Different Responses to Premature Atrial Complexes During Wide QRS Complex Tachycardia: What Is the Mechanism?

Figures

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  Figure 1:. The A–H interval was short and normalized with programmed atrial stimulation (A). Programmed ventricular stimulation (B) demonstrates retrograde right bundle branch block conduction and a ventricular echo beat exhibiting a right bundle branch block morphology.

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  Figure 2:. Pre-excited tachycardia was inducible only by ventricular stimulation (A) and stoppable by the “early” premature atrial stimulation (B). Note the differences in QRS morphology and H–V intervals following the termination of tachycardia by the “early” premature atrial contraction.

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  Figure 3:. Ventricular activation could not be advanced by “late” premature atrial contractions delivered from the coronary sinus distal electrode (single red star, on the left corner) but was advanced by only “early” premature atrial contractions delivered from the same electrode without changing the QRS morphology (double red star, on the right corner). Note that the morphology of the one antidromic echo beat by programmed ventricular stimulation (Figure 1B) was the same as that of tachycardia (Figure 3). A proximal coronary sinus recording is critical for evaluating septal refractoriness and excluding nodal tachycardia and other forms of nodal bystander pre-excitation (such as nodofascicular or nodoventricular re-entrant tachycardia) (compare the first and second rectangular boxes with regard to coronary sinus proximal electrogram morphology and cycle length). Abbreviations: AVN, atrioventricular node; PAC, premature atrial contraction.

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  Figure 4:. Three different responses to “late” (A) and “early” (B and C) premature atrial contractions (PACs). Whereas the ventricular activation could not be advanced by “late” PAC delivered from the coronary sinus distal electrode (A), it was advanced by only “early” PAC delivered from the same electrode without changing the morphology (B), and then finally tachycardia showed a termination response to the “early” PAC (C). Abbreviation: PAC, premature atrial contraction.