Sinus tachycardia is one of the most common presentations you will find in the Emergency Department, defined as a heart rate greater than 100 beats per minute. Remember, sinus tachycardia will always include p-waves on EKG and telemetry monitoring. This rhythm can be a ‘great masquerader’ in emergency medicine, given that many different etiologies can cause it.
Often, sinus tachycardia – equivalent to an elevated heart rate (HR) – is a compensatory response to an underlying etiology. To explain this concept, let’s recall the delivery of oxygen equation:
CaO2 = (1.34 x Hb x SaO2) + 0.003 x PaO2
The equation for oxygen delivery (CaO2 = arterial oxygen content, Hb = hemoglobin, SaO2 = arterial saturation of oxygen, PaO2 = partial pressure of oxygen in the arterial blood).
All cells require oxygen to survive, and In the lungs, oxygen attaches to hemoglobin molecules so that it can be transported – courtesy of the cardiac output – to the rest of the body. When the delivery of oxygen diminishes, the cardiac output (equal to HR multiplied by the stroke volume) may increase to help compensate for the total delivery of oxygen (as seen by the above equation) (1).