Cardiovascular Imaging with Coronary Angiography and Computed Tomography

While angiography has increasingly become the method of choice for interventional cardiovascular procedures, diagnosis with computed tomography (CT) can be done non-invasively and fast.

Information obtained during a CT scan can feed into interventional angiography procedures, which are used to treat the problem. CT and angiography may be required individually or used together to ensure the best possible diagnosis. Neither of these advanced imaging tools is the right one for every patient. Only physicians can decide which approach is best suited for each individual’s unique condition, and it is essential for physicians to have a variety of cutting-edge diagnostic imaging solutions at their fingertips to help diagnose and treat individual patients.

Computed tomography angiograms (CTA) are growing in use, however, coronary angiograms remain the “gold standard” for detecting significant narrowing of a blood vessel or artery that could require catheter-based intervention or surgery (such as bypassing). CTA technology has demonstrated the ability to rule out significant narrowing of the major coronary arteries and can non-invasively detect fatty matter in their walls. To date, coronary CTA has not been proven as effective as the coronary angiogram in detecting disease in the smaller heart arteries that branch off the major coronary arteries.

The key difference between the two tests is that CTA is non-invasive and requires less patient recovery time.

Coronary Angiography and Computed Tomography, page 2

Key Statistics

• In 1957, the first coronary angiogram was performed.¹

• In 2002 an estimated 1,463,000 diagnostic cardiac catheterizations were performed in the United States. From 1979 to 2002 the number of cardiac catheterizations increased 389 percent.²

• The American Heart Association (AHA) reports that in 2002 more than 70 million Americans had one or more forms of cardiovascular disease, claiming 927,448 lives. ³

• In 2002 an estimated 6,813,000 inpatient cardiovascular operations and procedures were performed in the United States; 4.0 million were performed on males and 2.8 million were performed on females.³

• The first multi-slice coronary CTA was performed in 1998.

• Approximately five million CTAs are currently performed each year.

¹ Sones FM, Shirey EK. Cine coronary arteriography. Mod Concepts Cardiovascular Disease. 1962;31:735-738

² American Heart Association. Heart Disease and Stroke Statistics -- 2005 Update

Data, National Center for Health Statistics, Washington D.C.

³ American Heart Association. Heart Disease and Stroke Statistics -- 2005 Update

	Angiogram	Computed Tomography Angiogram
What is the procedure?	An X-ray imaging examination of blood vessels. The images produced are called an angiogram.	A non-invasive imaging examination to help physicians determine if fatty or calcium deposits have built up in coronary arteries.
Who needs the procedure?	Patients whose physicians suspect they may have enlarged arteries, called aneurysms; narrow or blocked arteries; or malformed arteries.	Patients who have moderate to high-risk profiles for coronary artery disease, but who do not have typical symptoms (chest pain, shortness of breath, fatigue, etc.); unusual symptoms for coronary artery disease but low to intermediate risk profiles; or unclear or inconclusive stress test results.
Why is the procedure performed?	To view the heart and arteries. Also called a coronary angiogram or cardiac catheterization. Physicians perform angiograms if they suspect abnormal blood flow. When contrast is injected through the catheter into vessels and X-ray images are taken, radiologists can visualize a problem to enable the physician to determine an appropriate treatment.	To study narrow, blocked, enlarged or malformed arteries without invasive surgery. Information obtained during the CTA examination is used to identify the arteries and any blockages that may exist non-invasively, by creating 3D images on a computer. This enables the physician to determine appropriate treatment.
Procedure Requirements	Requires surgical incision in the groin area. Also requires a wire (catheter) to be threaded up the body to the heart through a major artery.	No incisions. Normally only requires an intravenous line (IV) in the arm. No catheter or other invasive procedure.
What does it see?	Only allows for the analysis of the lumen (the hollow space within the blood vessels).	In addition to analysis of the lumen, CTA provides information about the nature of blockages (soft plaque vs. hard calcified plaque) and the wall of the vessel.

