Radiology of Intra-Aortic Balloon Pump Catheters

Abstract

Radiographs play an important role in ascertaining appropriate placement of the intra-aortic balloon pump catheter. This imaging essay highlights correct and incorrect positioning of these catheters, with emphasis on the variability of radiopaque markers used with different catheter models and on axillary versus femoral catheter placement routes.

Keywords: Conventional Radiography, CT, Percutaneous, Cardiac, Vascular, Aorta, Anatomy, Cardiac Assist Devices, Catheters

© RSNA, 2022

Summary

Knowledge and awareness of the different intra-aortic balloon pump (IABP) catheter radiopaque markers and routes of placement are necessary to identify correct or incorrect positioning of the IABP catheter on radiographs.

Key Points

• ■ Intra-aortic balloon pump (IABP) catheters have different radiopaque markers that vary between model types and manufacturers.

• ■ IABP catheters are placed by two routes: the traditional femoral approach and the off-label axillary approach.

• ■ Close attention to IABP catheter markers is necessary to ensure appropriate positioning.

Correct Positioning on Radiographs

Like many intravascular devices, the components of the intra-aortic balloon pump (IABP) catheter are radiolucent. Traditionally, only a single radiopaque marker is placed near the tip of the catheter at the distal margin of the balloon (ie, the portion of the balloon first introduced into the patient and furthest from the exposed hub of the catheter after intravascular deployment) (Fig 1). When placed via the femoral artery, this end of the balloon and its marker should reside distal to the aortic arch, in the proximal thoracic aorta (Fig 2). Positioning in this region optimizes balloon functioning for cardiac support by reducing afterload (1) and ensures that the balloon tip does not migrate into or cover the smaller-caliber arch vessels, such as the left subclavian artery. Radiographically, this region is targeted by placing the marker approximately 1 cm below the top of the aortic knob and at or above the level of the carina (2). Figure 3 demonstrates the relationship of the aortic knob and the carina and the acceptable region for balloon tip positioning.

Figure 1:

Intra-aortic balloon pump catheter. The distalmost tip is rigid (black arrowhead), with a radiopaque marker near the distal tip of the balloon (black solid circle). The balloon is deflated but can be well seen between the markers. If present, a second radiopaque marker (black dashed circle) is positioned just proximal to the balloon (black arrowhead). The more proximal catheter (black arrow) extends off the superior margin of the image to the pump.

Figure 2:

(A) Femoral-approach positioning of an intra-aortic balloon pump catheter on a bedside frontal chest radiograph, with single distal marker (in white circle) projecting approximately 1 cm below the top of the aortic knob (dashed white curve). The carina is also marked with the dashed white angle. (B) Diagram demonstrates the layout of the catheter placed by a femoral approach. (Fig 2B used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.) (C) Fluoroscopic overhead image of the distal marker at time of placement by the interventionalist, showing the distal marker (in white circle), top of the aortic arch (dashed white curve), and the carina (dashed white angle).

Figure 3:

(A) Frontal radiograph and (B) oblique sagittal slab maximum intensity projection CT image reconstruction demonstrate the relationship of the carina with the aortic knob. The descending aorta is to the right of the CT image. In both images, the carina lies at the level of the solid white line. A level measured 1 cm below the top of the aortic knob is indicated by the dashed white line. The intra-aortic balloon pump tip and its marker should project between these two levels. Also marked on both images is the origin of the left subclavian artery (white arrowhead) nearest the top of the arch.

There is no standard for radiographic markers on IABP catheters, with markers varying by manufacturer and model type. All share the aforementioned distal tip marker. Some models now place a second radiopaque marker at the proximal aspect of the balloon (Figs 1, 4). When an IABP catheter is placed via a femoral approach, this second marker allows one to definitively locate the more caudal balloon tip. However, the appropriate positioning of this marker has not been well established in the literature, and, to our knowledge, no study has explored how often this marker is placed above, at, or below the mesenteric and renal arteries and documented associated relative risk of vascular complication.

Figure 4:

(A) Frontal radiograph shows the distal, doubled marker (in solid white circle) after femoral-approach catheter placement. On this catheter, the distalmost portion of the distal marker is less dense than that of the neighboring portion, which provides a sense of directionality to the catheter. Note, this catheter has a second, smaller marker just proximal to the balloon (in dashed white circle). Some catheters have similar-appearing proximal and distal markers that make directionality difficult to determine. (B) Diagram of the relationship between the two radiopaque markers. (Fig 4B used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.)

