Supraventricular tachycardia.

In evaluating episodes of SVT, much information can be gleaned from careful analysis of the surface ECG at the onset of and during the SVT. A number of findings have been outlined here that can help differentiate between automatic and reentrant forms of SVT. In addition, the major forms of reentrant SVT can be differentiated by determining the presence or absence of P waves during the SVT, the relative timing of the P waves to the preceding and succeeding QRS during SVT, the P wave configuration and axis relative to sinus P waves, the necessity for sudden PR prolongation with the onset of SVT, and the development of aberration during the course of SVT and its effect on the SVT rate. Thus by careful analysis of the surface ECG, a number of important conclusions can be drawn concerning the mechanism of SVT. With these findings in mind, preliminary therapeutic decisions can then be made.