A standard angiogram was performed and angioplasty was planned in all cases of ACS. Difficulty in engaging standard guide catheters was encountered in 34 cases. The femoral route was the preferred method for the operator in primary angioplasty for ACS. Difficulty in engaging guide catheters was defined as difficulty with two or more standard guide catheters in engaging the target artery with reasonable manipulations using discretion. The catheters chosen were predominantly Judkins catheters. The operator (i.e. the author) performed the procedures. Only 6F guide catheters were used in all cases. For the left coronaries, a 3.5 cm Judkins Left (JL) was used initially. If engagement failed, a 4.0, 4.5 or 5.0 cm JL was tried, depending on aortic dilation and curvature. In younger patients and with a less arched aorta, a 3.0 Judkins Left (JL) was used for engagement of the ostia. If this failed, Cordis® Extra Backup (XBU) catheters of similar dimensions were tried. For the right coronary system a 3.5 cm JR was used in the majority of cases. If engagement failed, a Cordis® JR 4 or Cordis® Amplatz Right (AR) 1 or 2 was used, depending on the patient's age and the shape of the aorta. If the catheter was approaching the ostium, another JR 3.5 was tried, depending on the procedural circumstances. Also, in all these cases insertion of a 0.014″ wire was attempted into the coronaries even when the guide catheter did not engage or was placed near the coronary ostium. However, in all cases, the diagnostic catheters engaged very well during the initial angiogram, so the same 6F Cordis® INFINITI diagnostic catheter was used to perform angioplasty. Figure 1 shows angiograms of angioplasty performed using diagnostic catheters. The diagnostic catheters have a luminal diameter of 1.4 mm, and the guide catheters have a luminal diameter of 1.8 mm.

Figure 1.

Angiograms of angioplasties and stenting performed using diagnostic catheters: angioplasty in the proximal left anterior descending (LAD) artery (A and B); angioplasty in the mid right coronary artery with clots (C and D); angioplasty of the proximal LAD in a patient in cardiogenic shock (E and F), and angioplasty of the proximal LAD in a critically ill patient (G and H).

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The mean age of the patients was 60±14 years, and 27 were male. The main causes of difficulty in engaging guide catheters encountered were tortuosity of iliofemoral arteries (12), mildly dilated aorta (9), slightly posterolateral origin of the right coronary (5), tortuous abdominal-thoracic aorta (4), and high origin of the left main artery (3). However, a combination of multiple factors in various degrees was the reason for difficulty in engaging guide catheters more often than any isolated cause. All injections were given by hand only; a power injector was not used for coronary visualization in any of the cases. Two patients had cardiogenic shock, in one of whom intra-aortic balloon counterpulsation was used, and the other patient was managed with inotropes. No mortality was encountered during the procedures. BMW (Abbott) wires were used in 30% of cases, All Star (Abbott) in 57.5% of lesions and Runthrough NS (Terumo) in the remaining 12.5%.

The lesions were discrete and critical, and caused 90-100% stenosis by visual assessment, predominantly with associated soft clots. In 16 cases, angioplasty was performed in the proximal left anterior descending (LAD) artery, eight in the circumflex artery and in the right coronary artery (RCA) in the other 10 patients. Calcified lesions were seen in six cases, three of them heavily calcified.

The stent length used was between 12 and 20 mm in 27 patients, 24 mm in four patients, 28 mm in two cases, and 8 mm in one patient. A total of 40 stents were used in these 34 cases. Direct stenting was the preferred technique. It was left to the operator's discretion to use the shortest possible stent length to avoid redundancy. In nine cases predilatation was performed. Tazuna semi-compliant balloons (2 mm×10 mm) were used in three cases, a 1.5×10 mm Sprinter balloon in one patient and Fast Track semi-compliant balloons (2 mm×10 mm and 2.5 mm×10 mm) were used in four other cases. The stent widths mainly ranged from 2.25 mm to 3.0 mm. In four cases, 3.5 mm stents were deployed without difficulty. The balloons were easily withdrawn into the catheter after stent deployment. Post-dilatation was performed in three cases with 3 mm×12 mm Fast Track semi-compliant balloons and a 2.75 mm×10 mm iTrack balloon.

Further catheter testing was performed in vitro to study the mechanisms of engagement by evaluating catheter pushability and trackability characteristics and by three-point bending and distal tip flexion tests. Eleven catheters were selected and analyzed in the testing laboratory. Lists of the diagnostic and guide catheters are shown in Figure 2. For three-point bending and distal tip flexion tests five catheters – diagnostic JL and JR, 6F JL and JR guide catheters and 5F XBU – were selected (Supplementary Table 3). The catheters used for distal tip flexion testing are listed in Supplementary Table 4.

Figure 2.

Lists of diagnostic and guide catheters and their identification names used in the study. I.D.: inner diameter.

