From Ask Dr Wiki
Even with the advent of new noninvasive imaging modalities such as Cardiac CT and MRI, coronary angiography remains the gold standard for detecting clinically significant coronary atherosclerotic disease. The technique was first performed by Dr. Mason Sones at the Cleveland Clinic in 1958. And still involves the same basic premise, using a series of specially designed catheters to deliver X-ray contrast medium to image the luminal integrity of the coronary epicardial bed. Additionally, through both arterial and venous access, each chamber of the heart can be hemodynamically assessed. Typically a complete left heart catheterization involves not only coronary angiography, but also some measure of the ventricular filling pressures and cardiac hemodynamics.
It is estimated that cardiac catheterization will be performed nearly 3 million times/year by 2010. While the overall risk for major complications is relatively low (<2%) it is not negligible. Therefore, patient selection and appropriateness of procedure is vital.
The full ACC/AHA guidelines for coronary angiography can be located on the web. .
There are no absolute contraindications to cardiac catheterization. Relative contraindications include:
- Decompensated congestive heart failure
- Uncontrolled Hypertension
- Refractory Arrythmia
- GI Haemorrhage
- Inability for patient cooperation
- Active infection
- Renal Failure
- Contrast medium allergy
The overall risk of Major complications with left heart catheterization is 1-2%. An include death, bleeding, vascular complications, MI, CVA , and contrast reaction.
Factors increasing patient risk include Age, LMT or 3 vessel coronary disease, decompensated heart failure, severe aortic stenosis, diabetes, renal failure, and prior CVA.
Common Femoral Arterial Access is the most common arterial access for performing left heart catheterization. The original catheterization procedure was performed via brachial access. This site is still commonly used in patients with lower extremity peripheral access issues. Arm access also facilitates internal mammary access, especially in patients with tortuous innominant or subclavian arteries. Radial artery access is also used commonly in some practice settings. Before radial access is performed, competence of the radial artery arch should be assessed with the Allen Test. Use of pulse oximetry can facilitate interpretation of the test.
Anatomic landmarks are used to identify the correct site of arterial puncture. For the femoral artery access, the femoral head provides the best visible landmark. Arterial puncture at this site remains below the inguinal ligament, is generally above the bifurcation of the superfical femoral and deep femoral arteries, and allows for hemostasis. It is recommended that this site should be observed under floroscopy in any patient prior to access. In obese patients the inguinal skin crease is generally too low(see figure).
After the administration of subcutaneous anesthetic, an 18G Cook needle is used to puncture the the front wall of the artery. This technique is known as the modified Seldinger technique and prevents posterior arterial bleeding or venous communication from the puncture. Complications from arterial access include arterial dissection, AV fistula formation, retroperitoneal hemmorhage, and pseudoanuerysm formation.
Once access is obtained, the Cook needle is steadied while the artery is accessed with a wire through the lumen of the Cook needle. The Cook needle is then removed and a sheath is inserted into the artery. Under floroscopy, catheters are then introduced using an 0.35 J-tipped guide wire into the aortic root. The catheters are then attached to a 3 way manifold. Manifold used allows for continuous pressure monitoring, saline flush instillation, and contrast administration through the catheter tip.
Catheter selection for a routine left heart catheterization is generally straight forward.
Most often, Judkins catheter types are most routinely used. For engagement of the left main coronary artery, A Judkins Left size 4 (JL4) catheter generally will generally engaged the left coronary artery in most patients with relative ease. Increasing catheter size (JL5) for tall patients or patients with dilated aorta or decreasing size (JL 3.5) in small patients is sometimes required. Engagement of the LMT is usually most straightforward in the LAO projection. For extremely dilated roots or anomalous arteries other catheters such as Amplatz catheters can be used. For the right coronary artery, a Judkins Right Size 4 (JR4) is most often used. The right coronary artery is engaged in the LAO projection. Usually slow clockwise rotation of the JR4 in the aortic root will engage the ostium of the RCA. Specialized catheters are available to engage anomalous origins of coronary arteries and saphenous and internal mammary artery bypass grafts.
Once the artery is engaged is is important to examine the pressure wave form. Normally, the waveform should mimic aortic root pressure. Dampening or ventricularization of the pressure waveform may indicate over engagement of the catheter or significant vessel stenosis. Extreme care should be taken before instillation of contrast medium without normal pressure waveforms.
