Contrast Media Injection Techniques—Power Versus Hand Injection

Contrast medium, a viscous, iodinated solution used to opacify the coronary arteries, can be injected by hand through a multivalve manifold. The tip of the syringe is kept pointed down (handle raised up) so that any small bubbles float up and are not injected into the circulatory system (Fig. 4-1). Flow rates are usually 2 to 4 ml/sec with volumes of 2 to 6 ml in the right coronary artery (RCA) and 7 to 10 ml in the left coronary artery (LCA). Hand injection has been used successfully for many years. The use of disposable manifolds, syringes, and tubing is cost effective and safe.

Figure 4-1 Pioneer Dr. Gensini performing coronary angiography. Note the raised angle (30 degrees) of the injection syringe to keep out air bubbles.

(From Gensini GG: Coronary angiography, Mount Kisco, NY, 1975, Futura.)

Power injection of the coronary arteries has been used in thousands of cases in many laboratories and is as safe as hand injection. A power injector at a fixed setting might require several injections to find the optimal contrast delivery flow rate. Power injectors now incorporate hand controls, permitting precise operator touch-sensitive variable volume injectors (Acist; Bracco Diagnostics, Med-Rad, etc.), and a computer touch screen for precise contrast delivery settings (Fig. 4-2). The system is highly effective at opacification of arteries through small diameter catheters (<5 F). In addition it is also highly cost affective with the contrast reservoir. Typical settings for power injections are as follows:

Figure 4-2 Power injector (Bracco Diagnostics, Princeton NJ). A, Operator touch screen to select injection of coronary arteries or ventriculography. B, On the injector, large contrast bottle permits multiple patient studies because only the hand control and patient injection tubing are sterile and changed for each patient. The injection syringe with piston has several valves and bubble detectors used to prevent contamination and inadvertent air injection.

Angiographic View Setup Keys

“The best panning is no panning.” Panning motion often overshoots the image targets and information is lost. One key to accurate, optimal coronary cineangiography, obtaining the most information for the least amount of movement, is the initial setup of the catheter on the fluoroscope screen. Figure 4-3 shows the catheter–left main artery setup keys for left anterior oblique (LAO) views in the straight (anteroposterior [AP]), cranial, and caudally angled projections. When the patient is positioned correctly and the setup key followed, only minimal panning is necessary to obtain the information. In the LAO view the operator pans down the left anterior descending (LAD) artery then rightward to identify collaterals going to the right coronary artery (RCA). If the circumflex (CFX) is occluded, then leftward panning will include collaterals going to the distal CFX artery. For the RCA, in the LAO position, the operator pans downward and to the left toward the LAD artery. This will visualize late filling collaterals from the right coronary system to the LAD artery. These motions are diagrammed in Figure 4-3.

Figure 4-3 Setup keys for panning during coronary angiography. A, Right coronary artery (RCA). B, Left coronary artery (LCA). C, Lateral views. LAO, Left anterior oblique view; RAO, right anterior oblique view.

In the right anterior oblique (RAO) projections for the LCA and RCA, the operator pans downward to the apex to identify late filling, left-to-left or right-to-left collaterals. The initial setup keys for catheter tip position on the fluoroscope are summarized in Table 4-2, help the operator include all crucial information for coronary angiography.

Nomenclature of Angiographic Imaging Views

To obtain optimal information from coronary cineangiography, the operator must use various angulations, unveiling overlapped vessel segments. These views or projections highlight specific and distinct segments of the coronary anatomy and permit discrete visualization of underlying pathologic conditions. Understanding of the usefulness of various radiographic views (and nomenclature) is essential.

For all catheterization laboratories the x-ray source is under the table, and the image intensifier is directly above the patient. The source and image intensifier (also known as a flat panel detector in fully digital laboratories) are moving in opposite directions in an imaginary circle around the patient positioned in the center. The body surface of the patient which faces the observer, determines the specific view. This relationship holds true whether the patient is supine, standing, or rotated (Fig. 4-4).

