Why Do Junctional Rhythms Occur?

A junctional rhythm occurs when the electrical activation of the heart originates near or within the atrioventricular node

, rather than from the sinoatrial node. Because the normal ventricular conduction system (His-Purkinje) is used, the QRS complex

QRS complex

It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the heart and contraction of the large ventricular muscles. In adults, the QRS complex normally lasts 80 to 100 ms; in children it may be shorter.

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QRS complex - Wikipedia

is frequently narrow.

What causes a junctional rhythm?

Junctional rhythm can be due to hypokalemia, MI (usually inferior), cardiac surgery, digitalis toxicity (rare today), sinus node dysfunction, or after ablation for AV node reentrant tachycardia. It can be caused by necessary medications (e.g., β-adrenergic blockers, verapamil, digitalis, sotalol, amiodarone).

What is the most common cause of junctional tachycardia?

An accelerated junctional rhythm is seen predominantly in patients with heart disease. Common causes include digitalis intoxication, acute myocardial infarction (MI), intracardiac surgery, or myocarditis. Only in rare instances does the cause of the arrhythmia remain unexplained.