Thallium heart scan

Definition
A thallium heart scan is a test using a special camera and a small amount of radioactive substance injected into the bloodstream to make an image of the blood flow to the heart.

Purpose
A thallium heart scan is used to evaluate the blood supply to the heart muscle. It can identify areas of the heart that may have a poor blood supply as a result of damage from a previous heart attack or blocked coronary arteries While exercise testing has long been a standard examination in the diagnosis of coronary artery disease, in some cases, the thallium scan may be more sensitive and more specific in the information it provides. In other words, the test may be better able to detect a problem and to differentiate one condition from another. A thallium heart scan may more accurately detect ischemic heart disease. This type of scan is most likely to be helpful in cases in which the exercise test is inconclusive, the patient cannot exercise adequately, or a quantitative evaluation of blood flow is required. In addition to evaluating coronary artery disease, thallium scanning can help to evaluate blood flow following treatment of clogged arteries with coronary artery bypass graft surgery or angioplasty.

MRI

What is MRI?
MRI is an imaging technique that takes advantage of the property of certain atomic nuclei to vibrate – or “resonate” – when exposed to bursts of magnetic energy. When the hydrogen nuclei resonate in response to changes in a magnetic field, they emit radiofrequency energy. The MRI machine detects this emitted energy, and converts it to an image.
Hydrogen nuclei are used because hydrogen atoms are present in water molecules (H2O), and therefore are present in every tissue in the body.
The images obtained by MRI scanning are remarkably precise and detailed. With current MRI machines, these images are generated as 3-D projections. And once a 3-D MRI image is obtained it can be “sliced” and examined in detail, and in any plane – almost like being able to do exploratory surgery on a computer screen.
Also, subtle differences in the hydrogen atoms between various parts of a tissue – differences caused, for instance, by differences in blood flow or in the viability of the tissue – emit different amounts of energy. These energy differences show up as different shades of gray on the MRI image. Thus, the MRI offers a potential means of detecting areas of cardiac tissue that have poor blood flow (as in coronary artery disease) or that has been damaged (as in a heart attack).
However, there are many technical problems in imaging moving structures like the heart with MRI. Movement of the heart during scanning significantly distorts the image (just as taking a photo of a moving object causes a blurring of the picture), and when the structures you are trying to see are small the movement problem becomes extremely difficult to overcome. Technology is progressing rapidly, however, and commercial MRI machines that can produce high-quality heart images are already being used in many research institutions.

How is cardiac MRI useful today?
While MRI machines abound in the United States, cardiac MRI, because of its complexity, has largely been limited to university hospitals where there is a strong research interest. Accordingly, much of the work with cardiac MRI has been done in the research setting.
Because of the difficulties in producing detailed MRI heart scans, only a few uses of cardiac MRI have become more-or-less routine. MRI has proven very useful in evaluating patients with aortic dissection prior to surgery. The detailed images offered by MRI tell the surgeon precisely where the “tear” in the wall of the aorta begins, and the full extent of the dissection. MRI can also locate and characterize the rare cardiac tumor. And in children with complex congenital heart disease, MRI can help to identify and “sort out” the various anomalies, and to plan potential surgical approaches to treatment.
While such applications of MRI are very helpful, these clinical situations are relatively rare. So cardiac MRI has yet to become a commonly used tool in clinical medicine.

What are some of the potential uses of cardiac MRI?
Once certain limitations are overcome – and that day seems to be rapidly approaching – the uses of cardiac MRI will explode.
MRI has the potential to diagnose heart attacks in patients presenting with chest pain. Not infrequently, a patient coming to the emergency room with chest pain will not have the typical ECG changes seen with myocardial infarctions, and the doctors end up waiting for an hour or two for the results of cardiac enzyme tests. If a heart attack is actually occurring, critical time is thus lost before therapy can begin. MRI can detect myocardial infarction immediately, and can reduce the time it takes to begin definitive treatment.
Strides are being made toward being able to diagnose coronary artery disease with MRI. A new MRI processing technique called “black-blood” MRI seems to be able to distinguish very nicely between normal and atherosclerotic coronary arteries. While further refinements are necessary, such techniques are bringing us very close to the day in which MRI will be able to replace cardiac catheterization for diagnosing coronary artery disease.
MRI can help distinguish between “stable” atherosclerotic plaques and “vulnerable” plaques. Vulnerable plaques are those that are prone to rupture, thus suddenly occluding a coronary artery and causing a myocardial infarction. If vulnerable plaques can be identified, those particular plaques can be targeted for intervention (angioplasty, stent, or bypass), while leaving the stable plaques alone.
MRI has already proven useful in the research setting for identifying restenosis after angioplasty. MRI might thus prove an accurate, noninvasive means of following patients after angioplasty.
MRI has the potential of detecting changes in the tiny blood vessels of the heart – the microvascular circulation – that are completely missed by cardiac catheterization. Detecting such changes seem to be useful in predicting the outcome of patients after a heart attack, and may prove to be useful in assessing patients with cardiac syndrome X, diabetes, and certain other conditions.
Ultimately, MRI may replace the x-ray tube in both diagnostic and therapeutic situations. Research is already being done in animals using MRI to image the coronary arteries – instead of using fluoroscopy – for angioplasty procedures.