Figure 4-4 Nomenclature for radiographic projections. The small black arrowheads show the direction of the x-ray beam. A, Anterior, posterior, lateral, and oblique. B, If the intensifier is tilted toward the feet of the patient, a caudal view is produced. If the intensifier is tilted toward the head of the patient, a cranial view is produced. C, Cranial (CR) and caudal (CA) oblique views.

(Redrawn from Paulin S: Cathet Cardiovasc Diagn 7:341-344, 1981.)

Cranial and caudal views are used to “open” overlapped coronary segments that are foreshortened or obscured in regular views. Note: Cranial views are best for the LAD artery; caudal views are best for the CFX arteries.

The rationale for these routine angiographic views is as follows. Tables 4-3 and 4-4 suggest best setup for visualizing the specific coronary artery.

Table 4-3 Recommended “Key” Angiographic Views for Specific Coronary Artery Segments

∗ Horizontal hearts.

Table 4-4 Routine Coronary Angiographic Views^∗

AP, Anteroposterior; LAD, left anterior descending artery; LAO, left anterior oblique; PDA, posterior descending artery (from right coronary artery); RAO, right anterior oblique.

∗ Note: The lateral view is a useful addition to these views for both coronary arteries. In addition, the four most common views for the left coronary artery when performed LAO cranial, RAO cranial, RAO caudal, and LAO caudal form a box around the patient. Look first at the LAD (cranial views) and then at the circumflex (caudal views). This box should be on every study with rare exceptions.

Left Coronary Artery

1. The AP caudal or shallow RAO view displays the left main coronary artery (LMCA) in its entire perpendicular length (Figs. 4-5, 4-6, 4-7, and 4-8). In this view, the proximal segments of the LAD and left CFX arteries are displayed, but the branches are overlapped. After the left main segment, slight RAO or LAO angulation may be necessary to clear the density of the vertebrae and the catheter shaft in the thoracic descending aorta from covering the artery.

2. The LAO-cranial view also shows the LMCA (slightly foreshortened), LAD, and its diagonal branches. Septal (coursing to the left) and diagonal branches (to the right) are separated clearly. The CFX artery and marginal branches are foreshortened and overlapped, although the posterolateral and posterior descending branches of left-dominant circulation are displayed clearly. Deep inspiration, which moves the density of the diaphragm down and out of the field, is helpful. The LAO angle (>30 degrees) should be set so that the LAD artery course is parallel to the spine and stays in the “lucent wedge” bordered by the spine on the medial edge and the curve of the diaphragm. Cranial angulation tilts the LMCA down and permits a view of the LAD/CFX bifurcation. LAO-cranial angulation that is too steep or inspiration that is too shallow produces considerable overlapping with the diaphragm and liver, degrading the image.

3. The RAO-caudal view shows the LMCA bifurcation, perpendicular to that of the LAO-cranial angle. The origin and course of the CFX/obtuse marginal branches, ramus intermedius branch, and proximal LAD segment are seen clearly. This view is one of the two best for visualization of the CFX artery. The LAD artery beyond the proximal segment is obscured by overlapped diagonals; however, the apical segment of the LAD artery is displayed clearly.

4. The RAO-cranial view is used to see the origins of the diagonals along the mid and distal LAD artery. Diagonal branch bifurcations are well visualized. The diagonal branches are projected upward. The proximal LAD and CFX usually are overlapped. Marginal branches may overlap, and the CFX artery is foreshortened, but posterolateral branches are well visualized.

5. The LAO-caudal view (“spider” view) shows the LMCA (foreshortened) and bifurcation of the LMCA into the CFX and LAD artery. Proximal and mid portions of the CFX artery are usually seen clearly with the origins of obtuse marginal branches. Poor image quality may be caused by overlapping of the diaphragm and spine. Good separation of the vessel is more difficult in vertically displaced hearts, such as in patients with chronic obstructive pulmonary disease, and more angulation is required to obtain an unobstructed view. The LAD artery is considerably foreshortened in this view.

6. A lateral view (image intensifier rotated 90 degrees, parallel with the floor) is the best view to show the mid and distal LAD artery. The LAD and CFX arteries are well separated. Diagonals are usually overlapped. The (ramus) intermedius branch course is well visualized. This view best shows insertions of bypass grafts into the mid LAD artery. Occasionally, slight caudal or cranial angulation is needed to visualize the segment of interest.

