A 68-year-old man with atrial fibrillation presented for elective pulmonary vein isolation via cryoablation. He underwent general anesthesia and transesophageal echocardiography probe placement (IE33 X7-2t xMATRIX array probe connected to a Philips CX50 ultrasound system, Philips Healthcare, Andover, MA) for assessment of left atrial appendage thrombus and guidance of interatrial septal puncture for placement of a left atrial ablation catheter. While assessing the interatrial septum for a patent foramen ovale using color-flow Doppler, the electrophysiologist passed a superstiff 0.032-inch guidewire (St. Jude Medical, St. Paul, MN) from the right femoral vein through the right atrium into the superior vena cava to position the transseptal guiding introducer (St. Jude Medical). During this time, the echocardiographer identified the sudden appearance of a high-velocity, left-to-right flow pattern (Fig. 1; Supplemental Digital Content, Videos 1 and 2, http://links.lww.com/AA/B84, http://links.lww.com/AA/B85). This flow seemed to originate from the interatrial septum, although a patent foramen ovale by color-flow Doppler had not been previously identified. Further interrogation of the interatrial septum in different echocardiographic planes revealed no defect but intermittent identification of a twinkling artifact. The twinkling artifact demonstrated brilliant rapid alternating hues with a flame-like appearance, just distal to the location of the guidewire. Increasing the Nyquist limit did not appear to significantly diminish this artifact. Removing the guidewire before positioning the transseptal guiding introducer in the fossa ovalis resulted in the disappearance of this artifact. An uneventful atrial septal puncture was performed and the introducer advanced into the left atrium.
The twinkling artifact is a complex phenomenon, and the mechanism is not completely understood. Some studies with kidney stones suggest that the twinkling artifact is caused by internal machine noise or phase jitter,1 whereas other studies suggest that microbubbles on the surface of the object cause this artifact.2 Phase (or clock) jitter is caused by the slight random time fluctuations in the digital clock that synchronize the firing of the ultrasound pulse transmissions. These slight variations in firing of the ultrasound pulses result in variation in path length of transmitted and reflected ultrasound waves, which are interpreted by the ultrasound machine as a Doppler shift and therefore depicted as color Doppler flow even if there is no true motion.1 Rougher surfaces also appear to enhance this artifact, and this may be because rougher surfaces potentially harbor more microbubbles and therefore accentuate the artifact.1–3 Several machine settings affect the appearance of the twinkling artifact, including color-write priority, gray-scale gain, color Doppler frequency, and color Doppler gain.1 Color-write priority determines whether a pixel is depicted as color or as gray scale. Increasing the color-write priority causes more color information to be displayed and thus enhances the twinkling artifact.4 However, increasing gray-scale gain will reduce the size of the twinkling artifact. Decreasing color Doppler frequency and increasing color Doppler gain are expected to increase the appearance of the twinkling artifact.5
To determine whether this artifact could be reproduced with a different guidewire and transducer, we suspended a Cordis guidewire (Johnson and Johnson, New Brunswick, NJ) in a water bath and assessed color-flow Doppler with a Philips L15-7io broadband compact linear array transducer connected to a Philips CX50 ultrasound system. The twinkling artifact was reproduced in the water bath (Fig. 2), suggesting that the twinkling artifact could also potentially occur during central venous cannulation when a linear array transducer is used with this ultrasound machine. We do not know whether all guidewires will produce this artifact.
This artifact has been described in areas where significant calcification occurs most commonly with urinary calculi, but also with cardiac valves, implantable surgical mesh used in herniorrhaphy, gallstones and pancreatic stones as well as shrapnel from penetrating trauma.5–7 The twinkling artifact is often helpful in these situations in which gray-scale imaging does not provide adequate information for a conclusive diagnosis.5 In our patient, the twinkling artifact most likely occurred as a result of placement of the guidewire in the right atrium that acted as a hyperechoic reflective surface. The twinkling artifact in this patient could potentially be misinterpreted as an atrial septal defect with left-to-right shunting. The additional use of spectral Doppler can help distinguish between the twinkling artifact and a true shunt because no spectral Doppler flow should be seen with the twinkling artifact.4 The twinkling artifact must also be differentiated from other color Doppler flow artifacts (Table 1), including aliasing (color reversal when Nyquist limit is exceeded), ghosting (color signal that bleeds into the tissue area of the image), flash artifact (sudden movement of the transducer producing Doppler shift that fills the entire color box with color), and excessive color Doppler gain (mosaic distribution of color signals throughout the color box). The twinkling artifact should be easy to recognize any time color-flow Doppler is used in the presence of a guidewire because of the characteristic flow pattern distal to the guidewire, the transient nature of the artifact, and absence of spectral Doppler flow.4
Because of the increasing demand for transesophageal echocardiography in the interventional cardiology and electrophysiology laboratories, it is important for the echocardiographer to be aware of potential pitfalls and artifacts with the hyperechoic guidewires being used for these procedures. Particularly, problems may arise with atrial septal defect and patent foramen ovale closures where twinkling artifact may be misinterpreted as a persistent shunt resulting in potential patient morbidity from further attempts at positioning.
Clinician’s Key Teaching Points
By Massimiliano Meineri, MD, Roman M. Sniecinski, MD, and Martin J. London, MD
- Twinkling artifact presents with a flame-like appearance of rapid alternating hues of color on color-flow Doppler. It was first described with imaging of renal stones or herniorrhaphy mesh, structures that have rough surfaces. It is potentially problematic because it resembles color-flow aliasing and thus can be confused with a high-velocity jet.
- Twinkling artifact is a complex phenomenon. It is partially explained by internal sonograph noise and unintentional variation in firing of ultrasound pulses. These minor variations in timing are processed as a Doppler shift despite absence of actual blood flow. Changing the Nyquist limit does not alter twinkling artifact, but increasing Doppler frequency and decreasing Doppler gain may help minimize it. Lack of a flow velocity envelope on spectral Doppler should help clarify the signal as artifact.
- In this case, twinkling artifact was appreciated on transesophageal echocardiography during percutaneous atrial cryoablation. High-velocity left-to-right flow was initially recorded on color-flow Doppler in the right atrium along the path of a stiff metallic wire next to the interatrial septum. This raised the possibility of a patent foramen ovale. However, the color-flow Doppler signal disappeared immediately after the wire was removed.
- Given the increasing use of transesophageal echocardiography in percutaneous catheterization laboratory procedures, echocardiographers should be aware of the twinkling artifact to avoid misinterpretation of intracardiac shunts and regurgitant jets.
Name: Jeremy M. Bennett, MD.
Contribution: This author drafted the manuscript.
Attestation: Jeremy M. Bennett approved the final manuscript.
Name: Juan C. Estrada, MD, MPH.
Contribution: This author made critical revisions to the manuscript.
Attestation: Juan C. Estrada approved the final manuscript.
Name: Moore Benjamin Shoemaker, MD.
Contribution: This author made critical revisions to the manuscript.
Attestation: Moore Benjamin Shoemaker approved the final manuscript.
Name: Mias Pretorius, MBChB, MSCI.
Contribution: This author obtained the ultrasound images and made critical revisions to the manuscript.
Attestation: Mias Pretorius approved the final manuscript and is the archival author.
This manuscript was handled by: Martin J. London, MD.
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