TECHNICAL REQUIREMENTS

High-quality coronary angiography requires excellent quality fluoroscopic and digital imaging and a C-arm capable of three-dimensional rotation. These may be either single plane or biplane. Biplane laboratories are most useful for pediatric angiography and studies where simultaneous biplane fluoroscopy is needed (e.g., electrophysiologic studies). The x-ray tube must have a high heat capacity and small and large focal spots so that large patients can be imaged. Digital image receptors should have multiple magnification modes so that the entire heart can be imaged with a large field of view, and the coronary arteries can be imaged with a smaller field of view at higher spatial resolution. The use of higher magnification modes requires more panning (table movement during angiography) and higher radiation dose. As in static image systems, a grid is placed on the face of the image intensifier to reduce the effect of scatter radiation on the radiographic image. Coronary cineangiograms are typically recorded at 15 frames/sec, 30 frames/sec, or 60 frames/sec depending on the indication for the study.

In the past, images were recorded on 35-mm cine film and viewed on a cine projector. Today, catheterization laboratories use digital recording with viewing on a computer monitor. Although the spatial resolution of cine film is higher, digital recording is so much more convenient that it has become the standard. Digital recording does not require film processing with its inherent requirements for quality control, and the storage space required for cine film and the cost of cine film are enormous compared with digital media storage and cost.

TECHNIQUE

TECHNIQUE DESCRIPTION

Coronary angiography is almost always performed via puncture of a femoral artery (Judkins’ technique). In a few patients, a brachial artery cutdown is performed (Sones’ technique). Coronary catheters used for Judkins’ technique are preshaped and come in various sizes to make selective cannulation of the left and right coronary arteries simple in most patients. So-called multipurpose catheters are occasionally used and can be directed into either coronary ostium, although with slightly more difficulty. The coronaries must be selectively engaged to obtain diagnostic quality studies with a minimum amount of contrast material.

When performing coronary angiography, the goal is to show optimally each part of each artery in at least two, preferentially orthogonal, projections, free of overlap with other vessels and free of foreshortening. This imaging requires a great deal of attention to radiographic and angiographic technique. Radiographic factors that contribute to the quality of the angiograms include the following:

Angiographic factors include the following:

ANGIOGRAPHIC VIEWS

Various angiographic projections are used to achieve the goal of viewing each coronary segment in at least two projections, free of foreshortening and free of overlap with other vessels. This goal was impossible before the advent of C-arms capable of triaxial motion. With modern equipment, angiographic views are limited only by physical impingement of the x-ray tube or image receptor on the patient or table, and the patient’s body habitus. In addition to rotation in the axial plane (generally from about 45 degrees right anterior oblique [RAO] to left lateral), the image receptor must be positioned over the patient’s shoulder to produce cranially angulated views and over the hip to produce caudally angulated views to image many coronary artery segments adequately. Cranial or caudal angulation is usually limited to about 25 degrees in most patients.

In most patients, the right coronary artery is best imaged with a combination of left lateral, cranial left anterior oblique (Cr-LAO), RAO, and Cr-RAO views. Although not used by many cardiologists, the lateral view (Fig. 7-1) has several advantages over a standard 60-degree LAO view because it usually allows better visualization of the mid right coronary artery and collaterals to the left anterior descending artery (LAD). The Cr-LAO view is necessary to lay out the posterior descending artery and posterolateral branches arising from the right coronary artery beyond the posterior descending artery (Fig. 7-2). In patients with large posterolateral branches, the Cr-RAO view projects the posterior descending artery and posterolateral branches clear of each other (Fig. 7-3). Usually, one should not use the Cr-RAO view to the exclusion of the RAO view (Fig. 7-4); however, because the body of the right coronary artery is foreshortened in the Cr-RAO view.

