Jewish World Review Dec. 28, 2001 / 13 Teves, 5762




Magnetic Resonance Imaging (MRI) detects coronary artery disease

By Robert A. Wascher, M.D., F.A.C.S.

http://www.NewsAndOpinion.com -- CURRENTLY, the "gold standard" test for diagnosing the narrowing or blockage of the coronary arteries is angiography. Using thin catheters inserted into the femoral artery in the groin, cardiologists inject a special dye into the coronary arteries that feed the heart, and use x-rays to define the anatomy of these critical blood vessels. The procedure is somewhat uncomfortable, expensive, and is occasionally associated with moderate-to-severe complications. In most cases, patients undergoing x-ray angiography must spend at least one night in the hospital following the test.

MRI scanners use powerful magnets to compose a stunningly detailed picture of tissues and organs. MRI is particularly valuable for studying the brain, spinal cord and the limbs. Unlike its older cousin, the CT scanner, MRI scanners do not expose patients to any radiation. However, most MRI scanners require much longer exposure times to create a useful image when compared to CT scanners. Historically, this factor has severely limited the use of MRI scanners to study parts of the body that are in motion, and the heart in particular.

The current volume of the New England Journal of Medicine reports on the adaptation of MRI to image the coronary arteries of the living human heart. Using updated three-dimensional MRI technology, the study evaluated 109 patients with MRI prior to undergoing coronary angiography with conventional x-rays. The two methods of coronary artery evaluation were then compared in terms of their sensitivity and overall accuracy.

Eighty-four percent of the major coronary arteries were visualized by MRI (versus 100% by x-ray angiography). Eighty-three percent of clinically significant coronary artery abnormalities later found on coronary angiography were also detected by the MRI scanner. This translated into an overall accuracy of 72% for the MRI scanner, versus 100% accuracy for the standard angiography technique. When analyzing the accuracy of MRI in detecting patients at greatest risk of a life-threatening heart attack (i.e., patients with a diseased left main coronary artery or three-vessel coronary artery disease), the overall accuracy of MRI increased to 87%.

The successful application of MRI to the coronary arteries is an exciting development, and holds great potential for non-invasively screening high-risk patients for coronary artery disease. In this study, approximately half of the patients could have avoided the use of x-ray coronary angiography based upon the MRI findings. The authors do point out, though, that in 16% of study patients, MRI was unable to successfully image the coronary arteries.

Another limitation of MRI, when compared to conventional angiography, is that patients found to have clinically significant narrowing of coronary arteries will still require x-ray angiography in order to dilate and stent the site of narrowing, or to prepare the patient for bypass surgery. Based upon this study, MRI appears to be capable of accurately diagnosing significant coronary artery disease in the majority of cases, but it cannot support any of the interventions necessary to treat this disease at the present time.

The primary use of this new MRI technique would appear to be for screening patients with multiple risk factors for heart disease, but who have no clinical symptoms of coronary artery narrowing. This is a major innovation, and more advances are certain to follow in the near future!

NEW DEVELOPMENT IN OBESITY RESEARCH

I have frequently reported on the epidemic of obesity in this country, and on the impact that this condition has on the health of obese Americans. Last week, I reviewed the generally disappointing recent findings for the hormone leptin, after it was originally hailed as "the golden bullet" for the treatment of human obesity. This week's Proceedings of the National Academy of Science features a compelling study related to the topic of obesity.

A substance known as C75, which blocks the production of fats in the body, is known to reduce food intake in both lean and obese mice. The study's authors looked at the effects of C75 on four different hormones that have been associated with appetite and eating. Neuropeptide Y (NPY) and agouti-related protein (AgRP) both stimulate appetite and food intake in mice (and, presumably, in humans as well). Two other hormones that suppress appetite were studied as well: pro-opiomelanocortin (POMC) and cocaine-amphetamine-related transcript (CART).

