 0.10, p < 0.001) and a shorter hemostasis time (odds ratio 0.01, p < 0.001). The new protocol for hemostasis after TRA was strongly associated with a shorter hemostasis time and a lower rate of RAO.

A Prospective Multicenter Study Using a Virtual 3 Fr Percutaneous Coronary Intervention System: The V3 Registry.

OBJECTIVES: To evaluate the safety and feasibility of virtual 3 Fr (V3), sheathless 5 Fr percutaneous coronary intervention (PCI). BACKGROUND: A small-diameter guiding catheter (GC) makes less-invasive PCI possible. The V3 is an extremely slender PCI system; however, the outcome of using this system has not yet been determined. METHODS: The V3 registry is a prospective, multicenter, non-randomized study that enrolled patients who underwent elective V3-PCI. The primary endpoint was clinical success rate, and the secondary endpoints were PCI success rate in all cases, major adverse cardiac and cerebrovascular event (MACCE) at 30 days, and access-site complications. RESULTS: A total of 260 patients with 321 lesions were enrolled. Of this group, 70% were male and the mean age was 70.8 ± 10.0 years. Type B2/C lesions comprised 50.7% of the total. The clinical success rate was 95.8%, and the PCI success rate was 99.2%. PCI failure was reported in 2 chronic total occlusion cases. No MACCE was reported. Although there was no major bleeding, hematoma occurred at the puncture site in 12.7% of cases. There was a single radial artery occlusion (0.4%) without symptoms. CONCLUSIONS: PCI with the V3 was safe and feasible. Radial artery occlusion and major bleeding complications were extremely low. However, access-site hematoma frequently complicated catheter exchange.

Safety and feasibility of the new 5 Fr Glidesheath Slender.

The aim of this study was to evaluate the safety and feasibility of the new 5 Fr Glidesheath Slender (GSS). The transradial (TR) approach has become popular because of several advantages, such as a reduced rate of vascular access site complications. However, because the radial artery is narrow, a limitation of TR access is the potential for artery spasm or occlusion. Studies of radial artery size demonstrate that 5 Fr sheaths are too wide for more than 10 % of patients. The GSS (Terumo, Tokyo, Japan) is a new radial sheath with a thinner wall and a hydrophilic coating. It has an inner diameter that is compatible with a 5 Fr guiding catheter, while the outer diameter is similar to that of a 4 Fr sheath. A total of 21 consecutive patients undergoing transradial angiography and/or transradial percutaneous coronary intervention with the 5 Fr GSS were included, and safety and feasibility of the device were assessed. Transradial angiography was performed in 10 patients, and transradial intervention in 11 patients. All procedures were successful, without the need for conversion to the transfemoral approach. The radial artery occlusion rate was 0 %, including a patient who had experienced six previous radial artery punctures. There were no cases of artery spasm, hematoma, major bleeding or functional disorders. One coronary artery perforation caused by a guidewire was reported, but it was unrelated to the sheath introducer. The new 5 Fr GSS was safe and feasible for transradial angiography and transradial intervention.

Potential influence of invisible coronary collateral circulation on fractional flow reserve of donor artery in the presence of severe stenosis of receiving artery.

We reported a case of 78-year-old male who had a severe stenosis in the right coronary artery (RCA) and an intermediate stenosis in the left anterior descending artery (LAD) without visible collateral flow to the RCA on angiogram. Fractional flow reserve (FFR) in the LAD lesion, which revealed significant value as 0.70, increased to 0.78 after revascularization of the RCA lesion. The FFR in an intermediate stenosis should be performed after PCI for severe stenosis in the other coronary arteries. Otherwise, the severity of the stenosis could be overestimated due to the presence of invisible collateral circulation.

Gastrointestinal symptoms and food/nutrition concerns after the great East Japan earthquake in March 2011: survey of evacuees in a temporary shelter.