Figure 4-5 A to E, Left coronary artery. F to I, Right coronary artery. B, Left coronary artery, C and D, Left coronary artery. E, Left coronary artery. F, Right coronary artery. G and H, Right coronary artery. I, Right coronary artery. AP, Anteroposterior; LAD, left anterior descending artery; LAO, left anterior oblique; RAO, right anterior oblique.

(From Bertrand ME, editor: Coronary angiography, Lille, France, 1979, French Society of Cardiology.)

Figure 4-6 A, Angiography of left coronary artery. Top left, Left anterior oblique cranial; top right, right anterior oblique (RAO) cranial; bottom left, RAO caudal; note origin of diagonal branches; bottom right, left anterior descending (LAO) caudal. Note origin of circumflex artery (circumflex) from left main coronary artery (LM). B, Angiography of right coronary artery in LAO, cranial.

Figure 4-7 Diagrammatic views of left coronary arteries showing special positioning to observe branch segments. LAD, Left anterior descending coronary artery; LAO, left anterior oblique; LCX-OM, left circumflex–obtuse marginal branch; RAO, right anterior oblique. See text for details.

(From Boucher RA, et al: Cathet Cardiovasc Diagn 14:269-285, 1988.)

Figure 4-8 Frames from coronary angiograms in several standard view. A, Left coronary artery in left anterior oblique (LAO), cranial projection. B, LAO caudal projection. C, Right anterior oblique (RAO), caudal projection. D, RAO cranial projection. E, Right coronary artery in LAO, cranial projection. F, right coronary artery in RAO, straight projection.

Usefulness of Biplane Coronary Angiography

Simultaneous biplane cineangiography, although uncommonly used, provides accurate images from two different simultaneous points of view and is advantageous in performing complete coronary or ventriculography with reduced contrast volumes and radiation exposure. Biplane angiography helps to unravel complex coronary or structural cardiac anatomy (Table 4-5). Biplane angiography is most useful in the pediatric population and those patients with renal failure. Biplane is advocated in some adult interventional procedures like complex electrophysiologic mapping or novel structural heart disease implant device placements (e.g., ventricular septal defect (VSD) occluders).

Table 4-5 Biplane Coronary Angiography

The value of biplane information must be balanced against cost and difficulty of use. The traditional set up for biplane coronary angiography required the patient’s heart to be in the exact center of the two planes (the isocenter) and then the AP and lateral planes were angled in orthogonal projections (e.g., LAO-cranial and RAO-caudal, Fig. 4-9) This setup often resulted in more difficulties than it solved. Depending on the team, operator frustration increased with the perceived additional set up and procedure time needed to center the patient and repeat images that were lost when panning in one plane and out of the other. The potential savings of contrast media and radiation exposure were also lost when the two orthogonal planes were not perfectly positioned.

Figure 4-9 Diagrams of biplane angiographic C-arm orientations. A, Biplane C-arms in perpendicular anteroposterior (AP) and lateral starting configuration. B, Biplane C-arms rotated in opposing cranial/caudal, left anterior oblique (LAO)/right anterior oblique (RAO) angulations. Panning in one plane will move the heart out of the other plane. C, Biplane C-arms rotated in a concordant cranial orientation. Panning will keep images visible on both screens.

A novel setup makes biplane angiography simple, quick, and effective. The method uses concordant cranial or caudal imaging views such as cranially angled LAO/RAO projections and then moving both C-arms to caudally angled LAO/RAO projections (see Fig. 4-9). In this way, angiographic information is not lost when panning because the heart moves in a similar direction albeit from the opposite side (but not cranial versus caudal). With the concordant biplane setup, contrast use was halved, the radiation dose reduced, and the procedure time shortened.

Biplane coronary angiography has not been generally considered critical for routine studies. However, if the laboratory has biplane capability, it should consider improving procedure times, contrast use, and information quality. Some initial orientation is necessary to start biplane imaging. One should spend a minute finding true isocenter in two simple steps: (1) center the heart under the AP tube and (2) bring in the lateral tube and center the heart by raising or lowering the table. Next, the operator should position the planes LAO/RAO and then angle both tubes cranially. This can then proceed to moving both tubes to caudal projections (concordance of cranial/caudal angulations).

