The term "Wenckebach block" is also used for some heart blocks, and can refer to a second-degree type I block in either the SA node or the AV node; however, the ECG features of the two are quite distinctly different.

SA nodal blocks

SA blocks rarely give severe symptoms, because even if an individual had complete block at this level of the conduction system (which is uncommon), the secondary pacemaker of the heart would be at the AV node, which would fire at 40 to 60 beats a minute, which is enough to retain consciousness

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