The Catheter Wall Simulating Thrombus Formation Seen on Pullout Angiograms: An Experimental Study 1

Diagnostic Radiology

Richard L. Mani, M.D., and Ronald L. Eisenberg, M.D. The authors investigated the nature of a radiolucent line that was seen paralleling the radiopaque catheter wall on more than 70 % of 176 pullout angiograms. Although this line may indicate a thrombus sleeve, accumulation of thrombus was rarely seen at the puncture site. A series of experiments demonstrated clearly that (a) an identical line could be reproduced in a bloodless model; (b) the width varied directly with the thickness of the catheter wall and appeared irregular in contour with 6.5,7, and 8 French catheters: and (c) this line represented the outer third of the catheter wall. I Nl:EX TERMS:

Catheters and catheterization

Radiology 123:601-604, June 1977

T

HE ACCEPTED METHOD for demonstrating thrombus

formation on the catheter wall during angiography is the pullout angiogram (1-6). This study is usually performed by withdrawing the catheter until the tip is 6-10 cm proximal to the puncture site, injecting 10 to 12 ml of a contrast agent, and simultaneously radiographing the puncture site, usually at 2 films per second for 2 seconds and 1 per second for the next 2 seconds (6 radiographs total). Thrombus formation is diagnosed if an irregular radiolucent line paralleling the indwelling catheter wall is seen on the pullout angiograms (Fig. 1). In a recent study of thrombus formation observed on pullout angiograms (5), one of us noticed a radiolucent line, usually smooth but sometimes irregular, which paralleled the opacified catheter in one or more films (Fig. 2). This line was observed in 132 (70 %) of 176 pullout angiograms. Despite the presence of this radiolucent line, which usually indicates a thrombus sleeve, there was no evidence of any thrombus accumulated at the puncture site in 98 % of these 132 cases. Hawkins and Kelley (3), in a study of heparin..coated angiographic catheters in pullout angiograms, also noted this radiolucent line which they initially thought represented a uniform fibrin or thrombus sleeve. They later concluded that it was not thrombus formation, but were unable to explain the phenomenon. To investigate the nature of this radiolucent line seen on pullout angiograms, we performed a series of experiments.

random from our stock of angiographic catheters. These were filled with 100 % solution of Renografin-60 4 and clamped at both ends. The outer "artery" was a clear polyethylene catheter (0.0.9 mm, 1.0.7 mm). It was filled with solutions of Renografin-60 varying in 100/0 increments from 10 to 100 0/0. Each model was taped to a pelvic phantom placed on the film changer. Two preparations for each catheter size (5, 6, 6.5, 7, 8 French) were radiographed with the same techniques and settings employed clinically for pullout angiograms (72 to 76 kV, 48 to 60 mAs). We then examined the films for the presence of the radiolucent line previously described. RESULTS OF EXPERIMENT I

A radiolucent line paralleling the opacified catheter lumen was demonstrated in all radiographs in which the inner catheter was surrounded by arterial contrast solution of 30-80 0/0, and in 25 % of the radiographs in which the contrast solution was greater than 80 %. The line was never seen when the contrast solution was under 30 °/0 . The width of the line varied directly with the size of the catheter wall, i.e., thinnest with the 5 French catheters and widest with the 8 French catheters. In addition, although the line was smooth in the radiographs of the 5 and 6 French catheters, it was irregular in the radiographs of the larger catheters (Fig. 3). MATERIALS AND METHODS OF EXPERIMENT II

MATERIALS AND METHODS OF EXPERIMENT I

The purpose of this investigation was to determine the nature of the radiolucent lines seen in Experiment I. The exact conformity in thickness and contour of this line to the wall of the inner catheter indicated that the line and wall were associated, although the possibility of parallel grid lines was also considered as a potential cause of the line. The radiolucent lines seen earlier on clinical pullout an-

A model was developed to simulate a radiopaque catheter within an artery during pullout angiography. This model consisted of an inner angiographic catheter inserted into a larger bore outer catheter that represented the artery. For inner catheters, we used 5, 6, 6.5, 7, and 8 French, radiopaque, polyethylene catheters 2 .3 taken at

