**4. ECG criteria favoring ventricular rather than supra-ventricular tachycardia in WCTs**

There are several algorithms that are currently used to help distinguish Supraventricular Tachycardia (SVT) with aberrancy and Ventricular Tachycardia (VT) (**Table 3**). Many of these algorithms and criteria have limitations [44–49, 50–64].

### **4.1 Sandler and Marriott criteria (1965)**

[RBBB morphology] Identical activation vector = SVT.

If the initial 20 ms of the QRS are the same in WCT as in sinus rhythm, SVT is favored with a positive predictive value (PPV) of 92%. The sinus rhythm ECG must be available for this analysis.

[RBBB morphology] An rSR' where S crosses baseline = SVT with a PPV of 91%.

[RBBB morphology] Triphasic QRS in V1 = SVT with a PPV of 92%.

[RBBB morphology, LBBB morphology] Precordial concordance = VT. A QRS, which is predominantly positive or predominantly negative in every precordial lead, overwhelmingly favors VT with specificity of 95–100% and a PPV of 89–100% [44–49, 50–65].

### **4.2 Wellens criteria of right bundle branch block**

AV dissociation = VT. Of all criteria, this is the most secure with specificity of 100% and PPV of 100%. It holds true regardless of bundle branch pattern or other morphology criteria.

*Electrocardiographic Differential Diagnosis of Narrow QRS and Wide QRS Complex… DOI: http://dx.doi.org/10.5772/intechopen.102568*


*RBBB; right bundle branch block, LBBB; left bundle branch block, SVT; supra-ventricular tachycardia.*

#### **Table 3.**

*ECG criteria favoring ventricular rather than supra-ventricular tachycardia in WCTs.*

[RBBB morphology] QRS duration >140 ms = VT with specificity of 57–75% and PPV of 89%.

[RBBB morphology] Left axis deviation = VT with PPVs of 88–94%. With extreme left axis (more negative than −90°), the PPV is 98%.

[RBBB morphology] Mono- or biphasic QRS morphologies in V1 favors VT with PPV of 82–83*%.*

If the V1 QRS is triphasic, an R:S ratio < 1 in V6 (that is, R wave smaller than S wave) favors VT with PPV of 90%.

[RBBB morphology] Rsr' ('Rabbit ears') = VT. In an unusual triphasic V1, with the left R wave taller than the right, and the S wave not crossing the baseline, favors VT with PPV of 100% [44–49, 50–64].
