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2nd-degree type I (Wenckebach)

Also called second-degree AV block type I, Mobitz I, Wenckebach.

The PR interval lengthens beat after beat until one P wave is not conducted and its QRS drops, then the cycle restarts. Longer, longer, longer, drop. Usually nodal and usually benign.

A 6-second EKG rhythm strip showing 2nd-degree type I (Wenckebach).
2nd-degree type I (Wenckebach), 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 I (Wenckebach)

Rate
Ventricular slower than atrial
Rhythm
Regularly irregular, in groups
P waves
Regular, more P waves than QRS complexes
PR interval
Lengthens beat after beat until a QRS drops
QRS
Under 0.12 s
Clincher
Longer, longer, longer, drop. Usually nodal and usually benign.

Rhythms it gets mistaken for

Treatment by certification level

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

Paramedic

Stable

Asymptomatic: watch it, do not treat the number.

  • Monitor, IV access, transport and reassess.
  • No atropine, pacing or infusion for the asymptomatic patient.
  • If it becomes symptomatic (hypotension, altered mental status, signs of shock, ischemic chest pain, acute heart failure): atropine 1 mg every 3-5 minutes (maximum 3 mg), then transcutaneous pacing, or dopamine 5-20 mcg/kg/min or epinephrine 2-10 mcg/min.

Unstable

Symptomatic bradycardia: atropine, then pacing or an infusion.

  • Oxygenation and ventilation support, IV access, monitor.
  • Atropine 1 mg IV every 3-5 minutes, maximum 3 mg.
  • No response: transcutaneous pacing (rate 60-80, mA up until capture, then slightly above). Confirm mechanical capture with a femoral pulse. Sedation and analgesia.
  • Or a chronotropic infusion: dopamine 5-20 mcg/kg/min, or epinephrine 2-10 mcg/min, titrated to effect.
  • Look for and treat the cause: hypoxia first, then medications and high potassium.
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 I (Wenckebach) on a fresh strip? See how many rhythms you can identify in one minute.

Try the 60-second rhythm challenge