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Figure 6.11a. From top to bottom: atrial electrogram, marker channel, and ventricular electrogram. Markers: A = atrial pacing; B = bradycardia window; F = ventricular fibrillation window; P = atrial sense; R = ventricular sense; S = sinus window; TS = tachycardia sensing; V = ventricular pacing.

ICD pulse generator: Atlas DR 243 (St Jude Medical, Sylmar, CA, USA). Tachycardia settings

Detection: VF = 300 ms; fast VT via VF = 270 ms; VT = 430 ms. Discrimination: onset 16%; stability = 30 ms; morphology discrimination ON. Therapy: VF = shock; fast VT and VT = antitachycardia pacing and cardioversion.

Bradycardia settings Mode: DDI 50bpm. AV = 275 ms.

Shocked Sinus

1. Presence of tachyarrhythmia?: Yes.

2. Assessment of the onset of the tachyarrhythmia triggering the device: the first VV interval in the tachycardia detection zone (*) indicates the onset of the tachyarrhythmia.

3. Comparison between atrial and ventricular rate: rate branch VV < AA.

4. Description of the atrial rhythm: the atrial electrogram shows large as well as small deflections. The small deflection represents far-field oversensing of the ventricular activity. The large deflection represents an atrial rhythm, cycle length ~ 420 ms, with a consistent morphology. The atrial electrogram demonstrates sinus tachycardia.

5. Characteristics of the ventricular electrogram during the tachyarrhythmia: the morphology of the ventricular activity is initially consistent during tachycardia. After 11 beats, the morphology is changing (arrow). The atrioventricular conduction pattern can be assessed from the marker channel. During the tachycardia, the marker channel demonstrates a consistent atrioventricular relationship of ~ 160 ms. The tachycardia has a ventricular cycle length of ~ 360 ms, with a stability of ~ 10 ms.

Diagnosis: appropriate detection of fast polymorphic ventricular tachycardia.

Action: reprogrammation of the bradycardia settings, increase of the lower rate and decrease of the AV interval.

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