Distinguishing Vtach from artifact is relatively easy, and you should be able to do it with a little troubleshooting and a trained eye. Distinguishing vtach from an abnormally widened svt can be much more difficult.
The first and most important thing you need to do in this situation is to check your patient. Are they pulseless? Then follow BLS and ACLS protocols. Are they showing signs of (presumably acute) profound hypoperfusion despite having a pulse? Then also follow ACLS protocols. Either case is a medical emergency, and you should get a code team there ASAP.
Do they look OK? Good. Then it's time to troubleshoot. Often you can attribute artifact to movement you see in the patient. Also, you will often see artifact more in some leads than in others. If you suspect artifact, get the patient to sit still, try moving the leads around, and try looking at as many leads as you can. Most 5 lead monitors you have in hospitals allow you to look at a number of different leads, not just lead II and the V lead. Get familiar with your monitoring system and see if you can do this. If you see a normal rhythm more clearly under the artifact in some leads, you can safely attribute the rhythm to artifact - either SVT or Vtach are present in all leads when they are present.
Distinguishing Vtach from SVT in a patient who is not coding can be surprisingly difficult. A cardiologist who is nearby can be useful, as can a 12 lead EKG. There are a lot of things that can hint at one rhythm vs the other, but some morphologies can be very difficult to sort out even by experienced practitioners using 12 lead analysis. In general, a few things can tend to point toward vtach and away from SVT
- A very wide QRS
- Presence of a fusion beat at the beginning of the tachycardia
- AV disassociation
- Extreme axis deviation
- Q only complexes in the V leads of a 12 lead.
- A pulseless or profoundly hypoperfused patient
And some things likewise might push me towards thinking I'm looking at some kind of widened non-ventricular tachycardia:
- Bundle branch block
- Irregularly timed beats with regular morphology (often suggests an underlying rhythm of afib with RVR)
- A history of SVT or wolfe-parkinson-white
- Relatively stable hemodynamics, patient in minimal distress
Some more in-depth learning tools:
VT versus SVT with aberrancy
ECG Learning Center - An introduction to clinical electrocardiography