RESUMEN
Prolonged cardiac repolarization causes fatal cardiac arrhythmias. There is evidence that these contribute to sudden death associated with nocturnal hypoglycemia in young people with diabetes. We measured cardiac repolarization (QT interval [QTc] and QT dispersion [QTd]) during experimental hypoglycemia with and without beta-blockade and potassium infusion to establish possible mechanisms. Two groups of 10 nondiabetic men (study 1 and study 2) each underwent four hyperinsulinemic clamps: two euglycemic (5 mmol/l) and two hypoglycemic (5 mmol/l and 2.5 mmol/l for 60 min each). Study 1 was performed with and without potassium infusion to maintain normal concentrations and study 2 with and without beta-blockade (atenolol, 100 mg/day for 7 days). QTd was unchanged during euglycemia but increased during hypoglycemia (55 ms, P < 0.0001 vs. baseline), which was prevented by potassium (6 ms, P = 0.78). QTc increased significantly during hypoglycemia alone (67 ms, P < 0.0001) and during potassium replacement (46 ms, P = 0.02). In study 2, the increase in QTd during hypoglycemia (68 ms, P < 0.0001) was prevented by beta-blockade (3 ms, P = 0.88). The increase in QTc during hypoglycemia (55 ms, P < 0.0001) was prevented by beta-blockade (1 ms, P = 0.98). Our data indicate that hypoglycemia causes an acquired long QT syndrome. Sympathoadrenal stimulation is the main cause, through mechanisms that involve but are not limited to catecholamine-mediated hypokalemia. These abnormalities are prevented by selective beta-blockade.
Asunto(s)
Presión Sanguínea/fisiología , Frecuencia Cardíaca/fisiología , Corazón/fisiopatología , Hipoglucemia/fisiopatología , Insulina/farmacología , Antagonistas Adrenérgicos beta/farmacología , Atenolol/farmacología , Glucemia/efectos de los fármacos , Glucemia/metabolismo , Presión Sanguínea/efectos de los fármacos , Epinefrina/sangre , Técnica de Clampeo de la Glucosa , Corazón/efectos de los fármacos , Frecuencia Cardíaca/efectos de los fármacos , Humanos , Hipoglucemia/inducido químicamente , Insulina/sangre , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Potasio/sangre , Potasio/farmacología , Valores de ReferenciaRESUMEN
AIMS: Sudden death in young diabetic patients has been associated with nocturnal hypoglycaemia perhaps as a result of cardiac dysrhythmias following abnormal cardiac repolarization during hypoglycaemia. It was therefore important to compare the effect of soluble human insulin (HI) and a rapid-acting insulin analogue, insulin aspart (IAsp), on these aspects of cardiac function. METHODS: A total of 17 healthy males underwent identical hyperinsulinaemic hypoglycaemic clamps with blood glucose maintained at 5 mm for 30 min and reduced to 2.5 mm after an additional 30 min. Subjects received either HI or IAsp on two different occasions separated by 4-6 weeks. Regular measurements were made of two measures of cardiac repolarization, QT dispersion and QTc as well as of counter-regulatory hormones. RESULTS: The blood glucose lowering effect did not differ between IAsp and HI and the clearance rates were similar (HI mean +/- SD 1.24 +/- 0.12 l h(-1) kg(-1), IAsp mean +/- s.d. 1.22 +/- 0.32 l h(-1) kg(-1)). There were similar significant increases but no difference between treatments in QTc after hypoglycaemia induced by either IAsp or HI (480 +/- 37 ms vs 480 +/- 25 ms; NS). However, QT dispersion during hypoglycaemia was less pronounced with IAsp than with HI (92 +/- 36 ms vs 107 +/- 42 ms; P < 0.05). Plasma adrenaline increased significantly and similarly after both insulins (initial and final concentration, HI, 0.23 +/- 0.01 to 4.87 +/- 0.48 nm, P < 0.001, IAsp, 0.24 +/- 0.01 to 4.99 +/- 0.48 nm, P < 0.001). Serum potassium decreased significantly but by a similar amount between the groups (initial and final concentration, HI, 4.18 +/- 0.3 to 4.2 +/- 0.2 mm, P < 0.001, IAsp, 4.2 +/- 0.3 to 4.2 +/- 0.3 mm, P < 0.001). CONCLUSIONS: Soluble human insulin and insulin aspart had similar effects upon hypoglycaemia-induced alterations in cardiac repolarization, presumably because the effects of both regular insulin and insulin aspart on the sympathoadrenal response and potassium concentration were the same.