In the average patient, the left main coronary artery is projected at true length in either a posteroanterior or a shallow LAO view (Fig. 7-5). The bifurcation and proximal portions of the LAD and left circumflex artery are usually best seen in the Cr-LAO¹ (Fig. 7-6) and RAO projections. Enough LAO rotation should be used to place the distal LAD between the spine and the diaphragm. In some individuals, the left main coronary artery has an up-going course. This requires using caudal angulation to eliminate foreshortening. The caudal LAO² view is the only angiographic view that should be performed with the patient holding his or her breath in expiration (Fig. 7-7). If the patient inspires, the effect of the caudal angulation is negated; this is most common in large patients and requires more exposure than nonangulated views resulting in a degraded image. Because the distal LAD frequently is superimposed on the diaphragm in the Cr-LAO view, a lateral view is often useful (Fig. 7-8).

At least two RAO views should be obtained in almost all patients. Because the proximal portion of the left circumflex artery curves posteriorly, one must use caudal angulation³ to visualize it and the origins of any proximally arising obtuse marginal branches adequately (Fig. 7-9). With regard to the LAD, the diagonal branches frequently are superimposed on the LAD in the straight RAO view, so cranial angulation of 20 to 25 degrees may be useful (Fig. 7-10).⁴ The straight RAO view can be added if the distal LAD is poorly visualized in the other RAO views (Fig. 7-11).

PITFALLS AND SOLUTIONS

Coronary angiography has many advantages over CT angiography and MR angiography of the coronary arteries. Spatial resolution and temporal resolution are superior to CT angiography and MR angiography. High spatial resolution allows one to visualize submillimeter vessels and narrower arterial lumens. High temporal resolution allows for evaluation of arterial filling patterns such as delay in flow, a valuable indicator of severe stenosis, and for assessment of collateral filling of obstructed arteries. Coronary angiography has several disadvantages, however, including the need for arterial puncture and direct cannulation of the coronary ostia, and the fact that the number of views is limited by radiation and contrast dose considerations. Because of limited views, one does not have the ability to look at the arteries from any angle, as one can with coronary CT angiography. Also, similar to all planar angiograms, coronary angiograms are luminograms—one cannot see the wall of the vessel, only the contrast-filled lumen. This becomes important for reasons discussed subsequently.

IMAGE INTERPRETATION

Coronary atherosclerosis is a diffuse process with focal exacerbations.⁵ Despite this, the time-honored method of evaluating coronary narrowing is by determination of percent luminal diameter narrowing. This evaluation requires comparing a region of narrowing with that of an adjacent vessel segment that appears to be relatively normal. The normal or reference region may be diffusely narrowed, resulting in underestimation of the degree of stenosis. If there is calcium in the wall of the coronary artery, one may be able to determine the actual diameter of the vessel at that point (Fig. 7-12); however, one still would not know whether that is the true size of the vessel before it became diseased because it may be dilated (see later). Coronary stenoses are rarely concentric, and the severity of narrowing may vary widely in different projections (Fig. 7-13). Some angiographers have tried to circumvent these limitations by calculating percent area narrowing; this still usually requires the assumption that the lesion is concentric, and in my opinion only adds another layer of imprecision to the assessment.

Generally, luminal diameter narrowing of 50% or greater is considered likely to be hemodynamically significant. Resistance through a stenosis is a function of many variables, however, including length and morphology—so this is only a crude gauge, similar to using a cardiothoracic ratio of 50% to identify cardiomegaly on a chest radiograph. Finally, unless one uses some type of caliper, there is a marked tendency to overestimate visually the severity of narrowing; this has been jokingly referred to as the “oculostenotic reflex,” but is a very real phenomenon. For these reasons, one should not rely solely on the angiographic appearance of a lesion in determining therapy.

Coronary narrowing can be broadly characterized as either discrete or diffuse. We know that atherosclerosis tends to be a diffuse process with focal exacerbations, so when we use the term discrete, it should be understood that we are accepting the limitations of angiography for characterizing lesions. Discrete stenoses (Fig. 7-14) tend to occur in the proximal portions of the epicardial coronary arteries. They may have noncalcified (soft) plaque, calcified (hard) plaque, or a mixture of the two. Soft plaque is less stable than hard plaque and accounts for most acute coronary occlusions. Patients with mostly hard plaque are more likely to present with chronic angina. Angiography does a poor job of distinguishing between the two.

