Coronary Calcium Scan
Coronary Calcium Scan – A Patient’s Guide
WHAT IS CORONARY CALCIUM SCAN ?
Coronary calcium scan measure the amount of calcium in the walls of your coronary arteries — the arteries that supply your heart with blood. Cardiologists use these scans to look for calcium in the coronary arteries.
Coronary artery disease is a leading cause of heart attacks. Coronary artery disease occurs when plaques build up and narrow your arteries (atherosclerosis). The plaques are made of fat, cholesterol and calcium. It is the calcium in those plaques that these scans can detect. The amount of calcium present can be used to calculate a score (coronary calcium score) that, when combined with other health information, helps determine your future risk of coronary artery disease or heart attack.
A high coronary calcium score may indicate that you have a higher risk of having a heart attack before you have any obvious symptoms of heart disease.
HOW IS CORONARY CALCIUM SCAN PERFORMED AND WHAT ARE THE RISKS OF PROCEDURE ?
Coronary calcium scan does not require any preparation. No injections are given and patients are not required to fast. The scan takes about 5 minutes to perform. The only risk to the patient is radiation exposure.
WHO SHOULD CONSIDER CORONARY CALCIUM SCAN ?
Men (> 45 years old) or women (> 55 years old) with at least one of the following risk factors (family history of heart disease, high cholesterol, high blood pressure, smoking or diabetes) could consider going for a coronary calcium scan.
If your coronary calcium score is high, more aggressive treatment of your heart attack risk factors, such as lifestyle change or medications may be needed.
Carotid Intima Media Thickness (IMT)
The carotid arteries are found in the neck and supply blood to the brain. These arteries are large and lie just beneath the skin, allowing easy visualization through ultrasound scanning.
The intima and media are the layers that line the artery. With increasing age and with the presence of certain risk factors (such as high cholesterol, high blood pressure, smoking, obesity, diabetes) cholesterol become deposited in these layers. This increases the thickness of the inner layers which can lead to narrowings and even complete blockage. The thickening also leads to an increased risk of blood clots forming within the blood vessel.
Changes in the carotid artery reflect changes in other arteries found in various organs. It is presently not possible to easily see the heart arteries without more complex testing. The measure of carotid IMT is therefore an easy and safe way to find out the health of arteries throughout the body.
HOW THICK IS THICK ?
In multiple studies, carotid IMT has been shown to be a predictor for future heart attacks and stroke. An increase in thickness of just 0.1 mm actually increases risk for these illnesses by 11%. In particular, a thickness that is greater than 1 mm doubles the chance of developing a heart attack or stroke in the next 6 years.
Persons without known heart disease but have increased thickness would therefore benefit from aggressive treatment of risk factors to prevent the onset of both stroke and heart attacks.
HOW IS IT DONE ?
Ultrasound is a safe imaging technique that uses no radiation. A person is asked to lie down and a colorless gel is applied to the neck. A scanner is applied with moderate pressure over the neck. The scanner is slowly brought up and down the neck to scan the entire length of the carotid artery. Thickness of the intima-media is measured and the flow rate of blood passing through the artery is also measured. The entire study usually takes less than 20 minutes.
Exercise and dobutamine stress echocardiography
STRESS TESTING – A PATIENT GUIDE
WHAT IS A STRESS TEST ?
Persons with heart artery blockages may have minimal or no symptoms at rest. However, symptoms of underlying blockages may occur during stress. Stressing the heart can be done by exercise or by using medicines that stimulate the heart. During exercise, healthy heart arteries enlarge to accommodate increased blood flow. Narrowed arteries are unable to compensate for increased blood flow needed during exercise. This compromises blood flow to the heart muscle resulting in heart muscle being “starved” of oxygen.
This “starvation” can result in
- Symptoms such as chest discomfort or shortness of breath
- ECG abnormalities
- Reduced contraction of the heart muscle supplied by the narrowed coronary artery. This can be detected by using a specialized ultrasound investigation called echocardiography.