Biplane angiography may provide additional information documenting the true path of anomalous coronary arteries beyond single plane imaging. For example, Wang et al (Cathet Cardiovasc Intervent 42; 73-78, 1997) used the biplane images and confidently demonstrated the several potential courses of the anomalous Left main artery (the retroaortic course, intraarterial, and anterior looping or intraseptal courses). The levophase of the ascending aorta also provides a good view of the posterior aortic wall further assisting in determining the course of the coronary artery. Biplane was helpful to obtain the “dot and eye” assessment of the anomalous left main (LM) from the right sinus of Valsalva with fewer views required (see Serota et al).

Assessment of Coronary Stenoses

Assessment of the Degree of Narrowing

The degree of an angiographic narrowing (stenosis) is reported as the estimated percentage lumen reduction of the most severely narrowed segment compared with the adjacent angiographically normal vessel segment, seen in the worst x-ray projection. Because the operator uses visual estimations, an exact evaluation is impossible. There is a ± 20% variation between readings of two or more experienced angiographers. Stenosis severity alone should not always be assumed to be associated with abnormal physiology (flow) and ischemia. Moreover, coronary artery disease is a diffuse process and thus minimal luminal irregularities on angiography may represent significant albeit nonobstructive CAD at the time of angiography. The stenotic segment lumen is compared with a nearby lumen that does not appear to be obstructed but that may have diffuse atherosclerotic disease (Fig. 4-10). This explains why postmortem examinations and intravascular ultrasound imaging (IVUS) describe much more plaque than is seen on angiography. The percent diameter is estimated from the angiographically normally adjacent segment. Because coronary arteries normal taper as they travel to the apex, proximal segments are always larger than distal segments, often explaining the large disparity among several observers’ estimates of stenosis severity. Area stenosis is greater than diameter stenosis and assumes the lumen is circular, whereas the lumen is usually eccentric. In general, four categories of lesion severity can be assigned:

1. Minimal or mild coronary artery disease (CAD), narrowings <50%

2. Moderate, stenosis between 50% and 75%

3. Severe, stenosis between 75% and 95%

4 Total occlusion

Figure 4-10 A, Diagram of coronary artery with stenosis (top) and corresponding intravascular ultrasound (IVUS) images demonstrating diffuse nature of coronary artery disease. B, The percent narrowing is compared only with the “normal”-appearing angiographic lumen, which may not be normal at all.

Technical note: Stenosis anatomy should not be confused with abnormal physiology (flow) and ischemia, especially for lesions 40% to 70% narrowed. For nonquantitative reports, the length of a stenosis is simply mentioned (e.g., LAD proximal segment stenosis diameter 25%, long or short). Other features of the coronary lesion may not be appreciated by angiography and require IVUS (Fig. 4-11).

Figure 4-11 Angiographic features that may not be appreciated on cine imaging and can be evaluated by intravascular ultrasound (IVUS).

Vessel Overlap

Because coronary angioplasty requires a clear view of the target vessel that may be overlapped, multiple angles are required to reveal locations of lesions not previously considered important. Steeper angles or even AP cranial or caudal views are often helpful. For lesions whose significance remains uncertain, IVUS or physiologic measurements (fractional flow reserve, coronary flow reserve) should be considered.

Poor Opacification

Poor contrast opacification of the vessel may lead to a false impression of an angiographically significant lesion or lucency that could be considered a clot. Inadequate mixing of contrast material and blood could be seen as a luminal irregularity. A satisfactory bolus injection of contrast material must be delivered if adequate opacification is to be achieved and the angiogram interpreted correctly. Contrast delivery can be enhanced by use of a larger catheter, injection during Valsalva maneuver phase III, or use of a power injector.