	Angiogram	Computed Tomography Angiogram
What happens during the procedure?	The patient is positioned on an X-ray table, and the heart and blood pressure are monitored. An IV is started so the patient receives fluids and medications. A small amount of X-ray dye (contrast) is injected into the vessels, which makes blood vessels visible on X-ray images. The catheter is inserted into the patient’s body, typically the groin, and is guided with the assistance of a fluoroscope, a special X-ray viewing tool. This allows the physician to determine how well blood moves through vessels of the body, commonly the heart, brain, lung, abdomen, arms and legs. Images are projected on a video screen to enable a diagnosis and treatment to be determined.	No incisions. Normally only requires an IV in the arm. No catheter or other invasive procedure. in the arm. The patient is positioned on the CT scanner’s table, and the heart and blood pressure are monitored. An IV is started so the patient receives fluids and medications. A small amount of X-ray dye (contrast) is injected into the vessels, which makes blood vessels visible on X-ray images. The part of the patient’s body to be examined is placed inside the opening of the CT scanner. X-rays pass through the body from several angles via a rotating device, and are picked up by special detectors in the scanner, creating cross sectional images without invasive surgery. Typically, higher numbers (16 up to 64) of these detectors result in clearer final images, so Coronary CTA often is referred to as “multi-detector” or “multi-slice” CT scanning.
How long does the procedure take?	Procedure requires an average of 30 minutes, plus a minimum of 24 hours recovery time.	Only 10 minutes from scan to diagnosis, with the actual CT scan only lasting for approximately 10 seconds. Patient can return to normal activity immediately after the procedure.

A recent study published in the Journal of the American Medical Association has drawn attention to the dose, and potential hazards, of radiation associated with the use of CT scans to assess the coronary arteries. CT angiography is an increasingly popular alternative to the more invasive form of coronary angiography, known as cardiac catheterization.

The new study, based on nearly 2000 cardiac computed tomography angiography procedures over 30 years in 50 centers throughout the U.S. and Europe is somewhat alarming to say the least. The study reveals both that the average radiation dose of these procedures is equivalent to roughly 600 chest x-rays, and that protocols to reduce radiation dose were not consistently applied. There was thus considerable, avoidable variation in the radiation to which patients were exposed.

These findings are disturbing, but call for reflection and interpretation in the proper context. There are, minimally, three salient considerations.

First, all medical testing involves risk. Mammograms, for instance, result in a small radiation exposure, and that exposure could, in theory at least, increase breast cancer (and total cancer) risk very slightly. But the net effect of mammography is to reduce the death toll from breast cancer, so any harms are outweighed by the obvious benefits.

Awareness of those harms is, of course, a call to action- if we can devise means to screen for breast cancer that confer comparable benefit while eliminating the radiation, we should do so. Such tests- thermography is an example- have, in fact, been developed, and are currently being assessed. The effort to minimize risk, and maximize the ratio of benefit to risk, should never stop. But as a patient, you need to accept that to derive the benefits of modern medicine, you will need to accept its risks- and there are always some risks. The disclosure that a powerful diagnostic tool carries some risk with it is not cause to flee from it in panic. Ponder, yes; panic, no.

Second, the radiation dose delivered with CT angiography can, and should, be minimized. This is an issue the JAMA study addresses. There is more variation in radiation exposure than there should be, and methods to minimize it are not consistently applied. This needs to be fixed, and the paper- shining a spotlight on the issue- should help ensure that it is. So as a current or potential patient, you should appreciate that a study like this is the medical field working as it should to scrutinize itself, and identify what needs fixing.

Third, and finally, is the big issue: you should only get a test when you really need it.

Since there is always risk in medical testing and treatment, you will only be the beneficiary of a favorable benefit-to-risk ratio if there is benefit to be derived. If you can't benefit personally from a test, no amount of risk is worth taking. While it would be pleasant to think that every medical test is cautiously, carefully, thoughtfully, and appropriately ordered- I can say from my years in those trenches, it is often, but not quite always, so. As a patient, you have to help make sure it is so for you, and for those you love.

