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Cardiac Arrhythmias: Difference between revisions
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→Abnormal Impulse Formation
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===Triggered Activity=== | ===Triggered Activity=== | ||
Triggered activity is activity of a cell triggered by a preceding activation. Due to early or delayed afterdepolarizations the resting membrane depolarizes and, when reaching threshold potentials, activates the cell. | Triggered activity is activity of a cell triggered by a preceding activation. Due to early or delayed afterdepolarizations the resting membrane depolarizes and, when reaching threshold potentials, 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. | ||
* In early afterdepolarizations depolarization occurs during the action potential (phase 2 and 3). | * In early afterdepolarizations depolarization occurs during the action potential (phase 2 and 3) by a diversity of causes. Early afterdepolarizations can increase duration of the repolarization phase of the action potential. This increase can create heterogeneity in refractoriness and thereby creating the substrate for a re-entry circuit (see below). | ||
* Delayed afterdepolarizations occur after the cell has recovered after completion of repolarization. | * Delayed afterdepolarizations occur after the cell has recovered after completion of repolarization. In delayed afterdepolarization an abnormal Ca2+ handling of the cell is probably responsible for the afterdepolarizations due to release of Ca2+ from the storage of Ca2+ in the sarcoplasmatic reticulum. The accumulation of Ca2+ increases membrane potential and thus depolarizes the cell when it reaches a certain threshold. | ||
==Disorders of Impulse Conduction== | ==Disorders of Impulse Conduction== | ||