Which of the following conditions could lead to syncope?

Severe dehydration can lead to syncope due to its impact on blood volume and blood pressure. When the body becomes significantly dehydrated, the reduction in blood volume can result in inadequate blood flow to the brain. This decreased cerebral perfusion can cause fainting or loss of consciousness, which characterizes syncope.

In this instance, as fluid loss continues, the body's compensatory mechanisms may become overwhelmed, leading to hypotension (low blood pressure) and ultimately syncopal events. It's important to understand that adequate hydration is crucial for maintaining blood volume and ensuring that organs, particularly the brain, receive sufficient blood supply.

While atrial flutter, hypertensive crisis, and congestive heart failure can all be associated with instances of syncope, the immediate mechanism in severe dehydration is distinctly related to fluid volume status and its effect on cerebral perfusion.