Abstract
A 40-year-old woman without structural heart disease was referred for nondocumented palpitations associated with ventricular preexcitation. The baseline electrocardiogram showed preexcitation suggestive of a posteroseptal accessory pathway (AP). With incremental right atrial pacing, atrioventricular (AV) conduction time over the AP was cycle length dependent (decremental) and maximal preexcitation was observed at pacing cycle length 320 milliseconds (Fig. 1). Retrograde conduction revealed earliest atrial activation at the orifice of the coronary sinus (CS 9–10) with decremental conduction and effective refractory period at the CS orifice of 430 milliseconds at a drive cycle length of 600 milliseconds. Wide complex tachycardia (cycle length 356 milliseconds) was observed during ventricular extrastimulus testing from the right ventricle (RV) apex (Fig. 2). A single premature ventricular contraction (PVC) delivered during tachycardia is shown in Figure 3. What is the mechanism of the tachycardia?
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