1 From the Departments of Radiology, The University of California School of Medicine. and Veterans Administration Hospital, San Francisco, Calif. Accepted for publication in January 1977. 2 Cook, lnc., Bloomington, Ind. 47401. 3 Becton-Dickinson, Rutherford, N. J. 07070. 4 Meglumine diatrizoate and sodium diatrizoate injection, manufactured by E. R. Squibb and Sons, Princeton, N. J. 08540. shan

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June 1977

intense illumination no light could be seen between them. This catheter model thus has a double lumen with lateral walls of single thickness and a medial wall of double thickness. Two such models, one filled with Renografin-60 and clamped at both ends, the other unfilled, were placed side-by-side and radiographed with a magnification factor of 1.6 using a small focal spot of 0.3 mm. The grid factors were 41-inch focus, 100 lines per inch, 12:1 grid ratio. The experiments were repeated without grids to eliminate the factor of grid lines. The resulting radiographic images of the parallel catheter models were examined and measured with a magnification optic (X 3, calibrated to 0.1 mm). Density measurements were made with a pinhole window densitometer (0.05 mm diameter). RESULTS OF EXPERIMENT II

Observations: The unfilled model provided the greater detail. The outer catheter walls appeared as single radiopaque lines, the contiguous inner walls as two parallel radiopaque lines flanking a central radiolucent line. In the contrast-filled model, only the central lucent line was seen;

Fig. 1. Radiographfrom pullout angiogram demonstrating irregular radiolucent line paralleling catheter wall and representing thrombus formation . Fig. 2. Radiograph from pullout angiogram demonstrating radiolucent line paralleling catheter wall. No accumulated thrombus was seen at puncture site.

giograms (5) and in the present simulated studies of Experiment I were extremely fine and, although easily seen by the naked eye, defied visual measurement (even with a magnification optic) or densitometry. We therefore developed a model for Experiment II to accentuate the radiolucent line, if it was part of the catheter wall, and to make it more demonstrable not only for direct inspection, but for subsequent measurements and densitometry. This model consisted of two, 20-cm segments of 7 French radiopaque polyethylene catheter" bound tightly in parallel by braided rubber bands (Fig. 4). The tension of these rubber bands was adjusted to prevent deformity of the catheter contours yet maintain the contiguous catheter walls under such constant tension that when placed under

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Cook, Inc., Bloomington, Ind. 47401.

Fig. 3. Experiment I: radiolucent lines paralleling catheters in bloodless model (indicated by black arrowheads). Contrast solutions from left to right are 40 %. 50 %. and 60 % .

CATHETER WALL SIMULATING THROMBUS FORMATION

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Fig. 4. Experiment II: two parallel catheters bound tightly together by braided rubber bands to form experimental model.

none of the opaque lines that on the unfilled model represented the inner and outer walls could be discriminated from the contrast-filled lumen (Fig. 5). Upon closer inspection with a magnification optic, the lucent line was not homogeneous, but rather showed a spectrum of gray ranging from dark gray in the center to a light gray on either side where it blended imperceptibly into the adjacent opacity (Fig. 6). Measurements: With a magnification factor of 1.6, the predicted thickness of the double wall was 1.2 mm, i.e ., 2.39 mm (0.0.) - 1.63 mm (lumen) == 0.76 mm (two wall thickness) X 1.6 (magnification) == 1.2 mm. With a magnification optic, the actual measurement of the central double catheter wall (two inner opaque lines central

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Fig. 6. Radiograph of unfilled parallel catheter model (magnified X 3) demonstrating the opaque double image produced by adjacent catheter walls and the nonhomogeneity of central radiolucent line .

