Evidence of myocardial dysfunction in Bartter's syndrome

Bartter's syndrome (BS) is characterized by arterial normohypotension despite biochemical and hormonal abnormalities generally associated with hypertension. An abnormal intracellular calcium homeostasis due to a reduced capacity to increase intracellular calcium has been demonstrated by us in BS and proposed as the main pathophysiological factor of the vascular hyporeactivity in BS. The present study was designed to assess whether this altered intracellular calcium homeostasis could also impair contractile recruitment at the myocyte level. Left-ventricular function of patients with BS and normal subjects (C) were studied by quantitative 2-D echocardiography at rest and by postextrasystolic potentiation (PESP), an inotropic stimulus able to recruit the maximal contractile reserve. A group of patients with hypokalemia other than BS (PB) was also included in the study to evaluate the effect of hypokalemia on myocardial contractile recruitment. Baseline left-ventricular end-diastolic volume (EDV) and ejection fraction (EF) did not differ in the 3 groups: EDV: 62 +/- 6 vs. 64 +/- 9 and 60 +/- 12 ml/m(2); EF: 64 +/- 9 vs. 67 +/- 8 and 64 +/- 8%. PESP determines an increase of EF in C and PB: 82 +/- 5%, p < 0.01 and 76 +/- 6%, p < 0.01, while in BS it is unchanged: 69 +/- 9% and is reduced in comparison with the increment of myocardial function shown by C and PB (p < 0.01). This study is the first demonstration in BS of a depressed inotropic recruitment causing an exercise-induced left-ventricular dysfunction likely due to an abnormal intracellular calcium homeostasis in the myocytes.