Coronary Angiography: Valve and Hemodynamic Assessment

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.913 Other potential but less commonly used sites include direct cutdown (brachial or femoral) and, in rare instances, direct left ventricular (LV) puncture.14



DIAGNOSTIC CATHETERIZATION TECHNIQUES



Indications


The most common reason to perform coronary angiography is to assess for the presence of clinically suspected CAD.1519 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.





ANGIOGRAPHY


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.



Left Coronary Angiography


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).






Angiographic Projections


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.








Graft Angiography


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).



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).



HEMODYNAMICS



Principles


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.


Jul 31, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Coronary Angiography: Valve and Hemodynamic Assessment
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