Index arrhythmia: out-of-hospital arrest, ventricular fibrillation.
Figure 6.14a. From top to bottom: wide-band electrogram, markers, and device activity channel.
ICD pulse generator: Defender IV DR 612 (ELA Medical, Le Plessis, France).
Discrimination: onset = 19%; stability = 47 ms; PARAD ON.
Therapy: VF = shock; VT = antitachycardia pacing and cardioversion.
Bradycardia settings Mode: DDD 60-120 bpm. Mode switch = ON. AV = 188 ms.
1. Assessment of the onset of the tachyarrhythmia triggering the device: the first VV interval in the tachycardia detection zone triggering the device is not available in the electrogram.
2. Comparison between atrial and ventricular rate: rate branch VV > AA.
3. Description of the atrial rhythm: the wide-band electrogram shows small deflections, which represent the atrial activity (arrows in the figure below). The marker channel and the numerical annotations on the device activity channel confirm the atrial cycle length of 344 ms. The device activity channel also shows a pattern of four consecutive atrial activations followed by a "pause" of 688 ms. The pause in atrial activation can be explained by the presence of ventriculoatrial crossblanking of the device. The morphology of the atrial activity is consistent. The atrial rhythm demonstrates either sinus or atrial tachycardia.
4. Characteristics of the ventricular electrogram during the tachyarrhythmia: the morphology of the ventricular activity is consistent during tachycardia. The tachycardia has a ventricular cycle length of ~ 406 ms. The wide-band electrogram shows a pattern of four consecutive ventricular activations followed by a longer interval. This pattern is confirmed by the device activity channel.
5. Atrioventricular relationship: The atrioventricular conduction pattern can be assessed from the marker channel. During the tachycardia, a consistent pattern of the atrioventricular conduction can be assessed by a ladder diagram (see further). Of the four consecutive atrial activations, the "first" atrial activity is blocked in the atrioventricular node. The next three atrial activations are conducted to the ventricular with a progressive increase in the atrioventricular conduction time. The "fifth" atrial activation coincides with the ventricular activation caused by the conducted "fourth" atrial activation. This pattern repeats itself as can be assessed in the original electrogram. (See Figure 6.14c)
Diagnosis: sinus or atrial tachycardia with atrioventricular Wenckebach conduction pattern. The p wave is hidden in the QRS complex, and is not
displayed on the marker as it is within the post ventricular atrial blanking period.
Action: No further action
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