Finding	Description
Bradycardia	Sinus bradycardia: sinus rhythm with HR < 50 bpm Atrial fibrillation with slow ventricular rate: ventricular rate with HR < 50 bpm Wandering pacemaker: at least three distinct P waves with HR < 50 bpm
Bradycardia-tachycardia syndrome	Present in 50% of patients at time of sinus node dysfunction diagnosis; atrial tachyarrhythmias alternating with bradycardia
Sinus node arrest	Complete loss of automaticity of the sinus node; prolonged asystole with or without escape rhythm (junctional or idioventricular)
Sinoatrial exit block	First-degree: conduction delay between the sinoatrial node and atrial tissue; bradycardia as above Second-degree type 1: single impulse blocked; pause following progressive decrease in the P–P interval* Second-degree type 2: single impulse blocked; distinct pause preceded by generally constant P–P interval* Third-degree: multiple impulses blocked within sinus node; pause followed by a beat originating with atrial depolarization (i.e., preceded by a P wave)