Iii

Impedances 1. pacing imp. [ohmj ♦ Shock imp. [ohm]

02/20 02/24

01/25/06 01/50

Figure 6.37a.

ICD pulse generator: Lexos VR-T (Biotronik Inc, Berlin, Germany). Epicardial lead system.

Tachycardia settings

Detection: VF = 300 ms; VT = 370 ms. Discrimination: onset = 16%; stability = 40 ms.

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

Bradycardia settings

Mode: VVI 50bpm.

Electrogram as Si if ¡6 S SS£ 3K S^Sr S8SSS SSI J5 sgs 5SK Si« SSK ( Si SI

as Si if ¡6 S SS£ 3K S^Sr S8SSS SSI J5 sgs 5SK Si« SSK ( Si SI

Figure 6.37b. Event which led to an aborted high-voltage shock. From top to bottom: marker channel, near-field ventricular electrogram, and wide-band ventricular electrogram. Markers: VF = sense in ventricular fibrillation window; VP = ventricular pace; VS = ventricular sense; VT-1 = sense in ventricular tachycardia window.

Figure 6.37b. Event which led to an aborted high-voltage shock. From top to bottom: marker channel, near-field ventricular electrogram, and wide-band ventricular electrogram. Markers: VF = sense in ventricular fibrillation window; VP = ventricular pace; VS = ventricular sense; VT-1 = sense in ventricular tachycardia window.

Interpretation

1. Presence of tachyarrhythmia?: No.

2. Presence of high-frequency noise on isoelectric baseline?: Yes.

3. Description of the ventricular electrogram: the morphology of the ventricular activity is consistent with a cycle length of ~ 1000 ms and a stability of ~ 10 ms. The marker channel demonstrates more sensed ventricular events than present on the ventricular electrogram. The wideband ventricular electrogram shows both large complexes as well as small sharp deflections, which have no relation with the ventricular depolarization. The sharp deflections represent oversensing of signals which is confirmed by the interval plot.

4. Interval plot: the interval versus time plot shows a "rail track pattern," which represents oversensing.

Interval plot (See Figure 6.37c)

Figure 6.37c. Each"+" represents sensed ventricular activity.

Diagnosis: oversensing of signals. Action

1. Local manupilation to provoke abnormal signals.

2. Measurement of lead impedance and shock system integrity.

3. Measurement of pacing and sensing characteristics.

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