Anatomic studies demonstrate that most celiac arteries arise from the aorta above the L1 vertebral body level (3). Figure 5 shows an IABP catheter placed via a femoral approach, with the cranial marker in the expected position below the aortic knob and above the carina. The caudal marker projects over the superior aspect of the L2 vertebral body. The accompanying CT image obtained just prior to balloon catheter placement clearly shows this vertebral body level to be well below the origin of the celiac and superior mesenteric arteries. Due to limitations in catheter size and length (Table), the catheter tip often covers the mesenteric and renal vessels in shorter patients (7,8). Even for the patient of above average height represented in Figure 5, the catheter often projects low into the distal aorta, even when the balloon is appropriately positioned more cranially.

Figure 5:

Images in a 61-year-old man measuring 183 cm in height. (A) Frontal radiograph centered on the diaphragm to include both the distal (solid white circle) and proximal (white dashed circle) markers of a femoral-approach catheter that measured 258 mm in length. The distal marker is appropriately positioned, with the proximal marker projecting over the superior aspect of the L2 vertebral body. (B) Sagittal slab maximum intensity projection reconstruction image obtained just before catheter placement demonstrates the relationship of the celiac (white arrow) and superior mesenteric artery (white arrowhead) origins relative to the L1 and L2 vertebral bodies.

Intra-Aortic Balloon Pump Catheter Sizes

Global malposition of the IABP catheter may increase complications associated with IABP catheter use, such as mesenteric and renal ischemia (9,10). As we commonly see these catheters covering the mesenteric vessels, we believe the most important task when a “low” or caudally migrating IABP catheter is identified is to ensure appropriate positioning of the cranial marker (Figs 2, 4, 5).

IABP Catheter Dual-Density Marker

As previously discussed, use of distal and proximal in this imaging essay refers to positioning of the radiopaque markers with respect to the balloon catheter (Fig 1). Currently, the most commonly used IABP catheter in the United States has two markers, one proximal and one distal to the balloon (Fig 4). However, several variations often exist between the types and models of these two markers, even within a single manufacturer (Fig 6). Use of a dual-density marker improves determination of catheter directionality. As shown in Figure 7, two distinct densities can be observed within the distal tip marker, with slightly lower density at the more distal portion. In Figures 4 and 7, the larger, dual-density marker is on the distal end of the balloon, and we can know confidently that this balloon was placed via the femoral approach. If the dual-density marker in Figure 7 on this femoral-approach catheter were reversed, we would know that the tip had passed over the top of the arch into the ascending aorta, into an unacceptable position.

Figure 6:

Frontal chest phantom image with three different overlying intra-aortic balloon pump catheters from the same manufacturer, with distal markers in solid white circles and proximal markers in dashed white circles. There is no standard for markers. While all have two markers, which is not always the case, note that catheter 3 has proximal and distal markers that are very similar, while catheters 1 and 2 have a longer, dual-density distal marker.

Figure 7:

(A) Frontal chest radiograph depicts a well-positioned femoral-approach dual-density distal tip marker within the descending aorta. (B) The magnified insert accentuates the relatively lucent distalmost portion of the catheter marker and the adjacent, more proximal dense portion of the marker. From a femoral approach, if these portions of the marker were reversed, with the denser portion located cranial to the less dense portion, the catheter would be positioned in the ascending aorta. Knowledge of this dual-density distal marker is often helpful, as is later shown in Figure 14.

It is important for clinicians to be aware of all catheter types used at their institutions. The varying nature of the IABP catheter and its small radiopaque marker or markers, often radiographed among many other lines, tubes, devices, and clips and indistinct due to motion blurring, increases the possibility of overlooking its presence or misinterpreting its position (Fig 8). An ordering history that notes “IABP positioning” can help cue the radiologist to closely examine the radiograph. For example, the routine bedside intensive care unit chest radiograph commonly obtained in intubated patients excludes the upper abdomen and thereby usually excludes the additional caudal (ie, the second marker at the proximal aspect of the balloon) IABP catheter marker. At our institution, a bedside radiograph ordered with the indication to “evaluate IABP positioning” triggers a bedside acquisition that includes the abdomen, centered on the diaphragm (Fig 9). We have found this very helpful to visualize both markers and to allow for a more complete characterization of balloon positioning. This dedicated image with unique coverage of the chest and abdomen—in a stack of images from bedside chest radiography—also has the advantage of alerting the radiologist to the presence of an IABP catheter and associated markers.

