CHAPTER 52 Coronary Angiography: Valve and Hemodynamic Assessment
After the first intravascular catheter was placed by Forsmann in the 1920s,1 techniques to achieve vascular access developed rapidly. Sones and coworkers performed the first selective diagnostic coronary catheterization in 1956.2,3 In 1977, Grüntzig performed the first coronary angioplasty.4,5 Angioplasty and the placement of intravascular stents has now become the predominant form of catheter-based intervention in all major vascular beds.
Coronary artery disease (CAD) is the leading cause of death in the United States,6 and this has remained relatively unchanged over the past several decades despite improvements in primary and secondary prevention and the management of acute coronary syndromes, including rapid reperfusion for ST-segment myocardial infarction.7 In addition to having high mortality, CAD is a significant cause of morbidity in the United States, with increasing rates of congestive heart failure (CHF) noted over the past decade.8
Access for right or left heart catheterizations can be performed via the brachial, radial, or femoral artery.9–13 Other potential but less commonly used sites include direct cutdown (brachial or femoral) and, in rare instances, direct left ventricular (LV) puncture.14
The most common reason to perform coronary angiography is to assess for the presence of clinically suspected CAD.15–19 Diagnostic angiography is also performed when a percutaneous intervention or surgical revascularization might be planned, or when valve replacement or repair or percutaneous procedures are planned. The risk-to-benefit ratio should be determined prior to angiography to identify patients who will benefit most from imaging.
The principal contraindications to coronary angiography include bleeding diathesis, renal failure (true or impending), fever, ongoing infection, and severe anemia (Box 52-1). Also, uncontrolled or uncorrected hypokalemia, hyperkalemia, digoxin toxicity, severe allergy to contrast dyes, and over-anticoagulation with an international normalized ratio (INR) of greater than 1.8 (although for radial access, this may not be a contraindication) are considered relative contraindications to catheterization.
Complications of coronary angiography primarily involve vascular access site complications. Catheter manipulation in atherosclerotic vessels may lead to emboli (thrombus, atherosclerotic debris, calcium, or air) or clot formation, potentially leading to stroke, myocardial infarction (MI), worsening renal function, or CHF (Table 52-1). Pseudoaneurysm or other vascular access complications may be as high as 3%20 in patients with severe peripheral arterial occlusive disease.
|Vascular access dissection or perforation||0.1-0.2|
Coronary angiography is performed by selective injection. In rare instances, nonselective coronary imaging is still performed, but this is usually to find the ostia of coronary arteries or bypass grafts.
The most common access for coronary angiography is the femoral artery, although brachial, radial, and axillary approaches are also used. The most common method of cannulation of the vessel is the Seldinger technique.21 In this method, the vessel is punctured and a guide wire, usually J-tipped, is advanced into the vessel.22,23 This wire then serves as a rail over which the dilator and sheath enter the vessel.
Once access is obtained, the sheath acts as an entry point for passage and exchange of catheters and devices over the J wire. Various preshaped coronary catheters and bypass graft catheters are available for coronary and bypass graft or conduit angiography. Once a catheter is advanced into the aorta, it is positioned either in the ascending aorta or in the descending aorta for clearing and flushing. The guide wire is withdrawn and the catheter is connected to a manifold system that allows, in a closed system, the ability to transduce the pressure at the tip of the catheter and allow contrast injections without reconnecting a second apparatus or device. Once the catheter is cleared, it is advanced with pressure monitoring into the ostia of the coronary artery. If the pressure waveform dampens, this suggests either an ostial coronary artery lesion or an unfavorable angle of the catheter. Care should always be taken with engagement and injection into any arterial conduit, so as to avoid dissection or lifting of lesion flaps in proximal atheromas. Contrast may be carefully injected to identify a proximal lesion or problem with the dampened waveform. At times, the original catheter may be downsized (5-French for a 6-Fr diagnostic catheter); small-volume contrast injection under cine or nonselective angiography may define the anatomy.
In cannulating the left main coronary ostium, a complete and safe study should be ensured by taking care to confirm that the pressure tracing is not dampened or ventricularized. Normally, a preshaped catheter such as a Judkins left 4 catheter (JL4) is used as a default catheter for left coronary angiography. It is successful in engaging the left main ostium approximately 80% of the time. If the aortic root is dilated or narrow, this can usually be accommodated with longer or shorter catheters (JL6 or JL3.5). In addition, if the anatomy is altered, with a left main origin that is posterior, an Amplatz catheter may be used to cannulate the ostium of the left main. The coronary anatomy is defined with contrast injections of 8 to 10 mL during cine runs. The angles taken during angiography allow three-dimensional reconstruction of the anatomy using orthogonal views to see the arteries in multiple planes. The left system begins with the left main, which then terminally bifurcates into the left anterior descending (LAD) and left circumflex (LCX) coronary arteries. In approximately one third of patients, the left main terminally trifurcates into the LAD, the LCX, and an intermediate branch (ramus intermedius) supplying much of the left ventricular free wall.24 The LAD gives off septal arteries as it courses down the interventricular groove, as well as various diagonal arteries supplying the anterolateral free wall of the left ventricle. The LCX gives off marginal arteries as it courses in the atrioventricular (AV) groove. The marginal arteries supply the lateral free wall of the left ventricle (Fig. 52-1).
