The Role of Chloride in Cardiorenal Syndrome: A Practical Review.

Chloride, long considered a passive extracellular anion, has emerged as a key determinant in the pathophysiology and management of heart failure (HF) and cardiorenal syndrome. In contrast to sodium, which primarily reflects water balance and vasopressin activity, chloride exerts broader effects on neurohormonal activation, acid-base regulation, renal tubular function, and diuretic responsiveness. Its interaction with With-no-Lysine (WNK) kinases and chloride-sensitive transporters underscores its pivotal role in electrolyte and volume homeostasis. Hypochloremia, frequently observed in HF patients treated with loop diuretics, is independently associated with adverse outcomes, diuretic resistance, and arrhythmic risk. Conversely, hyperchloremia-often iatrogenic-may contribute to renal vasoconstriction and hyperchloremic metabolic acidosis. Experimental data also implicate chloride dysregulation in myocardial electrical disturbances and an increased risk of sudden cardiac death. Despite mounting evidence of its clinical importance, serum chloride remains underappreciated in contemporary risk assessment models and treatment algorithms. This review synthesizes emerging evidence on chloride's role in HF, explores its diagnostic and therapeutic implications, and advocates for its integration into individualized care strategies. Future studies should aim to prospectively validate these associations, evaluate chloride-guided therapeutic interventions, and assess whether incorporating chloride into prognostic models can improve risk stratification and outcomes in patients with heart failure and cardiorenal syndrome.