There is a lesser-known, but common, heart disorder called paroxysmal supraventricular tachycardia (PSVT). Nearly two million Americans live with this alarming arrhythmia that can spike heart rate unexpectedly and suddenly from a normal 60-80 beats per minute (bpm) to more than 250. In addition to the trademark rapid pulse that can last from minutes to hours, symptoms may include dizziness, fainti…