Tackling the Treachery of Tachycardia.

Tachycardia is among the most common abnormalities encountered in emergency department (ED) patients and simultaneously one of the most frequently underappreciated. Although often attributed to benign or physiologic causes, tachycardia may represent the earliest-and occasionally the only-objective sign of life-threatening illness. Failure to appropriately contextualize tachycardia contributes to diagnostic error, premature closure, and adverse outcomes, particularly at ED disposition. This review reframes tachycardia as a compensatory physiologic signal rather than a primary pathology. We examine the hemodynamic and neurohumoral drivers of sinus tachycardia and identify high-risk clinical contexts in which tachycardia heralds' critical disease.