ABSTRACT
Multiple factors play a role in the development of abnormal cardiac rhythms. Alterations from the normal cardiac cell action potentials involving excitability, refractoriness, conduction, or automaticity predispose to arrhythmias. Electrophysiologic changes create a so-called substrate for arrhythmogenesis. Specific disorders associateded with arrhythmias include cardiomyocyte hypertrophy, cardiomyopathies with fat or fibrous tissue replacement of myocytes, abnormal ion channel structure or function, tissue inflammation, and congenital conduction anomalies, among other derangements. The electrophysiologic mechanisms underlying cardiac arrhythmias generally involve abnormalities of impulse formation or impulse conduction, or a combination of these. The sick sinus syndrome, preexcitation syndromes, and other arrhythmias can involve abnormalities of both impulse formation and conduction. Abnormal impulse formation can include an inappropriate sinus node rate for the patient's physiologic needs, or discharge from ectopic pacemaker cells, which normally are overdrive suppressed.