When a CT angiography is vitally important, the radiation exposure should of course be minimized, but the risk of it can then be shrugged off; the risks of the radiation are, in this context, less than the risks of NOT having the test. But not so if you don't need CT angiography in the first place!

How can you tell? By confronting your doctor with this series of questions any time a medical test is recommended for you or a loved one: (1) How will you use the results of this test to decide what to do next? Will the test results directly influence our options and next steps? (2) What are the risks associated with this test, and are you convinced they are outweighed by the benefits? (3) Is there another way to get the same information that carries less risk?

Ideally, your doctor will have gone over those very questions already in his/her head, but it's your body on the line- or that of someone you love- do you really want to take that chance? It's never wrong to ask a question, and if you find your doctor has a problem with it, I would recommend a new doctor.

When testing is done without a clear rationale, the results can be quite contrary to what is intended. Colleagues and I have found, for example, in a study of coronary CT imaging in healthy post-menopausal women, that testing can at times, talk patients out of taking good care of themselves. The value of a test begins with using it only when it is truly needed.

Medical testing is an effort to find, and fix, something wrong with your health. Applied judiciously, the fix looms large. But if decisions about medical testing are less robust than they should be, an effort that is all about looking for trouble- may find exactly that.

Don’t shun medical tests. Recognize that there are generally risks- sometimes quite dire- of opting out of medical testing or treatment that is truly warranted. But be assertive in questioning how modern medicine is applied to you to ensure you encounter the greatest likelihood of receiving its benefits, and the best chance of avoiding its inevitable risks.

-by

Dr. David L. Katz; www.davidkatzmd.com

Anatomy of coronary arteries

Origin:

Ø Left coronary artery:- left posterior aortic sinus

Ø Right coronary artery:- anterior aortic sinus

Branches

Left coronary artery

Ø Left anterior descending

­ Diagonal & septal branches

Ø Left circumflex artery

­ Obtuse marginal branches

Right coronary artery

Ø Sinoatrial

Ø Conal

Ø Right ventricular

Ø Acute marginal

Ø Posterior descending

Ø Posterolateral

CORONARY ARTERIOGRAPHY

Coronary arteriography is radiographic examination of coronary arteries supplying the myocardium. The primary purpose of coronary arteriography is to delineate the presence or absence of significant narrowing of coronary arteries. This information is then used to determine appropriate interventional therapy like balloon angioplasty, stenting laser angioplasty etc.

INDICATIONS:-

Ø History of Angina

Ø History of Myocardial infarction

Ø Chest pain of unknown origin

Ø Planned interventional therapy

Ø FUC case of revascularization by angioplasty or surgery

CONTRAINDICATIONS:-

Ø Hypertension

Ø Ventricular irritability

Ø Severe anemia

Ø Renal insufficiency

PATIENT PREPARATION

Ø The patient groin area from umbilicus to mid thigh should be clean shaven on both sides.

Ø The patient should be fasting atleast six hours prior to catheterization and should void on call to cath-lab.

Ø He/she should be with chest radiograph, ECG,blood report,signed consent etc.

Ø The patient should be educated about to take deep breaths and hold them during coronary injections.

Ø About 50 units of heparin per kg weight of the patient are given to prevent the thrombus formation.

Ø In patients with angina nitroglycerin is commonly given to reduce coronary spasm and proper visualization of coronary arteries.

Ø A continuous monitoring of the ECG & arterial blood pressure is important to know about activity of heart.

COTRAST MEDIA

Iodinated non-ionic contrast media:-

Ø Iodine content not less than 320mg/ml is used (320 -370mgI/ml).

Ø Volume of contrast used : 80-100 ml.

