As the sinus rate increases, activation arises from more superior aspects of the right atrium, resulting in a larger-amplitude P wave in the inferior leads. Table 5. ECG Criteria to Differentiate VT From SVT in Wide-Complex Tachycardia Findings or Leads on ECG Assessed Interpretation QRS complex in leads V1-V6 Lack of any R-S complexes implies VT R-S interval (onset of R wave to nadir of S wave) >100 ms in any precordial lead implies VT QRS complex in aVR (Vereckei Presence of initial R wave implies VT Initial R or Q wave >40 ms implies VT Presence of a notch on the descending limb at the onset of a predominantly negative QRS implies VT AV dissociation* Presence of AV dissociation (with ventricular rate faster than atrial rate) or fusion complexes implies VT QRS complexes in precordial leads all positive or all negative (concordant) Implies VT QRS in tachycardia that is identical to sinus rhythm78 Suggests SVT R-wave peak time in lead II78 R-wave peak time 50 ms suggests VT *AV dissociation is also a component of the Brugada criteria.73 AV indicates atrioventricular; ECG, electrocardiogram; SVT, supraventricular tachycardia; and VT, ventricular tachycardia. Table 4. Differential Diagnosis of Wide QRS Complex Tachycardia Mechanism Ventricular tachycardia SVT with pre-existing bundle-branch block or intraventricular conduction defect SVT with aberrant conduction due to tachycardia (normal QRS when in sinus rhythm) SVT with wide QRS related to electrolyte or metabolic disorder SVT with conduction over an accessory pathway (pre-excitation) Paced rhythm Artifact SVT indicates supraventricular tachycardia. Figure 6. Permanent form of junctional reciprocating tachycardia (PJRT). Tachycardia starts after 2 beats of sinus rhythm. Arrows point to the P wave, which is inscribed before the QRS complex. 