What about this week's report from Harvard on using MRI for diagnosing coronary artery disease?
Report in the New England Journal of Medicine constitutes another step forward, but MRI is still quite a ways from being ready to replace cardiac catheterization for most patients. While an accuracy of 72% is encouraging, it is certainly nowhere near the nearly 100% accuracy achieved with cardiac catheterization and coronary angiography. So, aside from the other disadvantages listed below, today the MRI is not accurate enough to substitute for coronary angiography when you really need to know the status of the coronary arteries. Indeed, while progress is ongoing, the MRI today is scarcely better in overall accuracy than the less inconvenient noninvasive tests that are used every day in cardiology.

Inflammation and Heart Attacks

From Richard N. Fogoros, M.D.,

Increased blood levels of an enzyme called myeloperoxidase (MPO,) a protein made by white blood cells, was strongly associated with a high risk of coronary artery disease and heart attack. In the Elevated blood levels of another protein, interleukin 6 (IL6,) was also associated with an increased risk of death in patients with heart disease. Elevated levels of MPO and IL6 were both better predictors of cardiac events than the more commonly used risk factors.

What does this mean?
That both MPO and IL6 turn out to be predictors of cardiac events adds significantly to the growing body of evidence that inflammation in the blood vessels can precipitate the rupture of plaque, and thus the sudden closing off of coronary arteries.
A heart attack is caused by the abrupt closure of the coronary arteries.
Clinicians have long been puzzled as to why many heart attacks occur from sudden blockages in coronary arteries that appear normal or near-normal when tested with coronary angiography. The most widely accepted explanation for such events has been the abrupt rupture of plaques that are either inapparent or that traditionally have been termed "non-significant" on angiography.

What does all this mean to you and your doctor?
Let's assume that the latest theory is right, and that inflammation can be an important factor in causing heart attacks. The best ways we know of at present to reduce factors of inflammation are aspirin and the statins.
As it turns out, both of these drugs ought to be taken already by the vast majority of patients who have coronary artery disease, or who have a high risk of developing coronary artery disease. While aspirin and statins are recommended for reasons other than their anti-inflammatory effects, those effects might turn out to be very important factors in why they work. If doctors and patients merely follow the current recommendations for risk reduction, then they will already be doing everything that is currently known to reduce inflammation.

Laser heart surgery - dead on the vine?

By DrRich
Medical science is actively exploring several new methods of treating coronary artery disease. Of these new therapies, one of the most promising has been direct myocardial revascularization (DMR). DMR uses a special laser tool to “drill” tiny holes into portions of heart muscle that are not getting sufficient blood flow (due to blockages in the coronary arteries supplying that muscle). These tiny holes, in theory, provide an alternate means of getting blood to the blood-starved muscle. Early results with DMR were very promising, leading several large biotech companies, high-profile medical centers, and well-known cardiologists to pursue this new technology with great vigor, investing significant time, money and prestige in delivering DMR to the clinical arena.

How is DMR done?
There are two major types of DMR: surgical DMR, and transcatheter DMR.
Surgical DMR has been an FDA-approved technique for several years. Surgical DMR is performed by cardiac surgeons in the operating room. A chest incision is made, the heart is exposed, the affected portion of heart muscle is identified visually, and the DMR laser tool is used to bore a series of tiny holes through that part of the muscle and into the cardiac chamber.
Transcatheter DMR, in contrast, is performed in the catheterization laboratory by cardiologists. In the transcatheter procedure a special catheter is inserted into the heart through a blood vessel. Using a high-tech mapping system to identify the affected portion of heart muscle, a series of laser holes are made into that affected portion, directly from inside the heart.

How is DMR supposed to work?
Leaving aside for the moment the question of whether DMR works at all, the most straightforward theory of how this procedure improves the heart is simply this: The new holes “drilled” into the heart muscle provide channels for the diffusion of blood directly into the blood-starved cardiac muscle.

What were the early clinical results?
Almost universally, early reports indicated that DMR significantly improved symptoms in many patients with severe coronary artery disease.
The usage of DMR has always been limited to patients who, in essence, had no other medical options. It has been offered only to patients whose heart disease was so severe that they were deemed not to be candidates for bypass surgery, angioplasty or stents, and their maximal drug therapy had proved insufficient for relieving their symptoms.
In using DMR to treat these difficult-to-manage patients, early results seemed extremely promising. Investigators reported many success stories, in which patients with refractory angina were remarkably improved after the procedure.

What does the improvement in the placebo group mean?
What causes the placebo effect is unknown. This phenomenon does, however, fit the growing perception within the medical profession that the mind has subtle, poorly understood, but important effects over the body.
As a general rule, it appears that the more desperate the patient, the more likely a novel treatment is to generate a placebo effect. Certainly the patients eligible for DIRECT had every right to feel desperate about their heart disease, and this may explain the magnitude of the placebo response observed in DIRECT.