2nd Degree Heart Block

Pathology

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.

Aetiology

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.

Signs

The signs of Mobitz type 1 and 2 include bradycardia and hypotension.

Symptoms

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.

Investigations

• ECG: To assess the rhythm, a Holter monitor may be used.
• Echo: If the LV function is impaired, the patient may benefit from cardiac resynchronisation therapy (CRT).

Treatment

• Stop any medications that may be causing the issue.
• Depending on the severity of the condition, a temporary pacing wire may be required.
• Mobitz type 2 will always require a permanent pacemaker.

Prognosis

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.