What is diabetic cardiomyopathy?

What is diabetic cardiomyopathy?

Cardiomyopathy means heart muscle disease. Diabetic cardiomyopathy is a special type of heart muscle disease in those with diabetes without associated disease of blood vessels of the heart, heart valve disease or risk factors like high blood pressure or high blood fat levels.

As the occurrence of diabetes in the general population is on the rise, so is diabetic cardiomyopathy. It initially manifests as an abnormal relaxation of the heart or heart failure with preserved ejection fraction. Ejection fraction is the fraction of the blood pumped out by the heart after full filling during relaxation after a contraction. In later stages of diabetic cardiomyopathy, the pumping function is affected and heart failure with reduced ejection fraction occurs.

Earliest description of diabetic cardiomyopathy date back to 1972, though it was not well accepted initially. This was because of the large number of heart failure in diabetics due to disease of blood vessels of the heart. It was difficult to tell which of the heart failure patients with diabetes had pure diabetic cardiomyopathy without silent disease of blood vessels of the heart.

In an important study known as Framingham Heart Study, it was found that diabetic women have five fold higher risk of heart failure and diabetic men a 2.4 fold higher risk. This was after adjustment of other risk factors for heart failure like age, high blood pressure and disease of blood vessels of the heart.

Diabetic cardiomyopathy is related to high blood sugar levels, resistance of the cells to insulin both in the body as a whole and in the heart muscle cells. This is associated with several abnormalities in the tiny structures within the heart muscle cells. Small blood vessels of the heart known as microcirculation is also abnormal. These lead to subtle scar formation in the heart and increase in the thickness of the wall of the heart chambers.

Increase in scar formation and thickness of the heart muscle initially causes impaired relaxation of the heart after a contraction. This reduces the ability of the heart to fill well. In late stages the force of contraction of the heart is also reduced. These two are responsible for heart failure with preserved ejection fraction and heart failure with reduced ejection fraction as mentioned initially.

Tests for diabetic cardiomyopathy are echocardiogram (ultrasound study of the heart), computed tomography (CT scan) and magnetic resonance imaging (MRI). Important blood tests are brain natriuretic peptide (BNP) which indicates heart failure and galectin-3 which indicate scar formation and inflammation in the heart muscle.

Special treatment strategies for diabetic cardiomyopathy are those which target scar formation, inflammation and insulin resistance. Though these have been promising in experimental studies, large scale studies in patients are awaited. Till the results of such studies are available, we have to depend on conventional strategies of good control of blood sugar and fat levels. This is in addition to medications used for treatment of heart failure in general.