Lifetime Risk -- A New Way to Determine Risk for Cardiovascular Disease

Framingham Risk Score

Nurses who counsel patients on reducing their cardiovascular risk often use the Framingham Risk Score (FRS) to estimate an individual's 10-year absolute risk for developing coronary heart disease (CHD).^[1] The FRS is particularly powerful in patients with multiple risk factors and a high risk (≥20%) of developing CHD in the next 10 years. For example, a 66-year-old male patient with a total cholesterol of 250 mg/dL, an HDL cholesterol of 39 mg/dL, who smokes cigarettes, and has an untreated systolic blood pressure (SBP) of 144 mm Hg has a 23% risk of developing CHD in the next 10 years. Nurses can use the FRS as a motivational tool to encourage patients to engage in lifestyle changes and drug therapies to reduce their risk. This gentleman can be shown that a cholesterol reduction to 150 mg/dL, an increase in HDL cholesterol to 45 mg/dL, quitting smoking, and a SBP reduction to 128 mm Hg will reduce his 10-year absolute risk for CHD from 23% to 13%.

The FRS is used in clinical guidelines, such as the Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III, or ATP III), to select appropriate patients for drug therapy in primary prevention of CHD.^[1] However, there is concern that by focusing on short-term risk, the FRS underestimates risk in women and young people. Individuals with low or intermediate 10-year risk for CHD may actually be at high risk in the long term because any single risk factor can cause cumulative damage and adverse outcomes if left untreated for many years.^[2] For this reason, Donald Lloyd-Jones, MD, ScM, FACC, FAHA, and colleagues at the Department of Preventive Medicine, Bluhm Cardiovascular Institute, Northwestern University Feinberg School of Medicine, Chicago, Illinois, promote the concept of lifetime risk estimation for cardiovascular disease (CVD).^[3]

Concept of Lifetime Risk

Lifetime risk conveys the cumulative risk of developing a disease during the remainder of an individual's life.^[4] Lifetime risk estimates are also used to assess the burden of disease in a population and to compare absolute lifetime risks of common diseases. Clinical and public health measures relative to these lifetime risk estimates can be implemented. For example, consider the lifetime risk for breast cancer -- 1 in 8 women at age 40 years. This knowledge has effectively led to education of women about the importance of self breast exams and the need for annual mammograms beginning at age 40 years, the inclusion of screening measures into clinical guidelines, and reimbursement of screening costs by governmental agencies and private insurers. A similar appreciation for the risk of CVD is urgently needed.

Communicating lifetime risk estimates for CVD may be particularly useful for patients who have low short-term risks despite having significant risk factors for CVD. Framingham Heart Study (FHS) cohorts have been used not only to develop a scoring system for the estimation of short-term (10-year) risk for developing CHD but also to estimate lifetime risk. The FHS, which began in 1948, includes careful documentation of risk factors and events as well as findings of long-term follow-up. These data have allowed investigators to examine factors that may modify lifetime risk for CVD. Therefore, Lloyd-Jones and colleagues used FHS patient cohorts to estimate lifetime risk for CVD and to examine overall survival with regard to established risk factors.^[5]

Predicting Lifetime Risk for CVD in Framingham Heart Study Participants

FHS participants were free of CVD (myocardial infarction, coronary insufficiency, angina, stroke, and claudication) at 50 years of age and were followed to 95 years of age. Risk factor measurements included height and weight, determination of body mass index (BMI), current smoking status by self-report, blood pressure, lipid panel, and diabetes status. CVD events were ascertained during follow-up, which included the occurrence of myocardial infarction, coronary insufficiency, death resulting from CHD, angina, atherothrombotic stroke, intermittent claudication, or other cardiovascular death. Participants included 3564 men and 4362 women who were followed for a total of 111,777 person-years. During follow-up, 1757 participants had an incident CVD event, and 1641 died from something other than overt CVD.^[5]

At baseline, only 3.2% of men and 4.5% of women had optimal risk factors, defined as total cholesterol < 180 mg/dL, blood pressure <120/<80 mm Hg, nonsmoker, and nondiabetic. Almost one fourth of the participants had at least one elevated risk factor, defined as total cholesterol 200-239 mg/dL, SBP 140 to 159 mm Hg, diastolic blood pressure (DBP) 90 to 99 mm Hg, nonsmoker, and nondiabetic. Approximately 40% of participants had 1 major risk factor, defined as total cholesterol ≥ 240 mg/dL, SBP ≥ 160 mm Hg, DBP ≥ 100 mm Hg, smoker, or diabetic. Twenty percent of men and 17% of women had 2 or more major risk factors.^[5]

Men who were free of CVD at 50 years of age had a lifetime risk (to 95 years of age) for developing CVD of 51.7% (95% confidence interval [CI], 49.3 to 54.2). Median overall survival for these men was 30 years. Women who were free of CVD at 50 years of age had a lifetime risk (to 95 years of age) for developing CVD of 39.2% (95% CI, 37.0 to 41.4). Median overall survival for these women was 36 years.