Trade name	Active Ingredient
Iohexol	Omnipaque
Iodixanol	Visipaque

CATHETER SIZE AND SELECTION

Left coronary artery is hooked by Judkins left coronary catheter while right coronary artery is hooked by Judkins right coronary catheter. The 4&5 F size catheters are used for standard aortas whereas 6&7 F for dilated aortas

ACCESS TO HEART

( Seldinger percutaneous femoral artery approach )

Ø Groin area cleaned and femoral pulse is palpated followed by injection of local anaesthesia

Ø A 18 gauge needle (medicut) is advanced at an angle of 30°to 45° 3to 5cm below inguinal ligament

Ø With good blood back flow, a small metal guide wire is inserted

Ø An 5 french arterial sheath with a dilator inside is passed over the guide wire

Ø The guidewire and dilator are removed so that sheath is in good intraluminal position

LEFT CORONARY ARTERY CATHETERISATION

The right coronary artery is hooked in 60 degree LAO projection as advancing catheter can be seen in full profile. A 4 F Judkins left coronary catheter preloaded with the guidewire is advanced into femoral artery up the descending aorta, around the aortic arch.When the catheter tip reaches the level aortic sinuses guidewire is withdrawn & catheter is further advanced and manipulated to engage the left coronary ostium. A test injection of contrast medium is given to confirm its proper catheterization & the following views are taken:

Projections :

45º LAO with 30º cranial

Left lateral 40° RAO with 15° caudal tilt

25° RAO 15°RAO with 30° cranial tilt

RIGHT CORONARY ARTERY CATHETERISATION

It is hooked in 45º LAO projection in the same fashion as left coronary. When catheter tip reaches the level of aortic sinuses the guide wire is withdrawn & the catheter is rotated clockwise by 180º so that its tip advances inferiorly to engage right coronary ostium. After confirming its proper position following views are obtained:

Projections:

30° RAO 45°LAO with 30° cranial tilt

EQUIPMENT

Variable frame rate pulsed fluoroscopic unit:-

Ø X-Ray pulses duration -- 2 to 10msec

Ø Frame rate for adults -- 25 frames/sec

Ø Frame rate for kids -- 50 frames/sec

Small FOV image intensifier ( 9inch or 23cm )

Ø Permits more cranial or caudal tilt

Ø Reduces patient dose

U or C – arm mounted X-ray tube and II

Ø Full range of obliques (LAO & RAO)

Ø At least 60° cranial & caudal tilt

Cine camera

Ø High frame rate :- 30 to 120 frames/sec

Ø Digital cine cameras are CCD based

LEFT VENTRICULOGRAPHY

It is usually performed with coronary arteriography to access chamber volume contractility (ejection fraction) & wall motion.

TECHNIQUE

The common route to heart is through Seldinger approach to femoral artery.

A 5-7F pigtail catheter is passed into femoral artery, up the descending aorta, around the aortic arch, into the left atrium through aortic valve.

When the catheter tip reaches left ventricle through mitral valve, guidewire is withdrawn & the catheter is connected to the pressure injector containing 35-45ml of contrast which is injected at the flow rate of 12 to 15 ml/sec. The left ventriculogram is performed in 30º RAO projection.

BALLOON ANGIOPLASTY

(Percutaneous Transluminal Coronary Angioplasty )

It is a therapeutic interventional procedure for myocardial revascularization

TECHNIQUE

Intraprocedural medication :

Ø Nitroglycerine (30-100μg/min)

Ø Heparin (5000 units)

Vascular access to heart:- Seldinger approach

Pacemaker insertion:- A temporary pacemaker is inserted into heart through femoral vein. It is particularly important in patients with high-grade conduction abnormalities.

BASIC ANGIOPLASTY SETUP

BALLOON SIZING:

Ø Balloon/artery ratio of about 1:1

Ø Undersizing causes residual stenosis

Ø Oversizing causes artery burst; bypass surgery

CROSSING THE LESION:-

Ø Narrowing lies between radiopaque markers

Ø Confirmation: guide arteriogram & contrast

BALLOON DILATION:-

Ø Balloon inflation using 50% contrast & 50% saline

Ø Rated burst pressure: - 3 to 10 atm

Ø Inflation time: - 15 sec to 2 min.

EVALUATION:-

Ø Balloon deflation and balloon catheter retraced

Ø Cine angiograms performed to access vessel patency

Ø Repeat 3 to 4 times till satisfactory blood flow.

