The QRS morphology in post-myocardial infarction ventricular tachycardia. A study of 100 tracings compared with 70 cases of idiopathic ventricular tachycardia

A hundred tracings of ventricular tachycardia (VT) belongingto 85 patients with myocardial infarction (MI) were comparedwith 70 cases of incessant, benign, idiopathic VT. The two groupsof tracings differed in terms of QRS axis, most often normalin idiopathic VT (75%) and outside normality in MIVT (74%).The sum of QRS amplitude in unipolar limb leads was greaterin idiopathic VT (4.3±1.3 mv, mean±S.D.) thanin MIVT (2.6±0.8 mv, P>0.001). The QRS width was alsodifferent: 135±11 ms in idiopathic VT vs. 171±32ms in MIVT (P>0.001). The QRS morphology in MIVT was characterizedby the presence of a QR pattern in leads other than VR, or aQS pattern in V₅–V₆. These two aspects were constantlyabsent in idiopathic VT, and they were present in 89%of MIVT.In only 38 MIVT tracings were the ECG signs of MI observed inthe same leads during sinus rhythm and during VT. In 51 MIVTtracings the location of the MI indicated by the VT tracingdiffered from that displayed in sinus rhythm. Rather than indicatingan extension of the infarcted area not apparent in the tracingsin sinus rhythm, such a discrepancy suggests that the QRS patternduring VT strongly depends on the point of origin of the VT.Conversely, this explains why the morphology of the QRS is anureliable means for localizing the VT origin if the locationof the MI is not taken into account. We conclude that both factorsshould be taken into consideration, and this might theoreticallypermit a better though complex approach to the VT origin incoronary heart disease using surface tracings.