Individual risk factors, such as elevated blood pressure and total cholesterol, were associated with increased lifetime risk for CVD and with shorter median survival in both men and women. The presence of diabetes at age 50 yielded the highest lifetime risk for CVD of any single risk factor: 67.1% for men and 57.3% for women through 75 years of age. CVD events occurred much earlier in smokers than in nonsmokers. Although lifetime risk for CVD is similar for smokers and nonsmokers, the risk of death from other smoking-related causes shortened the median survival of smokers by 5 years. Compared with participants who had 2 or more major risk factors at age 50, participants with optimal risk factor levels had much lower lifetime risks (5.2% vs 68.9% in men, 8.2% vs 50.2% in women) and significantly longer median survival (> 11 years in men, > 8 years in women). Additionally, when low HDL cholesterol (< 40 mg/dL in men, < 50 mg/dL in women) and obesity (BMI ≥ 30 kg/m²) were evaluated, lifetime risks for CVD were similar to those associated with major risk factors, such as elevated total cholesterol and blood pressure.^[5]

The results of this study fully support that CVD is the number one killer of Americans. For individuals free of CVD at age 50 years, more than half of men and almost 40% of women will develop CVD during their remaining lifespan. This represents the highest lifetime risk for any disease, including all cancers. For example, at age 50 years, the lifetime risk of a woman developing breast cancer is 12.5% and of a man developing prostate cancer is 19%.^[5] There is evidence of a disconnect between Americans' actual risk for disease and what they perceive as their greatest health threat. As recently as 2005, a nationally representative survey of women showed that only 55% identified heart disease as the leading cause of death, and this level of awareness was significantly greater among white participants than racial and ethnic minorities.^[6] In 2003, only 13% of women identified CVD as their greatest personal health risk, while 51% believed that cancer was their greatest health risk.^[7] Lifetime risk for CVD must be publicized widely so that Americans and their healthcare providers begin prevention efforts early to reduce or eliminate risk factors.

Short-term vs Long-term Risk

It's interesting to compare short-term (10-year) risk and lifetime risk for developing CVD. Performing this exercise demonstrates how important it is to convey this information to our patients. Using the ATP III Framingham Risk Calculator, a 50-year-old male with a total cholesterol of 250 mg/dL, an HDL cholesterol of 60 mg/dL, an untreated SBP of 160 mm Hg, who is a nonsmoker and a nondiabetic, has an estimated 10-year risk for CHD of 7%. In comparison, his average lifetime risk for CVD is almost 70%, and his median survival is more than 11 years shorter than that for a 50-year-old man with optimal risk factors.

A 50-year-old woman with the same risk factors has an estimated 10-year risk of only 2%, although her lifetime risk for CVD is 50% and her median survival is over 8 years less than a 50-year-old woman without these risk factors.^[5] If these data are presented to patients with risk factors, nurses may be more successful in motivating them to adopt therapeutic lifestyle changes and promoting adherence to medications.

Short- and long-term risk calculations have implications for how we use the ATP III guidelines^[1] for the assessment and management of elevated cholesterol. The premise of ATP III is that an individual's risk for CHD, as determined by the FRS, influences the intensity of prevention efforts. Individuals with multiple risk factors and an estimated 10-year CHD risk of > 20% are categorized as high risk. High-risk patients typically require drug therapy and therapeutic lifestyle changes to reach an LDL cholesterol goal of < 100 mg/dL. Individuals with an estimated 10-year CHD risk of 10% to 20% are categorized as intermediate risk. Therapeutic lifestyle changes are recommended for this group, with the option of further evaluation or lipid-lowering drug therapy. Individuals with an estimated 10-year risk below 10% are considered to be in the low-risk category, and therapeutic lifestyle changes are the only recommendation.

The CVD prevention community has expressed concern over the use of short-term (10-year) risk estimations in younger individuals, particularly the 20- to 50-year age groups, since the Framingham risk equations place the most weight on age in predicting absolute CHD risk. Therefore, mostly older patients with risk factors fall into the ATP III categories that warrant treatment.^[8] However, the presence of risk factors in a young or middle-aged individual will substantially contribute to the development of atherosclerosis if these risk factors are not modified early on.

Although calculating a patient's 10-year CHD risk provides useful information, adding the lifetime risk estimate will deliver a more powerful message when communicating CVD risk. The conversation goes something like this:

Mr. Jones, you are 45 years old and you have elevated total cholesterol and a "good" cholesterol level of 40; your blood pressure is in the prehypertensive range; and your body mass index places you in the obese category. It is excellent that you do not smoke. Looking at your risk factors together, you have a 3% chance of developing coronary heart disease in the next 10 years. But your lifetime risk is much higher than that. We have recent data to show that a man with your level of risk factors has a 50% chance for cardiovascular disease during the remainder of your lifespan. This is a 1 in 2 chance. We can lower your lifetime risk by lowering your risk factors now. This will involve lifestyle changes and, most likely, medication to lower your cholesterol.

Articulating the estimated 10-year risk for CHD along with lifetime risk to a younger or middle-aged patient may lead to greater motivation to adopt therapeutic lifestyle changes and adhere to medication recommendations. Currently, validation studies are underway for lifetime CVD risk estimates, and, in the near future, nurses will be able to communicate to patients a more comprehensive assessment of their CVD risk. Furthermore, since the absence of known risk factors is associated with a very low lifetime risk for CVD and a longer survival, nurses in primary care settings should focus their efforts on counseling patients to prevent the development of risk factors.

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