Arrhythmia

An arrhythmia (also called a dysrhythmia) is a disturbance in the rate, rhythm, or conduction of the heart's electrical activity. Normally the sinoatrial (SA) node paces the heart in a regular sinus rhythm; an arrhythmia occurs when impulses fire abnormally, travel by abnormal pathways, or are blocked along the conduction system.

Arrhythmias are classified by rate and by site of origin. Bradyarrhythmias are too slow (under 60 beats per minute) and include sinus bradycardia and AV blocks; tachyarrhythmias are too fast (over 100) and include sinus tachycardia, supraventricular tachycardia, and ventricular tachycardia. Origin matters clinically: atrial arrhythmias such as atrial fibrillation — an irregularly irregular rhythm with no discrete P waves — raise stroke risk from atrial clot formation, while ventricular arrhythmias like ventricular tachycardia and ventricular fibrillation can eliminate cardiac output entirely and cause sudden cardiac death.

The electrocardiogram (ECG) is the primary diagnostic tool: each arrhythmia has a characteristic pattern in its P waves, QRS complexes, and the intervals between them. Underlying mechanisms include abnormal automaticity, triggered activity, and reentry circuits, with common causes ranging from ischemia and electrolyte imbalances to structural heart disease and drug effects.

Arrhythmias are tested across the health professions. The USMLE Step 1 emphasizes mechanisms and ECG recognition within cardiovascular pathology, the CCMA exam tests rhythm analysis for medical assistants performing ECGs, and the PTCE covers the antiarrhythmic drug classes used to treat these rhythms.