Hypoglycaemia in Clinical Diabetes

272 MORTALITY, CARDIOVASCULAR MORBIDITY AND DIABETIC COMPLICATIONSImportance of Young People Without Typical Cardiac DiseaseWhen assessing the risk of sudden death in people with diabetes, the risks have to becompared with people without diabetes. Sudden unexpected death can occur in any youngperson irrespective of whether they have diabetes or not. The critical issue is whether suddendeath occurs more frequently in individuals with type 1 diabetes. Studies that have measuredthe frequency of sudden death in young people have reported rates around 1.3 to 8.5 per100 000 patient-years. Since they are based on large numbers of subjects these estimatesare probably more accurate than data reporting the risks in patients with type 1 diabetes.However, the figures suggest that the risk of sudden death is considerably greater in thosewith diabetes. Although it is difficult to be precise, the risk in patients with diabetes seemsto be around three times higher.RISK FACTORS FOR SUDDEN DEATHIn the general population, the most frequent cause of sudden death is a cardiac arrhythmia,mostly related to coronary heart disease; it is likely that the same problem occurs in peoplewith diabetes. Nevertheless, if sudden death is occurring more frequently in patients, thenadditional factors are probably responsible. Some of this increase may be a consequence ofthe more advanced or premature ischaemic heart disease which is associated with diabetes.In some people the development of hypoglycaemic convulsions may impose an additionalinsult, although the fact that most subjects were found with their bedclothes undisturbedis against the pre-terminal development of tonic-clonic convulsions. This scenario does notexclude other forms of seizure activity and a striking similarity exists between the syndromesof sudden death in epilepsy and diabetes (Brown et al., 1990; Nashef and Brown, 1996).A study using an implantable ECG recorder in 20 patients with epilepsy identified threepatients with potentially fatal asystole, and permanent pacemakers were inserted in fourpatients (Rugg-Gunn et al., 2004).When considering other factors, the strongest candidates are probably coexisting autonomicneuropathy and hypoglycaemia.Autonomic NeuropathyAutonomic neuropathy increases the risk of sudden death in patients with diabetes in some(Ewing et al., 1980) but not all (Sampson et al., 1990) studies. The exact cause of deathremains uncertain although most groups that reported increased risk of death have suggestedthat a cardiac arrhythmia is responsible. Some groups have reported lengthened QT intervalsin patients with autonomic neuropathy (Ewing and Neilson, 1990) highlighting the associationbetween prolonged QT intervals and the risk of sudden death in other conditionssuch as the congenital long QT syndrome (Ewing et al., 1991). However, it seems unlikelythat autonomic neuropathy alone could account for the greater risk of sudden death inyoung patients with diabetes. In those who died suddenly, autonomic function had seldombeen formally tested. Some subjects had advanced diabetic complications and would probablyhave had some degree of autonomic neuropathy, but a significant proportion of those