Arrhythmias and Coronary Heart Disease

Occasional cardiac arrhythmias have been demonstrated in normal subjects during experimental hypoglycaemia studies. It would now be considered unethical to perform hypogly-caemia studies in patients with known heart disease, but many studies were performed in an earlier era both in diabetic and non-diabetic patients with coronary heart disease to examine the effects of acute hypoglycaemia (Fisher and Frier, 1993). Sinus bradycardia has been reported in a very small number of cases (Pollock et al., 1996; Navarro-Gutierrez et al., a

Time (min)

Figure 12.5 Mean response of (a) heart rate, (b) systolic blood pressure and mean arterial blood pressure, and (c) left ventricular ejection fraction following intravenous injection of insulin at time 0. (R = autonomic reaction). Reproduced from Frier et al. (1987), with kind permission from Springer Science and Business Media

Time (min)

Figure 12.5 Mean response of (a) heart rate, (b) systolic blood pressure and mean arterial blood pressure, and (c) left ventricular ejection fraction following intravenous injection of insulin at time 0. (R = autonomic reaction). Reproduced from Frier et al. (1987), with kind permission from Springer Science and Business Media

2003). Atrial fibrillation has been described in some patients and in addition there are several case reports of atrial fibrillation following hypoglycaemia in insulin-treated patients who had no overt evidence of heart disease (Collier et al., 1987; Baxter et al., 1990; Odeh et al., 1990; Navarro-Gutierrez et al., 2003).

There is a single report of a transient ventricular tachycardia occurring during experimental hypoglycaemia in a non-diabetic patient with coronary heart disease, and ventricular tachycardia was recently documented in an elderly non-diabetic man who developed hypoglycaemia during emergency surgery (Chelliah, 2000). There have been case

Box 12.5 Cardiac effects of acute hypoglycaemia

• Increased heart rate

• Widening of pulse pressure

• Arrhythmias

• Silent myocardial ischaemia

Myocardial infarction reports, with ECG evidence, of ventricular ectopics, sustained ventricular tachycardia, ventricular fibrillation and asystole during hypoglycaemia in diabetic patients (Shimada et al., 1984; Burke and Kearney, 1999). Obviously this does not exclude the possibility of these arrhythmias occurring more frequently in clinical practice, as these arrhythmias will be fatal if uncorrected. In most instances it is unlikely that any precipitating cause of the arrhythmia would be sought; hypoglycaemia may not have been recognised and we have already alluded to the difficulties in establishing a putative diagnosis of hypoglycaemia at post-mortem.

Angina and Myocardial Ischaemia

The provocation of angina and myocardial ischaemia by exercise is well documented in clinical practice. By contrast, acute hypoglycaemia, which provokes a more intense haemodynamic response and in particular a greater increase in plasma epinephrine, has rarely been documented as provoking anginal chest pain, either in the experimental situation or in anecdotal case reports. A literature search of over 6000 insulin tolerance tests recorded only two episodes of angina. This may reflect the fact that coronary heart disease would be considered a contraindication to insulin tolerance testing, and in clinical practice clinicians may accept higher ambient blood glucose concentrations in diabetic patients with known coronary heart disease to avoid hypogly-caemia. It is also possible that the haemodynamic changes of hypoglycaemia are so profound that they are frequently fatal in patients with coronary heart disease, and hypo-glycaemia is probably overlooked as a provoking cause when determining cause of death.

It is now well established that many episodes of ST segment depression on the ECG are not associated with angina, and constitute 'silent ischaemia'. One case has been described during 24-hour ECG monitoring of hypoglycaemia that provoked silent ischaemia in a diabetic patient with suspected coronary heart disease (Pladziewicz and Nesto, 1989). More recently, 72-hour continuous glucose monitoring with simultaneous cardiac Holter monitoring was performed in 21 patients with coronary heart disease and insulin-treated type 2 diabetes (Desouza et al., 2003). A total of 26 episodes of symptomatic hypoglycaemia were documented, with ten episodes of chest pain, four of which were associated with ECG abnormalities. Twenty eight episodes of asymptomatic hypoglycaemia were documented, with no episodes of chest pain, and two of these were associated with ECG abnormalities. Hypoglycaemia was therefore frequently associated with ECG abnormalities, some of which also were associated with chest pain, in this group of well-controlled patients.

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