Info

I Dn Da Da aa

Figure 6.33a.

ICD pulse generator: Marquis DR 7274 (Medtronic Inc, Minneapolis, MN, USA).

Tachycardia settings

Detection: VF = 330 ms; fast VT via VF = 240 ms; VT = 360 ms. Discrimination: stability = 30 ms; PR Logic ON.

Therapy: VF = shock; fast VT = antitachycardia pacing and cardioversion; VT = monitoring.

Bradycardia settings Mode: DDD 70-120 bpm. Mode switch = ON. AV = 180 ms.

146 6. Clinical Case Studies Electrogram interpretation

146 6. Clinical Case Studies Electrogram interpretation

Figure 6.33b. From top to bottom: atrial electrogram, ventricular electrogram, and marker channel. Markers: AR = atrial refractory sense; AS = atrial sensing; TF. = ventricular sense, fast ventricular tachycardia window; TS = tachycardia sensing; VS = ventricular sense.

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 (upper electrogram). The subsequent VV intervals are in the ventricular tachycardia detection zone and fast ventricular tachycardia detection zone.

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 «700 ms, with a consistent morphology. The atrial electrogram demonstrates sinus rhythm.

5. Characteristics of the ventricular electrogram during the tachyarrhythmia: the morphology of the ventricular activity is consistent during tachycardia. The atrioventricular conduction pattern can be assessed from the marker channel. During the tachycardia, the marker channel demonstrates absence of a consistent atrioventricular relationship. The tachycardia has a ventricular cycle length of « 320 ms, with a stability of «20 ms.

Diagnosis: ventricular tachycardia, no therapy delivered because monitoring was programmed in the ventricular tachycardia detection zone.

Action: activation of antitachycardia pacing as therapy in the ventricular tachycardia detection zone.

Electrogram interpretation with tachogram (See Figure 6.33c)

Interval plot: the interval versus time plot demonstrates both an increase and a decrease in AA intervals, characterized by an "arrow" pattern. This

Figure 6.33c. From top to bottom: atrial electrogram, ventricular electrogram, and marker channel. Markers: AR = atrial refractory sense; TS = tachycardia sensing; VS = ventricular sense.

pattern is caused by the presence of far-field oversensing of ventricular activity during ventricular tachycardia with absence of a consistent atrioventricular conduction pattern. The increase is observed in AA intervals between atrial activity and far-field signal. The decrease is observed in AA intervals between far-field signal and atrial activity.

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