Alila Academy

Cardiac arrhythmias can be classified by site of origin: sinus rhythms originate from the sinoatrial node, or SA node; atrial rhythms originate from the atria; ventricular rhythms originate from the ventricles.

Sinus rhythm is the normal rhythm of the heart set by its natural pacemaker in the SA node. In a healthy heart, the SA node fires 60 to 100 times per minute resulting in the normal heart rate of 60 to 100 beats per minute. The most common variations of sinus rhythm include:

     *Sinus bradycardia: when the SA node fires less than 60 times per minute resulting in a slower heart rate of less than 60 beats per minute.

and

     *Sinus tachycardia: when the SA node fires more than 100 times per minute generating a faster heart rate of greater than 100 beats per minute.

Sinus bradycardia and sinus tachycardia may be normal or clinical depending on the underlying cause. For example, sinus bradycardia is considered normal during sleep and sinus tachycardia may be normal during physical exercises. 

Atrial rhythms:

Cardiac arrhythmias that originate from other parts of the atria are always pathological. The most common include: atrial flutter, atrial fibrillation and AV nodal re-entrant tachycardia. These are forms of supraventricular tachycardia, or SVT.

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