This definition includes sinus tachycardia. Often, however, in a clinical setting, it is used loosely as a synonym
for paroxysmal supraventricular tachycardia (PSVT), which refers to those SVTs that have a sudden, almost immediate onset. A person experiencing PSVT may see his heart rate go from 90 to 180 beats per minute instantaneously." [And often back to normal or nearly normal just as quickly].