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Figure 1 Schematic illustration of the dissociation of atrial activation between the orifice of the coronary sinus (CSOS) and the LSRA site during extrastimulation of fast–slow AVNRT from the HRA and the CSOS. The reentrant pathway of fast–slow AVNRT is illustrated schematically as a triangular circuit comprising the anterograde FP, retrograde SP and the perinodal atrium. (I) An atrial extrastimulus is delivered anteriorly from the HRA site ( ) during the posterior type of AVNRT in which the retrograde SP is located in the posterior septum. It is postulated in this hypothetical model that an anterior wavefront from the HRA extrastimulus (solid arrow) enters an anteriorly located FP via an anterior input and preexcites the His bundle and the ventricle, thereby resetting the tachycardia. During tachycardia resetting, the CSOS electrogram is being activated retrogradely by the previous tachycardia beat (dashed arrow), indicating atrial dissociation. (II) An atrial extrastimulus is delivered posteriorly from the CSOS site () during the anterior type of AVNRT in which the retrograde SP is located in the anterior septum. It is likewise postulated that a posterior wavefront from the CSOS extrastimulus (solid arrow) enters a posteriorly located FP via a posterior input and preexcites the His bundle and the ventricle, thereby resetting the tachycardia. During tachycardia resetting, the LSRA electrogram is being activated retrogradely by the previous tachycardia beat (dashed arrow), again indicating atrial dissociation. HBE = His bundle electrogram.
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