Sinoatrial block

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Sinoatrial block
Sinus rhythm (rate = 65/min) with Type II S-A (exit) block; (see laddergram). Note that the long cycles (191) are nearly identical to twice the short cycles (190).
Specialty	Cardiology

A sinoatrial block (also spelled sinuatrial block)^[1] is a disorder in the normal rhythm of the heart, known as a heart block, that is initiated in the sinoatrial node. The initial action impulse in a heart is usually formed in the sinoatrial node (SA node) and carried through the atria, down the internodal atrial pathways to the atrioventricular node (AV) node.^[2] In normal conduction, the impulse would travel across the bundle of His (AV bundle), down the bundle branches, and into the Purkinje fibers. This would depolarize the ventricles and cause them to contract.

In an SA block, the electrical impulse is delayed or blocked on the way to the atria, thus delaying the atrial beat.^[3] (An AV block, occurs in the AV node and delays ventricular depolarisation). SA blocks are categorized into three classes based on the length of the delay.