Abstract
In the era of evidence-based medicine, the use of guidelines to help clinicians manage common medical conditions is crucial. In developing guidelines, an enormous literature is reviewed so that the most up-to-date evidence is analysed to ensure that the appropriate conclusions are drawn. The current European Society of Cardiology/European Association for the Study of Diabetes (ESC/EASD) guidelines 1 provide a very detailed overview of the important issue of cardiovascular (CV) disease in the setting of patients with diabetes mellitus (DM).
Diabetes is a very common condition with an increasing prevalence worldwide. As CV complications are a major cause of early morbidity and mortality in patients with DM for physicians to have access to such guidelines should help ensure patients receive the most up-to-date and evidence-based care. There is a broad range of interactions between DM and CV disease, including, but not limited to, ischaemic heart disease; cardiomyopathy; arrhythmias, including atrial fibrillation; and peripheral vascular disease.
A major push among health organisations worldwide is to try and standardise the management of common conditions such as diabetes. It is felt this will result in improved outcomes for patients, reduced hospital admissions and naturally reduced health-care costs. Guidelines which are easily accessible to as many health-care professionals as possible should help ensure the standardisation of care where feasible.
For guidelines to be able to provide definitive advice concerning the appropriate investigation and treatment for specific conditions, there must be evidence available which the guidelines can draw on to justify their recommendations. One of the strengths of the current guidelines is looking at the areas where large trials provide convincing evidence of the benefit of certain therapies. This includes low-density lipoprotein (LDL) targets in the DM population and the advantage of surgical over percutaneous revascularisation in patients with multi-vessel disease. 2 The difficulty for the clinician occurs when using these guidelines in the context of managing an individual patient. Does the particular patient fit into the inclusion criteria for the particular trial while not having any of the exclusion criteria? One must remember these are guidelines and not rules, each patient is different and their overall treatment must be individualised to their particular situation. For example, in a DM patient with triple-vessel disease with discrete lesions but other co-morbidities which may make coronary bypass surgery too risky, percutaneous revascularisation may be the preferred therapy for that particular patient despite the guidelines recommending coronary bypass surgery in patients with DM and multi-vessel disease.
Another difficulty arises when trying to advise about areas where the evidence shows contradictory results. The guidelines summarise the major trials and try to draw appropriate conclusions. Such a controversy in the guidelines is the benefit of strict glycaemic control in reducing the risk of CV complications in patients with DM. The Diabetes Control and Complications Trial (DCCT) and United Kingdom Prospective Diabetes Study (UKPDS) trial showed a reduction in CV events in the intensely treated arm; however, in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial, 3 there was an increased mortality in the more aggressive glucose-lowering arm postulated to be due to increased hypoglycaemia. Thus, while the guidelines generally recommend achieving an HbA1C <7% in younger patients with shorter duration of DM, they acknowledge the need to approach this in an individualised manner. It is important that the attending physician assesses overall cardiac risk and is conscious of the potential dangers of short-term hypoglycaemia versus long-term risks of micro- and macrovascular complications.
The insightful commentary on the guidelines by Paneni 4 summarises areas where knowledge gaps exist in the area of CV disease and its interaction in DM subjects. The lack of level 1 evidence restricts definitive conclusions and recommendations to be drawn. In these areas, with a paucity of evidence, which are often very important for the clinician managing a diabetes patient, the guidelines cannot be relied on for how to deal with the specific issue. For example, screening an asymptomatic DM subject for the presence of coronary artery disease is a challenging area. It is well known that DM results in an increased risk of developing coronary artery disease, which is often asymptomatic, and this increases risk of sudden cardiac death and the development of a cardiomyopathy. Thus, intuitively, it would seem that detection of significant coronary artery disease and subsequent revascularisation should result in reduced morbidity and mortality in DM. However, no such evidence is available either in terms of which test to use in screening for the presence of coronary artery disease and whether revascularisation should be performed. In these areas, the decision will be based on the physicians own clinical judgement and personal preference with some limited guidance from the guidelines.
Thus, with the increasing focus on evidence-based medicine, comprehensive guidelines such as the recent ESC/EASD guidelines play a crucial role in helping ensure this occurs. Physicians can use these to help guide them in dealing with many areas of CV management in DM subjects with robust clinical trial data to back up their recommendations. Inevitably, knowledge gaps continue to exist, and it is impractical to expect all management decisions to be sourced from these guidelines. Ultimately, the physician will have to practice the ‘art’ of medicine in areas in which no reliable and reproducible evidence is currently available. In time, many of these areas will be addressed by current and future clinical trials designed specifically to address the areas where knowledge gaps exist.