Diagnosis

To diagnose ventricular tachycardia (VT), your doctor may initially use an electrocardiogram (ECG) test. Some arrhythmias, however, are intermittent and may not always show up during an ECG test. Your doctor may suggest other monitoring tests that can identify when you are having an arrhythmia and what type of rhythm it is.

There are two types of VTs that may be seen on ECG:

• Monomorphic VT looks the same from one beat to the next on the ECG
  
• Polymorphic VT has more than one shape on the ECG

Ventricular tachycardias are often defined when three or more fast heart beat come from the same place in the ventricle. A VT is also described by how long it lasts:

• Nonsustained VT is a fast VT that stops within 30 seconds
  
• Sustained VT is a fast VT that stops after 30 seconds or only after treatment

In cases of ventricular fibrillation (VF), patients usually lose consciousness very quickly. Doctors typically consider a diagnosis of VF when a person suddenly collapses and experiences sudden cardiac arrest. An ECG at the time of collapse can confirm that the rhythm problem is VF.

Further tests are usually necessary to determine the cause and possible treatments for VT or VF. An electrophysiology (EP) study test is a test used to evaluate heart rhythms from inside your heart.