Without resorting to another paragraph filled with arcane multisyllabic scientific words, let me summarize the results of this important study. Both lean and obese mice were given C75, which significantly reduced feeding behaviors in both groups of mice. In lean mice, the administration of C75 rapidly and almost completely blocked all food intake. C75 appeared to block the normal fasting-induced increase in brain levels of AgRP and NPY (the "I want to eat now" hormones) of these non-obese mice while, at the same time, the brain levels of CART and POMC (the "I am not hungry now" hormones) did not decline as would be expected after fasting. In obese mice, C75 also rapidly suppressed food intake, reduced body weight, and reversed obesity-associated high blood sugar levels. As was the case with lean mice, C75 also reduced brain levels of the "I want to eat now" hormones, but had no effect on the low levels of the "I am not hungry now" hormones associated with fasting.

These findings add to our understanding of the extraordinarily complex mechanisms used by our bodies to balance appetite and body weight. Such an understanding is critical so that better treatments can be identified when these intricate balancing mechanisms go awry, resulting either in anorexia or obesity. Most importantly, this study points to a possible mechanism by which obesity occurs, and is sustained. In the obese mice studied in this research project, C75 shut down feeding and reduced the brain levels of hormones associated with hunger and increased food intake.

However, unlike the non-obese mice, the obese mice experienced a decline in the brain levels of hormones known to suppress appetite despite receiving C75. This suggests a breakdown in the normal appetite regulation system of the brain in the obese mice. One caution, however. The early studies of leptin in mice suggested that obese mice had unusually low levels of this hormone. Leptin was quickly hailed as a potential cure for human obesity, until it was found that many obese humans actually have… elevated levels of leptin!

ADVERSE CHILDHOOD EXPERIENCES & THE RISK OF SUICIDE ATTEMPTS

It seems intuitive to correlate the risk of suicide attempts in adults with a history of traumatic childhood events. However, there have been few studies that have looked at these issues in sufficient detail to confirm such intuition. The current issue of the Journal of the American Medical Association presents just such a landmark study.

A retrospective study looked at 17,337 adult HMO patients who had previously completed a survey asking about childhood abuse, family dysfunction and suicide attempt history. Particularly noted was a history of emotional, physical or sexual abuse; familial substance abuse, mental illness or incarceration; and parental domestic violence, separation or divorce.

The overall risk of at least one suicide attempt among volunteers without any adverse childhood experiences was 1%. The presence of an adverse childhood experience in any of the listed categories was associated with a 2 to 5 times increase in the risk of suicide attempt. Study participants reporting 7 or more adverse childhood experiences were 31 times more likely to attempt suicide than people reporting a lack of serious childhood traumas.

Participants reporting childhood traumatic events also had a very high risk of illegal drug abuse, chronic depression or alcoholism during adulthood. This particular group of study participants also experienced an increased risk of suicide attempts, but not at the same level as previously traumatized people who did not report depression or drug/alcohol abuse. This suggests that depression and drug/alcohol abuse are probably being used by previously traumatized people as a method of compensation for their past traumas, and as an alternative to suicide attempts.

This study provides compelling evidence for the lifelong risks associated with childhood neglect, abuse, and other traumatic experiences occurring early in life. The limitations of this study are two-fold. First, it is a retrospective study. This means that the data cited in this study were previously collected for reasons unrelated to this particular study, and are therefore considered less compelling than had they been collected prospectively, and only for the purposes of this study.

Secondly, the data collected are based upon self-reporting, which is a notoriously subjective means of collecting information. Biases for and against the working hypothesis of this study (i.e., that childhood traumas increase the risk of suicide attempts even in adulthood) are easily introduced when people are asked to voluntarily recall and categorize childhood events, as well as suicide attempts during adulthood.

Still, this is a persuasive study that looks at a very large cohort of people over a reasonable period of time. The implications of this study point to the fragility of the young and developing mind in the face of familial instability, neglect, abuse, and a lack of nurturing; and the lifelong consequences that may follow when such conditions occur during childhood.

JWR contributor Dr. Robert A. Wascher is a senior research fellow in molecular & surgical oncology at the John Wayne Cancer Institute in Santa Monica, CA. Comment by clicking here.

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© 2001, Dr. Robert A. Wascher