Total Coronary Occlusion

Total occlusion of a vessel may be erroneously suspected if the catheter injection site is subselective or if an anomalous origin or course of a vessel is not recognized. A short LMCA may lead to selective opacification of only the LAD artery and a presumption of a CFX occlusion or anomalous origin of the CFX artery. To address this, an aortic cusp “flush” of contrast may reveal the second vessel. Subselective injections into each vessel separately may be necessary if the LMCA is too short to opacify both vessels simultaneously. Similarly, subselective injection into a large RCA conus branch may not adequately visualize the main RCA. When target vessels are not well seen, the operator should consider anomalous origins of the coronary artery and review the aortogram and left ventriculogram (see section on anomalous coronary arteries later in the chapter).

Coronary Spasm

Spontaneous or catheter-induced coronary artery spasm may appear as a fixed stenotic lesion. Catheter spasm has been observed in right and left coronary arteries (including the LMCA) and must be considered and excluded (by use of intracoronary nitroglycerin) before the narrowing is considered to be an organic lesion. Nitroglycerin alleviates coronary spasm and should be administered when a question of catheter-induced spasm exists. Catheter-induced spasm may occur not only at the tip of the catheter touching the artery, but also more distally. Repositioning of the catheter and administration of nitroglycerin (100 to 200 μg through the catheter) will determine if the presumed lesion is structural or spastic. A change to a smaller diameter (4 F or 5 F) catheter or catheters that do not seat deeply may help.

Special Problems

Left Main Coronary Artery Stenosis

A commonly encountered and potentially critical problem is safe coronary angiography of patients who have LMCA stenosis (Fig. 4-12). The approach to the patient with LMCA stenosis is one of the few situations in which the operator and team may directly affect the life and death of the patient. The LM stenosis may occur at the ostium, mid-body, or distal bifurcation of LAD/CFX and has implications for coronary artery bypass graft (CABG) and PCI decisions.

Figure 4-12 Cineangiographic frame showing distal left main coronary stenosis at the trifurcation branch of the left anterior descending (LAD), ramus intermedius, and circumflex arteries. In critical left main (LM) stenoses, only a few views are necessary. In this case only one view was obtained before recommending urgent coronary artery bypass graft (CABG) surgery.

LMCA stenosis is commonly associated with two clinical presentations:

1. Patients who show evidence of significant low workload ischemia or hypotension during exercise treadmill testing. Unstable angina may be caused by LMCA stenosis in about 10% of patients.

2. Patients with atypical angina. The clinical history and resting or stress electrocardiogram (ECG) may not be helpful, and often patients with resting or atypical chest pain syndromes do not have previous exercise test data.

Technical notes for the angiography of the LMCA stenosis:

1. Either the Judkins femoral or the radial artery technique can be used safely. Access should be based on the operator’s best working method.

2. Coronary angiography before left ventriculography is recommended to obtain the most important information first, should a complication occur.

3. Careful slow advancement and seating of the Judkins left coronary catheter prevent this preshaped catheter from jumping into the ostia. This maneuver is important for an ostial narrowing. Continuous observation of the arterial pressure for damping is important.

4. If the catheter can be positioned beneath the ostia, a “cusp” flush of contrast material in the aortic sinus in an AP or shallow RAO projection may identify an ostial LMCA stenosis.

5. After catheter engagement the operator should look for aortic pressure wave deformation (damping). If pressure damping occurs, a limited contrast flush (1 to 2 ml) and rapid catheter withdrawal (“hit and run”) during cineangiography should be performed to obtain a first look (Fig. 4-13). Rarely, aortic pressure damping occurs without LMCA narrowing because the coronary catheter is seated deeply and subselectively into the LAD artery. Gradual withdrawal and repositioning of the catheter may eliminate pressure damping. The absence of reflux of contrast media into the aortic root on coronary injection is associated with an ostial LMCA stenosis.

6. Limit the number of coronary injections. Distal coronary artery anatomy suitable for bypass grafting is assessed from the few views (usually two or three) that are available. Additional injections should be kept to a minimum. Two projections, an LAO (cranial angulation) and a steeper RAO with caudal angulation are usually sufficient. An LAO-caudal projection for an ostial narrowing is sometimes better. Sometimes one image may be sufficient. Frequent catheter engagement of the LMCA segment and contrast jet stimulation of the lesion may precipitate coronary spasm or occlusion. In less critical LMCA stenosis with 40% to 60% narrowing, more views may be necessary. In some cases IVUS or physiologic measurements (e.g., fractional flow reserve [FFR]) may be necessary.

