Interesting response of slow regular narrow QRS tachycardia to atrial extra stimulus

Unusual response to His‐refractory atrial premature complex: What is the mechanism?

“…This is not a challenge although technically could conceivably be a nodo‐fascicular NQT 11,12 . In AVNRT, an AES delivered when the His is refractory can conduct to the ventricle by the slow pathway 13‐17 . Indeed, a single AES by itself cannot always differentiate the atypical AVNRT from the AT because a very early AES may result in termination of an AT and even an early AES may not terminate an atypical AVNRT with an upper common pathway 11,18,19 .…”