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Cardiac Arrhythmias: Difference between revisions
→Triggered Activity
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===Triggered Activity=== | ===Triggered Activity=== | ||
Triggered activity is | Triggered activity is depolarization of a cell triggered by a preceding activation. Due to early or delayed afterdepolarizations the membrane potential depolarizes and, when reaching a threshold potential, activates the cell. These afterdepolarizations are depolarizations of the membrane potential initiated by the preceding action potential. Depending on the phase of the action potential in which they arise, they are defined as early or late afterdepolarizations (figure 3). | ||
* A disturbance of the balance in influx and efflux of ions during the plateau phase (phase 2 or 3) of the action potential is responsible for the early afterdepolarizations. Multiple ion currents can be involved in the formation of early after depolarizations depending on the triggering mechanism. Early afterdepolarizations can develop in cells with an increased duration of the repolarization phase of the action potential, as the plateau phase is prolonged. The prolonged repolarization might reactivate the Ca2+ channels that have recovered from activation at the beginning of the repolarization. Otherwise disparity in action potential duration of surrounding myocytes can destabilize the plateau phase through adjacent depolarizing currents. | * A disturbance of the balance in influx and efflux of ions during the plateau phase (phase 2 or 3) of the action potential is responsible for the early afterdepolarizations. Multiple ion currents can be involved in the formation of early after depolarizations depending on the triggering mechanism. Early afterdepolarizations can develop in cells with an increased duration of the repolarization phase of the action potential, as the plateau phase is prolonged. The prolonged repolarization might reactivate the Ca2+ channels that have recovered from activation at the beginning of the repolarization. Otherwise disparity in action potential duration of surrounding myocytes can destabilize the plateau phase through adjacent depolarizing currents. | ||
* Delayed afterdepolarizations occur after the cell has recovered after completion of repolarization. In delayed afterdepolarization an abnormal Ca<sup>2+</sup> handling of the cell is responsible for the afterdepolarizations due to release of Ca<sup>2+</sup> from the storage of Ca<sup>2+</sup> in the sarcoplasmatic reticulum. The accumulation of Ca<sup>2+</sup> increases membrane potential and depolarizes the cell until it reaches a certain threshold, thereby creating an action potential. A high heart rate can result in the accumulation of intracellular Ca<sup>2+</sup> and induce delayed afterdepolarizations. | * Delayed afterdepolarizations occur after the cell has recovered after completion of repolarization. In delayed afterdepolarization an abnormal Ca<sup>2+</sup> handling of the cell is responsible for the afterdepolarizations due to release of Ca<sup>2+</sup> from the storage of Ca<sup>2+</sup> in the sarcoplasmatic reticulum. The accumulation of Ca<sup>2+</sup> increases membrane potential and depolarizes the cell until it reaches a certain threshold, thereby creating an action potential. A high heart rate can result in the accumulation of intracellular Ca<sup>2+</sup> and induce delayed afterdepolarizations. | ||