Arrhythmia An "arrhythmia" refers to an abnormal rhythm or speed of rhythm of the<unk> beat. An abnormal rhythm or speed is defined as one that is not physiological. Speed A resting<unk>  that beats slower than 60 beats per minute, or faster than 100 beats per minute, is regarded as having an arrhythmia. A<unk> beat slower than 60 beats per minute is known as bradycardia, and a<unk> beat faster than 100 is known as a tachycardia. Physiological Some individuals, for example trained athletes, may have<unk>  beats slower than 60 beats per minute when not exercising. If the SA node fails to initialize, the AV junction can take over as the main pacemaker of the<unk> . The AV junction "surrounds" the AV node (the AV node is not able to initialize its own impulses) and has a regular rate of 40 to 60 bpm. These "junctional" rhythms are characterized by a missing or inverted P wave. If both the SA node and the AV junction fail to initialize the<unk>  impulse, the ventricles can fire the<unk>  impulses themselves at a rate of 20 to 40 bpm and will have a QRS complex of greater than 120 ms. Pacemakers In the event of arrhythmia, a pacemaker may be surgically inserted into the<unk>  system.
Electrical conduction system of the heart
Cardiac cycle
Coronary circulation
Parasympathetic nervous system
Myocardial contractility
Skeletal-muscle pump
Cardiac excitation-contraction coupling
Central chemoreceptors