Snapshot A 30-year-old man presents to the emergency room for palpitations and a syncopal episode. His blood pressure is 140/95 mmHg, pulse is 180/min, and respirations are 20/min. An electrocardiogram is ordered and reveals a supraventricular tachycardia. Vagal maneuvers are attempted with no effect. An intravenous medication that slows conduction through the atrioventricular node is started. (Adenosine) Introduction Two types of muscle cells exist in the heart login to view 12 more bullets Spread of Excitation SA node → atrial intermodal tracts → left and right atria → AV node → bundle of His → Purkinje system → ventricles SA node login to view 1 more bullet AV node login to view 3 more bullets His-Purkinje system is very rapid login to view 2 more bullets Relative conduction velocities login to view 1 more bullet