Intermittent failure of atrial impulses to be conducted through AV node and His bundle can be subdivided into Mobitz type 1 (Wenckebach) or Mobitz type 2.
Mobitz type 1: There is a noticeable delay in the AV conduction, which progressively increases until eventually an impulse is not conducted. On an ECG, this is reflected by an increase in the PR interval until a dropped beat is seen.
Mobitz type 2: This is characterised by intermittent failure of conduction in the atrial impulse to the ventricles, usually at a 2:1 ratio. Unlike Mobitz type 1, the PR interval will not lengthen.
Mobitz type 1 is often caused by an increase in vagal tone and typically occurs during the patient's sleep. Meanwhile, Mobitz type 2 is pathological in nature and has similar aetiology to first degree AV block.
The signs of Mobitz type 1 and 2 include bradycardia and hypotension.
Mobitz type 1 and 2 may be asymptomatic, but can also present with symptoms such as shortness of breath, chest pain, pre-syncope or syncope.
Both Mobitz type 1 and 2 can progress to complete heart block. Prognosis after PPM implantation is typically good, although there can be complications such as death or injury from syncope.
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