How many times have we heard in the lab, “What do you think of this lesion? Should we stent it? I don’t know, let’s take another view. Hey, Bob, what do you think?” And so it goes for another 5-10 minutes, 50 or more mLs of contrast and only one view, which may show a marginally more narrowed lumen diameter, if the operator or cath lab crew squint their eyes. I’ve done this and at times, I struggle. Admittedly, my bias, held for many years, is that I do not think the angiogram does its job as well as we need it to. Why, then, do we have such difficulty judging the severity of some lesions from the angiogram? How precise is the assessment if we need so many views to decide? Is the worst single view representative of the clinical importance of the narrowing? This problem also applies to computerized tomographic angiography (CTA), as well standard cineangiograms. CTA, however, will be the imaging modality of choice to view the pathways of the coronary arteries in three dimensions, but not necessarily the shape and severity of individual lesions. It is well known that many angulated radiographic views are routinely needed to get an appreciation of the luminal narrowing in several perpendicular projections, a reliable and necessary practice. Some lesions are especially difficult to image. Visualizing lesions at the ostium of the left main or RCA or major branch ostial narrowings is difficult, if not impossible at times, because there are no planes perpendicular to the origin take-off angle (see Figure 1). Lesions which are heavily calcified, partially thrombosed, complex or involved with overlapping branches may have no projection which reveals the true lumen diameter (Figure 2). Some intermediately severe lesions will always remain intermediate in all views. Lesions inside stented segments are very difficult to image well. For a lesion we cannot see well enough to gauge its clinical importance, additional information is needed. Overcoming the limitations of angiography is the reason ischemic stress testing, pressure wire fractional flow reserve (physiologic measures of lesion severity) and intravascular ultrasound imaging (IVUS, anatomic assessment of lesion severity) were developed. If the angiogram did its job in every case, we would not need these tools. Now, here’s the hardest part of lesion assessment. The old saw says, Seeing is believing. How can a lesion that looks severe in one (and perhaps only one) view not be hemodynamically significant, and vice versa? The reason is simple. Such lesions are elliptically shaped (Figure 1). Look at an example of an eccentric left main narrowing. One view is severe (Figure 3A); the orthogonal view (Figure 3B) shows the vessel to be minimally narrowed. Is this a significant left main (LM) narrowing? The fractional flow reserve (FFR) was 0.94. IVUS showed a heavily calcified oval-shaped ring, narrowed in the short axis and wide across the long axis (Figure 3C) with cross-sectional area >7mm2. Because the angiogram is so integral to cardiologic diagnosis, its accuracy is often unquestioned, justifiably so for most situations. A severe lesion or minimal lesion is easily and accurately diagnosed, with the angiogram being a highly reliable modality. But in many situations, such as the LM described above, some angiographers have difficulty in not believing their own eyes with the one and only one view that they see, showing a moderate to severe narrowing(Figure 1). Modern cath labs have IVUS and/or pressure wires to address the unknowns of the angiogram. The indications and the use of these angiographic adjunctive imaging modalities are described in the American Heart Association/ American College of Cardiology/ Society of Cardiovascular Angiography & Interventions Percutaneous Coronary Intervention guidelines (http://www.acc.org/clinical/guidelines/percutaneous/update/index.pdf.) and will likely be a future topic in this column. For now, the greatest hurdle to overcome when gauging lesion severity is deciding whether the angiogram has fulfilled its job. If the operator questions this or is uncertain, then there is strong justification for proceeding with additional testing, either in the lab with IVUS or FFR, or out of the lab with ischemic perfusion/functional imaging. How can the lab become facile with these helpful tools? The first step is to understand the concepts of lesion eccentricity, branch overlap, angulation and how best to show critical imaging points, and whether a lesion is well-defined. Next, become adept at setting up and using IVUS and pressure sensor guidewires. Extra time in the lab and delay during the procedure kills the enthusiasm for using these tools. Have the consoles ready with their connector plugs. Have the IVUS catheters or pressure wires stocked and readily available. Have the adenosine handy when FFR is called for. Don’t forget to heparinize before introducing guidewires. Have a team leader identified to help your colleagues set up, trouble-shoot and get the needed information to make the accurate and important decision for your patient. In angiography, seeing is not always believing, but we don’t have to be blind to what’s really happening.
Would you like to hear Dr. Kern in person? Join us at the Cath Lab Basics course, August 19th, 2006 in New Brunswick, NJ. More information is available at www.naccme.com