Sinus Arrest
Definition
Sinus arrest is intermittent failure of impulse generation by the sino‑atrial (SA) node, producing one or more pauses in atrial activity. On surface ECG it is seen as a sudden absence of P waves (and of QRS complexes if no escape rhythm occurs). Pauses are clinically significant when prolonged (commonly defined as ≥3 seconds) or when they cause symptoms such as presyncope or syncope (NICE CG109).
Etiology and pathophysiology
Sinus node dysfunction may be intrinsic or extrinsic.
- Intrinsic causes:
- Age‑related fibrosis of the SA node.
- Ischaemia affecting the SA nodal artery.
- Infiltrative disease involving the node.
- Primary sinus node disease (sick sinus syndrome).
- Extrinsic causes:
- Excessive vagal tone.
- Carotid sinus hypersensitivity.
- Drug‑induced causes:
- Beta‑blockers.
- Non‑dihydropyridine calcium‑channel blockers.
- Digoxin.
- Some antiarrhythmic agents.
If subsidiary pacemakers (junctional or ventricular) do not emerge, prolonged pauses or transient asystole result. If escape rhythms occur, they may be junctional (narrow QRS) or ventricular (wide QRS).