- Reduced functioning of heart muscle cells. This can be detected by a special investigation called a nuclear or “MIBI” scan
ECG changes during exercise can often produce false results. The ability to evaluate heart contraction or heart muscle cell function therefore produces more accurate results. As such, the use of nuclear scanning or echocardiography is more precise than the traditional use of ECG based exercise testing.
Echocardiography has the advantage of being completely radiation free. There is also the ability to evaluate the structure of the heart such as the muscles, valves and chambers. This is not possible with nuclear or ECG stress testing.
HOW IS STRESS ECHOCARDIOGRAPHY PERFORMED ?
A Stress Echocardiography test is conducted as an outpatient and does not require hospitalization.
A “resting” study is first performed with the person lying down. This provides a baseline examination, from which information regarding the size and function of the various chambers of the heart and structure and function of the valves may be obtained. Electrodes are attached to the chest and connected to wires to record the electrocardiogram (ECG).
A colourless gel is then applied to the chest and the Echo transducer is placed on top of it. The Cardiologist then makes recordings from different parts of the chest to obtain several views of the heart. The patient may be asked to move from the back to the left side. Instructions may also be given for the patient to breathe slowly of to hold their breath in order to obtain clear pictures of the heart.
Exercise is then initiated using a treadmill. In persons who are unable to complete a high level of exercise, stress to the heart is provided by medicines infused through an IV line inserted into the vein of an arm.
The initial stage is a warm-up phase and is done very slowly. The speed of the treadmill and slope is then increased every three minutes. The treadmill is stopped when the person exceeds 85% of the target heart rate (based upon person’s age). Exercise may be stopped earlier if the person develops symptoms such as chest discomfort, marked shortness of breath, weakness or dizziness. A Cardiologist would be in attendance throughout the test and the above problems are uncommon.
Immediately after the treadmill, the person moves directly to the examination bed and lies on the left side, where the Echo examination is immediately repeated.
By comparing the rest images with the post-exercise images the Cardiologist would look for any abnormalities in how the heart muscle contracts in response to exercise. Normally, exercise would result in a significant increase in heart muscle contraction. Reduced heart muscle contraction during exercise indicates the presence of blockages in one or more heart arteries. Depending on the severity of the abnormalities detected, further evaluation by Coronary Angiography may be indicated.
HOW SAFE IS STRESS ECHOCARDIOGRAPHY?
There are no known adverse effects from the ultrasound used during Echo imaging. The risk of the stress test is similar to the risks involved in any strenuous form of exercise. A Cardiologist would be present throughout the test to manage any rare complications that may occur. These problems could potentially have occurred if the same person performed an equivalent level of exercise at home or in a gymnasium.
WHO SHOULD CONSIDER STRESS ECHOCARDIOGRAPHY?
Stress Echocardiography is capable of diagnosing significant disease in more than 85% of persons with significant heart artery narrowing.
On the basis of currently available information, Stress Echocardiography may be considered as a reasonable test in the following situations:
- Persons with symptoms suggestive of coronary artery disease
- Persons with unclear or inconclusive ECG treadmill test
- Persons with known heart disease in order to evaluate progression of the disease
- To assess heart attack risk for persons who are about to undergo major surgery
- To assess persons with chronic severe heart valve abnormalities
WHAT PREPARATION IS REQUIRED FOR STRESS ECHOCARDIOGRAPHY?
Stress Echocardiography is an outpatient test and does not require hospitalization. The whole procedure takes approximately 90 minutes.
The following steps are required:
- Do not eat or drink for three hours prior to the procedure. This reduces the likelihood of nausea that may accompany strenuous exercise after a heavy meal. Diabetics, particularly those who use insulin, will need special instructions from their doctor.
- Specific heart medicines (e.g. beta-blockers) may need to be stopped one or two days prior to the test. Such instructions are generally provided when the test is scheduled.
- Wear comfortable clothing and shoes that are suitable for exercise.
Computer Tomographic coronary angiography and calcium score
CORONARY COMPUTED TOMOGRAPHY ANGIOGRAPHY (CORONARY CTA ) – A PATIENT GUIDE
WHAT IS CORONARY COMPUTED TOMOGRAPHY ( CTA ) ?