Diffuse narrowing is less commonly identified at angiography because of its inability to image the vessel wall. The narrowing may appear to involve only a relatively short distance (Fig. 7-15) or most of a vessel (Fig. 7-16). In the latter case, one may be unable to give an estimate of percent diameter narrowing. As mentioned previously, diffuse narrowing can cause underestimation of the severity of the relatively discrete stenoses occurring either within the diffusely narrowed area or on either end of it. The ability to see the wall of the coronary artery is one of the great advantages of coronary CT angiography compared with conventional coronary angiography.

In addition to narrowing, atherosclerosis can cause coronary artery enlargement. This enlargement can result from the dilation caused by early remodeling or from atherosclerotic ectasia. With ectasia, the area of dilation may be focal (Fig. 7-17) or diffuse (Fig. 7-18). In either case, it may harbor thrombus. Another problem caused by coronary dilation is that if the chosen reference segment is actually dilated rather than normal, the reference diameter may be greater than in the predisease state, and can result in overestimation of the severity of narrowing.

Coronary artery dissection can occur spontaneously or as the result of catheter-induced trauma or balloon angioplasty. The findings are similar to findings seen in aortic dissection with an intimal flap within the coronary lumen (Fig. 7-19). In some cases, the coronary artery may occlude, making the identification of dissection difficult in spontaneous cases.

Coronary thrombosis typically results from rupture of soft plaque, although it may be seen during coronary intervention and rarely in other circumstances, such as coronary artery compression by a mass or enlarged pulmonary artery. The clot may result in a filling defect within the lumen (Fig. 7-20) or an abrupt occlusion with a concave-appearing proximal border (Fig. 7-21).

Emboli to the coronary arteries are rare, and may be difficult to detect angiographically. A typical appearance would be that of an abrupt occlusion with a convex proximal border identical to that of a thrombus.

Evaluation of collateral flow to a diseased coronary artery is straightforward at angiography and difficult to impossible with coronary CT angiography. Collateral vessels typically are a consequence of slowly developing coronary artery stenosis, but can also be seen more immediately. Intracoronary collaterals directly bridge an obstructed coronary artery segment (Fig. 7-22). Intercoronary collateral vessels connect branches of different coronary arteries or branches of the occluded artery. The myriad intercoronary collateral pathways can seem confusing sometimes, but visualization is easier if one realizes that the connections must be made through shared myocardium. Collateral vessels do not course through the middle of chambers or usually cross another coronary artery. Collateral vessels are typically quite tortuous, but may look almost like a normal coronary artery. Common intercoronary collateral pathways are listed in Table 7-1 and shown in Figures 7-23 through 7-28.

TABLE 7-1 Common Coronary Collateral Pathways

LAD to RCA	LAD to PDA around the apex (see Fig. 7-23)
	LAD to acute marginals over RV free wall (see Fig. 7-24) through the interventricular septum (see Fig. 7-25) Conus artery to LAD

LCx to RCA Distal circumflex to distal RCA (AV groove artery) (see Fig. 7-26)   Obtuse marginals to posterolateral branches (see Fig. 7-27) RCA to RCA SA node to AV node through the atrial septum   Conus artery to acute marginal   Acute marginal to PDA LAD to LCx Diagonal to obtuse marginal (see Fig. 7-28)   LAD to obtuse marginal at apex LCx to LCx Left atrial circumflex artery   Obtuse marginal to obtuse marginal LAD to LAD Septal perforators   Diagonal to diagonal

AV, atrioventricular; LAD, left anterior descending artery; LCx, left circumflex artery; PDA, posterior descending artery; RCA, right coronary artery; RV, right ventricular; SA, sinoatrial.