1. Mahaim pathway tachycardia versus bystander ventricular tachycardia: A distinction without a difference 
Michael S. Wu, MD, James E. Ip, MD, FHRS, George Thomas, MD, Steven M. Markowitz, MD, FHRS, Jim W. Cheung, MD, FHRS, Christopher F. Liu, MD, FHRS, Bruce B. Lerman, MD, FHRS 
HeartRhythm Case Reports 
Volume 4, Issue 3, Pages (March 2018)
DOI: /j.hrcr
Copyright © 2017 Heart Rhythm Society Terms and Conditions

2. Figure 1
A: Preexcitation linked to conduction over the slow atrioventricular pathway. During atrial pacing at a cycle length of 370 ms from the proximal coronary sinus (CSp), a fusion beat (*) occurred coincident with abrupt prolongation of the AH interval (from 105 to 194 ms), which was followed by fully preexcited complexes. Surface leads 1, aVF, and V1 are shown, as well as intracardiac recordings from the distal His bundle (Hisd), CSp, and right ventricular apex (RVA). A = atrial activation; H = His. B: Effect of adenosine on preexcitation. Adenosine (12 mg) caused prolongation of atrioventricular (AV) nodal conduction, which was associated with AV prolongation, shortening of the HV interval, and reversal of relative ventricular activation recorded from the posteroseptal tricuspid annulus (TAps) and RVA. During the first 2 beats, conduction proceeds over the fast AV nodal pathway, the QRS complex is narrow, and the RVA is activated before TAps ventricular excitation. This relationship reverses as conduction switches to the slow AV nodal pathway and preexcitation becomes manifest. ΔV = relative ventricular activation of TA and RVA (ms); positive value indicates that TA ventricular activation precedes RVA; negative value indicates that RVA activation precedes TA activation.
HeartRhythm Case Reports 2018 4, 92-97DOI: ( /j.hrcr )
Copyright © 2017 Heart Rhythm Society Terms and Conditions

3. Figure 2
A: Initiation of wide complex tachycardia with atrial pacing. The preexcited beats during atrial pacing (220 ms) have the same morphology as the tachycardia (240 ms). Abbreviations are as previously defined. * fusion beat during atrial pacing resulting from conduction over Mahaim pathway and AV node; ** fusion beat during tachycardia. B: Wide complex tachycardia with AV dissociation. Abbreviations as defined in Figure 1.
HeartRhythm Case Reports 2018 4, 92-97DOI: ( /j.hrcr )
Copyright © 2017 Heart Rhythm Society Terms and Conditions

4. Figure 3
A: Termination of wide complex tachycardia with adenosine. Adenosine's effects on tachycardia are manifest before its effects on Mahaim pathway conduction or its abolition of conduction in the slow AV nodal pathway. Conduction over the Mahaim pathway via the slow pathway of the AV node is maintained during the first 2 sinus beats (labeled 1 and 2) following tachycardia termination. The third beat blocks in both the AV node and Mahaim pathway before conduction resumes over the fast AV nodal pathway without evidence of prexcitation (fourth beat). Abbreviations as defined in Figure 1. B: The best match during ventricular pace mapping (97%) was recorded from the ventricular insertion site of the Mahaim pathway, in the region of the posteroseptal tricuspid annulus. Note that there is also a near-identical QRS match when comparing the morphology during atrial pacing (from proximal coronary sinus) and the tachycardia morphology.
HeartRhythm Case Reports 2018 4, 92-97DOI: ( /j.hrcr )
Copyright © 2017 Heart Rhythm Society Terms and Conditions