Case 34 Atrial Flutter with 21 Conduction

Patient: 36-year-old male without structural heart disease, normal left ventricular function.

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

Figure 6.34a.

ICD pulse generator: Marquis DR 7274 (Medtronic Inc, Minneapolis,

Tachycardia settings

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.

Bradycardia settings

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.

Atrial Electrograms Atrial Flutter
Figure 6.34b. From top to bottom: atrial electrogram, ventricular electrogram, and marker channel. Markers: AR = atrial refractory sense; ST = sinus tachycardia; TS = tachycardia sensing; VS = ventricular sense.

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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