A Better Way to Monitor the Effectiveness of Cholesterol-Lowering Medications
Tuesday, March 20, 2001
Your doctor has just prescribed medication to lower your cholesterol, which will cost about $1,500 a year. Wouldn't you want to know if it actually works to prevent a heart attack and reduce the need for other treatment to avoid a serious coronary problem? Unfortunately, improved cholesterol levels sometimes mask the risk of heart disease that some patients still face. Indeed, 35 percent of heart attacks occur in people with favorable cholesterol levels below 200 mg/Dl, and up to 8 percent of patients being treated "successfully" with cholesterol-lowering medications - as measured by falling cholesterol levels - will still suffer a coronary problem such as a heart attack or angina. "Patients and doctors need to realize that even if the cholesterol level falls, that doesn't mean there is no risk," said Ronald G. Schwartz, M.D., director of Nuclear Cardiology at Strong Memorial Hospital of the University of Rochester Medical Center. "Even when the pill is working, there are some people whose health is not improving. We need to be able to identify those people whose heart health is not getting any better, who are still at risk." At the annual meeting this week of the American College of Cardiology in Orlando, Fla., Schwartz and co-author Thomas Pearson, M.D., Ph.D., director of Community and Preventive Medicine, are presenting evidence that a common imaging technique can help physicians keep closer tabs on a patient's continued risk. The team used a technique known as Cardiolite SPECT scanning to measure blood flow in the hearts of patients being treated with the cholesterol-lowering drug pravastatin. The researchers showed that the change in heart disease of patients didn't always match the change in their cholesterol numbers. The research team studied 25 patients with abnormal cholesterol levels who were taking pravastatin, a drug made by Bristol-Myers Squibb, which sponsored the study. To monitor the risk level of patients, SPECT heart scans were performed six weeks and six months after the initial study was ordered by a referring physician. Nine of the patients had prior heart attacks, while the initial cardiac SPECT scan demonstrated heart disease for the first time in 11 patients. During treatment, normally physicians monitoring a patient with high cholesterol would look for the overall cholesterol level and the lipid level to drop - and use the declining levels as their primary indication that a heart attack is less likely to occur. Indeed, after six weeks on pravastatin, all of the patients showed lower cholesterol levels. But it wasn't until the six-month SPECT scan that researchers could evaluate the level of heart disease: In most patients the level of heart disease was getting better, while in a few cases it was actually worse. It was months after cholesterol levels were reduced that an improvement was evident on the scan, mirroring the proven effectiveness of the medication months after cholesterol levels drop. "With the cardiac SPECT scan, we have demonstrated clear improvements in blood flow to the heart muscle with cholesterol-lowering therapy. Until the present study we remained unsure how often and how quickly to expect this improvement in blood flow," Schwartz said. Surprisingly, just how much heart disease improved was not indicated by any standard cholesterol tests, including measures of LDL (or "bad") cholesterol, HDL ("good") cholesterol, or triglycerides. Blood flow improved dramatically in some patients whose cholesterol was lowered slightly, while little actual improvement was seen in the hearts of some patients whose cholesterol fell a great deal. Schwartz believes that cholesterol levels during treatment are not a sufficiently reliable indicator of ongoing risk of a future heart problem, and some patients may need other forms of aggressive medical therapy, coronary intervention, or bypass surgery to treat their risk adequately. Schwartz said research studies have shown the clinical value and cost effectiveness of SPECT cardiac imaging as a diagnostic and risk prediction tool in coronary artery disease. Studies showing the value of this technology to monitor changes in coronary event risk during therapy are growing. For example, a clinical trial currently under way at the University of Rochester and other North American sites uses SPECT cardiac imaging to measure effectiveness of medicines and angioplasty to reduce heart attack risk. Although further study is warranted, Schwartz said, this preliminary research demonstrates the benefits of more focused and frequent use of SPECT imaging as a monitoring tool. The work comes at a time of heavy debate among doctors about the best ways to diagnose and treat heart disease. "This is a very exciting development in the prevention of heart disease and our ability to monitor the effectiveness of medical therapy," Schwartz said. SPECT, or single photon emission computerized tomography, is a routine test in which a radioactive tracer is given by vein to a patient. The tracer is taken up by the heart and emits a signal that is detected around the chest by a specialized CT scanner (gamma camera) and computer that create a three dimensional picture of the heart, its blood flow and function. SPECT scanners are readily available in virtually all hospitals, major medical facilities and many cardiology clinics across the country. Physicians know that routine stress SPECT scans of blood flow in the coronary arteries of the heart predict heart attack risk more accurately than cholesterol levels, standard stress tests, or coronary angiograms, but the technique is not currently used to monitor the effectiveness of cholesterol-lowering medication. "While cholesterol-lowering drugs greatly reduce the risk of a heart attack, they don't eliminate that risk, and knowing which patients are prone to problems will help doctors redouble their efforts in treating those patients," Schwartz says.