Pathophysiology
Clinical meaning
Cardiac rhythm interpretation is a foundational competency for registered nurses caring for patients on telemetry, in critical care, and in emergency departments. Understanding dysrhythmias requires knowledge of the electrical properties of cardiac cells, the mechanisms by which abnormal rhythms develop, and the clinical significance of each rhythm in guiding treatment decisions. Mechanisms of Dysrhythmia Formation at the Cellular Level: All dysrhythmias arise from one of three fundamental mechanisms: disorders of impulse formation, disorders of impulse conduction, or a combination of both. Understanding these mechanisms is essential because they determine both the clinical behavior of the rhythm and the appropriate treatment. Disorders of Impulse Formation (Automaticity): Normal automaticity resides in the pacemaker cells of the SA node, AV node, and His-Purkinje system. These cells possess the unique ability to spontaneously depolarize during phase 4 of the action potential due to the funny current (If), a mixed sodium-potassium inward current that gradually moves the membrane potential toward threshold. The SA node has the fastest intrinsic rate (60-100 bpm) and therefore normally suppresses all lower pacemakers through a mechanism called overdrive suppression: because...