Premature atrial contraction Premature atrial contraction Premature atrial contractions (PACs), also known as atrial premature complexes (APC) or atrial premature beats (APB), are a common cardiac dysrhythmia characterized by premature heartbeats originating in the atria. While the sinoatrial node typically regulates the heartbeat during normal sinus rhythm, PACs occur when another region of the atria depolarizes before the sinoatrial node and thus triggers a premature heartbeat. The exact cause of PACs is unclear; while several predisposing conditions exist, PACs commonly occur in healthy young and elderly people. Elderly people that get PACs usually don't need any further attention besides follow ups due to
Exposed node problem or the data rates are different) the problem may occur that the sender will not hear the CTS or the ACK during the transmission of data of the second sender. Exposed node problem In wireless networks, the exposed node problem occurs when a node is prevented from sending packets to other nodes because of a neighboring transmitter. Consider an example of 4 nodes labeled R1, S1, S2, and R2, where the two receivers (R1, R2) are out of range of each other, yet the two transmitters (S1, S2) in the middle are in range of each other. Here, if a