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Cardiac Arrhythmias: Difference between revisions
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== Abnormal Impulse Formation== | == Abnormal Impulse Formation== | ||
The mechanism of abnormal automaticity is similar to the normal automaticity of sinus node cells. Abnormal automaticity can be caused by changes in the cell ion channel characteristics due to drugs or changes in the electrotonic environment. Abnormal automaticity can result from an increase of normal automaticity in non-sinus node cells or a truly abnormal automaticity in cells that don't exhibit a phase 4 diastolic depolarization. | |||
===Abnormal Automaticity=== | ===Abnormal Automaticity=== | ||
===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. This mechanism can repeat itself en thus self-perpetuate. | |||
• In early afterdepolarizations depolarization occurs during the action potential (phase 2 and 3). | |||
• Delayed afterdepolarizations occur after the cell has recovered after completion of repolarization. | |||
==Disorders of Impulse Conduction== | ==Disorders of Impulse Conduction== | ||
Conduction block or conduction delay is a frequent cause of bradyarrhythmias, however tacharrhythmias can also result from conduction block and produce a reentrant circuit. Conduction block can develop in different conditions, for instance a deceleration block or a acceleration block. These conduction block develop due to deceleration or a slow heart rate or a acceleration or fast heart rate respectively. It is important to assess the cause of conduction block as explained in the section of bradyarrhythmias [link], for it is important in the treatment of the conduction delay or block. | |||
===Reentry=== | ===Reentry=== | ||
Reentry or circus movement can arise when an area is slowly conducting thereby remaining active while the rest of the heart depolarizes. When the rest of the heart has recovered from this refractory state, and can be reactivated, the impulse in the slow conducting zone can activate the heart. This process can repeat itself and thus form the basis of a reentry tachycardia. These areas of slow conduction can be anatomical or functional or a combination of both. Examples of reentry tachycardias are atrial flutter, atrial fibrillation and ventricular tachycardias originating from an infarct zone. | |||
[[Cardiodrugstemplate]] | [[Cardiodrugstemplate]] | ||