Heart attacks often occur without warning. A new imaging technology called Coronary Computed Tomography (a specialized type of X-ray test) is used to scan the heart in just minutes. This can detect deposits of cholesterol in the heart arteries that may lead to a heart attack.
In the past, exercise testing was the usual way for screening for heart disease. The only way to directly look at the heart arteries was through a procedure called a Coronary Angiogram, which is invasive (a small tube was passed into the body), and hence associated with a small risk of serious complications.
Coronary CTA provide pictures of the coronary arteries which supply blood to the heart muscle in a non-invasive manner. It enables your Cardiologist to look for narrowings some of which cannot be detected by the more traditional exercise testing. It is estimated that up to 3/4 of heart attacks occur in narrowings that are less than 50% in severity. These narrowings will often be missed by exercise testing and only be picked up by Coronary CTA. When such narrowings are detected, it is important that the person initiates medications that can prevent a heart attack in the future.
HOW IS CORONARY CTA PERFORMED AND WHAT ARE THE RISKS OF THE PROCEDURE ?
Patients undergoing a Coronary CTA scan receive a dye as an IV (intra-venous) solution to ensure the best images possible. A very small needle is placed in the vein of the arm and allows the dye to be given. A medication to temporarily slow the patient’s heart rate for clearer images is sometimes given. During the examination, which usually takes about 10 minutes, X-rays pass through the body and onto a “detector”. The higher the number of detectors, the clearer the final images. The latest generation of scanners can acquire 64 “image slices” of the heart in a minute.
In people allergic to iodine which is found in the dye, pretreatment with medications is necessary to prevent allergic reactions. In people with abnormal kidney function and/or diabetes, the dye may worsen kidney function. Finally, there is radiation exposure which is similar to that of a conventional coronary angiogram. In summary, coronary CTA is a very safe test for most people, but should only be undergone when ordered by a doctor familiar with the patient.
WHO SHOULD CONSIDER CORONARY CTA ?
Despite the high safety profile, Coronary CTA should not be used as a “screening” test for all.
On the basis of currently available information, Coronary CTA may be considered as a reasonable test for persons with:
- In persons who are at high risk of developing coronary artery disease due to risk factors such as smoking, high cholesterol levels, hypertension, diabetes or those with a strong family history.
- Unclear or inconclusive stress-test (treadmill test) results.
- Persons with symptoms that could suggest underlying heart artery narrowing.
HOW ACCURATE IS CORONARY CTA ?
If the Coronary CTA is normal or only mildly abnormal, it makes the likelihood of a severe narrowing/blockage of the coronary arteries extraordinarily small (< 1%).
Conversely, if a narrowing is seen on a coronary CTA, there is a high probability that a narrowing that would compromise heart function is present. In such situations, a coronary angiogram would be needed for further evaluation and possible treatment.
Occasionally, a person with moderate narrowings is found. In such situations, exercise stress testing can be complimentary to the coronary CTA in making a decision on further management.
WHAT TYPE OF CORONARY CTA IS USED AT THE NOVENA HEART CENTRE ?
The Novena Heart Centre uses the latest generation, state-of-the-art multi-slice CT Scanner (Toshiba 64-Slice Coronary CTA scanner) which can simultaneously acquire 64 image slices of the heart in one minute, resulting in highly detailed images of the coronary arteries and the heart.
WHAT PREPARATION IS REQUIRED FOR A CORONARY CTA ?
Coronary CTA is performed as an outpatient procedure and does not require hospitalization. The whole procedure takes approximately 20 to 30 minutes. The following steps are required:
- Do not eat or drink for four hours before the scan. Caffeine (coffee or tea) should be avoided because it may cause irregular heart beats which may compromise the quality of the images.
- An IV line is inserted into the vein in the arm, and is used both to give a medication to slow or stabilize the patient’s heart rate for better imaging and administer an iodine-containing dye.
- Patients are required to hold their breath for 10 to 12 seconds during scanning. This is essential for obtaining high quality images.
