MYOCARDIAL DYSFUNCTION AND ABNORMAL LEFT-VENTRICULAR EXERCISE RESPONSE IN AUTONOMIC DIABETIC-PATIENTS

In diabetic patients, the pathophysiologic mechanisms of exercise-indu ced left ventricular (LV) dysfunction remain controversial. In this st udy, the role of myocardial contractility recruitment in determining a n abnormal LV response to isometric or dynamic exercise has been inves tigated in 14 diabetic patients with autonomic dysfunction. Ischemic h eat disease was excluded by the absence of LV wall motion abnormalitie s induced by isotonic and isometric exercise and by coronary angiograp hy. Left ventricular and myocardial function were studied at rest, aci d during isometric and isotonic exercise, by two-dimensional echocardi ography; moreover, recruitment of an inotropic reserve was assessed by postextrasystolic potentiation at rest and at peak handgrip. An abnor mal response of LV ejection fraction to isometric (9/14) or to dynamic (8/14) exercise was frequent in study patients. In these patients, ba seline myocardial contractility was normal, and the significant increa se in ejection fraction by postextrasystolic potentiation indicated a normal contractile reserve (65 +/- 7% vs. 74 +/- 6%, p = 0.001). Never theless, the downward displacement of LV ejection fraction-systolic wa ll stress relationships during exercise suggests an inadequate increas e in myocardial contractility. However, the abnormal ejection fraction at peak handgrip was completely reversed by postextrasystolic potenti ation (67 +/- 6% vs. 58.1 +/- 10%, p = 0.008), a potent inotropic stim ulation independent of the integrity of adrenergic cardiac receptors. A defective inotropic recruitment, despite the presence of a normal LV contractile reserve, plays an important role in de-exercise LV dysfun ction in diabetic patients with autonomic neuropathy.