Coronary Angiography

Diagnostic coronary angiography has become one of the primary components of cardiac catheterization. In a coronary angiogram, the details of individual coronary anatomy are recorded,anatomic or functional pathology, thrombosis, congenital anomalies or focal spasm and also the presence of intercoronary and intracoronary collaterals. Despite many advances in non-invasive imaging, selective coronary angiography remains the “gold standard” for coronary imaging.

Techniques

The coronary angiogram can be performed by two approaches:

1) The femoral approach

2) The brachial/radial approach

1) The Femoral Approach

This approach involves the insertion of a catheter over a guidewire i.e. inserted into a sheath in the right femoral artery. Systemic anticoagulation is used (heparin). A series of preformed catheters are employed for the procedure – commonly the Judkins left and right catheter and the pigtail catheter though a host of other catheters are available for individual anatomical variations.The common size of catheters used are: 5F, 6F, 7F and 8F. The 6F size is now commonly used all over the world for diagnostic adult procedures.

Catheters Used

Cateters used in coronary angiography

Indications for Coronary Angiography

Source: Braunwald’s Heart Disease–A Textbook of Cardiovascular Medicine, 7th edn., Zipes, Libby,Bonow and Braunwald.

Procedure

The catheter is inserted into the femoral sheath and advanced to the level of the left mainstem bronchus over the guidewire. After removal of the guidewire, the catheter is attached to the manifold system which is designed to permit flushing, pressure monitoring and contrast administration through its ports. The catheter is immediately double flushed – blood is withdrawn and discarded and heparinized saline flush is injected through the catheter lumen. Once the catheter has been flushed with saline solution, tip pressure should be displayed on the monitor at all times. Next the catheter is filled with contrast solution. Then the catheter is engaged into the desired coronary ostium for selective coronary angiography. The left and right coronary catheters are engaged in the LAO view. The left Judkins catheter often engages the left coronary ostium with minimal manipulation. The right coronary catheter, however, requires clockwise rotation by almost 180 ° for engaging the right coronary ostium. If there is trouble with engaging the left or right coronary ostia, other catheters like the Amplatz catheter may be used.

2)The Brachial/Radial Approach

This technique involves performing the coronary angiogram through the right brachial artery in the right ante-cubital fossa. Usually a 5F or 6F sheath is inserted and using a special catheter called the Sones catheter (designed by Dr. F. Mason Sones Jr.), the same process of cannulating the left and right coronary ostia under fluoroscopic guidance is performed. The same catheter is used for cannulating the left and right coronary ostia.

Other Approaches

More recently, coronary angiography by the radial approach is very popular — particularly because it has fewer complications than the brachial approach. Rarely coronary angiography may have to be performed by axillary approach in special circumstances.

Coronary Anatomy

The main coronary trunks can be considered to lie in one of two orthogonal planes. The anterior descending and the posterior descending coronary arteries lie in the plane of the interventricular septum, whereas the right and left circumflex trunks lie in the plane of the atrioventricular valves.

Coronary anatomy in relation to the anatomic planes—interventricular septum and
atrioventricular valves. L Main—Left main, LAD-left anterior descending, D—Diagonal, S-Septal,
CX-Circumflex, OM-Obtuse marginal, RCA-right coronary artery, CB-Conus branch, SN-Sinus
node, AcM-acute marginal, PD-posterior descending, PLV-posterior left ventricular

The numeric coding and official names of the coronary segments

Right Coronary Artery: 1: Proximal, 2: Middle, 3: Distal, 4: Posterior descending, 5:Posteroatrioventricular, 6: first posterolateral, 7: second posterolateral, 8: third posterolateral, 9:inferior septals, 10: acute marginals.

Left Coronary Artery: 11: Left Main, 12: Proximal left anterior descending, 13: Middle left anterior descending, 14: Distal left anterior descending, 15: first diagonal, 16: second diagonal,17: septals, 18: Proximal circumflex, 19: Middle circumflex, 20: Distal circumflex, 21, 22, 23:first, second and third obtuse marginals, 23: left atrioventricular, 24, 25, 26: first, second and third posterolaterals, 27: left posterior descending, 28: Ramus intermedius, 29: Third diagonal Right Dominant Circulation: In 85 per cent of patients, the right coronary artery goes on to form the AV nodal artery, the posterior descending and posterior left ventricular branches which supply the inferior aspect of the left ventricle and interventricular septum.

Left Dominant Circulation: In 8 per cent of the patients, the coronary circulation is left dominant – the posterior left ventricular, posterior descending and AV nodal arteries are all supplied by the terminal portion of the left circumflex coronary artery.

Balanced Co-dominant Circulation: In 7 per cent of patients, there is a balanced system in which the right coronary artery gives rise to the posterior descending artery and then terminates and the circumflex artery gives rise to all the posterior left ventricular branches and also to a parallel posterior descending branch that supplies part of the interventricular septum.

The SA nodal artery arises from the RCA in 60 per cent of cases and from the LCX in 40 per cent of cases.

Grading of Stenosis and Grading of Coronary Artery Disease 

Multiple views are necessary to quantify coronary stenosis accurately. Further, there should be no foreshortening, no artifact and no other vessels crossing that area and obscuring the viewer’s judgment. Though the width of the vessel may appear almost normal, thinning of the contrast column will eventually give out the severity of luminal narrowing. The ability of the coronary angiogram to quantify the degree of stenosis at various points is limited by the fact that it consists of a “lumen-o-gram” in which stenosis is evaluated by comparison with the adjacent “reference” segment which is presumed to be normal and free of disease.

