Dual Chamber discriminators : Dual tachycardia

Patient

Seventy-six year old patient implanted in secondary prevention with a dual chamber ICD Virtuoso DR (post-infarct ischemic cardiomyopathy, sustained VT and syncope). The patient consults because has received an electrical shock.

Trace

Patient in atrial fibrillation (atrial rhythm very fast and irregular in both frequency and amplitude) with a moderately fast and irregular ventricular response;
Acceleration of the ventricular rate : change in the morphology of the VEGMs : probable monomorphic regular VT;
Detection of a dual tachycardia (VT + SVT);
The first therapy of the VT zone is delivered : burst;
Burst failed to stop the tachycardia;
Detection of a VF (FD);
Burst during capacitor charging;
Burst successful; the VT stops; (AF persists);
End of capacitor charging; detection of a relatively short cycle; to divert the shock no event in the VT zone +60ms should be detected.
An electrical shock (34.9 Joules) is delivered; it converts AF to sinus rhythm.

Comments

Diagnosing a dual tachycardia is probably the most challenging for the ICD… and also for the cardiologist. Nevertheless, in this case, some elements favor the diagnosis of dual tachycardia : a conducted AF, a sudden rate acceleration at the ventricular level followed by a stable ventricular rhythm, the change in the VEGMs morphology, efficacy of the burst pacing during charge :
1) AF counter fulfilled
2) AV dissociation
3) Regular ventricular rhythm (regularity > 75%)

Take home message

Two detection zones are programmed; only the PR Logic is activated; the ICD recognizes a dual tachycardia (VT + SVT); after the first burst, the episode is classified VF which triggers a shock; another burst is delivered during charging of the capacitor.

Pacing & Defibrillation

ECG

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