Percutaneous coronary intervention for significant coronary artery disease
Coronary angiography is the process of injecting dye into the arteries of the heart to allow the cardiologist to see what the arteries look like and where there may be narrowing.
Coronary angioplasty (often referred in short as PTCA or PCI) is a procedure to open up arteries of the heart that are significantly narrowed or blocked. The procedure usually consists of several steps.
- Getting entry into an artery that leads to the heart. This commonly involves either the leg artery (groin area) or the hand artery (wrist). A small tube is placed in the artery that allows introduction of different devices that may be needed.
- Angiography is performed. The doctor injects dye from a long tube (catheter) inserted from the leg or hand artery that goes to the opening of the heart arteries. X-rays are taken and the pictures are seen immediately on a display.
- The cardiologist can gauge the size, the branches and course of the arteries of the heart. The severity of the narrowing can then be estimated from these pictures.
- If the narrowing is considered severe enough to compromise the flow of blood and oxygen to the heart muscle, angioplasty is performed. This usually is done by first introducing a very fine wire (similar to the thickness of your hair) across the narrowing. A balloon can then be brought to the narrowing and the artery stretched open. It is common then to place a fine wire mesh (stent) to the stretched area to ensure that the narrowed portion of the artery remains open.
Risks of procedure
The overall risks of such procedures are uncommon. Angiography has a lower risk usually estimated at less than 1% overall for all serious complications. Angioplasty however has a slightly higher risks and this includes
- Risk of Death < 1%
- Risk of stroke <1%
- Risk of heart attack <2%
- Complication resulting in need for urgent bypass surgery <0.5%
- Abnormal heart rhythms requiring electrical shock to restore normal rhythm <0.1%
- Damage to the arteries in the groin or wrist that requires surgical repair <1%
- Need for blood transfusion <0.5%
- Life threatening allergic reaction to the dye <0.1%
- Radiation exposure resulting in burns or cancer <0.0003%
- Kidney damage due to the dye is rare in persons who have normal kidney function.
Angioplasty is associated with a small but appreciable risk. The decision for angioplasty should be considered carefully to ensure that the benefits outweigh the potential risks. The risks also vary with each individual depending on age, heart function, other diseases and whether the procedure is done as an emergency or in a stable setting.
Longer term complications
The risks mentioned above refer to complications that usually occur during the procedure or shortly thereafter. However, longer term problems include
- Re-narrowing. This usually occurs within 6 months to a year after the procedure. With uncoated stents, this can occur in about 20-30% of cases. With drug-coated stents, this occurs usually in <10% of cases. Re-narrowing can be treated with repeat angioplasty or surgery.
- Clot formation in stents. This is a very serious problem as a clot forming within a stent can block the artery totally and cause a heart attack. This usually occurs within the first month of a stent insertion and occurs in <1% of cases. Clots forming after a month are rare following placement of an uncoated stent. Drug coated stents however appear to have a risk of 0.5% to 0.6% of clots forming up to 4 years after insertion.
The choice of using a drug coated stent or an uncoated stent should be discussed based on individual factors and patient preference.
Coronary artery bypass grafting (CABG) can be considered as an alternative to angioplasty. However, CABG requires a significantly longer time for recovery when compared to angioplasty. CABG may be preferable in certain patients including those with multiple narrowings, left main (the main heart artery) narrowing and diabetics.
Medical treatment or taking only medicines is an alternative. Present clinical studies suggest that angioplasty is superior to medical treatment in patients for relieving symptoms such as chest pain or breathlessness. Angioplasty does not appear to have a benefit in reducing death or heart attacks. The number of long term medications for symptom relief following successful angioplasty however can be dramatically reduced. These studies however apply to patients with stable symptoms and not those who are experiencing heart attacks or have unstable situations.
Additional tools used during angiography or angioplasty
IVUS or intravascular ultrasound is a miniaturized ultrasound probe that can be placed into the heart arteries. This can help the cardiologist determine the inside of the heart artery in terms of the severity of narrowing and the amount of cholesterol deposits within the wall of the artery. The results from an IVUS can give very specific information on the diameter and size of the artery and can also be used to see if a stent is well placed and expanded within the artery. A well placed and appropriately sized stent reduces the longer term problem or re-narrowing and clots.
