Atrioventricular Re-Entrant Tachycardia – a reentrant tachycardia between the atrium and ventricle using the AV node and an abnormal accessory pathway that connects the atrial to ventricular tissue at the level of the annulus. Orthodromic AVRT uses the accessory pathway as the retrograde limb of the circuit and is a regular narrow-QRS tachycardia (rate 150-250/min) whereas antidromic AVRT uses the accessory pathway as the antegrade limb of the circuit and is a regular wide-QRS tachycardia. When the P waves are seen, they follow the QRS, but not as closely as in AVNRT. Because the atrium is activated retrogradely, the p-waves are negative in II, III and aVF.
