Case 15 ATP Observed During Routine Control

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Patient: 74-year-old female with ischemic heart disease, old inferoposterior wall myocardial infarction, left ventricular ejection fraction 0.19, documented paroxysmal atrial fibrillation.

Index arrhythmia: out-of-hospital cardiac arrest, ventricular fibrillation.

Complaint: no complaints were noted at follow-up, only events treated with antitachycardia pacing were obtained from the device's memory.

Electrogram

7» 734 728 728 734 734 720 742 T% 726 752 4W 430 422

7» 734 728 728 734 734 720 742 T% 726 752 4W 430 422

VI detected

VI detected

25 nn/sec

Figure 6.15a. From top to bottom: marker channel, atrial electrogram, and ventricular electrogram. Markers: CNT = count in tachycardia detection window.

25 nn/sec

Figure 6.15a. From top to bottom: marker channel, atrial electrogram, and ventricular electrogram. Markers: CNT = count in tachycardia detection window.

ICD pulse generator: Phylax AV (Biotronik Inc, Berlin, Germany).

Tachycardia settings

Discrimination: onset = 15%; stability = 40 ms; SMART ON.

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

Bradycardia settings Mode: DDD 60-120 bpm. Mode switch = ON.

1. Presence of tachyarrhythmia?: No.

2. Presence of high-frequency noise on isoelectric baseline?: No.

3. Description of the atrial rhythm: the atrial electrogram shows both large as well as small deflections (upper electrogram). The small deflections represent far-field oversensing of the ventricular activity. The large deflection represents an atrial rhythm, cycle length «730 ms, with a consistent morphology. The atrial electrogram demonstrates sinus rhythm. The large deflections represent the baseline rhythm, cycle length «730 ms.

4. Description of the ventricular electrogram: the ventricular electrogram shows both large sharp deflections as well as small waves occurring at an interval of 320 ms after each sharp deflection. The sharp deflections represent the ventricular rhythm with a cycle length of « 730 ms. The marker channel demonstrates more sensed ventricular activities than present on the ventricular electrogram. In Figure 6.15b, the sensed activities on the marker channel are related to ventricular electrogram. Sensed ventricular activity is displayed as "R" and "T" represents the T wave.

Diagnosis: T-wave oversensing caused inappropriate detection of ventricular tachycardia.

Action: programmation of specific sensing parameters to prevent T-wave oversensing. Automatic sensitivity control begins to adjust sensing threshold after a blanking period of 121ms. This blanking period can be prolonged and/or the sensing threshold can be increased.

Relation between marker channel and ventricular electrogram

Wave Oversensing
Figure 6.15b.

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