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WHAT IS CT CORONARY ANGIO ?

 

 

CT CORONARY ANGIOGRAPHY - A NEW TOOL FOR EARLY DIAGNOSIS & PREVENTION OF HEART DISEASE

 

††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† †††††††††††††††††

 

Question: ††††††† What is MSCT coronary angiography?

 

Answer: †††††††††† Multi slice CT Coronary Angiography with 64-slice technology is emerging as the most reliable non-invasive modality for evaluation of heart disease. Impressive image quality and non-invasive nature of Multi Slice Computed Tomography (MSCT) angiography makes it a powerful tool in evaluation of heart disease. CT Angiography (CTA) is an examination that uses x-rays to visualize blood flow in coronary arteries which supply blood to the heart. CT combines the use of x-rays with computerized analysis of the images. Beams of x-rays are passed from a rotating device through the heart from several different angles to create cross-sectional images, which then are assembled by computer into a three-dimensional picture of the heart.

 

Speed and sensitivity of 64 slice CT, now gives physicians a new way to view the heart and surrounding structures. Coronary CT angiography captures thousands of images of a beating heart in mere seconds. 3D reconstructed images are then formatted, allowing physicians and their patients to easily review and understand findings of the CT scan. Most patients undergo CT angiography without being admitted to a hospital. The ability of this technology to non-invasively image the coronary artery lumen and wall constitutes an attractive addition to currently available diagnostic tools such as nuclear perfusion imaging or conventional selective coronary angiography, for patients with suspected CAD.

 

Question: ††††††† When is MSCT coronary angiography needed?

 

Answer: †††††††††† When a doctor needs to diagnose disease in the heart arteries (i.e. coronary artery disease) especially when ECG, stress tests or other indicators have revealed a potential cardiac problem, the next step for the doctor is to get a close look at the arteries of the heart, to see where there might be blockage. In this case, cardiac catheterization with conventional coronary angiography is the best tool, in which a cardiologist inserts a catheter into the circulatory system, advances it to the heart and injects dye into the coronary arteries. Because the X-ray is a "shadow" image that is two-dimensional, the doctor has to interpret a number of different "camera angles" that were shot to determine the presence and shape of any obstruction to the blood flow. However a detailed 3D virtual model of patientís heart prepared on MSCT is a better alternative -- so that the doctor could rotate, zoom and move through the heart's anatomy at any angle at will, as if it were a video game & that too without impacting on the patient! In less than 30 minutes, without the invasiveness of a cardiac catheterization, a patient can have an MSCT done to determine if there are any arterial blockages that require an intervention, such as an angioplasty or stent.

 

Question: ††††††† Which groups of patients require it?

 

Answer: †††††††††† 64 slice CT angiography is especially useful for patients who are asymptomatic but at high risk of having coronary artery disease (i.e. there are no problems, such as chest pain or breathlessness, but heart disease needs to be ruled out). The main risk factors are dyslipidemia, diabetes, family h/o CAD, smoking, hypertension, obesity and those with equivocal or unclear results on exercise tests. People with multiple risk factors (2 or more of the above) are at much higher risk than those with 1 risk factor. However Diabetes alone is the only risk factor which may warrant screening for exclusion of heart disease.

 

 

 

 

All patients who are at risk and have been found to be having definite coronary artery disease on other tests should undergo invasive routine angiography, but there are many patients who are not willing for conventional angiography considering it to be an invasive procedure. There counseling should be done for conventional angiography; but if still not willing they can have coronary CT angiography. The advantages in these patients can be that they can go with proper planning for revascularization at a later date.

 

The appropriate indication of MSCT in the work up of patients with chest pain needs to be carefully defined. A 64-slice CT is exceedingly well suited for quickly and non-invasively evaluating patients with equivocal presentation, non-diagnostic ECG and initially negative serum markers of myocardial injury. CT scan allows physicians to quickly diagnose whether the patient is having coronary artery disease, aortic dissection, pulmonary embolism or no abnormality at all. All these three are life-threatening conditions; with the same symptom of chest pain.

 

Question: ††††††† What are the preparations for the procedure?

 

Answer:††††††††††† The patient will be asked not to eat or drink for 2 hours, to avoid caffeinated drinks & exercise for 6 hours prior to the procedure.  The patient will be asked to complete a safety questionnaire to identify any allergies to foods, drugs, and iodine.  In certain situations, the patient may need a blood test to assess kidney functions.

