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Accurate discrimination of VT by a dual-chamber ICD

Patient

63-year-old man implanted with a Lumax 740 DR-T single-chamber ICD for ischemic cardiomyopathy; recording of a VT episode treated with an ATP burst; programming of a VT1 zone with SMART discrimination.



Trace

4 channels are available: the markers with the time intervals, the shock channel (FF: far field) between the ventricular lead coil and the pulse generator, the atrial sensing channel (A) and the right ventricular sensing channel (V).

  1. sinus rhythm;
  2. onset of a ventricular arrhythmia with a clear modification of the morphology of the QRS complexes; sensing in the VT1 zone; initially probable 1:1 retrograde atrial conduction;
  3. slight acceleration of the ventricular rhythm and sensing in the VT2 zone; atrioventricular dissociation with ventricular rate faster than the atrial rate;
  4. sensing of a VT2 episode; discrimination in the PP > RR arm; the average PP during the initial classification (594 ms) is calculated based on the average of the 4 PP intervals prior to classification; the average RR for the initial classification (298 ms) is calculated based on the average of the 4 RR intervals prior to classification; an ATP burst is delivered
  5. termination of the arrhythmia and return to sinus rhythm.

Comments

The addition of an atrial lead opens an additional and valuable sensing window: dual-chamber discrimination is based on the combined analysis of atrial and ventricular electrograms. The SMART algorithm uses various criteria to discriminate between VT and SVT: rate (atrial and ventricular), rate stability (atrial and ventricular), multiplicity (n/1 A and V ratio) and presence or absence of a sudden onset of the arrhythmia. Depending on the analysis of these parameters, the arrhythmia is classified as VT or SVT. For each interval corresponding to one of the VT zones, the discrimination algorithm carries out a series of analyses to arrive at the diagnosis of VT or SVT. An interval classified as VT is labeled VT1 or VT2 depending on the rate zone to which it belongs. An interval classified as SVT is labeled AFib for atrial fibrillation, AFlut for atrial flutter, SinT for sinus tachycardia or 1:1 for atrial tachycardia.

The SMART algorithm uses sliding windows of 4 intervals in the atrium and in the ventricle to compare these 2 rhythms. This allows determining whether the ventricular rhythm is faster, identical or slower than the atrial rhythm. For each new interval, the average is recalculated by eliminating the first of the 4 previous intervals.  .

This analysis is essential since, as in this example, if the ventricular rhythm is deemed to be faster than the atrial rhythm, the device determines a diagnosis of VT without any additional discrimination.

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