Figure 8:

(A) Frontal chest radiograph demonstrates how the diminutive intra-aortic balloon pump (IABP) marker is often hard to resolve from the neighboring coronary bypass graft clips and other objects. (B) Same image with the IABP marker in the white circle.

Figure 9:

Two images in the same patient, with acquisition separated by several minutes. (A) Bedside frontal chest radiograph image of the chest and abdomen centered on the diaphragm to better visualize both markers on the intra-aortic balloon pump catheter placed via a femoral approach. The caudal marker (white dashed circle) is visible in the abdominal aorta, projecting over the L4 vertebral body. The position of this caudal marker suggests a low-lying catheter. (B) Interestingly, the frontal chest radiograph demonstrates how motion at time of image exposure in A can completely obscure the more cranial marker (white solid circle). As shown, it lies below the level of the carina (lower than expected) and accounts for the low-lying caudal marker observed in A.

Routes of Placement

Traditionally, IABP catheters are inserted via a femoral approach. However, off-label placement of catheters via an “upper” approach, through the subclavian, axillary, or brachial artery, has been pursued to provide sustained mechanical support for patients awaiting heart transplantation (11,12). We have found that this route of placement often goes unrecognized by the radiologist. Placement via an upper route may improve mobility and enable physical strengthening of patients as they await heart transplantation. In the United States, the presence of an endovascular support device such as an IABP increases the patient's priority for donor heart allocation (13).

We term the upper-approach placement as axillary, in keeping with the naming and placement employed by the interventionalists at our institution, though others may percutaneously or surgically access the subclavian or brachial arteries. It is important that radiologists be familiar with this placement route if their institution has a heart transplantation program.

Regarding the use of radiopaque markers on an axillary-approach catheter, a single distal marker would be difficult to detect at routine bedside chest radiography, as it would project over the midabdominal aorta (Fig 10), often below the included field of view. As a result, evaluation of its positioning relative to the aortic arch would be impossible. A dual-marker catheter is therefore necessary. Moreover, the interpreter of the image must recognize this difference in approach, as the proximal marker of the catheter will now be positioned at the proximal descending thoracic aorta, below the aortic knob. Although we continue to define these markers on the basis of their placement relative to the catheter tip (distal) and hub (proximal), this terminology may be confusing depending on the route of access; therefore, we recommend that radiologists routinely state the catheter placement route (ie, femoral or axillary) and refer to the markers as cranial (projecting below the aortic knob) and caudal (projecting over the mid aorta) (Fig 11). In certain cases, a sheath may be visualized in the region of the axilla, confirming the axillary route of placement (Fig 11D).

Figure 10:

Diagram of axillary-approach catheter with the distal balloon marker projecting over the mid aorta. If a single-marker catheter is employed by this approach, the balloon positioning cannot be verified on a radiograph. (Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.)

Figure 11:

Marker positions for (A, B) femoral and (C, D) upper- (axillary-) approach intra-aortic balloon pump catheters. The distalmost tips are marked with solid white circles and proximal markers with dashed white circles in B and D. Note that in A and B, the cranial marker represents the distal tip of the catheter in A and B and the proximal tip in C and D. The balloons are appropriately positioned in both frontal radiographs. An access sheath (white arrows in D) is often seen with the axillary approach. (Fig 11A and C used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.)

Cases of Catheter Malposition

Despite the use of upper-approach IABP catheters at our institution for several years, we have come across common pitfalls when evaluating catheter positioning because of incomplete understanding of this approach and lack of recognition of the markers on the IABP catheters used at our center.

Four illustrative image sets (Figs 12–15) are included. In all cases, multiple radiologists reviewing multiple radiographs overlooked or misinterpreted important findings regarding the IABP catheters.

Figure 12:

Images in a 44-year-old man with heart failure. (A) Initial frontal chest radiograph demonstrates the proximal marker from an axillary-placed intra-aortic balloon pump (IABP) catheter (dashed white circle), originally thought to be a clip. This presumed “clip” projects above the aortic arch. The presence of an IABP catheter was not recognized by multiple radiologists for several days, even after more proximal migration of the proximal marker into the left axillary artery on (B) the follow-up radiograph. On close inspection, the follow-up radiograph demonstrates a high distal marker (solid white circle), a high proximal marker (dashed white circle), a faint axillary sheath (white arrows), and an inflated balloon projecting through the arch (white arrowheads).

