ECG QRS Complex

• If present, is the QRS complex normal?

  • should be around 0.1 seconds long (half a large square)
  • ECG 2 and 3 show premature ventricular ectopic (PVC)
  • can be seen on an ECG as coming in early and is quite broad
  • due to ventricular ectopic causing it to depolarise
  • ECG 2 is unifocal as it only points in one direction, ECG 3 is multifocal as it points in 2 directions

  
• When PVC's are dangerous:

  • Ventricular Quadrigeminy - PVC occurs every 4 QRS complex
  • Ventricular Trigeminy - PVC occurs every 3 QRS complex
  • Ventricular Bigeminy - PVC occurs every 2 QRS complex

  
• When PVC's are dangerous:

  • Ventricular Couplets - 2 consecutive PVCs
  • Ventricular Triplets - 3 consecutive PVCs
  • 3 or more PVCs in a row and a rate more than 100 bpm = ventricular tachycardia

  
• • Unifocal PVC - Arising from a single irritable ectopic focus in ventricular muscle; each PVC is identical
  • Multifocal PVC - Arising from two or more irritable ectopic foci in ventricular muscle - multiple QRS morphologies
  • Broad QRS complex, Premature i.e. occurs earlier than would be expected for the next sinus impulse – noted as a “palpitation"
• Where do PVCs come from?

  • One or a small number of irritable hotspots i.e. a single /a small number of ventricular muscle fibres generate APs on their own time line
  • Once generated these APs spread across the ventricular muscle mass via gap junctions. (= odd shape)
  • The timing of this electrical activity (the PVC) is independent of the rate of APs generated by the prime pace-maker i.e. SAN or lower hierarchy pacer in the case of SAN dysfunction
• • 3 or more PVC’s in a row AND rate > 100 bpm = VT
  • VT = Ventricular tachycardia an inherently unstable rhythm prone to ominous deterioration
• Ventricular tachycardia – VT:

  • Potentially life-threatening – contractile rates of ~ 170 bpm
  • Impaired CO, hypotension, circ. collapse, and acute cardiac failure
  • VT can be pulseless or with pulse
  • Narrow complex ventricular tachycardia usually has pulse while broad complex may or may not
  • Prompt recognition and initiation of treatment(e.g. electrical cardioversion) is required in all cases of VT
  • Pulseless ventricular tachycardia is cardiac arrest and requires immediate CPR
• Ventricular Fibrillation – VF:

  • Imminently life-threatening
  • Ventricular fibrillation is usually derived from deteriorating ventricular tachycardia
  • Severely limited / “NO” CO – due to complete loss of organised contractile events
  • This is cardiac arrest
• VF:

  • Ventricular tachycardia has regular QRS complexes on ECG while ventricular fibrillation has irregular QRS complexes
  • Ventricular tachycardia may be narrow or broad complex while ventricular fibrillation cannot be subdivided
  • Ventricular fibrillation is Always Pulseless
  • Requires immediate CPR
• Ventricular arrhythmias:

  • Broad QRS complexes = electrical activity originating outside the intrinsic conduction system
  • Premature ventricular contraction (PVC) if isolated – are generally benign
  • When patterns emerge or more than 1 irritable “hotspot” of myocardium produces electrical activity - that’s when the problems start
  • Ventricular tachycardia can be with a pulse or pulseless – both are life-threatening
  • Ventricular fibrillation is cardiac arrest