Mechanism of Cardiac Arrhythmias

Cardiac arrhythmias result from abnormal impulse formation or defective heart conduction. Common causes include ectopic pacemaker activity, where electrical impulses originate outside the SA node, and reentrant circuits that create looping electrical impulses. Additional factors include hypoxia, ischemia, electrolyte imbalances, excessive catecholamine exposure, drug toxicity, and myocardial damage that disrupts normal conduction pathways.

Bradyarrhythmias are characterized by slow heart rates, typically below 60 beats per minute, often resulting from SA node or AV node dysfunction. Tachyarrhythmias feature rapid heart rates exceeding 100 beats per minute and can originate from the atria or ventricles. Both types disrupt synchronized electrical activity, but their opposing rate effects produce different clinical symptoms including palpitations, dizziness, and unconsciousness.

Ectopic pacemaker activity occurs when areas of the heart outside the SA and AV nodes generate abnormal electrical impulses, termed enhanced automaticity. This disrupts the typical sequence of electrical activation and causes the heart to beat irregularly. Unusually high intracellular calcium levels can trigger delayed afterdepolarizations, further contributing to abnormal impulse formation and arrhythmia development.

Reentrant circuits involve circular movement of electrical impulses within the heart due to abnormal conduction pathways or areas with varying conduction properties. Myocardial damage can alter normal conduction routes, creating self-sustaining loops of electrical activity. This continuous cardiac stimulation causes the heart to beat abnormally fast or irregularly, representing a major mechanism of arrhythmia development.

Heart block occurs when diseases of conducting structures, such as AV node fibrosis, disrupt normal electrical conduction. These conditions lead to varying degrees of conduction impairment, ranging from mild delays to complete blockade. Heart blocks represent defective conduction mechanisms that contribute to bradyarrhythmias and irregular heart rhythms, requiring diagnosis through electrocardiogram analysis.

Electrocardiogram (ECG) analysis is the primary diagnostic tool for detecting arrhythmia anomalies by recording the heart's electrical activity. Additional diagnostic tools include Holter monitoring for continuous rhythm tracking, event recorders for intermittent episodes, and electrophysiology studies for detailed electrical mapping. These methods help determine arrhythmia type, severity, and underlying cause to guide treatment decisions.

Antiarrhythmic drugs target specific ion channels and conduction pathways to restore normal rhythm. Antiarrhythmic drugs class I agents as sodium channel blockers reduce abnormal impulse formation, while antiarrhythmic drugs class III agents as potassium channel blockers prolong repolarization. Class II and IV agents work through different mechanisms to normalize electrical activity and prevent arrhythmia recurrence.