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Treatment guidelines have proliferated in cardiology, although most guideline recommendations are not supported by clinical trial evidence. What is considered to be a normal cholesterol level has progressively declined over the past 50 years, with the increasing realization that "normal" is far from optimal and that lower is better. The first important United States and Canadian cholesterol guidelines were published in 1988, and recommended diet for 6 months to be followed by consideration of bile acid sequestrants or nicotinic acid. Over the ensuing 25 years guidelines have changed rapidly and dramatically in response to a large number of definitive clinical trials, usually with statins. Low-density lipoprotein cholesterol targets have moved progressively lower, and in some guidelines, have been abandoned entirely. The concept of selecting patients for treatment according to the absolute risk reduction expected from treatment on the basis of clinical trial data seems to be a rational approach. For secondary prevention, some patients are still untreated or undertreated, presenting an opportunity for improving outcomes.

Lipid abnormalities are prevalent among persons living with HIV infection and contribute to increasing the risk of cardiovascular events. Antiretroviral therapy (ART) is associated with lipid abnormalities, most commonly hypertriglyceridemia, but also increases in low-density lipoprotein cholesterol and total cholesterol. Different classes of ART, and different drugs within classes, have differing effects on lipid levels, but in general newer drugs have more favourable effects compared with older ones. Low-level inflammation and chronic immune activation act on lipids through a variety of mechanisms to make them more atherogenic. As a consequence, risk is higher than would be expected for any given cholesterol level. Clinical outcome trials of cholesterol-lowering therapies have not yet been completed in people living with HIV, so that treatment decisions depend on extrapolation from studies in uninfected populations. Traditional risk assessment tools underestimate cardiovascular risk in individuals with HIV. Statins are the mainstay of lipid-lowering drug treatment; however, drug-drug interactions with ART must be considered. Simvastatin and lovastatin are contraindicated in patients taking protease inhibitors, and the dose of atorvastatin and rosuvastatin should be limited to 40 mg and 10 mg/d with some ART combinations. Switching from older forms of ART to lipid-friendly newer ones is a useful strategy as long as virologic suppression is maintained, but adding a statin lowers low-density lipoprotein cholesterol more effectively. Studies indicate that lipid abnormalities are not treated as aggressively in individuals living with HIV as they are in uninfected people, making this an opportunity to improve care.

Since 2014, guidelines for the management of lipid disorders to reduce cardiovascular (CV) events have been updated in the United States, the United Kingdom, Europe, and Canada. Some of these guidelines are almost entirely evidence-based whereas others are a mix of evidence and expert opinion. Guidelines differ on such simple questions as to whether blood samples should be fasting or nonfasting, and whether low-density lipoprotein cholesterol (LDL-C) or another lipid parameter should be the primary focus of treatment. Different risk assessment tools are recommended by different guidelines. Lifetime risk is highlighted in some guidelines, with the suggestion that earlier treatment will reduce lifetime risk in younger people even when short-term risk is low. Some guidelines have numerical treatment targets that differ according to level of risk, while others eschew targets but recommend statins at high or moderate intensity to reduce LDL-C by ≥ 50% or 30%-50%, respectively. Statins are the backbone of therapy in all guidelines. Ezetimibe produced a 6.4% relative risk reduction in the only large clinical outcomes trial in which it was tested, and is recommended for high-risk patients with an inadequate response to statins, despite the high number needed to treat to prevent 1 CV event. Proprotein convertase subtilisin/kexin 9 inhibitors lack outcome data to support their use, but are approved for patients with familial hypercholesterolemia or clinical atherosclerotic CV disease who require additional LDL-C lowering beyond statins. All these new guidelines are aimed at improving the problem of undertreatment of high-risk groups, leading to better outcomes for these patients.

Biomarkers and imaging trials have often been used as guideposts in the development of drugs for atherosclerosis. This article explores the role of biomarkers and imaging trials in the development of 4 drugs: rimonabant, torcetrapib, ezetimibe, and niacin. Rimonabant, a selective cannabinoid-1 receptor, causes weight loss and exerts favourable effects on lipid biomarkers. An intracoronary ultrasound study showed no effect for the primary but significant benefit for the secondary end point. A large clinical outcomes trial was halted when it became apparent that the drug caused serious psychiatric side effects, including suicide. Torcetrapib, a cholesteryl ester transfer protein inhibitor, lowers low-density lipoprotein (LDL) cholesterol and induces a marked increase in high-density lipoprotein (HDL) cholesterol. However, a large clinical outcomes trial was halted very prematurely due to a 58% increase in all-cause mortality. Neutral imaging studies were reported later. Ezetimibe lowers low density lipoprotein cholesterol but did not reduce carotid intima-media thickness, and there is as yet no clinical trial evidence that it reduces cardiovascular events after a decade on the market. Niacin exerts favourable effects on lipid biomarkers and has shown regression of atherosclerosis in small carotid imaging trials, but did not reduce events in a recent clinical trial that was stopped early due to a lack of efficacy. In summary, favourable effects on lipid biomarkers often do not translate into clinical benefit, and imaging trials, which focus on a narrow measurement of atherosclerosis, are also often not helpful.