Cardiac pacemaker heart. There are 3 main stages in the generation of an action potential in a pacemaker cell. Since the stages are analogous to contraction of cardiac muscle cells, they have the same naming system. This can lead to some confusion. There is no phase 1 or 2, just phases 0, 3, and 4. The key to the rhythmic firing of pacemaker cells is that, unlike other neurons in the body, these cells will slowly depolarize by themselves and do not need any outside innervation from the autonomic nervous system to fire action potentials. As in all other cells, the resting
Heart rate premature mortality; every 10 beats per minute increase in resting heart rate has been shown to be associated with a 10–20% increase in risk of death. In one study, men with no evidence of heart disease and a resting heart rate of more than 90 beats per minute had a five times higher risk of sudden cardiac death. Similarly, another study found that men with resting heart rates of over 90 beats per minute had an almost two-fold increase in risk for cardiovascular disease mortality; in women it was associated with a three-fold increase. Given these data, heart rate should