When sinus tachycardia is a reflex response to altered physiology, the resulting increase in cardiac output is usually beneficial.
Tachycardia resolves when conditions return to normal.
The sinus node is located in the high lateral right atrium at the junction of the superior vena cava and the crista terminalis. It runs a superoinferior course toward the inferior vena cava in the majority of patients. In about 10 percent of patients, however, the node remains more superior, with its head extending across the crest of the atrial appendage into the interatrial groove to create a horseshoe-shaped structure around the superior vena cava. It is unlikely that a single cell type serves as the pacemaker. The nodal cells function as electrically coupled oscillators, discharging synchronously because of mutual entrainment.