If a man is as old as his arteries you should, according to one traditional axiom, add 20 years for diabetes. Heart disease accounts for between two-thirds and three-quarters of all deaths in type 2 diabetes, and is the leading cause of death in type 1, not least because it abolishes the premenopausal protection from coronary disease enjoyed by women. 30 years ago, these effects attracted less attention: a coronary epidemic was sweeping through the general population, diabetes was less common, and the workload of a coronary care unit was not greatly affected. Cardiologists were well aware of the poor outcome of heart disease in diabetes, but did not consider this amenable to therapy, to the extent that affected individuals were often excluded from their clinical trials.
All this has changed. For one thing, there has been a sharp downturn in the number of coronary heart attacks within the general population. The invention of the biochemical infarct, known by the barbarous acronym NSTEMI (non-ST-elevation myocardial infarction), has helped to fill the beds of the interventional cardiologists, but the rise of diabetes, a disease in which coronary risk has not diminished, has been another major development. Some two out of three patients admitted to the coronary care units in developed countries now have glucose intolerance or overt diabetes.
Cardiologists have, therefore, started to learn a lot more about diabetes, and diabetologists have become more involved in the follow-up of cardiac patients. Hence the rationale for this excellent book, well edited by Miles Fisher and John McMurray. Diabetic Cardiology provides a useful meeting point for two specialties that do not routinely associate together. In part, this lack of common ground is a matter of temperament, for the high-adrenaline activities of the interventional cardiologist bear little resemblance to the more pedestrian life of the diabetologist.
Basic research has helped to bring the specialties together. Cardiologists segregate according to their interest in the lumen or the lining of arteries. Luminal cardiology combines the skills of the electrician with those of a plumber—albeit to an exalted degree—but the aspiring researcher will often find the endothelium a more challenging area of investigation. And here both cardiologist and diabetologist encounter one of the mysteries of diabetes, the elusive quantum of risk that remains when all other known risk factors have been accounted for. Associated risks arise by virtue of the overlap between diabetes, hyperlipidaemia, hypertension, central obesity, and a clutch of other emerging cardiovascular risk factors. Behind all this looms insulin resistance: cause, consequence, or collateral of middle-age spread in our population, and the career equivalent of the Bight of Benin for many a young investigator (“Sailor beware the Bight of Benin, there's one comes out for forty goes in”).
Insulin resistance causes confusion because the term has a precise meaning in specific contexts, but very little in its general application. Although a mere comparative measure, it is all too easily portrayed as a state or entity, thus providing an excellent example of the nominal fallacy in medicine. Perdition confronts the investigator who applies this misty notion to the welter of cytokines, inflammatory markers, and haemostatic variables that stray from their normal paths in the course of the metabolic syndrome (another example of the nominal fallacy), and who goes on to pour the resulting mix into the blender of logistic regression analysis. The utility of this proceeding was well described by the biologist Ernst Mayr when he commented that “in dealing with a complex system, an explanation can hardly be considered very illuminating that states: ‘Phenomenon A is caused by a complex set of often interacting factors, one of which is B’. Yet this is about all that one can say”.
Diabetic Cardiology has the wisdom to skim lightly yet knowledgeably over this disputed territory and to focus on the more practical clinical outcomes. Here, in contrast, it is impressive to see how much useful practical information has been gained and neatly packaged. It is particularly helpful to be steered through the proliferation of cardiac trials with uplifting acronyms (GUSTO is a personal favourite). We have learned a great deal about the effect of drugs on the outcome of the coronary episode, and of their added relative benefit in high-risk patients with diabetes. Curiously, the one agent the use of which remains uncertain is insulin itself. As a houseman, I well remember putting up glucose, potassium, and insulin infusions on the coronary care unit, a manoeuvre that was considered by the junior staff to presage the early demise of the recipient. Now, even after the two DIGAMI studies, uncertainty still reigns. Good glucose control is a potentially life-saving intervention, but it remains to be determined what we should use, when, and how vigorously we should use it, and for how long. As always, the simplest questions are the most difficult to answer.