Vocabulary

angiogram - An x-ray of one or more blood vessels produced by angiography and used in diagnosing pathological conditions.

artery—a blood vessel that carries blood away from the heart to the body.

atherosclerosis/arteriosclerosis—commonly called “hardening of the arteries”; a variety of conditions caused by fatty or calcium deposits in the artery walls causing them to thicken.

blood pressure—pressure of blood against the walls of a blood vessel or heart chamber.

bypass—an alternative passage created surgically to divert the flow of blood around a blockage.

capillaries—tiny blood vessels between arteries and veins that distribute oxygen-rich blood to the body.

cardiac—pertaining to the heart.

cardiac catheterization—a diagnostic procedure in which a tiny, hollow tube (catheter) is inserted into

an artery or vein in order to evaluate the heart and blood vessels.

cardiology—the clinical study and practice of treating the heart.

cardiovascular (CV)—pertaining to the heart and blood vessel (circulatory) system.

catheter—a small, thin tube; may refer to a tube used during a cardiac catheterization procedure to inject dye, obtain blood samples and measure pressures inside the heart.

cholesterol—a substance normally made by the body, but also found in foods from animal sources, like beef, eggs and butter. Too much cholesterol in the body can lead to narrowing and blockage of the arteries,

especially those that feed the heart and keep it healthy. Ideally, blood cholesterol levels should be less than

200mg/dL.

coronary arteries—two arteries that come from the aorta to provide blood to the heart muscle

exercise electrocardiogram (ECG or EKG)—a test to assess the cardiac rhythm and function by having

the patient exercise on a treadmill or bicycle.

Coronary thrombus- A fibrinous clot formed in a blood vessel or chamber of the heart.

Emboli/embolus- A mass, such as an air bubble, a detached blood clot, or a foreign body, that travels through the bloodstream and lodges so as to obstruct or occlude a blood vessel.

graft—to transplant or implant (living tissue, for example) surgically into a bodily part to replace

a damaged part or compensate for a defect.

heart attack (aka myocardial infarction)—occurs when one or more regions of the heart muscle

experience a severe or prolonged decrease in oxygen supply caused by a blocked blood flow to the heart muscle.

ischemia—decreased flow of oxygenated blood to an organ due to obstruction in an artery.

left atrium—the upper left chamber of the heart. It receives oxygen-rich (red) blood from the lungs via the

four pulmonary veins, and then sends this blood to the left ventricle.

left ventricle—the lower left chamber of the heart. It receives oxygen-rich (red) blood from the left atrium and pumps it into the aorta, which takes the blood to the body. The left ventricle must be strong and

muscular in order to pump enough blood to the body to meet its requirements.

lipid—a fatty substance in the blood.

open heart surgery—surgery that involves opening the chest and heart while a heart-lung machine performs for the heart and lungs during the operation.

plaque—deposits of fat or other substances attached to the artery wall.

platelet- a component of blood found in the plasma of mammals, functions to promote blood clotting. Also called blood platelet, thrombocyte.

pulmonary—pertaining to the lungs and respiratory system.

pulmonary artery—the blood vessel connecting the right ventricle to the lungs, allowing oxygen-poor (blue) blood to receive oxygen.

pulmonary vein—the vessel that carries oxygenated blood from the lungs to the left side of the heart.

right atrium—the upper right chamber of the heart, which receives oxygen-poor (blue) blood from the body and sends it to the right ventricle.

right ventricle—the lower right chamber of the heart, which receives oxygen-poor (blue) blood from the right atrium and sends it to the pulmonary artery.

risk factor—a condition, element or activity that may adversely affect the heart.

saturated fat—fat that is found in foods from animal meats and skin, dairy products and some vegetables.

(Saturated fats are usually solid at room temperature).

stroke- a blockage or rupture of a blood vessel to the brain, can cause a sudden loss of brain function characterized by loss of muscular control, diminution or loss of sensation or consciousness, dizziness, slurred speech, or other symptoms that vary with the extent and severity of the damage to the brain.

thrombus- A fibrinous clot formed in a blood vessel.

vein—a blood vessel that carries blood from the body back to the heart.