 

Question: ††††††† How to proceed further after getting the report?

 

Answer:††††††††††† A growing number of studies have suggested that 64 slice coronary CT angiography is highly accurate for the exclusion of significant coronary artery stenosis with negative predictive values of 98%-100% in comparison with invasive selective coronary angiography. This means that when the study is reported to be normal, it will be normal. This makes it a more accurate test than stress-testing, stress-echocardiography, stress-thallium and stress-perfusion MRI. Hence MSCT provides a less invasive and less expensive method of ruling out the need for additional intervention if no blockages are detected.

If significant blockages are found, then the patient is referred for cardiac catheterization with a probable angioplasty or stenting. If previous tests show a very high likelihood of patient having significant coronary artery disease, then MSCT angiography probably is not indicated, because the patient will no doubt have to go to interventional treatment anyway.

An interesting feature of CT Angiography scans comes into play if some disease is found, but it is not advanced enough to require revascularization using angioplasty / stenting or coronary artery bypass surgery (CABG). Physicians have reported that when patients see such a clear and understandable picture of their heart, they are much more motivated to make lifestyle and other changes to lower their risk factors. Drug therapy is very useful in these patients to help prevent progression of blockages and heart attacks.

 

Question: ††††††† What are the main advantages of MSCT angiography?

 

Answer: †††††††††† The main advantage is that it is non-invasive, fast, painless and requires no hospitalization. The patient is fully prepared for revascularization procedure when he is going for conventional procedure of coronary angiography. Precious time in cardiac catheterization laboratory is saved which is currently wasted for performing mere diagnostic angiograms and can be more cost effectively dedicated to more patients who require actual intervention.

 

 

 

 

An inherent advantage of CT for imaging of the coronary arteries is the cross sectional nature of this technology. Because of its unsurpassed spatial resolution, conventional catheter angiography is widely accepted as the gold standard for detection of CAD. However it only shows the vessel lumen and degree of luminal narrowing in a cast like manner. It fails to visualize the coronary artery wall, on the other hand contrast enhanced CT scan delineates calcified / non-calcified or even non-stenotic lesions within coronary artery wall itself.

 

 

Question: ††††††† What are the main disadvantages / misconceptions about MSCT angiography?

 

Answer: †††††††††† Relative contraindications of the procedure are - patients with hypersensitivity to iodinated contrast agents, renal insufficiency, congestive heart failure, atrial fibrillation and inability to hold breath for 10 seconds.

 

The technique is also vulnerable to a few drawbacks resulting in inability to diagnose accurately. These are - extensive calcification obscuring the arteries, motion artifacts due irregular beating of the heart or inadequate breath hold.

 

As it is not a dynamic study so it very difficult to comment whether it is near total occlusion with antegrade flow or total occlusion with retrograde flow.

 

There is lot of misconception about the substantially higher radiation dose for MSCT angiography in comparison to conventional angiography. In routine retrospectively gated helical (RGH) MSCT the radiation dose is approximately 10-15 mSv and for conventional coronary angiography the approximate dose of 6-8 mSv. However in newer machines MSCT coronary angiography is performed with prospectively gated transverse coronary (PGT) technique with approximate radiation dose of only 3-6 mSv.

 

There is also some misconception about the contrast media used in this technique. Since proper opacification is needed only for a couple of seconds, so what really matters is the ability of the machine to catch the good quality contrast (Iso- osmolar) at the appropriate time and not the quantity of the contrast. Study is completed with minimum amount of contrast to the range of 50 to 60 ml of non-ionic iso-osmolar contrast media which is as much contrast being used in hundreds of CT examinations done everyday like in CT Abdomen and Chest.

 

 

Question: ††††††† What is the future of MSCT coronary angiography?

 

Answer: †††††††††† The future of MSCT technology holds great promise for non-invasive diagnosis of heart disease. The introduction of 64 slice scanners has greatly improved spatial resolution. It holds the promise of reaping the benefits of diagnosing heart disease without invasive conventional coronary angiography. This tool is likely to develop further as a complimentary tool rather than a replacement to conventional angiography, especially in patients where heart disease needs to be ruled out.

 

 

 

 

 

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