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 turbulence the heart. Especially after a heart attack, sympathetic nervous activity tends to be increased. A healthy HRT indicates the presence of a healthy amount of parasympathetic activity, countering sympathetic activity. To take a wider view, however, it may be that a healthy HRT is also an indication of a healthy brain, and is the reason small HRT also predicts a likelihood of death from non- cardiac causes as well as from cardiac causes. Heart rate turbulence Heart rate turbulence (HRT) is the return to equilibrium of heart rate after a premature ventricular contraction (PVC). It consists of a brief speed-up