PR Logic and sinus tachycardia

Tracing
N° 34
Manufacturer Medtronic Device ICD Field Discrimination
Patient

Patient with ischemic cardiomyopathy implanted with a dual-chamber ICD (Evera XT DR) with slow VT episodes (125 beats/minute); programming of a slow VT zone at 520 ms; this tracing highlights the functioning of the PR Logic algorithm and the diagnosis of sinus tachycardia.

Graph and trace

The graph shows a 1:1 tachycardia with a gradual slowing of the rate; no therapy was delivered following the diagnosis of sinus tachycardia.

  1. the EGM shows a 1: 1 tachycardia;
  2. diagnosis of sinus tachycardia;
  3. the Sinus Tach option was programmed to ON.
Comments

This patient had multiple episodes of symptomatic slow VT requiring special programming with a relatively low VT zone (520 ms), increasing the risk of overlap with the sinus rates observed during exertion. This episode presents the characteristics of a sinus tachycardia (1: 1 ratio between the atria and ventricles, progressive acceleration and deceleration) well diagnosed by PR Logic.

When the Tach sinus option is programmed to ON, various steps are used for arriving at the diagnosis of sinus tachycardia:

  1. the first step is to demonstrate that there is indeed a 1:1 ratio between atria and ventricles; this may correspond to 2 situations: tachycardia with detection of one atrial signal for one ventricular signal, or tachycardia with detection of 2 atrial signals for one ventricular detection signal if there is oversensing of the far-field R-wave by the atrial channel; one of the specificities of this algorithm is to monitor this oversensing by highlighting the repetition of short interval-long interval sequences at the atrial level; the device then corrects the atrial rate and re-establishes a 1:1 ratio in its analysis.
  2. the second step consists in determining whether the RR intervals are compatible with a sinus tachycardia; for each ventricular interval, the device determines an adaptive range of expected RR intervals (based on an average value of the previous RR intervals); each RR interval is therefore defined as either expected (in the expected range for sinus tachycardia) or unexpected (outside the expected range for sinus tachycardia).
  3. the third step consists in determining whether the PR intervals are compatible with sinus tachycardia; for each interval, the device determines an adaptive range of expected PR intervals (based on an average value of the preceding PR intervals); each interval PR is thus defined as expected (in the expected range for sinus tachycardia) or unexpected (outside the range expected for sinus tachycardia).
  4. in the fourth step, the device establishes a sinus tachycardia counter according to the analysis of the RR intervals and the successive PR intervals. This algorithm thus allows correcting for possible oversensing, remains valid in the presence of ventricular extrasystoles and is functional even in the presence of aberrant conduction. During 1:1 tachycardia, if PR Logic concludes to sinus tachycardia, Wavelet (if programmed to ON) is not integrated in the discrimination and therefore cannot modify the diagnosis. Conversely, if PR Logic concludes to VT with 1/1 retrograde conduction, Wavelet (if programmed to ON) is integrated in the discrimination. If the morphology of the ventricular tachycardia complexes is considered different from the reference, the device confirms the diagnosis of VT (therapy delivered). Conversely, if the morphology is considered to be similar, the device corrects the diagnosis and concludes to supraventricular tachycardia (therapy not delivered). 
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