Figure 52–1 Coronary angiographs of the left (left) and right (right) coronary arteries. AcM, acute marginal artery; D, diagonal artery; LAD, left anterior descending artery; LCX, left circumflex artery; OM, obtuse marginal artery; RCA, right coronary artery; RPDA, right posterior descending artery; RPLB, right posterolateral branch artery.
The right coronary artery (RCA) is usually engaged with a Judkins right 4-cm catheter (JR4). The RCA courses in the interventricular groove and gives off acute marginal and right ventricular branches that supply the right ventricular (RV) free wall. The RCA terminally bifurcates at the crux to form the right posterior descending and right posterolateral coronary arteries, which supply the inferior and inferolateral segments of the left ventricle, respectively. The right posterior descending artery courses in the posterior interventricular septum, supplying the septum as well (see Fig. 52-1).
The dominance of the coronary circulation depends on which artery supplies the posterior circulation—namely, the posterior descending artery or the posterolateral artery.25 About two thirds of the population is right-dominant (the RCA provides both of these branches), 25% is codominant (the RCA supplies the posterior descending artery and the LCX gives off the posterolateral artery), and 15% is left-dominant (the LCX provides both of these branches).25
Several coronary anomalies exist. Most are anatomic variants, such as dual ostia for the LAD and LCX. Others may be congenital, such as those involving the origin of the LCX from the RCA (Fig. 52-2).26–32 Most congenital anomalies, such as these, have little impact on coronary circulation. However, in the case of the LAD originating from the RCA or right coronary cusp and coursing posteriorly, there is an associated increased mortality, usually secondary to arrhythmias and ischemia.29,31
When performing angiography in the coronary circulation, as when performing any other angiography, it is necessary to obtain multiple views in various orthogonal planes of a vessel to fully and clearly define all its segments. Without orthogonal angulation, an inexperienced eye might not see a significant coronary lesion. Generally, all views are reported by convention with left or right angulation first, followed by the cranial or caudal angulation. For example, a 30/25 left anterior oblique (LAO)/cranial is 30 degrees LAO with 25 degrees of cranial angulation.
All major coronary arteries lie in one of two planes: the interventricular septum or the AV groove (Fig. 52-3). The image projections are designed to display the intended anatomy in profile. For example, the right posterior descending artery coursing along the interventricular septum and the inferior wall is best seen with the interventricular septum in its longest profile, the flat right anterior oblique (RAO) projection. On the other hand, the LCX, which courses along the AV groove, is best visualized in the anteroposterior (AP) or RAO caudal projection, looking at the AV groove in profile.
Figure 52–3 Representation of coronary anatomy in relationship to the interventricular and atrioventricular valve planes as seen in two views: right anterior oblique (RAO) and left anterior oblique (LAO). Coronary branches are as follows: AcM, acute marginal; CB, conus branch; CX, circumflex; D, diagonal; L Main, left main; LAD, left anterior descending; OM, obtuse marginal; PD, posterior descending; PL, posterolateral left ventricular; RCA, right coronary; RV, right ventricular; S, septal; SN, sinus node www.lww.com.
(Used with permission from Coronary angiography. In: Baim DS, Grossman W, editors. Grossman’s cardiac catheterization, angiography, and intervention. 6th edition. Philadelphia: Lippincott Williams and Wilkins; 2000.)
The left main coronary artery is best seen in a shallow LAO with slight caudal projection for its middle and distal segments, and with some cranial angulation for its proximal or ostial segment. Another helpful view is the steep LAO/caudal (also called the spider view) of the terminal left main bifurcation. This last view is not helpful with a horizontally positioned heart, and for these patients it may be best viewed with a steep RAO/caudal view.
The course of the LAD is anterior and inferior to the left main. It then enters the interventricular groove and courses to the apex of the heart. No one view is best for the entire course of the LAD. The proximal LAD is best seen in the steep LAO projections with cranial angulation. The middle and distal segments are generally best visualized with LAO and RAO with some caudal angulation. In some cases, when the proximal LAD is not well seen (horizontal heart), an RAO/cranial of 30 degrees each is sufficient to open the proximal LAD and bifurcation with the LCX.
The diagonal arteries, the major branches of the LAD, course off the LAD toward the lateral free wall of the left ventricle. The best view for most of the diagonal arteries, their origin, and their distal segments is usually a steep LAO with steep cranial angulation (50/45-50). In some cases, the first diagonal artery is the only diagonal artery given by the LAD. This vessel then supplies the entire diagonal system (we sometimes refer to this as a twin LAD, given the importance of this vessel to epicardial blood flow).