7. Nonionic or low-osmolar contrast agents are now routinely used. Historically, ionic, high osmolar contrast agents (e.g., meglumine diatrizoate) were associated with lethal complications of hypotension, bradycardia, and reduced coronary perfusion, findings not generally present with nonionic, low-osmolar contrast agents.

8. After the left coronary views are completed, right coronary angiography is performed. In symptomatic patients with RCA occlusion and a critical LMCA stenosis, abdominal aortography and insertion of an intraaortic counterpulsation balloon, intensive care unit admission, and early CABG surgery should be considered.

Figure 4-13 Damping of aortic (Ao) pressure in the left main coronary artery with ventricularization in which immediate angiography was performed with removal of the catheter in a “hit-and-run” maneuver, rapidly restoring flow and perfusion after contrast media injection.

Angiography of Common Coronary Anomalies

Misdiagnosis of an unsuspected anomalous origin of the coronary arteries is a potential problem for a busy angiographer. Because the natural history of a patient with an anomalous origin of a coronary artery may depend on the initial course of the anomalous vessel, it is the angiographer’s responsibility to define accurately the origin and course of the vessel. It is an error to assume that a vessel is occluded when it has not been visualized because of an anomalous origin. Even experienced angiographers have difficulty delineating the true course of the anomalous vessel. Although computerized tomographic angiography (CTA) is a superior technique to angiography, the diagnosis often is still required in the catheterization laboratory.

For the most critical anomaly, the left main anomalous origin from the right cusp, a simple “dot and eye” method for determining the proximal course of the anomalous artery from RAO ventriculogram, RAO aortogram, or selective RAO injection is proposed. The RAO view best separates the normally positioned aorta and pulmonary artery (PA). Placement of right-sided catheters or injection of contrast material into the PA is unnecessary and often misleading.

Anomalous Origin of the Left Main Coronary Artery from the Right Sinus of Valsalva

When the LMCA arises from the right sinus of Valsalva or the proximal RCA, it may follow one of four pathways:

1. Septal course. The LMCA runs an intramuscular course through the septum along the floor of the right ventricular (RV) outflow tract (Fig. 4-14). It then surfaces in the mid septum, at which point it branches into the LAD artery and left CFX artery. Because the artery divides in the mid-septum, the initial portion of the CFX artery courses toward the aorta (the normal position of the proximal LAD), and the LAD artery is relatively short (i.e., only mid and distal LAD are present). During RAO ventriculography, aortography, or coronary angiography the LMCA and the CFX coronary artery form an ellipse (similar to the shape of an eye) to the left of the aorta. The LMCA forms the inferior portion and the CFX artery forms the superior portion. Septal perforating arteries are evident branching from the LMCA.

Note: This variant is considered benign and is not associated with myocardial ischemia.

2. Anterior free wall course. The LMCA crosses the anterior free wall of the right ventricle, and then divides at the mid-septum into the LAD and CFX arteries (Fig. 4-15). Because the artery divides at the mid septum, the initial portion of the CFX artery courses toward the aorta (the normal position of the proximal LAD), and the LAD artery is relatively short (i.e., only mid and distal LAD are present). During RAO ventriculography, aortography, or coronary angiography, the LMCA and the CFX artery form an ellipse (“eye”) to the left of the aorta with the LMCA forming the superior portion and the CFX forming the inferior portion.

Note: This variant has not been associated with myocardial ischemia.

3. Retroaortic course. The LMCA passes posteriorly around the aortic root to its normal position on the anterior surface of the heart (Fig. 4-16). It divides into the LAD and CFX arteries at the normal point and gives rise to LAD and CFX coronary arteries of normal length and course. During RAO ventriculography, aortography, or coronary angiography, the LMCA is seen “on end,” posterior to the aorta, and appears as a radio-opaque dot. This retroaortic dot signifies a posteriorly coursing anomalous vessel. (It is also seen with anomalous origin of CFX from right sinus.)

Note: This variant is considered benign, and evidence of myocardial ischemia has been reported in only a few individuals.

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