Lesson 8, Topic 5
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Ventricular Premature Contractions

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Ventricular premature contractions (VPCs) are depolarizations from an ectopic focus in the ventricular myocardium.

ECG Findings:

  1. The QRS complexes are usually wide and bizarre.
  2. If several ectopic foci are present, the morphology of the QRS will vary with each focus (multi-form VPCs).
  3. Most VPCs are accompanied by a pause or delay after, prior to the onset of the next sinus beat. A time measurement that includes the pause can be used to discriminate between VPCs and SVPCs. For a representation please see diagram under question 33.
  4. VPCs may occur as fusion and as interpolated beats.
    • A fusion beat is a QRS with a morphology that is neither identical to the sinus QRS, nor to a typical VPC. It is also a QRS which occurs on time (i.e. it is not premature). It represents a fortuitous situation wherein part of the ventricular mass was depolarized as a result of the sinus beat and the remainder of the ventricular mass was depolarized as a result of the ectopic ventricular focus.
  5. An interpolated beat is a special form of VPC wherein the presence of the VPC did not interrupt the underlying sinus rhythm.
Ventricular Premature Contractions (VPCs) in the dog – slide to highlight ECG findings


  1. Myocardial disease causing ventricular concentric hypertrophy or eccentric hypertrophy
  2. Hypoxemic states as anemia, gastric dilation volvulus, heart failure
  3. Metabolic derangements such as acidosis or hypokalemia
  4. Trauma (traumatic myocarditis)
  5. Circulating cytokines in neoplastic and systemic inflammatory disorders
  6. Drugs such as digoxin, barbiturates, some antiarrhythmic agents


  1. If enough premature beats are present, cardiac output may fall due to dyssynergy of contraction and high heart rate.
  2. May predispose to ventricular fibrillation.


  1. If IV anti-arrhythmic therapy is necessary, choices include lidocaine, procainamide, beta blockers, or in some cases amiodarone, with lidocaine being the first choice.
  2. Oral anti-arrhythmic choices include mexiletine (lidocaine analog), sotalol, pure beta blockers, or amiodarone