Different Responses to Premature Atrial Complexes During Wide QRS Complex Tachycardia: What Is the Mechanism?

A wide complex tachycardia may result from supraventricular tachycardia (SVT) with bundle branch block (pre-existing or tachycardia-related), SVT with atrioventricular conduction over an accessory pathway (AP), or ventricular tachycardia (VT). The timing of PACs and their effect on tachycardia can help differentiate between atrioventricular nodal re-entry tachycardia variants and AP-mediated tachycardias. A proximal coronary sinus recording is critical for evaluating septal refractoriness and excluding nodal tachycardia and other forms of nodal bystander pre-excitation (such as nodoventricular or nodofascicular re-entrant tachycardia).