In general, the DefensePlanning Guidance tells the Army what missions and scenarios to or-ganize and train for. Internal Army processes lead to decisions aboutspecific types of units to create, whether those units should be re-serve or active, and whether those units should be resourced fully orat some lower level.
There are actually two pacemakers. The SA node is the primary; the atrioventricular node (AV node), located in a bundle of tissues on the border between the right atrium and the right ventricle, is the secondary. When the SA node sends out an electrical impulse, the first place it goes is to the AV node. While the SA node sets the rhythm of your pulse, the AV node sets the rhythm of your heart contractions. It delays the signal on its way to the ventricle, giving the atrium time to contract first.
The SA node is the primary; the atrioventricular node (AV node), located in a bundle of tissues on the border between the right atrium and the right ventricle, is the secondary.