Device Interrogation Unmasking Flecainide-Induced Wide Complex Tachycardia

Figures

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  Figure 1. 12-Lead Electrocardiogram Demonstrating Wide-Complex Tachycardia With Left Bundle Branch Block Morphology

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  Figure 2. Baseline 12-Lead Electrocardiogram Showing Similar Left-Axis Orientation but Narrower QRS Duration (∼130 ms), Confirming Interval Widening During Flecainide Toxicity

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  Figure 3. Initial Device Interrogation Marker channel shows VS-VS at 496 ms cycle length (121 beats/min). No atrial (AS) markers are visible, however atrial electrograms are visible on the intracardiac tracing (channel 2). This reflects Rate Responsive PVARP extension (effective PVARP ≈365 ms) in this Abbott DDD pacemaker programmed with Max Track Rate 110 beats/min and Sensed AV Delay 180 ms. With flecainide-prolonged AV conduction, the resulting ventriculoatrial interval falls within the PVARP window, rendering atrial events invisible on the marker channel. AS = atrial sensed; AV = atrioventricular; PVARP = postventricular atrial refractory period; VS = ventricular sensed.

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  Figure 4. Ventricular Overdrive Pacing to Characterize Tachycardia Mechanism After the programmed stimulus (vertical line at ∼21 s), ventricular pacing at ∼496 ms was initiated. The atrial cycle length did not accelerate to the ventricular pacing rate and continued undisturbed at 551 ms, confirming the atrium was not captured. This demonstrates AV dissociation during ventricular pacing and confirms an independent atrial tachycardia, effectively excluding AVRT and VT with 1:1 retrograde conduction. After pacing cessation, a pause of 879 ms precedes the first ventricular event (AS-VP), after which the device immediately resumes 1:1 AV tracking at the atrial tachycardia cycle length (551 ms) with an AV delay of 176 ms, confirming atrial-driven ventricular activation. AS = atrial sensed; AV = atrioventricular; AVRT = atrioventricular reentrant tachycardia; VP = ventricular paced; VT = ventricular tachycardia.

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  Figure 5. Intact AV Conduction Confirms Aberrancy After 1:1 tracking resumes (AS-VP at ∼555 ms), Ventricular Intrinsic Preference (VIP) extends the AV delay and finds intrinsic conduction. The rhythm transitions from VP to VS at cycle lengths of 551-563 ms, demonstrating intact AV nodal conduction and confirming the wide QRS represents aberrancy, not ventricular tachycardia. AS = atrial sensed; AV = atrioventricular; VP = ventricular paced; VS = ventricular sensed.

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  Visual Summary. Diagnostic Pathway for Wide-Complex Tachycardia in a Pacemaker-Dependent Patient on Flecainide Pacemaker interrogation identified 3 sequential findings that distinguished SVT with aberrancy from VT: 1) VS-VS at 496 ms with absent AS markers due to PVARP extension; 2) independent atrial rate during ventricular overdrive pacing, excluding AVRT and reentrant VT; and 3) VP-to-VS transition via the VIP algorithm, confirming intact AV conduction. AS = atrial sensed; AT = atrial tachycardia; AVRT = atrioventricular reentrant tachycardia; AV = atrioventricular; CL = cycle length; IV = intravenous; LBBB = left bundle branch block; PVARP = postventricular atrial refractory period; SVT = supraventricular tachycardia; VIP = Ventricular Intrinsic Preference; VP = ventricular paced; VS = ventricular sensed; VT = ventricular tachycardia.