On March 11, 2011, a 9.1 magnitude earthquake occurred in the eastern Pacific Ocean off the coast of northern Japan. A resulting tsunami struck the Japan Pacific coast, causing >20,000 deaths, injuries and missing persons. Survivors' post-tsunami health and nutritional status were surveyed one month after the disaster in a school shelter in Ishinomaki City. Hyogo College of Medicine's disaster relief team observations and survivors' questionnaires were used to assess the disaster's effects on survivors' lifestyles and gastrointestinal symptoms while residing in temporary shelters. Of 236 disaster evacuees 9-88 years of age (mean age 52 years), 23% lost weight and 28% reported decreased food intake one month after the earthquake. Up to 25% of the participants presented with gastrointestinal symptoms, including constipation (10%), appetite loss (6.4%), vomiting (6.4%), and nausea (2.1%). Although the victims preferred more vegetables (44%) or fruit (33%), most food aid received, such as rice balls or bread, was carbohydrate-based, possibly because of easy provision and abundance in emergency food pantries. The authors asked the volunteers and the Japan Self-Defense Forces to provide a more balanced diet, including vegetables and fruit. Consumption of imbalanced diets may have caused more gastrointestinal symptoms for the survivors. Because of the victims' hesitation to request more balanced diets, and because of poorly controlled existing chronic disease and mental stress, professional public health providers should assure emergency food nutrition after disasters.

Comparison of frequency of radial artery occlusion after 4Fr versus 6Fr transradial coronary intervention (from the Novel Angioplasty USIng Coronary Accessor Trial).

The frequency of radial artery occlusion was compared between patients receiving 4Fr versus 6Fr transradial coronary interventions (TRIs) in an open-label randomized trial (ClinicalTrials.gov identifier: NCT00815997). The primary outcome measure was radial artery occlusion on the day after TRI. The secondary outcome measures were the procedural success, major advanced cardiac events, access site-related complications, procedural times, fluoroscopy times, and contrast dye usage. A total of 160 patients were included. The procedure was successful in 79 of 80 patients (99%) in both groups. Whereas the 4Fr group showed no access site-related complications, the 6Fr developed 5 (6%), including 3 radial artery occlusions and 2 bleedings (1 radial artery perforation and 1 massive hematoma; p = 0.02). Although the radial artery occlusion rate was lower in the 4Fr versus the 6Fr groups, the difference was not significant (0% vs 4%, p = 0.08). The mean hemostasis time was significantly shorter in the 4Fr than in the 6Fr groups (237 ± 105 vs 320 ± 238 minutes, p = 0.007). In conclusion, these findings suggest that 4Fr TRI may become a less invasive alternative to 6Fr TRI in treating coronary artery diseases.

Effect of bare-metal nitinol stent implantation and paclitaxel-eluting nitinol stent implantation on vascular response in the superficial femoral artery lesion assessed on intravascular ultrasound.

BACKGROUND: Although previous intravascular ultrasound (IVUS) studies reported that the drug-eluting stent (DES) has successfully decreased in-stent restenosis (ISR) by inhibiting neointimal hyperplasia (NIH) in the coronary artery lesion, no IVUS data for vascular response after DES implantation in the superficial femoral artery (SFA) have been published. METHODS AND RESULTS: We retrospectively analyzed 38 de novo SFA lesions from 32 patients who underwent endovascular therapy (EVT) with self-expanding bare-metal nitinol stent (25 lesions; BMS group) or self-expanding paclitaxel-eluting nitinol stents (13 lesions; PES group). At 6 months after EVT, follow-up IVUS was done to evaluate NIH. Serial IVUS volumetric analysis was done after stent deployment and at follow-up. Mean stent, lumen and neointimal areas were calculated as the volume divided by the stent length. The primary endpoint of this study was mean late lumen loss at 6-month follow-up. The mean follow-up period was 189±39 days. Mean neointimal area was smaller in the PES group compared to the BMS group (3.3±1.0mm(2) vs. 10.2±4.1mm(2), P<0.001). Mean late lumen loss was significantly lower in the PES group compared to the BMS group (-2.3±3.7mm(2) vs. 2.1±4.7mm(2), P<0.05). CONCLUSIONS: EVT with DES in SFA lesions might decrease NIH associated with ISR in short-term follow-up.

