Performing cardiac stress tests that measure exercise capacity andheart rate recovery can improve dramatically on existing techniquesthat predict who is most likely to suffer a heart attack or die fromcoronary heart disease (CHD), the leading cause of death in the UnitedStates, a team of cardiologists at Johns Hopkins reports.
In the Sept. 13 edition of the journal Circulation, the Hopkins teamreports that 90 percent of men and women with no early signs of CHDwho, nevertheless, died from it had had below average results fromtheir cardiac stress tests conducted 10 to 20 years earlier.
The team's analysis showed these asymptomatic people were twoto four times more likely to die from CHD within 10 to 20 years thanpeople with average or better-than-average stress test results, eventhough traditional scoring for major risk factors for the disease, suchas such as age, blood pressure, blood cholesterol levels and smokingstatus, had determined the asymptomatic people to be at low orintermediate risk of having heart problems.
According to the cardiologists, these exercise stress testsare easy to perform, lasting less than 20 minutes and requiring onlythat a person walk on a treadmill at progressively higher speeds andinclines every three minutes until they become markedly fatigued.During the test, people are hooked up to a heart monitor.
"This is the strongest evidence to date that selective use ofcardiac stress testing improves prediction of who is really at highrisk of suffering a fatal heart attack when traditional risk assessmentsuggests they are not at high risk of a heart attack within the next 10years," says senior study author and cardiologist Roger S. Blumenthal,M.D., an associate professor and director of the Ciccarone PreventiveCardiology Center at The Johns Hopkins University School of Medicineand its Heart Institute.
The traditional risk factors combine to give a score calledthe Framingham Risk Score, or FRS, that was developed in the last 20years. Considered the gold standard, the score is based on a summaryestimate of the major risk factors for heart disease: age, bloodpressure, blood cholesterol levels and smoking status. It consists of apercentage range of how likely a person is to suffer a fatal ornonfatal heart attack within 10 years.
However, Blumenthal says that many people, especially women,with cardiovascular problems go undetected despite use of theFramingham score, which does not factor in a person's family history,weight or exercise habits. Blumenthal is also a spokesman for theAmerican Heart Association, which estimates that 656,000 Americans diedfrom CHD in 2002, the last year for which statistics are available.
More than 6,100 people took part in the study, conducted from1972 to 1995, and part of a larger project known as the Lipid ResearchClinics Prevalence Study. All participants in this smaller Hopkinsstudy were age 30 to 70. None had early signs of heart disease, butevery participant did have at least one major risk factor for it.
At 10 medical centers across the United States, studyparticipants were given a physical examination, had blood testsperformed and were scored on the FRS. Each participant also underwentcardiac stress testing, which included stress testing for exercisecapacity and heart rate recovery, plus any changes in the heart'selectrical signaling that are typical of decreased blood flow to theheart muscle.
Those with a Framingham score of less than 10 percent weregauged to be at low risk for future CHD, while participants with ascore between 10 percent and 20 percent were ranked at intermediaterisk for future CHD, and those with a score higher than 20 percent werejudged to be at high risk of CHD.
Once participants were ranked by Framingham score, theresearchers monitored their health every six months until death or theend of the study to find out who did or did not die from a heart attackor CHD.
Cardiac stress testing is used to gauge how well the heartworks when it has to pump harder and use more oxygen, for example,while walking on a treadmill. The exercise, sustained for five to 10minutes, mimics the strain placed on the heart when arteries areblocked or narrowed.
The researchers goal, however, was to determine if moreaccurate prediction of whether or not a person will die from a heartattack could be made by adding exercise capacity and heart raterecovery to current assessment techniques that relied mostly onmonitoring the heart's electrical signaling.
During stress testing, a person's breathing, blood pressure andheart rate are monitored while the intensity of their exercising isslowly increased to see how their heart responds. The amount, in numberof beats per minute that the heart rate drops two minutes afterexercise stops, is also recorded to determine heart rate recovery.
Using tables that take into account a person's age, gender andweight, the results can be compared against average scores to see if aperson is below, at or above the norm. There is very little risk ofharm associated with the testing because participants are closelymonitored.
The researchers report that 246 participants died from CHD eventhough they had initially been categorized by their FRS as at eitherlow or intermediate risk of the disease. However, 225 of those who diedalso had below average test scores for exercise capacity and heart raterecovery.
"Our best means of preventing coronary heart disease is toidentify those most likely to develop the condition and intervenebefore symptoms appear," says the study's lead author, cardiologistSamia Mora, M.D., M.H.S., then a research fellow at Hopkins.
"Cardiac stress testing could significantly improve ourabilities to find and aggressively treat these people so that they aremuch less likely to suffer a heart attack."
According to the researchers, these latest results supportconclusions from earlier this year that traditional risk assessmentwith the FRS can be improved with selective use of cardiac CT scans tomeasure calcium scores in individuals with more than one risk factor,such as obesity, smoking, sedentary lifestyle or a family history ofheart disease.
Funding for the study was provided by the Maryland Athletic Club Charitable Foundation in Lutherville, Md.
Other researchers involved were Rita Redberg, M.D., M.Sc., fromthe University of California in San Francisco; and A. Richey Sharrett,M.D., Dr.P.H., from Hopkins.
Materials provided by Johns Hopkins Medical Institutions. Note: Content may be edited for style and length.
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