Patient: 36-year-old male without structural heart disease, normal left ventricular function.
Index arrhythmia: out-of-hospital cardiac arrest, ventricular fibrillation. Observation
Detection: VF = 300 ms; fast VT = 260 ms; VT = 370 ms.
Discrimination: stability = 40 ms; PR Logic ON.
Therapy: VF = shock; fast VT = antitachycardia pacing and cardioversion;
VT = monitoring zone.
Electrogram interpretation (See Figure 6.34b)
1. Interval plot: the interval versus time plot demonstrates alternating AA intervals characterized by two rows of stable AA intervals. The alternating AA intervals represent far-field oversensing of ventricular activity. The marker channel in the electrogram confirms the alternating AA intervals, 160 ms and 190 ms.
2. 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 ~ 360 ms, with a consistent morphology. The atrial electrogram demonstrates sinus tachycardia.
3. Comparison between atrial and ventricular rate: rate branch VV = AA.
4. Assessment of the onset of the tachyarrhythmia triggering the device: the first VV interval in the tachycardia detection zone (depicted as 1 in the electrogram) indicates the onset of the tachyarrhythmia. The subsequent VV intervals are in the tachycardia detection zone and when the programmed number of intervals for tachycardia detection (NID = 16) is reached, the annotation is ST (see marker channel).
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 a consistent atrioventricular relationship, ~ 160 ms. The tachycardia has a ventricular cycle length of ~ 360 ms, with a stability of ~ 10 ms.
Diagnosis: appropriate detection of sinus tachycardia with consistent far-field R-wave oversensing.
Action: no reprogrammation of the device. The consistent far-field R-wave oversensing is used by PR Logic in Medtronic dual-chamber ICDs to withheld device therapy during sinustachycardia. In case of consistent far-field R-wave sensing, it is recommended to activate the feature "other 1:1 SVTs" in PR Logic.
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