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 (RV).
- tachycardia in the VT1 zone with 1:1 atrioventricular ratio; the ventricular events are classified as Tsin (sinus tachycardia);
- SVT classification in the PP=RR arm; average PP at initial classification 379 ms, average RR at initial classification 379 ms; stable rhythm, with measurement of the stability criterion at 2 ms for a 24-ms programmed threshold; stable PP intervals; stable PR interval without monotonous change; in this instance, the sudden onset criterion is not fulfilled (measured at 1% for a 20% programmed threshold, the diagnosis made by the device is thus that of SVT (sinus tachycardia);
- gradual slowing of the heart rate at the end of the exertion and exit from the VT1 zone (VS intervals).
The vast majority of 1:1 tachycardias are of supraventricular origin (sinus tachycardia, 1:1 atrial tachycardia). VTs with 1:1 retrograde conduction constitute only 10% of these tachycardias. This episode corresponds to an accurately discriminated sinus tachycardia.
As explained previously, the first discrimination step when the SMART algorithm is programmed is a comparison between ventricular and atrial rates. In this example, the two rates are strictly identical (column RR=PP). The device analyzes the stability of the RR intervals and considers in this example that the ventricular rhythm is stable followed by the stability of the PP intervals which is also deemed stable (difference between an atrial interval and the preceding three intervals does not exceed the programmed value).
When the atrial and ventricular rhythms are stable and similar, different arrhythmias may coexist (dual tachycardia, VT with retrograde conduction and sinus tachycardia). Different parameters are analyzed to discriminate these arrhythmias:
- monotonous variation of the PR interval: when the atrial and ventricular rhythms are deemed stable and identical, the device looks for the PR intervals to evolve according to a characteristic profile. The PR intervals are classified as monotonous if on a rolling window of 4 intervals, the PR intervals increase or decrease with respect to each other in a constant manner (AV n < AV n-1 < AV n-2 < AV n-3 or AV n-> AV n-1 > AV n-2 > AV n-3) indicating the presence of atrioventricular dissociation. Indeed, if there is a trend in terms of the PR interval (if there is a prolongation or a progressive shortening of the PR interval measured by the device), the atrial and ventricular rhythms certainly have a similar rate but can be considered as independent. The small but constant difference between the 2 rates induces a steady variation of the PR interval and the device concludes to a dual tachycardia;
- if, as in this example, the atrial and ventricular rhythms are stable without monotonous variation in PR interval, the algorithm uses the Onset criterion (same operation as described for single-chamber devices) to differentiate VT from 1:1 retrograde conduction (abrupt onset) and sinus tachycardia (progressive onset as in this example). The intervals classified as sinus tachycardia are labeled SinusT and decrement the VT counter by -1/4.