Figure 15:

Images in a 38-year-old woman with heart failure. (A, B) Frontal chest radiographs that emphasize the directional nature of the distal marker (solid white circle). (A) The axillary-placed catheter distal tip is in the expected position, with the more lucent radiopaque portion distalmost. (B) The catheter tip has folded back on itself, with the densest portion of the distal marker now distal. Note that the distance between the distal and proximal (dashed white circle) markers has shortened. (C) Oblique coronal slab CT image with arterial phase contrast enhancement demonstrates the distal tip flipped back upon itself (curved white arrow). The metal tip should project distal to the balloon (at the base of the white arrow), not along the periphery of the distal balloon. The left axillary sheath is also marked with white arrows in B.

Case 1

Figure 12A demonstrates the high position of an axillary-approach catheter. Several days later, this balloon is now in the much smaller left subclavian artery (Fig 12B). This example highlights the importance of being vigilant, as multiple signs point to malposition. The cranial marker was thought to represent a clip, and the chest radiograph initially did not include the abdomen or the more caudal marker. Additionally, the axillary sheath and inflated balloon in Figure 12B were not recognized.

Case 2

Figure 13 demonstrates the complexity of determining the position of the simple IABP catheter if the route of placement and catheter markers are not understood. In Figure 13A, the dual-density marker projects over the proximal descending thoracic aorta in the expected position of a femoral-approach catheter. Note that the orientation of the distal marker dual-density tip is that of an axillary approach. The dual-density marker is flipped, and the neighboring metal density initially interpreted as a clip (dashed circle) is too close to the cranial marker, though it represents the radiopaque marker at the proximal aspect of the catheter. As shown in the Table, IABP catheter balloons range in size from 13.9 to 17.4 cm. Only 3 to 4 cm separates these markers. An axillary sheath can also be seen in Figure 13A.

Figure 13:

Images in a 66-year-old man with heart failure. (A) Frontal chest radiograph that was initially labeled as “normal, with tip projecting over the arch.” While this was technically correct, the radiologist did not recognize that this was an axillary-approach catheter with a dual-marker distal tip (solid white circle) and a second proximal marker (white dashed circle). Had this been a femoral-approach catheter, the distal dual marker would project over the ascending aorta (note the more lucent part of the marker that is distalmost on the catheter is reversed from that expected for a femoral-approach tip in the descending aorta). Also, the proximal marker of the catheter projects over the proximal arch. The distance between the markers is only several centimeters, so clearly the catheter is folded upon itself. This distal marker should be at or off the inferior margin of view for a correct axillary-approach placement. A sheath (white arrows) can be seen overlying the left axilla. (B) Oblique sagittal unenhanced average intensity projection chest CT image demonstrates abnormal positioning of the balloon (dashed white line).

Case 3

The catheter shown in Figure 14 has a dual marker that lacks the dual density of the distal marker (unlike Fig 13), though in this case, the distal balloon catheter marker is slightly larger than the proximal marker. As such, this catheter could be interpreted as low, projecting over the descending aorta at the mid sternum, with the smaller clip thought to represent a mediastinal clip. While lack of a dual-density marker limits the radiologists’ understanding of the catheter placement method, catheter malposition is indicated by presence of the balloon in the arch (Fig 14A).

Figure 14:

Images in an 80-year-old woman with heart failure. Frontal chest radiographs depict a misplaced catheter. (A) The inflated balloon (white arrowhead) during diastole and (B) the deflated balloon during systole confirm the balloon's presence in the arch, which was placed via an axillary approach. The high distal markers (solid white circle), low proximal markers (dashed white circle), and short distance between the markers further confirm the abnormal position of the balloon.

Case 4

Figure 15 demonstrates a finding that we have noted several times. After axillary approach, the cranial marker projects over the proximal descending aorta, as expected. The caudal marker projects over the mid aorta. Note, over time, that the directional distal (ie, caudal) marker has flipped. This was confirmed at CT (Fig 15C). The balloon was not flipped, but rather, the rigid distal tip with its marker was bent back upon itself. We believe this is due to Venturi effect and observed its occurrence in several different patients. We have not witnessed this event since downsizing to a shorter balloon with less volume. This catheter was removed to minimize potential future complications from the bent device.

Conclusion

Understanding of, and close attention to, IABP catheter markers and route of placement is necessary to ensure appropriate positioning.