Impaired inotropic response in type 2 diabetes mellitus: a strain rate imaging study

Left ventricular (LV) concentric geometry and hypertrophy, depressed wall mechanics, and abnormal diastolic properties have been described in the diabetic heart. However, the cardiac response to dynamic exercise in diabetic patients remains controversial. The present study assessed strain rate (SR) imaging during dobutamine stress, to investigate inotropic response in patients with type 2 diabetes mellitus and without coronary artery disease.

Twenty-four diabetics and 16 controls, both free of coronary artery disease, underwent Doppler echocardiography at rest and during dobutamine stress. Tissue Doppler systolic (S(m)) and early diastolic (E(m)) velocities, SR, and strain of middle posterior septum were measured at rest, low-dose, and high-dose dobutamine.

Diabetics had higher LV mass and relative wall thickness, lower midwall shortening, and transmitral pattern of abnormal LV relaxation. At rest, E(m) was significantly lower but S(m), SR, and strain were similar between the two groups. At low-dose and high-dose dobutamine, without difference of S(m), SR and strain were significantly lower in diabetics. At every level of dobutamine, strain increased with increasing heart rate (HR) in either group (both P < .0001), but the slope of the overall relation between HR and strain was lower in diabetics (b = -0.08) than in controls (b = -0.14) (P < .01).

In type 2 diabetes SR imaging allows detection of reduced longitudinal mechanics during dobutamine stress. The blunted slope of the relation between HR and regional strain suggests the impairment of the myocardial force-frequency relation, indicating altered contractile reserve in uncomplicated diabetes.