MORPHOLOGY CRITERIAFor RBBB-type complexes Is there an rSR’ morphology in V1? Is there an RS complex in V6 (small septal q OK)? Is the R/S ratio in V6 > 1?For LBBB-type complexes Is there an rS or QS complex in V1 and V2? Is the onset of the QRS to the nadir of the S in V1 < 70 ms? Is there an R wave in lead V6 without a Q?
AVR CRITERIA Presence of an initial R wave Width of an initial r or q wave >40 ms, Notching on the initial downstroke of a predominantly negative QRS complex Ventricular activation–velocity ratio (vi/vt), the vertical excursion (in millivolts) recorded during the initial (vi) and terminal (vt) 40 ms of the QRS complex. When any of criteria 1 to 3 was present, VT was diagnosed; when absent, the next criterion was analyzed. In step 4, vi/vt >1 suggested SVT, and vi/vt ≤1 suggested VT.
VENTRICULAR TACHYCARDIA Absence of typical RBBB or LBBB morphology Extreme axis deviation (“northwest axis”) Very broad complexes (>160ms) AV dissociation (P and QRS complexes at different rates) Capture beats — occur when the sinoatrial node transiently ‘captures’ the ventricles, in the midst of AV dissociation, to produce a QRS complex of normal duration. Fusion beats — occur when a sinus and ventricular beat coincides to produce a hybrid complex.
Positive or negative concordance throughout the chest leads, i.e. leads V1-6 show entirely positive (R) or entirely negative (QS) complexes, with no RS complexes seen. Brugada’s sign– The distance from the onset of the QRS complex to the nadir of the S-wave is > 100ms Josephson’s sign – Notching near the nadir of the S- wave
TAKE HOME MESSAGE No criteria is 100% sensitive nor specific Never go blindly by ECG Give equal imortance to history, clinical presentation, Vitals If you are 100% sure that it is SVT, then proceed. Having even 1% doubt, then treat it as VT