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Rhythm

Ventricular paced rhythm

Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

A ventricular paced rhythm shows pacing spikes followed by wide QRS complexes. With a lead in the right ventricular apex the QRS has an LBBB-like morphology with left axis deviation, because the right ventricle is activated first.

ECG criteria

  • Pacing spike (a narrow vertical deflection) before each paced QRS complex; small and sometimes hard to see on digital recordings, especially with bipolar leads.
  • Wide QRS (usually 140 ms or more), with LBBB-like morphology (negative in V1) and left or extreme axis deviation for right ventricular apical pacing.
  • Rate regular at or above the programmed lower rate; secondary ST-T changes opposite in direction to the QRS.
  • In dual-chamber pacing an atrial spike precedes the P wave and a ventricular spike follows it after the programmed AV delay.
  • Pacing may be intermittent (demand), with native beats between paced beats.

Mechanism

The pacemaker delivers an electrical impulse through a lead and depolarises the myocardium locally, so activation spreads cell to cell rather than through the His-Purkinje system. The paced ventricle contracts earlier than the other, giving a wide QRS whose morphology depends on the lead position.

Common causes

  • Indications for pacing: symptomatic bradycardia, sick sinus syndrome, high-grade or complete AV block.
  • Conduction disease after myocardial infarction, cardiac surgery or TAVI.
  • Cardiac resynchronisation therapy for heart failure with wide QRS (biventricular pacing).
  • Temporary pacing in acute settings (overdose, electrolyte disturbance, acute infarction).

Management principles

Check that pacing is capturing and sensing appropriately, and review the device interrogation and clinical state; failure to capture or sense warrants urgent device evaluation. Management of the underlying condition and of device problems follows local guidelines and the cardiology or device service.

High-level principles for study. Treatment decisions follow local guidelines and the clinical situation.

Pitfalls and mimics

  • A paced rhythm with LBBB-like morphology masks ST-T changes of ischaemia; the modified Sgarbossa criteria (concordant ST elevation, concordant ST depression in V1-V3, excessively discordant ST elevation) can help, as in LBBB.
  • Pacing spikes can be small or missed on digital ECGs, so a paced rhythm may be mistaken for LBBB or ventricular tachycardia.
  • Failure to capture (spikes without QRS) or failure to sense (inappropriate spikes) indicates device or lead malfunction.

Practise in the ECG trainer — Recognise this pattern on generated tracings.

References

  1. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. European Society of Cardiology (2021) — Tier 2 (guidelines / primary literature)
  2. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. American College of Cardiology / American Heart Association / Heart Rhythm Society (2018) — Tier 2 (guidelines / primary literature)
  3. Wagner GS, Strauss DG. Marriott's Practical Electrocardiography. Wolters Kluwer, 12th edition (2013) — Tier 3 (textbook)

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