Clinical meaning
Cardiac arrhythmias result from abnormalities in impulse generation, impulse conduction, or both within the heart's electrical system. The normal conduction pathway flows from the SA node through the atria, AV node, bundle of His, bundle branches, and Purkinje fibers. Disruption at any point produces characteristic rhythm disturbances. The SA node normally fires at 60-100 bpm, but ectopic pacemaker sites (AV node: 40-60, ventricles: 20-40) can take over when the SA node fails. Arrhythmias range from benign (premature atrial contractions) to immediately life-threatening (ventricular fibrillation). Recognition of lethal rhythms and prompt emergency response are essential competencies.
Exam relevance
Risk factors: - Electrolyte imbalances particularly potassium and magnesium - Myocardial ischemia or acute infarction - Heart failure with structural cardiac remodeling - Medication toxicity from digoxin or antiarrhythmics - Stimulant use including caffeine, amphetamines, or cocaine
Diagnostics: - Continuous cardiac telemetry monitoring - 12-lead ECG for rhythm identification - Serum electrolytes (K+, Mg2+, Ca2+) - Cardiac biomarkers if ischemia suspected - Holter monitor for intermittent arrhythmias