The LCX is best seen in caudal projections. The proximal portion of the LCX is best seen in the RAO/caudal angulation. This angle also serves to show the marginal arteries, as well. The alternative for the mid segment of the LCX and marginal arteries is the steep LAO/caudal (spider view). In obese patients, this view can be challenging, as the x-ray has to penetrate extra tissue, so the image may be distorted, dark, or hazy.
The RCA enters the anterior AV groove and courses distally. The proximal segment of the RCA is best seen in the flat LAO angulation. If the ostium of the RCA is of interest, then a steep (50-degree) LAO projection is best. The mid segment of the RCA is best seen in the LAO and flat RAO projections. The crux, or distal RCA, and the proximal portions of the right posterior descending and right posterolateral arteries are best seen with an AP or slight LAO with 20 to 30 degrees of cranial angulation. The middle and distal segments of the right posterior descending artery are best visualized with a flat RAO projection.
Commonly, saphenous vein grafts to the right and left coronary circulations arise from the anterior surface of the aorta several centimeters from the sinus of Valsalva. RCA grafts generally arise from the right anterior aorta and the left system grafts commonly arise from the left anterior side of the aorta, with the LAD grafts usually being lower than the LCX grafts. In many cases, the surgeon may place a ring at the origin of a graft that can greatly reduce the chance of missing a graft because one cannot cannulate or find it. The best views for the LAD/diagonal grafts are flat LAO and RAO projections to visualize the graft in its greatest profile. The distal (native) vessel is then imaged with some cranial or caudal projection to define all its segments after the distal anastomosis according to the vessel of interest (i.e., cranial for the LAD, and caudal for the LCX). These images are usually easier to obtain and evaluate because there is less overlap of other coronary anatomy to deal with. However, the ability to view well the origin or distal anastomosis may be challenging for some grafts. The RCA grafts are usually best seen with flat LAO and RAO projections. Again, after the graft has been imaged, the native vessel is imaged with some cranial or caudal angulation to fully define the anatomy after the distal anastomosis (Fig. 52-4).
Figure 52–4 A, Graft angiography. Diag, diagonal artery; OM1,2, obtuse marginal arteries 1 and 2; RCA, right coronary artery; SVG, saphenous vein graft. B, Internal mammary artery (IMA) angiography. IMA TD, IMA touchdown; LAD, left anterior descending artery.
Since the mid 1990s, the internal mammary artery (IMA) has increasingly been the conduit of choice for the LAD and in some cases for the RCA because of the high patency of these conduits.33 Generally, the IMA is cannulated after the subclavian artery is engaged with the preformed catheter and J wire. The catheter is advanced and cleared. Then, the catheter is withdrawn and a gentle counterclockwise torque is applied until the catheter engages the origin of the left IMA (LIMA). Once the vessel is engaged, the catheter is given a gentle clockwise torque to remove any excess tension on the catheter.34 The views for angiography for the LIMA are generally AP or slight RAO/cranial (0-20/40) for the proximal and mid segments of the graft, and steep flat LAO to lateral projection for the anastomosis of the LIMA with the LAD. The right IMA conduit is similarly engaged from the right subclavian artery. The views for the mid segment, origin, and anastomosis are, generally, flat LAO with some cranial and steep AP cranial, respectively (see Fig. 52-4).
The hemodynamic assessment performed during coronary angiography is as integral a part of the procedure as is the imaging of the coronary vasculature. At any given moment, the hemodynamics reflect a culmination and interaction between various ongoing dynamic processes determining cardiac output, coronary artery disease, left ventricular function, systemic metabolic needs, and systemic and pulmonary pressures.35,36 Hemodynamic measurements (vessel or ventricular pressures), measurement of cardiac output, and the evaluation of shunts are an integral part of diagnostic coronary evaluation. All pressures should be measured with a transducer that will allow direct real-time measurements. An important element for this process is the establishment of a zero reference. The reference is usually accepted as the mid chest level in the anterior-posterior direction.
The measurement of right heart (RH) pressures and oxygen saturations is a very good and easy method of obtaining the current cardiovascular status. Cardiac output (CO) is the flow of blood from the heart to the body and is reported in liters per minute. To standardize this number for a patient’s size, these units are divided by the patients body surface area (BSA), which leads to the cardiac index (CI) in liters per minute per meter squared.
During the RH catheterization (RHC), oxygen saturations should be obtained from the superior vena cava (SVC), right atrium, right ventricle, pulmonary artery (PA), and pulmonary capillary wedge pressure (PCWP) positions. When obtained with an arterial saturation, the CO or CI can be calculated, and it allows possible shunt evaluation (see Shunts, later).
Pressure tracings are obtained at each level of the advancement of the RH catheter. Normal values for the RH and systemic arterial (left ventricular) pressures are shown in Table 52-2 and Figure 52-5. Since the introduction of the balloon-tipped RH catheter,37 RHC has become very common in the catheterization laboratory.