Thermodilution-derived coronary blood flow pattern immediately after coronary intervention as a predictor of microcirculatory damage and midterm clinical outcomes in patients with ST-segment-elevation myocardial infarction.

BACKGROUND: Despite a sufficient coronary blood flow after primary percutaneous coronary intervention for patients with ST-segment-elevation myocardial infarction; some patients have a poor outcome because of microcirculatory damage. This study evaluates whether the thermodilution-derived coronary blood flow parameters immediately after primary percutaneous coronary intervention predict early microvascular damage and midterm outcomes in patients with ST-segment-elevation myocardial infarction. METHODS AND RESULTS: Using a pressure sensor/thermistor-tipped guidewire, we measured the index of microcirculatory resistance at maximum hyperemia, and coronary blood flow pattern was assessed from the thermodilution curves after successful primary percutaneous coronary intervention in 88 patients with ST-segment-elevation myocardial infarction. Coronary blood flow pattern was classified into 3 groups according to the shape of thermodilution curve: a narrow unimodal (n=41), a wide unimodal (n=32), or bimodal (n=15). All patients had contrast-enhanced cardiac magnetic resonance scans within 2 weeks. The index of microcirculatory resistance values were significantly higher both in a wide unimodal and in a bimodal groups than in a narrow unimodal group (65±41 and 76±38 versus 20±9U; P<0.001). Bimodal group had higher prevalence of microvascular obstruction on contrast-enhanced cardiac magnetic resonance when compared with the other groups (100%, 78%, and 30%; P<0.001). Patients in bimodal group had a higher risk of death and heart failure rehospitalization at 6 months (73%, 6.3%, 7.3%; P<0.001). Multivariate analysis revealed that bimodal shape of the thermodilution curve was the only independent predictor of cardiac death at 6 months after ST-segment-elevation myocardial infarction (P<0.01). CONCLUSIONS: A bimodal shape of the thermodilution curve, which may indicate myocardial edema and consequent extrinsic compression of the capillary network, is associated with microcirculatory damage and poor midterm clinical outcomes rather than index of microcirculatory resistance value itself.

Impact of post-procedural intravascular ultrasound findings on long-term results following self-expanding nitinol stenting in superficial femoral artery lesions.

BACKGROUND: Previous intravascular ultrasound (IVUS) studies have reported that a tiny reference cross-sectional area (CSA), stent under-expansion, stent asymmetry, stent edge dissection, and tissue protrusion are associated with target lesion revascularization (TLR) after coronary intervention. In the lower limb, however, it has not been reported that these findings correlate with TLR after endovascular therapy (EVT). METHODS AND RESULTS: A total of 236 consecutive superficial femoral artery (SFA) lesions in patients who underwent IVUS after self-expanding nitinol stent implantation, were analyzed. Stent expansion ratio was calculated as minimum stent CSA/reference lumen CSA, radial stent symmetry index as minimum/maximum stent diameter, and axial stent symmetry index as minimum/maximum stent CSA. TLR was defined as clinically driven revascularization with ≥75% restenosis of the target lesion. The mean follow-up period was 34±15 months. TLR were performed in 42 lesions (17.8%). There were no significant differences in stent expansion ratio, stent symmetry indices, and tissue protrusion between the TLR and no-TLR groups. Multivariate analysis indicated that total stent length (odds ratio [OR], 1.004; P<0.05), distal reference CSA (OR, 0.91; P<0.01), and stent edge dissection (OR, 3.51; P<0.01) were independent predictors of TLR. CONCLUSIONS: Stent implantation in tiny vessels and stent edge dissection in SFA lesions are indicators of high risk of TLR. Post-procedural stent under-expansion and stent asymmetry, however, were not associated with TLR.

A case of acute thrombotic occlusion of the popliteal artery occurring immediately after the total knee arthroplasty recanalized by ballooning alone.

Arterial complications associated with total knee arthroplasty are rare but occasionally life-threatening. Although popliteal artery injuries have been repaired by bypass surgery historically, there are potentially multiple useful methods for the restoration. In this report, we describe a case of acute thrombotic occlusion of the popliteal artery occurring immediately after total knee arthroplasty, and successfully repaired by endovascular therapy with endoluminal balloon inflation. .

