One of the main mechanisms of tachyarrhythmias is accelerated impulse formation. This can be due to enhanced automaticity of either the SA node, for example, sinus tachycardia, or latent pacemaker, for example accelerated junctional rhythm.

Tachycardias from accelerated impulse formation can also be due to triggered automaticity, wherein a depolarization leads to spontaneous afterdepolarizations. Afterdepolarizations are depolarizations that result from a preceding impulse and are sufficient to trigger a cardiac cycle. These may lead to propagated action potential, for example, a single premature atrial complex, or PAC, or if repetitive, atrial tachycardia.

Tachyarrhythmias can also be due to altered impulse conduction producing reentry, which requires a dual pathway, slowed conduction and unidirectional block.

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