Supraventricular tachycardia differentiating SVT from VT
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Supraventricular tachycardia Microchapters |
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Differentiating Among the Different Types of Supraventricular Tachycardia |
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Differentiating Supraventricular Tachycardia from Ventricular Tachycardia |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
See also: Wide complex tachycardia
Overview
Most supraventricular tachycardias have a narrow QRS complex on the EKG. It is not infrequent, however, for aberrant conduction to be be present, sometimes as a result of the more rapid rate of conduction. This widening of the QRS complex yields supraventricular tachycardia with aberrant conduction (SVTAC) which produces a wide-complex tachycardia that may mimic ventricular tachycardia (VT). In the clinical setting, it is important to determine whether a wide-complex tachycardia is an SVT or a ventricular tachycardia, since they are treated differently. Ventricular tachycardia has to be treated appropriately, since it can quickly degenerate to ventricular fibrillation and death. A number of different algorithms have been devised to determine whether a wide complex tachycardia is supraventricular or ventricular in origin.[1]
In general, a history of structural heart disease, ischemic heart disease or congestive heart failure increases the likelihood that the tachycardia is ventricular in origin.
Differentiating SVT from VT
For a detailed discussion of how to distinguish ventricular tachycardia (VT) from supraventricular tachycardia (SVT), please visit the wide complex tachycardia differential diagnosis page.
In brief, the diagnosis of VT is more likely if:
- There is a history of myocardial infarction, congestive heart failure or structural heart disease
- VT is more common in the elderly
- The electrical axis is -90 to -180 degrees (a “northwest” or “superior” axis)
- The QRS is > 140 msec
- There is AV dissociation. P waves are normal in morphology, upright, but dissociated from the QRS complex (i.e. "march through" the QRS complex)
- There are positive or negative QRS complexes in all the precordial leads
- The morphology of the QRS complexes resembles that of a previous premature ventricular contraction (PVC).
- Rate: More than 100 bpm and usually 150-200 bpm
- Rhythm: The rhythm is regular
- PR interval: Variable PR interval
- Response to Maneuvers: VT does not terminate in response to adenosine or vagal maneuvers