Multiple complex coronary atherosclerosis in diabetic patients with acute myocardial infarction: a three-vessel optical coherence tomography study.

AIMS: The main cause of acute myocardial infarction (AMI) is the disruption of a thin-cap fibroatheroma (TCFA) and subsequent thrombosis. Mortality increases in diabetic patients due to cardiovascular events; there may be differences in the vulnerable plaques between diabetic and non-diabetic patients. We used optical coherence tomography (OCT) to assess the incidence of vulnerable plaques in diabetic patients with AMI. METHODS AND RESULTS: OCT was performed in all three major coronary arteries of 70 AMI patients: 48 non-diabetic and 22 diabetic patients. The OCT criterion for TCFA was the presence of both a lipid-rich plaque composition and a fibrotic cap thickness of <65 µm. A ruptured plaque contains a cavity in contact with a lumen and a residual fibrous cap. OCT identified 68 plaque ruptures (1.0 per patient; range, 0-3) and 162 TCFAs (2.3 per patient; range, 0-5). The incidences of plaque rupture and TCFA at culprit lesions were similar. However, non-culprit-lesion TCFAs were observed more frequently in diabetic patients than in non-diabetic patients. CONCLUSIONS: Although the prevalence of vulnerable plaque in culprit lesions was similar between diabetic and non-diabetic patients, vulnerable plaques were observed in non-culprit lesions more in diabetic patients than in non-diabetic patients.

Safety and efficacy of endovascular therapy with a simple homemade carbon dioxide delivery system in patients with ileofemoral artery diseases.

BACKGROUND: Carbon dioxide (CO(2)) has been used as an arterial contrast agent for high-risk patients who were allergic to iodinated contrast material and for those with chronic kidney disease (CKD). The feasibility, safety, imaging quality and therapeutic role of CO(2) angiography in the endovascular therapy (EVT) for patients with CKD was evaluated. METHODS AND RESULTS: EVT was performed in 107 consecutive patients with iliofemoral artery disease (148 limbs; mean age, 73±9 years) who were admitted to our hospital from January 2010 to April 2011. Intravascular ultrasound (IVUS)-guided EVT with CO(2) was applied for the treatment of 50 patients (70 limbs) with CKD (group 1). IVUS-guided EVT with iodinated contrast media was applied for the treatment of 57 patients (78 limbs) without CKD (group 2). CO(2) was injected by hand using a simple homemade delivery system. The overall technical success was 100% in both groups without any major complication. Preprocedure and postprocedure ankle-brachial indices significantly improved in the both groups (0.93±0.11 vs. 0.59±0.19, P<0.01; 0.95±0.13 vs. 0.62±0.22, P<0.01, respectively). All of the CO(2) arteriograms were good or acceptable imaging quality if assessed by 2 independent observers. CONCLUSIONS: CO(2) arteriograms, using an inexpensive simple homemade delivery system, are feasible and safe in patients with CKD in the evaluation and for EVT of iliofemoral artery disease.

The utility of intravascular ultrasound for the diagnosis and management of spontaneous coronary artery dissection in a middle-aged woman with acute inferior myocardial infarction.

Spontaneous coronary artery dissection (SCAD) is an infrequent cause of acute myocardial ischemia and is associated with various pathophysiologies, such as pregnancy, postpartum, and collagen diseases. It is frequently fatal and most cases are diagnosed at autopsy. Therefore, the early diagnosis of SCAD and initiation of treatment may be life saving. In this report, we describe a case of SCAD of right coronary artery, possibly triggered by transient high blood pressure, with no apparent atherosclerotic involvement detected by intravascular ultrasound (IVUS) and successfully treated with stent implantation. The IVUS helped us to confirm the diagnosis, navigate the guidewire into the true lumen, and understand the mechanism for the appearance of a lotus root formation.

The impact of plaque characterization assessed by intravascular ultrasound on myocardial perfusion after primary angioplasty in patients With ST-segment elevation myocardial infarction.

