CT Coronary Angiography - A new tool for the diagnosis of heart disease
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.
When a cardiologist needs to diagnose disease in heart arteries( coronary artery disease),i.e If EKG's, stress tests or other indicators have revealed a potential cardiac problem, the next step is for the cardiologist to get a close-up look at the arteries in the heart, to see where there might be blockages.In this case, cardiac cathetrization with conventional coronary angiography is the best tool. during which a physician 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 cardiologist has to interpret a number of different "camera angles" that were shot to determine the presence and shape of any obstructions to the blood flow. But a much better diagnostic option would be a detailed 3D virtual model of the patient's heart -- so that the cardiologist could rotate, zoom and move through the heart's anatomy at any angle at will, as if it were a video game. And without impacting on the patient! MSCT angiogram overcomes these limitations 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. The only immediate impact on the patient is an IV injection with iodine-containing contrast and possibly a beta-blocker to slow the heart beat (the equivalent of saying "cheese" and holding still for the photographer).
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. The 64 slice CT captures images of anatomy as thin as a credit card. 3-dimensional reconstructed images are then formatted, allowing physicians and their patients to easily review and understand findings of the CT scan. 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 known or suspected CAD.
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 to a cardiac catheterization with a probable angioplasty or stent.An interesting feature of CT Angigraphy scans comes into play if some disease is found . 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.As MultiSlice CT becomes more widespread, it is likely that several of heart related tests will become less and less used.
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(TMT), stress-echocardiography, stress-thallium and stress-perfusion MRI. More importantly, the heart does not have to be stressed to get this information. Early stages of coronary atherosclerosis can be detected before the development of coronary arterial narrowing. Methods of characterizing the type of plaque in the arteries has been refined, so that "vulnerable" plaques that are more likely to rupture can be pinpointed for treatment, reducing the risk of heart attack. Right now, MSCT provides a significant "next step" to patients whose stress tests have proven inconclusive, and who may have a good chance of being "screened out" for coronary artery disease.
Which group of patients require it?
The CT coronary angiography may be employed in a variety of clinical settings.
- Identify narrowing of coronary arteries
- Identify buildup of plaque in the coronary arteries before the development of arterial narrowing
- Evaluate bypass grafts after coronary artery bypass surgery
- Evaluate congenital anomalies of the coronary arteries or great vessels.
- Coronary vein assessment for pacemaker implantation
- Detect aortic aneurysm or dissection
64 slice CT angiography is specially useful for patients who are aymptomatic 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). This includes patients who are chronic smokers, diabetics, hypertensives, strong family history of premature heart disease and those with equivocal or unclear results on exercise tests.People with multiple risk factors ( 2 or more of the above) are at 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.
As the technical obstacles for the clinical application of this test are being overcome, the appropriate indication of this test in the work up of chest pain patients needs to be carefully defined. A 64-slice CT however seems exceedingly well suited for quickly and non-invasively triaging patients with equivocal presentation, non-diagnostic ECG and initially negative serum markers of myocardial injury. It is helpful in those patients with chest pain with no ECG changes. Here a triple out CT scan allows physicians to quickly diagnose if patient is presenting with coronary artery disease, a dissected aorta, or a pulmonary embolism or no abnormality at all. All these three are life-threatening conditions all with the same symptom, chest pain.
Preparing for the procedure
The patient will be asked not to eat for 1 hour and to avoid caffeinated drinks and exercise for 6 hours prior to the procedure. The patient will be asked to comlete a saftey questionnaire to identify any allergies to foods, drugs, and iodine. In certian situations, the patient may need a blood test to assess kidney function and to exlude pregnancy prior to the scan.
ADVANTAGES AND DRAWBACKS OF CT ANGIOGRAPHY
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 cathetrization 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 and non-calcified, non-stenotic lesions within coronary artery wall itself.
Patients with hypersensitivity to iodinated contrast against renal insufficiency with serum Creatinine >1.5 mg/dl, congestive heart failure, atrial fibrillation and inability to hold breath for 5 seconds should not be referred for CT Coronary Angiography.
The technique is also vulnerable to few drawbacks resulting in inability to diagnose accurately. These are the obscuring arteries due to extensive calcification, motion artifacts due to beating of the heart. Beta-blocker drugs can also be administered orally to slow the heart rate and provide greater time for image requisition.
The future of Multislice CT technology holds great promise for non-invasive diagnoses 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 complementary tool rather than a replacement to conventional angiography, especially in patients where heart disease needs to be ruled out.
For information of this facility contact :-
Delta Heart Centre ,70 K Sarabha Nagar opposite PAU Gate # 1 ,
Near Deepak Hospital
Ferozepur Road Ludhiana