This is a wire (thickness of a hair) with a miniature pressure probe at the tip of the wire. In certain situations, narrowing within the arteries can seem intermediate on angiography. In these cases, the pressure wire can help determine if the narrowing is compromising blood flow. The wire can be placed before the narrowing in the artery and the pressure at this point can be compared to a point in the artery beyond the narrowing. The pressure drop caused by the narrowing can then be assessed. If the pressure drop across the narrowing is greater than 20%, angioplasty should be considered.
These additional tools help your cardiologist determine with greater accuracy if angioplasty for intermediate narrowings should be performed.
Some narrowings have large deposits of calcium and this produces a narrowing that is not easily dilated with such balloons or stents. In most situations, the balloons used under high pressures can overcome such narrowings. However, with severe deposits of calcium, a device known as a rotablator may be required. This is a miniature “drill” with a metal tip shaped like an olive and coated with small diamond chips. The tip can be rotated at 160000 rpm and this is advanced gently through the narrowing, reducing the calcium deposits into fine powder. Once the calcium is removed, stenting can be successfully carried out. Overall complication rate of the angioplasty is about 2-3% if rotablation is performed.
Additional tools used during angiography or angioplasty
Acute or emergency angioplasty
Acute angioplasty is performed in the setting of a heart attack. A heart attack most commonly occurs when a clot chokes up a pre-existing narrowing resulting in no blood flow to the heart muscle. To reduce damage to the heart muscle, angioplasty is considered the ideal treatment as it is able to restore blood flow in more than 90% of cases and be done in a timely fashion. The risk of an emergency angioplasty for serious complications is between 5-10%. Factors such as a person’s age, the size of the heart attack can influence the risk during the procedure.
Chronic Total Occlusions
Chronic total occlusions also known as CTOs, are narrowings that are totally occluded that have been present for some time. These are different from the total occlusions that occur in the acute setting of a heart attack. The blockages in the CTOs are sometimes very resistant to penetration and dilation and the success rates can vary between 50-90%. Predictors of success include the age of the CTO, the amount of calcium deposits in the artery, the length of the total blockage and position of the blockage. A CTO can take many hours to successfully unblock. Occasionally, a special X-ray called a CT angiogram done before angioplasty can help in developing a strategy to successfully overcome a CTO.
SAPHENOUS VEIN GRAFT
In bypass surgery, veins often taken from the leg are used as new pipes to supply blood to the heart muscle. These veins can become narrowed or blocked after initial successful surgery. The veins unlike the heart arteries degenerate over time and develop very severe accumulation of soft cheese like material in the walls of the veins. If angioplasty was performed to these vein grafts, there is a high risk that these soft materials would dislodge into smaller particles and flow downstream to the smaller arteries in the heart muscles causing a total blockage. Special techniques are needed to prevent this down stream flow of debris and ensure a successful result. These include uses of filters and balloons to catch the debris during angioplasty and to remove them from the body where they would do no harm.
Left Main Stenting
The left main is the main artery that gives rise to two main branches of the heart artery. If the left main is blocked, about 2/3 of the heart muscle will lose their blood supply. Due to the importance of the left main, conventional treatment for left main narrowings is bypass surgery. Angioplasty is an alternative treatment option. However, with the problem of ensuring good flow to both branches and the concern over stent clots, left main angioplasty should only be performed after considering the bypass option.
Hybrid Revascularization procedures
HYBRID CORONARY REVASCULARISATION
WHAT IS HYBRID REVASCULARISATION ?
This is a procedure that combines both minimally invasive bypass surgery with percutaneous angioplasty (balloon and stenting). This type of procedure is not new and has been done since the mid 1990s.
WHY NOT COMPLETE ANGIOPLASTY OF ALL BLOCKED VESSELS ?
