Diagnosis of bradyarrhythmias

Sinus bradycardia

Slow ventricular rate with normal P waves, normal PR interval and 1:1 AV conduction.

Heart block

Normal P waves, a prolonged PR interval and 1:1 AV conduction suggest 1° heart block. In 2° heart block the ventricles fail to respond to atrial contraction intermittently. This may be associated with regular P waves and an increasing PR interval until ventricular depolarisation fails (Mobitz I or Wenkebach) or a normal PR interval with regular failed ventricular depolarisation (Mobitz II). In the latter case the AV conduction ratio may be 2:1 to 5:1. In 3° heart block there is complete AV dissociation with a slow, idioventricular rate.

Absent P wave bradycardia

Absent P waves may represent slow atrial fibrillation or sino-atrial dysfunction. In the latter case there will be a slow, idioventricular rate.

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