EKG
Paced rhythms & ICD basics
EKG

Paced rhythms & ICD basics

Recognize pacing spikes, understand modes (DDD, VVI), know when device failure is happening.

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◆Pacing on the strip

  • •Pacing spike before P = atrial pacing; before QRS = ventricular pacing; before both = dual-chamber
  • •Paced ventricular QRS looks like LBBB (RV apical lead) — wide, broad in V6
  • •DDD: dual chamber sensed + paced (most common in dual-lead pacers)
  • •VVI: ventricle only, demand-paced — used in AFib/AFlutter with bradycardia

◆Indications for pacing

  • •Symptomatic sinus brady (incl. sick sinus)
  • •Mobitz II AV block
  • •Complete (3°) AV block
  • •Symptomatic bifascicular/trifascicular block

◆Indications for ICD (primary prevention)

  • •EF ≤35% from ischemic cardiomyopathy ≥40 days post-MI (NYHA II–III)
  • •EF ≤35% from non-ischemic cardiomyopathy on optimal medical therapy ≥3 mo
  • •HCM with risk features, Brugada with syncope, long QT with syncope on β-blocker
  • •Prior cardiac arrest from VT/VF (secondary prevention — Class I)

◆Pacemaker failure

  • •Failure to capture: spike present, no QRS — lead displacement, low battery, fibrosis
  • •Failure to sense: spike during a beat (could induce arrhythmia)
  • •Pacemaker syndrome: ventricular pacing with retrograde atrial conduction → cannon A waves, fatigue, hypotension — fix with dual-chamber upgrade

High-yield pearls

  • ◆MRI-conditional pacemakers/ICDs are now common — verify model before declining imaging
  • ◆AICD shock + patient awake → check rhythm; if rhythm appropriate VT/VF, device worked; if inappropriate, deactivate with magnet
  • ◆Always interrogate device after syncope — captures rhythm at time of event
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