What physiological change triggers hyponatremia in heart failure?

Hyponatremia in heart failure is primarily related to the reduction in cardiac output. When the heart is unable to pump effectively, it leads to inadequate blood flow and perfusion to various organs, including the kidneys. This decreased cardiac output activates compensatory mechanisms in the body, one of which is the release of hormones such as antidiuretic hormone (ADH). Elevated levels of ADH cause the kidneys to retain water, diluting the sodium levels in the bloodstream, resulting in hyponatremia.

Additionally, the reduction in cardiac output can cause a decrease in renal perfusion, prompting a series of neurohormonal responses that further exacerbate fluid retention and contribute to the dilutional effect on sodium. A drop in cardiac output is thus key in understanding the development of hyponatremia in patients with heart failure.