There are three main arteries of the heart. They are the left anterior descending artery (LAD), right coronary artery (RCA) and left circumflex artery (Lcx). The LAD artery runs down the front of the heart and in the majority of people is the most important of the three arteries as it supplies the bulk of the muscles of the left heart chamber.
Present evidence gained from many years of experience still suggests that certain types of grafts used in bypass surgery can last longer than using stents. In particular, a graft taken from the breast bone called the left internal mammary artery (LIMA) when connected to the left anterior descending artery (LAD) of the heart provides a long lasting result. Such grafts have also proven to increase life span. The expected failure rate of the LIMA to LAD graft is only about 10% after 10 years.
Stents on average may have a re narrowing rate of up to 20% by the first 6 months. Even drug coated stents have rates of re narrowing that are at best about 5-10% by the 1st year. In addition, narrowings in the artery that are not stented have a chance of progressing to become more narrowed with time. Drug coated stents also have a down side which is called thrombosis (sudden formation of blood clots) that can occur after the initial stenting. This is rare, occurring in about 0.5-0.6% of people per year who have have drug coated stents placed. However, a stent in the LAD artery which suddenly clots has a high likelihood of causing death.
WHY NOT TRADITIONAL BYPASS SURGERY ?
While the LAD artery lies on the front surface of the heart, the other two arteries run a course to the back and bottom of the heart. To do a full bypass of all three arteries, the patient is usually placed on a heart-lung bypass machine and the heart is made to stop beating. The increased manipulation of the heart during operation can lead to increased risk of complications. Another problem termed “pump head” can occur when patients are placed on the heart-lung bypass machines. This is due to small showers of debris that can cause tiny “strokes” and may result in memory loss and forgetfulness after the operation.
Grafting of the other two arteries (RCA and Lcx) are also usually performed by using veins taken from the legs. These veins are not as robust as the LIMA artery with blockage rates of up to 20% by the first year after operation.
HOW IS HYBRID REVASCULARISATION DONE ?
Essentially beating heart surgery is done and the LIMA artery is grafted to the LAD artery. This avoids the need to stop the heart and therefore the need to place a patient on heart-lung bypass. Excessive manipulation of the heart is also avoided as the LAD artery lies on the front surface of the heart. The scars following such surgery is also much smaller and there is no need to take veins from the legs.
Narrowings that may be present in the other two arteries can then be done by angioplasty following surgery. Presently, drug coated stents can be placed which provide low rates of re narrowing. If clots formed in such stents, they would usually be less dangerous than would have occurred if the stents were in the LAD artery.
WHO SHOULD GO FOR HYBRID REVASCULARISATION ?
The approach of bypass surgery alone or angioplasty alone remain the mainstream ways of improving blood flow in blocked heart arteries. Hybrid revascularisation should only be considered in patients with appropriate types of blockages and/or who may be too high risk for the more traditional approaches. Hybrid revascularisation requires surgeons and cardiologists to work closely together and co-ordination of such approach needs to be carefully arranged. In the majority of patients, there may not be an added advantage for this hybrid approach due to the increased need for procedures and cost involved. There are also specific advantages and disadvantages of this hybrid approach. Patients considering such an approach should have a careful discussion with both their surgeon and cardiologist before a decision is taken to undergo this form of procedure.
Heartmate II Left Ventricular Assist Device
Heart failure is a chronic disease process that will progressively worsen. The definitive answer to advanced heart failure is heart transplantation. However, there are a shortage of donor hearts worldwide in comparison with the number of patients who would benefit from transplantation. A viable alternative is to implant a left ventricular assist device, a so-called artificial heart. This device can take over the function of the failing heart and provide the patient with a reasonable quality of life.
Technological breakthroughs have enable minaturization of the device and the current version is the HeartMate II LVAD which is small enough to be implanted into smaller adults, especially women and Asians. It is an axial flow device which means it has few moving parts and in a recent randomized controlled study, it was shown to be superior in terms of durability and complication rate when compared to a pump of an older design. It is very quiet in operation and is implanted into the abdominal cavity. It is ideal for patients who have advanced heart failure and who are dependent on inotropes or who have frequent hospitalizations for heart failure.