Fig. 1
The episode showed a sequence of sinus tachycardia (during exercise), followed by a few beats of PACs with a ‘jump’ into the slow pathway (black dashed line) after the first beat, further PR interval prolongation with crossing over until PR of 320 ms after the 8th beat. That last beat could be conducted retrogradely into the fast atrioventricular nodal pathway (echo beat, red dashed line), initiating AVNRT (PACs Premature atrial contractions, AVNRT atrioventricular nodal reentrant tachycardia)