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The OptiCross (Boston Scientific) intravascular ultrasound (IVUS) catheter was chosen, and the ability of this catheter to pass through the diagnostic catheters was assessed in both JL and JR 6F catheters.

All the diagnostic catheters used were 6F Cordis®. The angioplasty procedure with stenting was successfully performed using diagnostic catheters, stents being easily placed in the lesion site in the coronaries. In total, 40 stents were used: Endeavor Resolute (1), Excel (6), Biomatrix Flex (1), Endeavour Sprint (11), Onyx (1), Ultimaster (4), Nobori (6), Yukon Choice PC Flex (5), Resolute Integrity (3) and Xience Alpine (2). A slight dampening of pressure tracings was observed during the procedure except in newer-generation stent delivery systems, in which the pressure tracings could be visualized more clearly. This could be due to the thinner shafts of these delivery systems. Standard procedures were followed during the angioplasty. During the procedure, a second wire could be taken through the diagnostic catheter if required and parked in the coronaries. However, in none of the cases was bifurcation stenting performed. During the angioplasty, opacification of the coronaries was less than with guide catheters, but even so the coronaries and the lesion location were clearly visualized. Immediately after stent placement, the coronaries were visualized by contrast injection, and the stent was visualized clearly. The stent could be easily and safely taken inside the diagnostic catheter and then to the lesion. In an emergency setting, complex interventional cases can also be tackled with this technique, as shown in Figure 3.

Figure 3.

Complicated stenting of right coronary artery performed with diagnostic catheters. The proximal right coronary artery (RCA) was 100% occluded (A), and the lesion was crossed with a BMW wire with balloon support, and balloon dilatation was performed (B). A dissection was observed in the mid RCA (C), and stenting was performed from proximal to mid RCA (D and E).

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Thrombus aspiration was not performed in any of the cases. Peri-procedural complications or noreflow phenomenon was not seen in any of the cases and none of these 34 patients suffered reinfarction in a one-month follow-up. One patient had a coronary artery dissection at the distal edge of the stent, which was stented. No dissection was observed at the site of coronary ostial engagement. There were no deaths, and contrast-induced nephropathy (32% increase in creatinine from baseline) was seen in only one patient, in whom creatinine levels improved over the following few days.

The trackability tests measured the force required to advance the catheters along a tortuous femoral path. The displacement forces required to advance the catheter were measured. Pushability was measured as the ratio of distal to proximal forces. Results of the pushability and trackability tests are given in Figures 4 and 5.

Figure 4.

Results of pushability and force transmission measurements of the catheters. DC: diagnostic catheters; GC: guide catheters.

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Figure 5.

Results of trackability measurement of the catheters by force-distance curves. DC: diagnostic catheters; GC: guide catheters.

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The force transmission parameters are shown in Supplementary Tables 1 and 2. The diagnostic catheters require more force (mean 7.83±1.57 vs. 4.06±2.29 N). However, the ratio between proximal and distal forces was 0.28 for diagnostic catheters, and for guide catheters it was 0.51. The diagnostic catheters have more maneuverability, as reflected by the maximal force parameters (10.03 vs. 7.73 N), but the guide catheters have high force transmission ratios.8–12 To ensure successful procedures in real time, better maneuverability parameters enable easier engagement of catheters in the coronary ostium.8–12

Figure 6 summarizes the results of distal tip flexion testing on five catheters. The distal tip flexion of the diagnostic catheters show balanced force displacement curves. The area inside the curve shows the hysteresis between elasticity and plasticity. The 5F XBU shows large displacement with small forces, whereas the 6F JL and 6F JR guide catheters show less displacement with large forces. The slope of the curve represents the stiffness of the catheters. The diagnostic catheters show optimal stiffness; the guide catheters have more stiffness and the 5F XBU catheter is less stiff.8–12

Figure 6.

Results of distal tip flexion tests and maximum force distance table. DC: diagnostic catheter; GC: guide catheter.

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The three-point bending tests were performed at 4.5 cm and 10 cm from the distal tip of the catheters. The force displacement curves of the catheters are shown in Figure 7A and B. The diagnostic catheters have a balanced force displacement compared to the guide catheters, with less plastic deformation as shown by a smaller area inside the curves.

Figure 7.

Results of three-point bending test measured at 4.5 and 10 cm from the distal tip with maximum force distance parameters. DC: diagnostic catheter; GC: guide catheter.

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The IVUS catheter (OptiCross 3.1 F) could be taken inside the 6F JR and JL diagnostic catheters and could be exteriorized through the distal tip of the catheters with ease, as observed in bench testing.

It is feasible to perform angioplasty and stenting using 6F Cordis® diagnostic catheters as an emergency procedure in ACS. This technique could be used as a bailout procedure, although it is not advisable for routine use. Difficulty in engagement often subjects the operator to psychological stress, especially when patients have ongoing angina or MI. The major advantage of this technique is that it minimizes procedural time as well as contrast use.