Normal Range of Caliber of Vessels

Vessel                 Range of Caliber

Left main 4.5 + 0.5 mm

Left anterior descending 3.7 + 0.4 mm

Left circumflex (Dominant) 4.2 + 0.6 mm

Left circumflex (Non-dominant) 3.4 + 0.5 mm

Right coronary (Dominant) 3.9 + 0.6 mm

Right coronary (Non-dominant) 2.8 + 0.5 mm

By comparing the diameter of the disease free segment of the coronary artery to the size of the diagnostic catheter (6F=2mm), we can surmise that those vessels that are less that the diameter of the diagnostic catheter may, infact, be diffusely diseased.Presently available data indicates that a stenosis that reduces lumen diameter by 50 per cent (hence reducing the cross sectional area by 75 per cent) is “hemodynamically significant” because it reduces the normal three to four fold flow reserve of a coronary bed. A 70 per cent diameter stenosis (90 per cent cross sectional area) eliminates any ability to increase flow above resting level. In clinical practice, the degree of stenosis is estimated visually from the coronary angiogram and consequently there is likely to be significant operator variability.

Grading of Stenosis

Accurate stenosis assessment is possible by:

1) Digital calipers

2) Computer assisted algorithm

These techniques reduce observer variability and help to judge severity of lesions more accurately.

Apart from the severity of the lesion, lesion morphology is another important parameter of assessment. The following characteristics should be looked for:

1) Eccentricity

2) Ulceration

3) Thrombus

4) Calcification

5) Dissection

6) Physiologic significance of the lesion direct flow or distal pressure measurement may be necessary for this parameter to be assessed. In fact less severe (50 per cent) lesions may be more dangerous because they have a larger lipid core and thinner fibrous cap.

Coronary Angioplasty

The concept of coronary angioplasty – enlargement of the lumen of a stenotic vessel by a catheter technique was first proposed by Dotter and Judkins in 1964. The concept was to advance a guidewire over a stenotic lesion. This would serve as a rail over which progressively larger inflatable non-elastic balloons could be passed and the lesion could progressively be dilated till the lumen of the narrowed segment of the coronary artery is opened. The first percutaneous coronary angioplasty was performed on a conscious patient on Sept. 16, 1977. The success rate of PTCA is 98 per cent and the requirement for emergency CABG is 1 per cent and procedural
mortality is 1 per cent. Much of the success of the technique is due to improvements in technology, stents, and advancements in anticoagulant and antiplatelet therapy.

Coronary angioplasty

Components of an Angioplasty System

1) Guiding catheter: The ideal guiding catheter must have a lumen diameter i.e. at least twice that of the diagnostic catheter. Current guiding catheters are available in shapes similar to the conventional Judkins and Amplatz curves as well as a wide range of custom shapes such as hockey stick, multipurpose and Voda systems for better engagement, support and balloon advancement.

2) Guidewires: Present day guidewires are “steerable” have better wire sizes (0.009 inch), tip stiffness, shaft support and lubricious coating. Modern day guidewires combine tip softness,trackability around curves, radiographic visibility, and precise torque control which allow the wire to be steered past tortuous and stenotic segments.

3) Balloons: Balloons of various sizes and compliance are used depending on operator requirement for dilation of stenotic lesions.

4) Indeflator: It is a screw powered, hand held inflation device with a pressure dial for inflating the balloon to desired levels (atmospheres) for optimum results. 

Mechanism of Angioplasty

Inflation of stenotic segment causes stretching of the vessel, fracture of the intimal plaque, partial disruption of the media and adventia and enlargement of the vessel lumen and outer diameter.Further, there is true plaque compression and extrusion of the contents of the plaque leading to plaque compression.

Stents

Stents are metallic scaffolds that are deployed within a diseased segment of a coronary artery to establish and then maintain a widely patent lumen. Stents come in various designs as shown in the diagram below:

Balloon Mountable Stents

Balloon mountable stents are delivered into the coronary artery in the collapsed state mounted on the balloon. The various types of balloon expandable stents are:

1) Wire coils

2) Slotted tubes

3) Modular stents

Self Expandable Stents

Mechanism of Angioplasty

This stent is delivered into the vessel in a collapsed state constrained by an outer membrane. The moment the membrane is retracted, the stent expands inside the vessel lumen and can be balloon inflated if necessary for better results. Types of self expanding stents are:

1) Wall stent (Magic wall stent)

2) Radius stent

Indications for Stenting

1) Acute or threatened closure

2) Elective stenting of Focal De-Novo Native Coronary Lesions

3) Saphenous vein graft lesions

4) Restenosis after previous angioplasty

5) Chronic total occlusion

6) Acute myocardial infarction

7) Long lesions

8) Small vessels

9) Aortoostial lesions

10) Bifurcation lesions

11) Intramyocardial bridging and coronary vasospasm

12) Multivessel stenting

Special Stents

1) Coated stents

2) Drug eluting (Medicated) stents – reduce restenosis

3) Radioactive stents

4) Covered stents