Surrogate end-points of cardiovascular disease can provide useful information in cross-sectional, prospective and interventional studies. They provide information on association with risk factors, natural history and factors associated with disease progression. Because every participant can reach an end-point, sufficient power can be attained with much smaller numbers of subjects in surrogate end-point studies than in studies that use clinical endpoints, so that the costs are likely to be substantially less. Measures of carotid intima-media thickness (IMT) by B-mode ultrasonography and of coronary calcification by electron beam computed tomography (EBCT) appear to be the most promising surrogate end-points.

In one of the biggest dilemmas facing cardiovascular clinical research, clinical trials are increasingly being required to show benefits on clinical end-points rather than surrogate end-points, while at the same time the incremental benefits of newer treatments are getting smaller. These two factors have a huge impact on sample size, which has led some investigators to design trials to show that the new treatment has an effect similar to that of the standard, rather than outright superiority. Recent examples of fibrinolytic trials that have demonstrated similar effects of two drugs are ASSENT (Assessment of the Safety and Efficacy of a New Thrombolytic)-2, GUSTO (Global Use of Strategies to Open Occluded Coronary Arteries)-III, and COBALT (Continuous Infusion Versus Double-Bolus Administration of Alteplase) [1,2,3,4]. However, as discussed by several authors [5,6,7,8], there are issues with trials of this type that make them considerably less credible than superiority trials.

Treatment to prevent progression of heart failure has been targeted to reverse the consequences of heart failure and to a lesser extent the cause – the atherosclerotic plaque itself. Less than 50% of patients with heart failure are treated with lipid intervention. Heart failure (New York Heart Association [NYHA] functional classes I and II) is associated with an increase in low-density lipoproteins (LDL) and triglycerides while high-density lipoproteins (HDL) is lowered. In NYHA class IV, cholesterol is reduced due to depressed production in the liver. Although lipoproteins, especially LDL and HDL, may have some protective effect in binding and neutralising endotoxins released from the intestine during terminal heart failure, observational studies in patients with heart failure strongly suggest that lipid modification with statins may reduce progression of heart failure as well as reducing heart failure mortality.

The publication of the results of the Swedish Trial in Old Patients with Hypertension-2 (STOP-2) and the termination of the doxazocin arm of the Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack (ALLHAT) study again raise the question of whether all antihypertensives deliver equal cardiovascular outcome benefits. Data from research on congestive heart failure and from the Heart Outcomes Prevention Evaluation (HOPE) trial illuminate the roles and possible mechanisms of humoral mediators of vascular damage, suggesting, first, that some antihypertensives (thiazides, beta-blockers, and angiotensin-converting enzyme inhibitors) can deliver more improvement in outcomes than other agents and, second, that decisions on whom to treat are best made based on risk appraisal, not merely pressures.

Statins reduce mortality of patients with coronary artery disease (CAD). However, by protocol, trials have excluded patients with chronic heart failure. Since the prevalent etiology of heart failure is CAD, preventing CAD may prevent heart failure progression. Statins may have other beneficial effects besides cholesterol lowering, such as anti-inflammatory properties and improvement of endothelial function. On the contrary, high levels of cholesterol can be beneficial in heart failure patients on the basis of the ability of serum lipoproteins to modulate inflammatory response. Furthermore, statins affecting mitochondrial function can have a deleterious effect on skeletal or cardiac muscles. Despite all these conflicting data, there is no evidence from trials on the effects of statins in patients with heart failure. For this reason, the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico (GISSI) investigators planned a controlled trial testing the effect of statins in patients with heart failure of different etiology.

Treatment decisions related to disease prevention are often based on two conventional and related assumptions. First, an intervention-induced change in a surrogate marker (such as high-density lipoprotein [HDL]-cholesterol) in the desired direction translates into health benefits (such as reduction in coronary events). Second, it is unimportant which interventions are used to alter surrogate markers, since an intervention benefit is independent of the means by which it is achieved. The scientific foundation for these assumptions has been questioned. In this commentary, the appropriateness of relying on low levels of HDL-cholesterol for treatment decisions is reviewed. The Veterans Affairs - HDL-Cholesterol Intervention Trial (VA-HIT) investigators recently reported that only 23% of the gemfibrozil-induced relative reduction in risk of coronary events observed in the trial could be explained by changes in HDL-cholesterol between baseline and the 1-year visit. Thus, 77% of the health benefit to the participants was unexplained. Other possible explanations are that gemfibrozil has multiple mechanisms of action, disease manifestations are multifactorial, and laboratory measurements of HDL-cholesterol are imprecise. The wisdom of relying on levels and changes in surrogate markers such as HDL-cholesterol to make decisions about treatment choices should questioned. It seems better to rely on direct evidence of health benefits and to prescribe specific interventions that have been shown to reduce mortality and morbidity. Since extrapolations based on surrogate markers may not be in patients' best interest, the practice of medicine ought to be evidence-based.

Research Article: Current Controlled Trials in Cardiovascular Medicine

The observational studies of hormone users are compromised by systematic biases that lead to an overestimation of benefit and an underestimation of risk. Studies of mechanism could support either benefit or harm. The results of clinical trials of oral hormone therapy in women with existing coronary heart disease (CHD) have been uniformly disappointing. The largest trial found an early increased risk for CHD and for venous thromboembolism. Postmenopausal hormone therapy should not be considered for CHD prevention until methods for excluding high-risk women have been established, and until the results of the long-term trials have shown benefit. There is a need for clinical trials of nonoral estrogens.

Clinical trialists and statisticians are very wary of subgroup analysis, for good reasons. Clinicians have to deal with situations in which subgroups of patients differ widely from one another in their prognosis and response to treatment. Few trials are large enough to demonstrate convincingly these differences in outcome, but often provide suggestive evidence. Should we ignore this and treat all patients as the same, or should we allow dubious statistical evidence to buttress biological plausibility in making clinical decisions?

Large numbers of observational studies have described a decrease in the incidence of cardiovascular disease in women taking hormone replacement therapy (HRT). The potential mechanisms for this effect are numerous, including direct effects on lipid levels and lipid metabolism, cardiovascular dynamics, and endothelial reactivity. The beneficial effects of HRT are probably affected by various factors, including the age of onset of therapy, the presence of coronary artery disease, the type of estrogen and whether it is used in combination with progesterone, concurrent modification of other cardiac risk factors, and duration of therapy. Until further prospective clinical trials are done, HRT should be considered in those women for whom the potential benefits exceed the potential risks, on the basis of an individualized patient evaluation.