sexta-feira, 25 de julho de 2008

Rastreamento de doença coronariana subclínica ou redução de fatores de risco

coracaodobrasil/estrategiasdeprevençao/Conn JACC
Screening for Risk Factors or Detecting Disease? DEBATE Divides the CV Community
Heartwire — aShelley Wood
ACS Case Study Video Follow the case of a 58-year-old male presenting to the EmergencyDepartment with chest pain, nausea, and diaphoresis. Watch a video presentation.
July 22, 2008 — A new fissure is creeping through the cardiology community, dividing those in favor of risk-factor screening and prevention on one side from those who advocate early screening for the disease itself. The debate is playing out online July 29, 2008 in the Journal of the American College of Cardiology, with Drs Jay Cohn and Daniel Duprez (University of Minnesota Medical School, Minneapolis) arguing in favor of early identification of disease through simple screening tests, and Drs Philip Greenland and Donald Lloyd-Jones (Northwestern University, Chicago, IL) urging clinicians to focus on risk factors and steer clear of unproven tests for identifying early vascular and cardiac disease [1, 2].
The chivalrous war of words is the latest chapter in a debate that has centered chiefly on the newest and most expensive tests such as coronary calcium scans and multislice CT--neither of which Cohn and Duprez champion in their Viewpoint. But the counterargument, in an editorial by Greenland and Lloyd-Jones, takes exception to the cancer-screening analogy made by Cohn and Duprez, pointing out that in the cancer field there is outcomes research to justify the use of mammography and other screening tests. As Greenland and Lloyd-Jones point out, the screening tests for cardiovascular disease, while promising, have been shown to detect only disease: no large-scale, multicenter studies have proven that identifying early disease has any impact on course of treatment or, more important, can improve patient outcomes.
The interesting and curious thing is that we actually have evidence that if you go to the trouble of screening for risk factors and treating them, patients have better outcomes.
"And we do have that evidence for risk-factor screening," Greenland reminded heartwire. "Even though people criticize risk-factor assessment because it is not sensitive enough or not accurate enough, the interesting and curious thing is that we actually have evidence that if you go to the trouble of screening for risk factors and treating them, patients have better outcomes. We do not have that evidence for any of these other tests."
But Cohn insists screening for early disease "is not rocket science."
"They're saying that we can’t identify disease very effectively so let's just stick with risk factors, which we know are very poorly predictive and nonspecific. It boggles my mind as to why they won't open up their minds to the importance of moving forward in finding better strategies to identify the disease that we are treating. It's very strange. They criticize these disease markers because they are not predictive of events, but they are looking at very short-term outcomes. We're interested in lifetime risk. We're screening people in their 40s who are concerned about morbid events in their 60s and 70s, and no trials are going to track them that long."
At some point, Cohn continues, "you have to accept the pathophysiologic reality that heart attacks don't occur in the absence of coronary disease, and coronary disease doesn't occur in the absence of endothelial dysfunction and vascular disease, all of which now can be identified."
A 10-Test Screening Algorithm
Cohn and Duprez, in their Viewpoint, describe a 10-test screening algorithm they have started using at their center. Named for the center's benefactor, the Rasmussen score includes tests for large and small artery elasticity (compliance), resting blood pressure, blood-pressure response to moderate treadmill exercise, optic fundus photography, carotid intimal-media thickness (IMT), microalbuminuria, electrocardiography, left ventricular (LV) ultrasonography for LV volume and mass, and brain natriuretic peptide (BNP). Each test results is scored out of 10 for low, intermediate, or high risk, and the combined results yields a score that Cohn et al believe is more predictive than any of the existing standalone tests.
It boggles my mind as to why they won't open up their minds to the importance of moving forward in finding better strategies to identify the disease that we are treating. It's very strange.
To heartwire, Cohn emphasized that these 10 tests were chosen as the "most comprehensive and effective tests" that could all be easily performed in an hour, in a single room, by a single technologist. Each has been individually validated as predictive of morbid events, he says, and outcomes data--not yet published--that he and his coinvestigators have collected suggest that the Rasmussen score is more highly predictive of subsequent morbid events than Framingham or levels of cholesterol or blood pressure.
