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Evidence of myocardial dysfunction in Bartter's syndrome
L Calò1, R Scognamiglio, S Nistri
1Institute of Internal Medicine, Division of Nephrology, University of Padova, Italy.
Insights
Bartter's syndrome (BS) impairs heart muscle contractile recruitment due to abnormal intracellular calcium handling. This leads to reduced left-ventricular function, particularly during exercise, unlike in healthy individuals.
Area of Science:
- Cardiology
- Physiology
- Calcium Homeostasis
Background:
- Bartter's syndrome (BS) presents with normohypotension despite hormonal imbalances typically seen in hypertension.
- Previous research suggests impaired intracellular calcium regulation contributes to vascular hyporeactivity in BS.
Purpose of the Study:
- To investigate if altered intracellular calcium homeostasis in Bartter's syndrome affects myocardial contractile recruitment at the myocyte level.
- To assess the impact of this alteration on left-ventricular function.
Main Methods:
- Quantitative 2-D echocardiography was used to study left-ventricular function in BS patients and normal controls (C).
- Postextrasystolic potentiation (PESP) was employed as an inotropic stimulus to assess maximal contractile reserve.
- A group with hypokalemia (PB) was included to isolate the effect of hypokalemia.
Main Results:
- Baseline left-ventricular volumes and ejection fractions were similar across all groups.
- Postextrasystolic potentiation significantly increased ejection fraction in controls and hypokalemia patients (p < 0.01).
- In Bartter's syndrome patients, ejection fraction remained unchanged with PESP, showing reduced contractile recruitment compared to controls and hypokalemia patients (p < 0.01).
Conclusions:
- This study demonstrates depressed inotropic recruitment in Bartter's syndrome.
- Exercise-induced left-ventricular dysfunction in BS is likely caused by abnormal intracellular calcium homeostasis within myocytes.
Abstract:
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/m2; 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.