Primary VF is the arrhythmia that occurs within minutes to few hours after acute coronary ischemia .This is most common fatal arrhythmia following STEMI accounting for 90% of all pre hospital deaths.
It occurs within 4 hours after onset of symptom and the risk rapidly fade as the hours go by.One variant of primary VF is the re-perfusion arrhythmia after thrombolysis .This can occur up to 12 hours or so.Primary VF responds well to prompt defibrillation.Follow up anti arhythmic drugs are not required in most situations.
What is secondary VF ?
- As a rule secondary VF is not related* to index event of ischemia but to the anatomical substrates of Infarcted myocardium or pump failure
- It generally occurs after 24 hours .Response to defibrillation is less favorable .Continued anti- arrhythmic drug therapy is required.
- Few of them may end up with ICD.
(*However,a role for ongoing ischemia can never be disproved ! What about a small re-infarct trigggering another episode of primary VF ? )