PHILADELPHIA — Decreased coronary flow reserve during periods of hypoglycemia may raise the risk for myocardial ischemia in patients with type 1 diabetes, a researcher said here.
“Low blood sugar provokes profound hemodynamic effects through sympathoadrenal stimulation. It is associated with an increase in heart rate and myocardial contraction and, thereby, cardiac output. Also it decreases central blood pressure and increases arterial elasticity in normal individuals, causing the heart to generate a pulse wave that bounces off the central arteries during diastole, thereby aiding coronary filling. However, in patients with type 1 diabetes, especially of longer duration, arterial stiffness causes the pulse wave to return during systole and there is suboptimal filling of the coronary flow,” Radzi M. Noh, MRCP, of the Royal Infirmary of Edinburgh, said during a presentation. “In addition to increasing myocardial workload, it increases the risk for myocardial ischemia.”
To evaluate whether periods of hypoglycemia worsened this risk, Noh and colleagues examined participants during periods of experimental hypoglycemia. They included 16 participants with type 1 diabetes of varying duration and 10 healthy, age-matched controls. These participants were aged 18 to 46 years (median, 29 years); had HbA1c ranging from 7% to 9% (median, 8.3%), no microvascular complications and were being treated with insulin only.
The researchers used a hyperinsulinemic glucose clamp to induce hypoglycemia and measured coronary flow reserve during euglycemia, defined as 4.5 mmol/L, and hypoglycemia, defined as 2.5 mmol/L. They employed transthoracic echocardiography to assess coronary blood flow velocity in the left anterior descending coronary artery before and during adenosine-induced microvascular hyperemia. Coronary flow reserve is measured as the maximum hyperemic blood flow velocity divided by baseline blood flow velocity.
Data indicated a trend toward lower coronary flow reserve in patients with diabetes vs. the control arm (3.69 vs. 4; P=.07). Further, at 3.56, patients with a longer duration of diabetes had the lowest coronary flow reserve when compared with both patients with and without diabetes. In contrast, coronary flow reserve rose slightly in the control group vs. the diabetes group (4.08 vs. 3.53; P<.05).
“During acute hypoglycemia, a modest reduction of coronary flow reserve may be well tolerated in healthy individuals, but may promote ischemia in older people with diabetes who have coronary heart disease,” Noh concluded. – by Melissa Foster
For more information:
Noh RM. Abstract #171-OR. Presented at: the American Diabetes Association’s 72nd Scientific Sessions; June 8-12; Philadelphia.
Disclosure: Dr. Noh has received a research grant from the Scottish Chief Scientists Office.