Atherosclerotic Cardiovascular Disease Risk and Evidence-based Management of Cholesterol.

An elevated level of low-density lipoprotein cholesterol is directly associated with development of atherosclerotic cardiovascular disease, which may present as coronary heart disease, stroke, and peripheral arterial disease. The new cholesterol management guidelines from the American College of Cardiology and the American Heart Association aim to address a comprehensive approach to prevent and reduce the risk of atherosclerotic cardiovascular disease. The new guidelines recommend initiation of heart healthy lifestyle modifications and 3-hydroxy-3-methylglutaryl coenzyme-A reductase inhibitor ("statin") therapy in individuals who are at a high risk for atherosclerotic cardiovascular disease. It is estimated that these guidelines could result in "statin" therapy for one in every three adults in the United States. This article presents a review of the current cholesterol management guidelines, recommendations from relevant randomized controlled trials and meta-analyses obtained from the searches in Medline/PubMed and Cochrane Database of Systematic Reviews, and publications from the Centers for Disease Control and Prevention, the Centers for Medicare and Medicaid Service, and the United States Preventive Services Task Force.

Introduction

Heart disease is the leading cause of death in the United States. High cholesterol increases the risk of developing cardiovascular (CV) disease.[1] About 45% of Medicare beneficiaries have high cholesterol, making it the second most common condition among all of the out-patient medical office encounters.[2] An elevated level of low-density lipoprotein cholesterol (LDL-C) is directly associated with development of atherosclerotic cardiovascular disease (ASCVD), which includes coronary heart disease (CHD), stroke, and peripheral arterial disease (PAD).[3] Although approximately 71 million adults in the United States have elevated LDL-C, less than half receive treatment, and only a third have LDL-C in the desired target level.[4]

Old concept

In the United States, cholesterol screening has been recommended for men of ages 35 and older, for women of ages 45 and older, and for men and women of ages 20 and older if they are at increased risk for CHD.[5] The practice of cholesterol management is based on the recommendations to treat elevated LDL-C beyond a specific goal in individuals who fall into a specific cardiovascular disease (CVD) risk category as per the guidelines of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults, also known as Adult Treatment Panel-III (ATP-III).[6]

New concept

The goals of the new cholesterol management guidelines include the prevention of ASCVD, improving the management of individuals who have ASCVD, and promoting optimal ASCVD care.[3] An expert panel was appointed for detection, evaluation, and treatment of cholesterol in adults (Adult Treatment Panel-IV)[7] in order to develop evidence-based guidelines, which follow the practice guidelines and the evidence-based standards set by the Institute of Medicine report.[8] The recommendations made by the expert panel aim to assess CV risk, reduce CV risk by modification of lifestyle factors, guide maintenance of an ideal body mass index, and manage blood cholesterol. After an extensive review of the data from randomized controlled trials (RCTs), systematic reviews and meta-analyses of RCTs, the panel developed these cholesterol management guidelines in order to reduce risk of ASCVD, not just the prevention of CVD alone as proposed by the ATP-III.[9] The RCTs have shown that the increased ASCVD risk is not only associated with elevated LDL-C levels, but also factors such as gender, race, tobacco smoking, hypertension, and diabetes mellitus should be included in the comprehensive management of cholesterol.[10] The guidelines recommend beginning cholesterol screening in all adults who are 21 years or older.[3] The panel did not find evidence to support the titration of cholesterol lowering drug therapy to achieve target LDL-C or nonhigh-density lipoprotein cholesterol (non-HDL-C) levels.[36] Lifestyle modifications are the critical components of ASCVD risk reduction.[3] These include adherence to a heart healthy diet, regular exercise, maintenance of a healthy weight, and avoidance of tobacco products.[11] The panel also found that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (“statins”) are the only cholesterol lowering drugs that have shown ASCVD risk reduction,[12] and each 39 mg/dL reduction in LDL-C by a statin reduces the risk of ASCVD by 20%.[3] In order to reduce the risk of ASCVD an appropriate intensity of statin therapy should be used [Table 1]. As far as the nonstatin cholesterol-lowering drugs are concerned, the panel found no evidence to support the use of this category of drugs either as monotherapy or in combination with a statin.[1314] The panel also identified the high-risk groups that do not benefit from statin therapy.[3]

Table 1

Intensity of statin therapy

New Management Guidelines

The benefits of lipid lowering drug “statin” therapy outweigh the risks in the four groups of patients who are at increased risk of ASCVD [Table 2, Figure 1].[151617181920212223242526272829303132333435363738] In patients with LDL-C greater than 190 mg/dL and/or triglyceride greater than 500 mg/dL it is necessary to investigate and correct the common causes of secondary hyperlipidemia [Table 3] before initiation of statin therapy.[48] The panel does not support “statin” therapy in patients who are older than 75 years without clinical ASCVD,[4950] who are on hemodialysis,[19] and who suffer from New York Heart Association class II, III, or IV heart failure.[51] The role of additional factors, such as biomarkers and noninvasive tests, [Table 4] is limited to patients who either do not qualify in the four statin benefit groups, or in whom it is unclear to make a decision of initiating statin therapy.[3]

Table 2

Key recommendations: Four statin benefit groups

Figure 1

Flow Diagram of Cholesterol Management. (ASCVD = Atherosclerotic Cardiovascular Disease; LDL-C = Low-density Lipoprotein Cholesterol; DM = Diabetes Mellitus; MIST = Moderateintensity statin therapy; HIST = High-intensity statin therapy; M-HIST = Moderate to high-intensity statin therapy.)

* See Table 4.

