Martin Flack, a medical student, was the first to discover the sinoatrial (SA) node in the early 1900s. The SA (sinus) node represents a cluster of myocytes with pacemaker activity. Under normal circumstances, it generates electrical impulses that set the rhythm and rate of the heart. The mass of the sinus node is too small to create a substantial electrical signal that can be detected on the electrocardiogram (ECG). Instead, SA nodal pacemaker activity must be inferred indirectly from P waves generated by the atrial activity. Any dysfunction of the sinus node can affect the heart’s rate and rhythm. Noticing and understanding the various types of sinus node dysfunction can help with management decisions.
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