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2nd-degree type II (Mobitz II)

Also called second-degree AV block type II, Mobitz II.

The PR on conducted beats is constant and never lengthens, yet P waves are intermittently not conducted and a QRS drops without warning. It sits below the AV node and can progress abruptly to complete block.

A 6-second EKG rhythm strip showing 2nd-degree type II (Mobitz II).
2nd-degree type II (Mobitz II), 6 seconds of strip. Each small box is 0.04 seconds and each large box is 0.20 seconds.

How to identify 2nd-degree type II (Mobitz II)

Rate
Ventricular slower than atrial
Rhythm
Irregular where beats drop
P waves
Regular, more P waves than QRS complexes
PR interval
Constant on every conducted beat
QRS
Narrow here; can be wide
Clincher
A constant PR, then a QRS drops without warning. It sits below the node and can progress to complete block.

Rhythms it gets mistaken for

Treatment by certification level

Open your level. Treat the patient, not the strip.

Paramedic

Stable

Stable, but watch it closely.

  • Monitor, IV access, transport and reassess.
  • This block can progress abruptly to complete block. Put the pads on now so pacing is ready.
  • If it becomes symptomatic, go to pacing or dopamine 5-20 mcg/kg/min, or epinephrine 2-10 mcg/min, titrated to effect. Do not rely on atropine: the block sits below where it acts.

Unstable

Symptomatic high-grade block: go to pacing.

  • Do not rely on atropine: the block sits below where it acts. Atropine 1 mg may be tried while the pads go on, but it never delays pacing.
  • Transcutaneous pacing (rate 60-80, mA up until capture, then slightly above). Confirm mechanical capture with a femoral pulse, not a carotid.
  • Sedation and analgesia; recheck the blood pressure once captured.
  • No capture or still poorly perfusing: dopamine 5-20 mcg/kg/min, or epinephrine 2-10 mcg/min, titrated to effect.
  • Expert consultation: this patient may need a transvenous pacer.
AEMT

Stable

Pulse present and stable.

  • Oxygen only if hypoxic or short of breath, IV access, monitoring.
  • Acquire and transmit a 12-lead ECG. Interpreting it is a Paramedic skill.
  • Transport and reassess. Request a paramedic if the patient worsens.

Unstable

Symptomatic bradycardia with a pulse.

  • Support oxygenation and ventilation, establish IV access, and move the patient.
  • Expedited transport, with a paramedic intercept if that is genuinely faster than reaching the hospital.

Synchronized cardioversion and pacing are Paramedic-only, so the AEMT has no electrical option for a patient with a pulse. Never put the AED on this patient.

EMT

Stable

Pulse present: assess and support.

  • Treat the patient, not the rhythm name: airway, breathing, circulation, vital signs.
  • Oxygen if the SpO2 is under 94%, the patient is short of breath, or shows signs of shock.
  • Request ALS and transport promptly. Reassess on the way.

An AED goes only on a patient who is unresponsive, not breathing and pulseless. It cannot feel a pulse, so on a patient with a pulse it can advise a shock that would do harm.

Unstable

Pulse present but poorly perfusing: this patient needs ALS fast.

  • Treat the patient, not the rhythm name: airway, breathing, circulation, vital signs.
  • Oxygen if the SpO2 is under 94%, the patient is short of breath, or shows signs of shock.
  • Request ALS and transport promptly. Reassess on the way.

An AED goes only on a patient who is unresponsive, not breathing and pulseless. It cannot feel a pulse, so on a patient with a pulse it can advise a shock that would do harm.

Could you pick out 2nd-degree type II (Mobitz II) on a fresh strip? See how many rhythms you can identify in one minute.

Try the 60-second rhythm challenge