BACKGROUND: Previous studies described that inadequate tissue perfusion after primary angioplasty in ST-elevation myocardial infarction (STEMI) patients is associated with adverse cardiac events. This study evaluated whether plaque morphological intravascular ultrasound (IVUS) characteristics affects tissue perfusion after stent implantation in STEMI patients. METHODS AND RESULTS: A total of consecutive 306 STEMI patients who underwent primary angioplasty with IVUS were analyzed. Maximum ST-segment elevation before angioplasty was compared with ST-segment levels 60min after angioplasty. Percent ST-segment resolution (STR) was calculated and categorized as complete (>70%), partial (30-70%), and absent (<30%). Qualitative and quantitative IVUS analyses were performed using standard methods. Plaque with ultrasound attenuation was defined as IVUS finding with backward signal attenuation behind plaque >180° without dense calcium. One-hundred-fifty patients had complete, 101 had partial, and 55 had absent STR. The incidence of in-hospital death tended to be higher in absent STR than in partial and complete STR groups. Multivariate analysis indicated that remodeling index (P=0.004), the presence of ultrasound attenuation (P=0.02), percentage stent expansion (P=0.03), and the presence of deep calcium (P=0.049) were the independent predictors related to the occurrence of absent STR after angioplasty. CONCLUSIONS: Positive vessel remodeling, plaque with ultrasound attenuation >180°, deep calcium, and stent overexpansion as assessed by IVUS are associated with the absence of STR after primary angioplasty in patients with STEMI.

The impact of pravastatin pre-treatment on periprocedural microcirculatory damage in patients undergoing percutaneous coronary intervention.

OBJECTIVES: This study evaluated the effect of pravastatin pre-treatment on post-procedural index of microcirculatory resistance (IMR) values that are introduced for assessing the status of the microcirculation independently of the epicardial area. BACKGROUND: Pre-treatment with statins decreased the incidence of cardiac enzyme increase after percutaneous coronary intervention (PCI). However, 2 different etiologies, distal embolization of atheroma or ischemia caused by side-branch occlusion, cannot be differentiated by measuring cardiac enzyme levels. METHODS: Eighty patients with stable angina were randomly assigned to either pravastatin treatment (20 mg/day, n = 40) or no treatment (n = 40) 4 weeks before elective PCI. An intracoronary pressure/temperature sensor-tipped guidewire was used. Thermodilution curves were obtained during maximal hyperemia. The IMR was calculated from the ratio of the mean distal coronary pressure at maximal hyperemia to the inverse of mean hyperemic transit time. Creatine kinase-myocardial band and troponin I values were measured at baseline and at 8 and 24 h after PCI. RESULTS: Post-PCI troponin I levels tended to be lower in patients with pravastatin treatment (median: 0.13 [interquartile range (IQR): 0.10 to 0.31] vs. 0.22 [IQR: 0.10 to 0.74] ng/ml, p = 0.1). However, patients with pravastatin treatment had significantly lower IMR than did patients without pravastatin treatment (median: 12.6 [IQR: 8.8 to 18.0] vs. 17.6 [IQR: 9.7 to 33.9], p = 0.007). Multivariate analysis revealed that the lack of pravastatin pre-treatment was the only independent predictor of post-PCI impaired IMR (p = 0.03). CONCLUSIONS: Post-PCI measurement of the IMR confirmed that pre-treatment with pravastatin was associated with reduced microvascular dysfunction induced by PCI regardless of side branch occlusions. These data suggest that pre-treatment with statin is desired in patients undergoing elective PCI. (The Impact of Pravastatin Pretreatment on Periprocedural Microcirculatory Damage After Percutaneous Coronary Intervention; UMIN000002885).

[Slender PCI].