Basics of Coronary anatomy
The trileaflet aortic valve gives rise to 3 cusp or sinuses in the aortic root. The left coronary and right coronary cusp give rise to their respective coronary arteries while the noncoronary cusp which arises from the posterior root usually does not give rise to a coronary artery.
The major epicardial vessels supplying the myocardium are the left main coronary artery that divides into the Left anterior Descending artery and Left Circumflex Artery, and the Right Coronary artery. These arteries lie on the epicardial surface and supply smaller branch vessels that eventually give rise to the microvascular network supplying the myocardium.
Coronary dominance is based on the vessel that gives rise to the posterior descending artery (PDA) which travels in the posterior interventricular groove and supplies the Atrio-ventricular node (AV node). This vessel, which can be recognized by the presence of septal perforating branches, arises from the RCA in 80% of the population and the LCx in 10% of the population. Co-Dominance of the arterial circulation is found in 10% of the population where the posterior interventricular artery is formed by both the RCA and LCx.
The Left main coronary artery or Left Main Trunk (LMT) originates from the left coronary cusp and bifurcates to give rise to the Left anterior descending (LAD) and Left Circumflex (LCx) coronary arteries. Occasionally, a third branch vessel, the Ramus Intermedius (RI) arises from the LMT. The LMT varies in length in many patients and in a small number of patients, the two major branch vessels arise from separate origins.
The Left anterior descending coronary artery (LAD) provides blood supply to the anterior wall of the left ventricle. As it courses through the anterior intraventricular groove it provides multiple septal branches to the interventricular septum and diagonal branches to the anterior lateral wall. The LAD then courses to the ventricular apex and in some patients wraps around the apex to supply a small amount of the posterior apex.
The Left Circumflex coronary artery (LCx) courses around the lateral or left atrio-ventricular groove and gives rise to multiple marginal or lateral branches. The branches are termed obtuse marginal (OM) or lateral branches depending on institutional preference. OM branches are sequentially numbered (OM1, OM2 etc…) while Lateral branches are termed based on the segment of the lateral wall they supply (High Lateral, Lateral, Posterior Lateral). As the LCx courses the AV groove it also gives rise to several atrial branches, and occasionally the sino-atrial branch (40% of the population).
The Right Coronary artery (RCA) arises from the right coronary cusp. This vessel follows the right AV groove and provides branches to the right ventricle. The most proximal branches of the RCA are the conus-branch which supplies the Right ventricular outflow tract and a branch that supplies the sino-atrial (SA) node (60% of patients). The RCA then courses through the interventricular and gives rise to marginal branches and branches to the atrium. Manipulation of the coronary arteries in 3-dimensions via spacial reconstructions of the coronary arteries is helpful in interpreting coronary angiographic images.
Standard Angiographic Views
For the beginner angiographer the anatomic landmarks formed by the spine, catheter and diaphragm provide information to discern which tomographic view from which the image is obtained. In the LAO view (figure 1) the catheter and spine are seen on the right side of the image, while in the RAO (figure 2) they are found on the right. PA imaging (figure 3) places these landmarks in the center of the image. Cranial angulation can usually be distinguished from caudal angulation by the presence of the diaphragm. For cranial imaging, the patient should be asked to inspire to remove the diaphragmatic shadow from the image.
LEFT CORONARY ARTERY
The Left main coronary artery gives rise to the left anterior descending artery and the left circumflex coronary artery. Complete visualization of these arteries and their branches requires care and rigor to ensure complete anatomical documentation. Often bifurcations and vessel foreshortening and overlap cause errors in stenosis estimation. There are no steadfast rules in which tomographic views are most useful. Generally, for circumflex and proximal epicardial visualization the caudal views are most useful. For LAD and LAD/diagonal bifurcation visualization the cranial views are most useful. Overall, if there is not a significant limitation on contrast utilization, standard 'around the world' angiography using a selection of the following angiographic views will document left coronary anatomy.
RAO 20 Caud 20
PA 0 Caud 30
LAO 50 Caud 30
LAO 50 Cran 30
PA 0 Cran 40
RIGHT CORONARY ARTERY
The Right coronary artery is engaged in the LAO position.
Initial angiographic imaging of the RCA in this view (LAO 30) gives the best view of significant ostial and proximal RCA disease.
The mid RCA is best visualized in the straight RAO 30 position.
The bifurcation of the distal RCA and rPDA is best seen in the PA 0 Cran 30 view with a small breath in.
Move on to Ventriculography..