Fig. 5. Experiment II: radiograph of contrast-filled (left) and unfilled (right) parallel catheter models.

radiolucent line) was approximately 1.2 mm. The central radiolucent line, measured on both filled and unfilled models, was 0.36 mm or 30% of the double wall thickness. Densitometry: Numerical values for the radiographic densities of the unfilled catheter model were as follows: Background (air) 2.8 Outer opaque line 1.9 Lumen 2.2 Inner opaque line 1.8 Central radiolucent line 2.0. These values show clearly that the central radiolucent line does not represent artifact or air but rather the outer third of each catheter wall.

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RICHARD L. MANI AND RONALD L. EISENBERG

Fig. 7. Line drawing depicting the parallel catheter model. Note the outer curvature of the catheter wall is less thick; the catheter wall, therefore, produces two distinct radiographic images.

DISCUSSION

Angiographic catheters are rendered radiopaque by the impregnation of the catheter material with heavy metal salts such as barium, bismuth, or lead-usually 20-30% by weight. It has been assumed that the walls of these catheters, when radiographed, produce a single homogeneous opaque image. The results of Experiments I and II demonstrate that the radiographed catheter wall produces a distinct and discernible double image, i.e., an inner radiopaque line and an outer radiolucent line. Experiment I demonstrated the following findings: 1. A radiolucent line parallel to the catheter wall seen on pullout angiograms can be experimentally reproduced in a bloodless model. 2. The width of the line varies directly with the thickness of the catheter wall. 3. Large catheters (6.5, 7, 8 French) can produce a line that is irregular in contour and closely simulates a thrombus sleeve. 4. The lucent line is best seen when the surrounding contrast medium is diluted to 30-80 %, which may explain why this line is usually seen in the middle films of pullout angiogram series when the contrast material is diluted by blood. Solutions over 80 % tend to obscure the entire catheter. Experiment II demonstrated that:

June 1977

1. The radiopaque catheter wall produces a double image, a medial opaque line, and a lateral lucent line. 2. The lucent line represents the outer 30 % of the catheter wall. 3. The lucent line can only be seen when the catheter is "framed" by some denser opacity, e.g., contrast material as in a pullout angiogram or a contiguous catheter wall as in the parallel catheter model of Experiment II. The best explanation for the phenomenon of the radiolucent line is that the curvature of the angiographic catheter wall produces a radiographic image that reflects the rapid medial to lateral decrease in wall thickness (Fig. 7). The corresponding dramatic variation in radiographic densities is perceived as distinct radiopaque and radiolucent lines. The clinical implications of these investigations may be summarized. First, the radiolucent line paralleling the contrast-filled catheter lumen on pullout angiograms may represent the outermost portion of the catheter wall and not thrombus formation. Second, this image may be irregular in contour, especially with larger catheters, and may therefore closely simulate a thrombus or fibrin sleeve.

Richard L. Mani, M.D. Department of Radiology, M-380 University of California School of Medicine San Francisco, Calif. 94143

REFERENCES 1. Cramer R, Moore R, Amplatz K: Reduction of the surgical complication rate by the use of a hypothrombogenic catheter coating. Radiology 10$:585-588, Dec 1973 2. Formanek G, Frech S, Amplatz K: Arterial thrombus formation during clinical percutaneous catheterization. Circulation 41:833-839, May 1970 3. Hawkins IF Jr, Kelley MJ: Benzalkonium-heparin-coated anglographic catheters: experience with 563 patients. Radiology 109:589-591, Dec 1973 4. Jacobsson B, Schlossman D: Angiographic invesUgation of formation of thrombi on vascular catheters. Radiology 93:355-359. Aug 1969 5. Mani RL: Computer analysis of factors associated with thrombus formation observed on pullout angiograms: preliminary communication. Invest RadioI10:378-384, Jul-Aug 1975 6. Siegelman SS, Caplan LH, Annes GP: Complications of catheter angiography: study with oscillometry and "putlout" angiograms. Radiology 91:251-253, Aug 1968

The catheter wall simulating thrombus formation seen on pullout angiograms: an experimental study.

The Catheter Wall Simulating Thrombus Formation Seen on Pullout Angiograms: An Experimental Study 1 Diagnostic Radiology Richard L. Mani, M.D., and...
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