Currently the 0.014-inch guidewire is commonly used for coronary intervention and all devices are 0.014 inch-compatible. The size of common guiding catheters is 6Fr. However, PCI requires oral administration of dual antiplatelet agents, and punctured-site complications such as hemorrhage and hematoma occur more frequently with use of a 6Fr guiding catheter compared to a 5Fr guiding catheter. Moreover, 6Fr or larger guiding catheters may cause radial arterial occlusion, although the transradial approach causes less punctured-site complications compared to the transfemoral approach. Recently, 0.010-inch guidewires applicable for the kissing balloon technique (KBT) using a 5Fr guiding catheter and 0.010-inch guidewire-compatible balloons have been developed in Japan, and a 3Fr angiography catheter has also been developed. We refer to these devices as the "slender system", and we have used this system for active treatment of bifurcation lesions and chronic total occlusion (CTO). In this report, we describe angiography using a 3Fr catheter, the KBT using a 5Fr guiding catheter and 0.010-inch guidewires, and treatment of CTO using a 5Fr catheter and 0.010-inch guidewires. For CTO treated using the slender system at our facility, the transradial arterial approach was used in 90.7% of cases, treatment using the slender system alone succeeded in 65.1%, and the overall success rate was 89.5%. Therefore, our results show that complex lesions may be treatable using the slender system, and that not all complex lesions require a 6Fr or larger guiding catheters, a femoral arterial approach, or bilateral guiding catheters.

Endothelium-dependent coronary vasomotor response and neointimal coverage of zotarolimus-eluting stents 3 months after implantation.

BACKGROUND: Zotarolimus-eluting stents (ZES) have a higher rate of neointimal coverage than the first-generation drug-eluting stents on optical coherence tomography (OCT). OBJECTIVE: To determine whether neointimal coverage of stent struts detected by OCT can be used as a surrogate for endothelial function after ZES implantation. DESIGN: Cross-sectional observational study. SETTING: Three months after ZES implantation. PATIENTS AND METHODS: OCT was performed in 20 patients with a ZES at 3 months after stent implantation to evaluate strut coverage. Endothelium-dependent coronary vasomotion was estimated by infusing incremental doses of acetylcholine into the coronary ostium. The vascular response was measured in the 10 mm segments proximal and distal to the stent. RESULTS: Of 20 ZES, 15 (75%) were covered completely with neointima, but the remaining 5 ZES had exposed struts. The high-dose acetylcholine infusion produced significant vasoconstriction in the proximal (-9.8±10.1%) and the distal stent segment (-29.7±22.7%). However, the degree of vasoconstriction to acetylcholine varied between individuals (from -0.6% to -77%). Although no relationship was observed between coronary vasomotor response (percentage change in diameter after acetylcholine administration) and average neointimal thickness, the number of cross-sections with uncovered struts showed an inverse correlation with coronary vasomotor response in proximal and distal stent segments (r=-0.57, p=0.007 and r=-0.83, p<0.001, respectively). CONCLUSIONS: The existence of exposed struts was associated with abnormal vasoconstriction to acetylcholine at 3 months after ZES implantation. The findings suggest that complete neointimal coverage of stent struts assessed by OCT could be used as a surrogate for vasomotion impairment at 3 months after ZES implantation.

Preprocedural evaluation and endovascular treatment of iliofemoral artery disease without contrast media for patients with pre-existing renal insufficiency.

BACKGROUND: Generally, both the preprocedural evaluation and endovascular therapy (EVT) for lower limb arteries require contrast media that is harmful for patients with chronic renal insufficiency. In the present study these procedures were performed without using nephrotoxic contrast media in patients with preexisting renal insufficiency and iliofemoral artery disease. METHODS AND RESULTS: The 36 consecutive patients with chronic renal insufficiency underwent preprocedural evaluation with duplex examination, magnetic resonance angiography (MRA) without contrast media, and plain computed tomography (CT). A total of 51 lesions were treated using intravascular ultrasound (IVUS) without contrast media. The overall technical success was 100% without any complications. Pre- and postprocedural ankle-brachial indices changed from 0.59 ± 0.23 to 0.92 ± 0.14. The mean serum creatinine concentration before and after treatment, and 3 months after treatment did not change (2.1 ± 1.4, 2.0 ± 1.4, and 2.1 ± 1.6 mg/dl, respectively). The overall 3-month survival rate and limb salvage rate was 100%. CONCLUSIONS: EVT comprising duplex, MRA, and CT for preprocedural evaluation and IVUS-guided procedure is feasible and may avoid intra-arterial contrast injection in selected patients deemed at high risk for renal failure from nephrotoxic contrast material.