Case 6 An Uncommon Initiation of an Arrhythmia

Patient: 66-year-old male with ischemic heart disease, congestive heart failure, left ventricular ejection fraction 0.30, left bundle branch block (QRS width 142 ms) and permanent atrial fibrillation. The patient was listed for cardiac transplantation.

Index arrhythmia: sustained monomorphic ventricular tachycardias, cycle length 300 ms.

Complaint: Syncope and shock therapy by the ICD. Electrogram

;VF Rx 1 Defib

Figure 6.6a. From top to bottom: far-field ventricular electrogram, near-field ventricular electrogram, and marker channel. Markers: FD = fibrillation detected; FS = fibrillation sensing; VP = ventricular pace; VS = ventricular sense.

;VF Rx 1 Defib

Figure 6.6a. From top to bottom: far-field ventricular electrogram, near-field ventricular electrogram, and marker channel. Markers: FD = fibrillation detected; FS = fibrillation sensing; VP = ventricular pace; VS = ventricular sense.

ICD pulse generator: Gem 7227 VR (Medtronic Inc, Minneapolis, MN, USA).

Tachycardia settings

Detection: VF = 290 ms; VT = 340 ms. Discrimination: stability = 30 ms.

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

Bradycardia settings Mode: VVIR 60-120 bpm.

Electrogram interpretation (See Figure 6.6b)

1. Presence of tachyarrhythmia?: Yes.

2. Assessment of the onset of the tachyarrhythmia triggering the device: A second premature beat initiates a fast tachyarrhythmia.

Figure 6.6b.

3. Characteristics of the ventricular electrogram during the tachyarrhythmia: the morphology of the ventricular activity is variable in both ventricular electrograms. The morphology cannot be compared to the baseline rhythm, as no electrogram was stored before arrhythmia onset. Additional information can be provided by the stored electrogram after delivered device therapy. The ventricular rhythm has a cycle length of ~ 225 ms, with a stability of ~ 30 ms.

4. Characteristics of the ventricular electrogram after device therapy: the morphology of the ventricular activity after device therapy changed as compared to morphology during the tachyarrhythmia (Figure 6.6c).

Diagnosis: fast polymorphic ventricular tachycardia induced by a ventricular premature beat in a short-long-short sequence.

Action: the lower rate of the pacemaker can be increased, but this may increase the percentage of right ventricular pacing.

Figure 6.6c. From top to bottom: far-field ventricular electrogram, near-field ventricular electrogram, and marker channel. Markers: CD = charge delivered; CE = charge end; VR = ventricular refractory; VS = ventricular sense.

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