"We're just saying, can we as a society and as a profession accept the idea that there is a link between the vascular abnormalities and the events?" Cohn says. "And that that linkage is tight enough that it should allow us to accept slowing of progression of the vascular abnormalities as an adequate marker for slowing disease progression, without waiting for events to occur? As soon as you use the word surrogate, people jump up and say we have all these markers that we know don't work well--things like premature ventricular contractions [PVCs] on the electrocardiogram, LDL, HDL--but those are not the markers we're talking about. We’re talking about structural and functional changes in the blood vessel and in the heart."
Cohn continued: "There's so much that needs to be done in terms of evaluating this. Greenland and Lloyd-Jones, instead of conceding that what we're claiming is exceedingly rational and that we now really need to investigate this in the most effective way we can, they're essentially saying, no, this isn't important, let's go back to risk factors. Which is really foolish."
Major Problems, Unknown Benefits
Greenland, in response, says that the composite tests in the tool Cohn is proposing haven't been validated for improving outcomes, they've been validated as measures of vascular disease. "That's not to say that these technologies are poor for certain uses, but we think that they're untested in a screening situation," he says. The algorithm "has reasonable base solidity," Greenland acknowledged, "but I can tell you it has major problems, too." He points out that Cohn and Duprez do not explain who should undergo testing, how regularly the test would need to be repeated, or what to do if certain tests came back high risk and others low or no risk.
He points to Tim Russert, whose medical tests prior to his death were the subject of so much recent media scrutiny. "That's a perfect example of how people who are on the screening bandwagon have sort of missed the point," Greenland argues. "Russert actually had multiple tests that were abnormal, including a coronary calcium test, but he had an exercise test that was normal. So there is an example where you have discrepancies between two test results--and what do you do?"
Polarizing Effects
Where Cohn and Greenland appear to agree is on the need for large-scale outcomes studies and on the fact that, in the meantime, the screening debate is carving the community in two.
"When I speak on this topic," says Cohn, "the response I get veers widely between people who are fascinated and say oh my God, that's the way to do this, and those who are highly critical and immediately say, we already measure blood pressure and cholesterol--there's nothing more to do here. And I would disagree."
Greenland too, acknowledged: "This area has definitely polarized the cardiology community, and it's rather interesting, in my view, how this has happened. Because it's not always the case that the most invasive cardiologists are in favor of screening. There are many, many people on the invasive side who say, wait a second, this is bad. So I think the only way that this issue is going to get resolved is not by editorials or opinions like mine or Jay Cohn's but by more data, and the data that are needed are clinical trials."
Cohn believes too much circumspection will hold the field back and hints that opinions like Greenland's are harming, not helping, the cause. "They're not really embracing the idea that yes, this is a wonderful idea, that's go out and prove it. I think their view represents that of the AHA, which has aggressively focused on risk-factor identification and treatment: that approach is outmoded. . . . This whole research agenda will take us years to work through, but the sooner we start it, the sooner we can achieve a more effective preventive strategy."
Greenland, for his part, respectfully disagrees. "There are those, like Drs Cohn and Duprez and others, who feel that the new test options are sufficiently mature to justify their routine application. There are many others, and I am one of them, who feel that screening unselected people or even a moderately targeted group of people requires evidence and careful analysis, which to date, we do not have for any of the 'new tests,' including coronary artery calcium and carotid IMT, etc."
He points to classic cases--hormone-replacement therapy, antiarrhythmic drugs for PVCs--where intuition and the best intentions have produced more harm than good.
"Debate is healthy," Greenland says. "Acting without evidence is not necessarily unhealthy but certainly can be wrong."
Cohn is a director of and holds equity in Cohn Prevention Centers, LLC.
Cohn JN, Duprez DA. Time to foster a rational approach to preventing cardiovascular morbid events. J Am Coll Cardiol 2008; 52:327-329.
Greenland P, Lloyd-Jones D. Defining a rational approach to screening for cardiovascular risk in asymptomatic patients. J Am Coll Cardiol 2008; 52:330-332.

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