Lawrence Ang, MD, FSCAI; Debabrata Mukherjee, MD, MS, FSCAI; and Konstantinos Boudoulas, MD, FSCAI

Using rotating single-element intravascular ultrasound (IVUS) catheters for coronary artery imaging offers several technical advantages, including a higher image resolution due to the higher frequencies and larger effective aperture size, as compared to a nonrotating phased-array IVUS catheter¹ (see Table 1). However, these catheters may be less commonly used in clinical practice² due to more cumbersome catheter assembly and flushing requirements before use. Instructions for use of rotating IVUS catheters^3-4 indicate that these devices should be flushed with heparinized saline until all air bubbles are expressed from the interior of the catheter within the clear distal shaft, as this provides the acoustic coupling media required for ultrasonic imaging. Warnings advise that air entrapped in the catheter and flushing accessories can cause potential injury or death, since expression of air from an IVUS catheter positioned within the coronary artery can cause a problematic air embolism. In this Tip of the Month, we present a simple and effective technique and tips for operators to ensure a completely flushed rotational IVUS catheter before use.

Standard Catheter Flushing Technique^3-4

1. Retract the movable inner-imaging core to the full proximal position within the outer telescope shaft (see Figure 1A).
2. Flush the inner core twice continuously using a 3 ml flushing syringe attached to the flush port or until all bubbles are visibly expressed from the interior of the catheter within the clear distal shaft. Avoid flushing with excessive pressure.
3. Advance the imaging core to the full distal position (see Figure 1B).
4. Examine the imaging core within the clear distal shaft to ensure no air is in the system. If air is present, retract, reflush, readvance, and recheck the imaging core.
5. Initiate imaging to ensure proper function of the catheter by observing a pattern of bright concentric rings on the monitor (see Figure 2).

Tips for the Catheter Flushing Technique With Real-Time Imaging

1. Due to residual entrapped air that frequently occurs despite careful adherence to the standard catheter flushing technique, perform additional maneuvers to ensure complete IVUS catheter flushing.
2. After the completion of standard flushing, manually submerge the catheter tip and contained imaging core within a bowl of saline and maintain the imaging core in close proximity (within a 5 mm distance) to the wall of the bowl. Simultaneous flushing of the IVUS catheter and real-time imaging of the bowl wall should produce a sharply defined white (echogenic) line.
3. Confirm the presence of residual air being actively purged from the IVUS catheter by A) visible microbubbles and B) multiple transient air bubble artifacts (with the appearance of imaging “sparkling” due to rapid alternation between normal versus dark/dull artifact images) during real-time imaging.
4. Ensure the complete clearing of the IVUS catheter when the bowl wall maintains a sharply defined echogenic appearance during sustained catheter flushing without production of additional microbubbles or air artifacts (see Figure 3).

Conclusion

The optimal and safe use of high-resolution rotational IVUS catheters can be hindered by incomplete device flushing and removal of air from the imaging element and distal catheter shaft. Using a simple and effective catheter flushing technique with real-time imaging to ensure high-quality imaging and the elimination of microbubbles can help operators optimally prepare rotational IVUS devices for safe and successful use during their procedures.

Table 1. Comparison of rotating and nonrotating IVUS catheter characteristics.¹

1. Boston Scientific, Marlborough, MA
2. Philips Volcano, San Diego, CA
3. Infraredx, Bedford, MA
4. ACIST Medical, Eden Prairie, MN

Figure 1. Demonstration of rotational IVUS inner catheter full retraction (A) and full advancement (B) when performing flushing and removing entrapped air prior to use.

Figure 2. During standard flushing of a rotational IVUS catheter (A), initial imaging demonstrates poor visualization of the catheter shaft prior to flushing (B), followed by clear visualization of bright concentric rings after complete flushing and removal of air (C).

Figure 3. Deairing of a rotational IVUS catheter is confirmed by using real-time imaging while the imaging element is submerged in a bowl of saline (A). Initial imaging produces a dark/dull appearance of the bowl wall due to air artifacts before flushing (B), followed by the consistent appearance of a bright and sharply defined bowl wall after complete flushing and removal of air (C).

References

1. Peng C, Wu H, Kim S, et al. Recent Advances in Transducers for Intravascular Ultrasound (IVUS) Imaging. Sensors (Basel). 2021 May; 21(10): 3540.
2. Millennium Research Group. U.S. Market Track Internal Sales Data. On file with Philips Volcano.
3. Philips Refinity Short-tip rotational IVUS catheter. Brochure. https://www.documents.philips.com/assets/20180612/12c4e10490bc40a18458a8fd015a7482.pdf.
4. Boston Scientific. OptiCross™ HD and OptiCross™ 6 HD 60 MHz Coronary Imaging Catheters. https://www.bostonscientific.com/content/dam/elabeling/ic/50726168-01A_OptiCross_HD_6HD_eDFU_en-USA_s.pdf.
5. Makoto™ Intravascular Imaging System. Brochure. https://www.infraredx.com/wp-content/uploads/2020/08/IFX022-JAPAN_BROCHURE_2018.pdf.
6. ACIST HDi^â High-definition IVUS System. Brochure. https://acist.com/wp-content/uploads/2021/02/Kodama_SpecSheet_EN.pdf.
7. Philips Eagle Eye Platinum RX digital IVUS catheter. Brochure. https://www.documents.philips.com/assets/20180620/bbbcb433187247fb8085a905011e4a74.pdf.