Case 29 A Sudden Change in Ventricular Rate

Patient: 70-year-old male with ischemic heart disease, paroxysmal atrial fibrillation, coronary artery bypass grafting, left ventricular ejection fraction 39%.

Index arrhythmia: polymorphic sustained ventricular tachycardia.

Complaints: 6 weeks after ICD implantation multiple episodes treated with antitachycardia pacing.

Electrogram

Figure 6.29a. From top to bottom: far-field electrogram (A-tip to V-ring), markers, and marker channel. Markers: TD| = tachycardia detected; TS = tachycardia sensing; VS = ventricular sensing.

ICD pulse generator: Jewel AF (Medtronic Inc, Minneapolis, MN, USA).

Tachycardia settings

Detection: VF = 320 ms; VT = 460 ms. Discrimination: stability = 40 ms; PR Logic ON.

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

Bradycardia settings Mode: DDD 50-120 bpm. Mode switch = ON. AV = 150 ms.

Electrogram interpretation

Figure 6.29b.

1. The first step in electrogram interpretation is the comparison between atrial and ventricular rate, which results in VV > AA branch.

2. The second step is a description of the atrial rhythm. The atrial activity on the marker channel shows a fast atrial rhythm with an atrial cycle length «280 ms. The atrial activity on the far-field electrogram shows a stable morphology. The atrial rhythm can either be an atrial tachycardia or an atrial flutter.

3. The third step is the assessment of the onset of the tachyarrhythmia triggering device therapy. The marker channel demonstrates a stable ventricular rhythm with a consistent atrioventricular (AV) conduction pattern, depicted as 1 in the electrogram. A premature beat (depicted as 2 in the electrogram) initiates a tachycardia (depicted as 3 in the electrogram).

4. Finally, we describe the ventricular electrogram morphology and the atrioventricular conduction pattern during the tachycardia. The morphology of the ventricular activity is consistent during tachycardia. However, the morphology cannot be compared to the baseline rhythm, as no electrogram is stored before arrhythmia onset. The atrioventricular conduction pattern can be assessed from the marker channel. The baseline rhythm (depicted as 1 in the electrogram) demonstrates a consistent atrioventricular conduction pattern. During the tachycardia, the marker channel demonstrates no consistent atrioventricular conduction pattern. The tachycardia has a ventricular cycle length of «360 ms, with a stability of «10 ms.

Diagnosis: ventricular tachycardia during atrial flutter or atrial tachycardia.

The electrogram alone was not sufficient for the diagnosis.

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