Hypoglycemia-induced silent myocardial ischemia

Abstract

Out-of-hospital ambulatory Holter monitoring of the ST segment in patients with coronary artery disease has shown that most silent ischemic events occur during activities of daily living. 1 Particular activities that may trigger silent ischemia include smoking, cold exposure and mental stress. 2 Recent studies have also shown that silent ischemia may be more common in diabetics with coronary disease than their nondiabetic counterparts. 3,4 We recently studied a diabetic patient with coronary artery disease in whom episodes of symptomatic and asymptomatic ischemic ST segment depression were documented on Holter monitoring. This report describes an episode of silent ischemia triggered by insulin-induced hypoglycemia and offers an explanation for its occurrence. This diabetic patient with coronary artery disease had multiple episodes of myocardial ischemia during ambulatory Holter monitoring. One of the episodes of silent ischemia occurred at rest, was induced by an insulin reaction and occurred at a heart rate well below that associated with ischemia on exercise testing. The circumstances surrounding this episode are similar to most silent ischemic events that are probably triggered by a modest increase in myocardial oxygen demand and a concomitant decrease in coronary blood supply. Hypoglycemia causes the release of 4 counterregulatory hormones: epinephrine (and to a lesser extent, norepinephrine), glucagon, cortisol and growth hormone. 5 The catecholamines have the greatest immediate cardiovascular effect because they increase myocardial oxygen demand but may also decrease coronary blood supply by promoting vasoconstriction at the sites of coronary stenoses. 6 Other activities at rest that may trigger silent ischemia, such as public speaking and mental stress, are associated with elevated catecholamine levels and may have a similar underlying pathophysiologic basis. As asymptomatic ischemia may be more common in diabetics than nondiabetics with coronary artery disease, such episodes of hypoglycemia-induced silent ischemia may go undetected. For the diabetic patient with coronary artery disease, excessive insulin administration resulting in hypoglycemia should be considered a trigger stimulus for silent ischemia.