Table 3

Common causes of secondary hyperlipidemia

Table 4

Additional ASCVD risk factors

ASCVD Risk Assessment

A comprehensive tool, known as Pooled Cohort Risk Assessment Equation (PCRAE),[10] for the prediction and assessment of 10-year risk of an ASCVD event has been developed, which contrasts with the conventional risk assessment of CHD alone.[9] This equation was developed after an extensive review of diverse participants from several large studies. This equation should be used in women and men aged 40–79 who have LDL-C levels of 70–189 mg/dL. The equation includes risk factors such as: gender, age, race (African-American or non-Hispanic Caucasian), total cholesterol, HDL-C, systolic blood pressure, receiving treatment for hypertension, diabetes mellitus, and smoking. The risk of ASCVD is generally lower in Hispanic and Asian populations, and higher in American-Indian populations compared with non-Hispanic Caucasians. For the purpose of risk assessment, patients of all other races should be entered as non-Hispanic Caucasian. The PCRAE calculator is easy to download as a Microsoft Excel auto-calculator.[3]

It is evident that gender, age, and race play major role in the risk assessment; changes in lifestyle can modify factors like blood pressure, diabetes mellitus, and smoking, which can alter the calculated 10-year risk of ASCVD in the same patient [Table 5]. The new guidelines are designed to address the context of a patient to be the prime basis of decision-making by the clinicians. Several concerns have been raised regarding potential recruitment of a larger number of the United States’ population for statin therapy following the current cholesterol guidelines,[52] but the recommendations are based on the current evidence-based data that supports global CV risk reduction.[353]

Table 5

10-year risk of ASCVD by pooled cohort risk assessment equation

Most Effective Therapeutic Agent – Statin

The data from RCTs and meta-analysis of RCTs[3] has shown that use of a “statin” provides substantial benefits in primary prevention of ASCVD and risk reduction in patients with LDL-C levels of 70 mg/dL and above.[1654] Statins have also shown similar benefits in patients with hypertension,[55] diabetes,[39] low HDL-C,[15] elevated C-reactive protein,[38] etc. Additionally, it has been confirmed by the Cochrane meta-analysis[17] and the meta-analysis by the Cholesterol Treatment Trialists[1218] that statin therapy for primary prevention reduces fatal and nonfatal ASCVD.

An effective dose statin therapy has been defined as high-intensity or moderate-intensity [Tables 1 and 6]. The panel found that both high-intensity and moderate-to-high-intensity statin therapy are effective and safe in ASCVD risk reduction. On the contrary low-intensity statin therapy (e.g., Simvastatin 10 mg, Pravastatin 10–20 mg, Lovastatin 20 mg, Fluvastatin 20–40 mg, Pitavastatin 1 mg) may achieve a target LDL-C goal (as per ATP-III guidelines) without effective ASCVD risk reduction.[3] Similarly, patients may receive an ineffective low-intensity statin therapy with a nonstatin drug combination for presumed safety concerns of statin in order to achieve a specific target LDL-C goal, which does not offer ASCVD risk reduction either.[3] Patients on statin should be monitored for muscle injury, hepatic injury, new-onset diabetes, and other safety concerns [Table 7]. The risk of statin associated myopathy and hemorrhagic stroke is minimal compared with the excess risk of ASCVD due to lack of statin therapy.[12] Additional factors that influence ASCVD risk [Table 4] should be considered in the group of patients in whom the benefit of statin therapy for ASCVD prevention is less clear, such as in the case of patients without clinical ASCVD and without diabetes mellitus who are aged between 21 and 39 years and have LDL-C in the range of 71–189 mg/dL.[3]

Table 6

Evidence based recommended statins

Table 7

Statin safety: NHLBI grading the strength of recommendations

Clinical Impact

It is estimated that the new cholesterol management guidelines could result in statin therapy for one in every three adults in the United States.[52] The new cholesterol management approach is primarily geared toward a comprehensive risk reduction of ASCVD, not just to attain a specific LDL-C goal level [Figure 2]. There are some limitations of the new guidelines in specific groups, such as younger adults (aged 21–39 years), individuals with low 10-year ASCVD risk but high lifetime risk based on additional factors, individuals with serious comorbidities, such as HIV infection, rheumatologic disorders, solid organ transplant recipients. Future guidelines may provide management of hypertriglyceridemia, use of non-HDL-C in decision making, or use of therapeutic markers, such as Apo B, Lp(a), LDL particle size. More recent studies suggest a proper method of estimation of LDL-C level based on a calculation that uses a variable ratio of triglyceride (TG) and very low-density lipoprotein cholesterol (VLDL-C), and not just the standard 5:1 ratio of TG:VLDL-C as proposed by the Friedewald equation.[6364] This may change the estimation of LDL-C level and allow clinicians to assign their patients appropriately into more accurate ASCVD risk category.

Figure 2

Suggested Steps to Manage Cholesterol. (ASCVD = Atherosclerotic cardiovascular disease, LDL-C = Low-density lipoprotein cholesterol, DM = Diabetes mellitus, HIST = High-intensity statin therapy, MIST = Moderate-intensity statin therapy, HD = Hemodialysis, NYHA = New York Heart Association.) Information from reference 3.

Conclusion

The current cholesterol management guidelines provide a comprehensive approach toward ASCVD risk reduction. It is a major shift from the old approach in which a target LDL-C was aimed in order to reduce cardiovascular risk only for the specific cardiovascular risk stratified patient categories. Moderate-intensity and high-intensity statin therapies are safe and effective interventions that have shown major ASCVD risk reduction in statin benefit groups. Clinicians are encouraged to use clinical judgment based on risks, benefits, drug interactions, and patient preference to statin therapy.