Frequent exchanges of catheters are often associated with increased procedural and fluoroscopy times and thus with procedural complications,13 increased contrast use,14,15 infections or bacteremia,16 and thrombotic complications.13 As a bailout procedure, this technique is useful and feasible in ACS, when difficulty in engagement is encountered with guide catheters. The contrast load is reduced, in contrast to the larger contrast quantity commonly required in such situations. Also, in life-threatening situations in which a perfect result is not a major concern and time is of the essence, this method can be very useful.6,7 In our study, in more than 50% of cases the contrast load used was less than 50 ml including the diagnostic angiogram. Maximum contrast use was 110 ml in one patient, and the mean was 45 ml.

GuideLiner, deflectable tip or steerable catheters are some of the other options available in the present scenario for difficult cannulation.17,18 However, these techniques are expensive and time-consuming, and are not available in all catheterization centers.

The other difficulty is the assessment of pressures, which are damped to a certain extent; this would be a limitation on the use of diagnostic catheters as a routine technique. Although pressures are slightly damped, the pressure tracings are visible, and it is feasible to perform the procedure. As an observation, the pressure tracings were better visualized with newer-generation stent delivery systems.

It is also important to mention that all these procedures were performed with Cordis® diagnostic catheters only. There are no other comparative studies on the use of other diagnostic catheters for this purpose. It was the operator's choice to use these catheters. It is worthwhile noting that in 10 out of 34 cases the procedures were performed for right coronary artery lesions, in which difficulty in engaging guide catheters is more frequent.

In bench testing the trackability characteristics were better for diagnostic catheters than for guide catheters. Also, the diagnostic catheters sustained more proximal force, and the distance at maximal force was more than 53 cm in the 54 cm tortuous path defined in the study protocol (mean 53.3±0.25 cm). The mean distance for the guide catheters was 49.6±4.17 cm.

The diagnostic catheters have better pushability characteristics. The diagnostic catheters sustained more proximal force and had better distal force transmission compared to guide catheters as reflected by the ratio of proximal and distal force. Also, the guide catheters cannot sustain as much proximal force as diagnostic catheters, which is often required in tortuous or calcific iliac arteries and aortas.

The comparisons of three-point bending tests (Figure 7A and B) show that the area under the curves, which indicates the work performed or the kinetic energy stored in the catheters during catheter deformation, is higher for diagnostic catheters than for guide catheters. Also, the area inside the curves is less for the diagnostic catheters, which indicates less plastic deformation. The slope of the force-distance curve indicates the acceleration of the movement, which is also greater than in guide catheters.9,10

The distal tip flexion tests show good characteristics in the diagnostic catheters compared to guide catheters. The 3.5 JR demonstrates large plastic deformation, while the 3.5 JL and 3.0 XBU show less elastic properties.

Currently available IVUS and optical coherence tomography (OCT) catheters are about 3F or less with hydrophilic coating, and they are 5F guide compatible. Hence, these imaging catheters can also be safely used in these diagnostic catheters. Bench evaluation of the OptiCross IVUS catheter demonstrated that it could easily go through the 6F JR and JL diagnostic catheters. The OptiCross catheter's shaft is 3.1F (1 mm), and hence this is feasible. The Dragonfly™ OCT catheter (St. Jude Medical) has a shaft diameter of 2.7 F. This is comparable to the shaft diameters of stents like Endeavor (2.8F), Onyx (2.7F), Nobori (2.5F) and Yukon Choice (2.6F). Since all these stents can pass through 6F Cordis® diagnostic catheters, OCT and IVUS are feasible for use in these diagnostic catheters.

Emergency angioplasties are associated with a high incidence (15-20%) of contrast-induced nephropathy. In our series contrast-induced nephropathy was seen in only one patient, in whom creatinine increased from 1.3 mg/dl to 1.8 mg/dl, and after a few days decreased to 1.2 mg/dl. Contrast volume is a major determinant of contrast-induced nephropathy.19–21 In this series, the mean contrast volume was only about 45 ml, and no mortality was observed. However, the total number of cases was less.

Using this method bifurcation lesion therapy and thrombosis aspiration22 before stenting cannot be performed. In our center, it is the operator's choice that thrombosis aspiration is not performed routinely in all acute emergencies, but only in cases with a very high clot burden. The routine treatment of choice in ACS is direct stenting. Predilatation and stenting are used when direct stenting is not feasible. There are increasing reports of the benefits of direct stenting.23,24 In bifurcation lesions in an emergency setting, provisional stenting is the preferred method. Bifurcation lesion therapy and thrombosis aspiration may not always be required in routine emergency procedures. Also, in this study a switch to a radial approach was not tried when the femoral route failed, which is another available option. This is due to the operator's choice of the femoral route in ACS. However, the diagnostic catheter technique is an easy method for the majority of lesions in an emergency setting. Simplicity of the procedure is also a common priority in most cases of ACS, in which time and contrast load are major concerns, especially in patients with ongoing angina or MI.