Microport - Pacing / Detection
Content
Atrial pacing
No automatic atrial threshold measurement performed by Microport CRM-Sorin pacemakers.
Ventricular pacing
Operating principles
- Auto-threshold on auto: regular measurements of the ventricular stimulation threshold + programming adaptation; Auto-threshold on monitoring: regular measurements of the ventricular stimulation threshold but without programming adaptation; Auto-threshold on no: no threshold measurement and fixed values;
- Threshold performed systematically every 6 hours based on analysis of the evoked response
- 4 threshold measurements per day with adjustment for the following 6 hours (no cycle-by-cycle verification)
- automatic adjustment of the amplitude to twice the threshold value (100% safety margin) within the limits of a programmable minimum value (1.5, 2, 2.5, 3, 3.5, or 4 V)
Ventricular autosensing in practice
The capture test is based on the differentiation between the evoked potential response (EPR) and the residual polarization of the probe (Polar).
After an effective stimulus, during a period of 65 ms, both potentials are present (EPR + Polar) and measurable, whereas after an ineffective stimulus, only the residual polarization of the probe is present (Polar) and can be measured.
Waiting phase
The objective of this phase is to stabilize the rhythm; 8 stimulations at 5 V are delivered.
Calibration phase
The objective of the calibration phase is twofold:
- Identify an initially high stimulation threshold (greater than 2 V)
- To evaluate the evoked response measurement
In order to increase the probability of capturing the ventricle, the current AV delay is shortened by 65 ms (dual-chamber pacemaker) or the escape interval is shortened by 65 ms (single-chamber pacemaker).
Three 4V stimulations (at the programmed pulse width) are delivered, and only the last two are followed by measurement of the evoked potential response/polarization.
Three 2V stimulations (at the programmed pulse width) are delivered, and only the last two are followed by measurement of the evoked potential response/polarization. These three 2 V stimulations are each followed, after the measurement period (65 ms), by a safety stimulation at 2.5 V with a pulse width of 1 ms. The purpose of these safety stimulations is to ensure ventricular capture in the event of a stimulation threshold greater than 2 V. If these two series give acceptable and comparable measurements, the stimulator proceeds to the next step.
Two “0 V stimulations” are followed by a period of measurement of the evoked potential response/polarization; these enable a diagnosis of fusion, which can alter the threshold measurement. If spontaneous evoked potentials are measured after a “0 V stimulation,” this indicates the presence of possible fusion or ectopic depolarizations during the previous measurements (at 2 and 4 V). The calibration phase is then repeated with a short AV delay (65 ms) to avoid fusion. If, despite this adjustment, fusion is still detected, the test is stopped and the ventricular voltage is forced to 5 V for the next six hours.
Ventricular stimulation threshold measurement phase
Once calibration is complete, the stimulation threshold test begins at 1.95 V with a decrement of 0.15 V until capture loss voltage or a minimum of 0.15 V is reached. Each stimulation is followed by a measurement period (65 ms). If capture loss is detected, a safety stimulation at 2.5 V with a pulse width of 1 ms is delivered.
In this example, the V threshold is 1.5 V. The amplitude is programmed to 3 V output for the next 6 hours. The value of 1.5 V is displayed on the Auto Threshold curve along with the stimulation voltage applied during the next 6 hours.
Programming
Ventricular Auto Threshold is not available in SafeR mode. It is activated if the heart rate is less than 95 bpm. The ventricular pacing amplitude cannot be programmed when the V Auto Threshold function is set to “Auto.” It is no longer possible to program ventricular pulse duration values greater than 0.5 ms when the Autothreshold V function is programmed to “Follow” or “Auto.” The AV rest delay is reprogrammed to 125 ms if it was previously set to a value less than 125 ms.
Monitoring of the V stimulation threshold in memory
On the AIDA Diagnostics screen, in the PM tab, clicking on the AutoThreshold Curves button displays the curve of average values for the 4 daily measurements from the V AutoThreshold function. The ventricular output voltage applied is shown in parallel.
During device checks, Autoseuil V (with a slightly different calibration phase and starting voltage) is part of the automatic sequence of probe measurements with EGM visualization for confirmation. This optional sequence is called SmartCheck.
Detection
Principle
It is possible to program the Atrial and Ventricular Autosensing function with automatic adjustment of A and V sensitivities to variations in the amplitude of detected events. The amplitude of atrial and ventricular events is continuously monitored with automatic cycle-by-cycle adjustment of sensitivities. The amplitude of the signals is averaged over 8 consecutive cycles and the sensitivity is programmed to approximately one third (37.5%) of this average value.
Following an atrial extrasystole, atrial arrhythmia, or atrial stimulation, atrial sensitivity is forced to 0.4 mV. The amplitude of the PAC is not included in the average. It is replaced by the value 0.4 mV for the calculation of the average amplitude. Autosensing A applies a sensitivity ranging from 0.4 mV to 3 mV.
Similarly, following ventricular pacing, ventricular sensitivity is forced to 1.5 mV in unipolar mode and 2 mV in bipolar mode. Autosensing V applies a sensitivity ranging from 1.5 mV (in unipolar mode) or 2 mV (in bipolar mode) to 6 mV.
Programming
Autosensing can be programmed to:
- MONITORING, which measures the amplitudes of P waves (sinus and pathological) and R waves (normal and PVC) without adjusting the sensitivity settings, which remain fixed
- AUTO, which measures the amplitudes of P waves and R waves with automatic adjustment of sensitivities as described above
There are a number of restrictions: atrial autosensing can only be programmed to auto if atrial sensitivity is bipolar (if unipolar, only follow mode) and the AV rest delay is greater than 65 ms.
Stored data
The amplitude measurements of detected events are presented in the form of distribution histograms. Detection quality can also be assessed using trend curves for the last 24 hours, where the accuracy (average value) is approximately 8 minutes per point, and trend curves for the last 6 months, where each point represents the average detection value for one day.
In the PM tab of the AIDA Diagnosis screen, clicking on the Autosensing magnifying glass displays the distribution of P waves; clicking on the P/R Waves button displays the distribution of R waves; clicking on the Track over the last 24 hours button displays the trend curves for P and R waves over the last 24 hours.
“Sinusoidal” P waves represent P wave detections outside the WARAD. “Retrograde” P waves represent P wave detections occurring during the retrograde phase (DDI). P wave detections occurring during the suspected phase are not taken into account.
PVCs represent R-wave detections whose coupling is 25% shorter than the average of the preceding 4 “normal” ventricular cycles.
Note that in Symphony, the measurement period represents the last 6 months. In Reply, Reply 200, and Kora 100, the measurement period is equivalent to the last 2 months.
In the PM tab of the AIDA Diagnostics screen, clicking on the Probe Measurements magnifying glass displays the atrial detection trend curves; clicking on the V Probe button displays the ventricular detection trend curves.
