Pacing & Sensing in Boston Scientific pacemakers |
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Pacing & Sensing in Boston Scientific pacemakers
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The sensitivity feature can be programmed either to AGC or Fixed sensing. The device has independent AGC circuits for each chamber and the atrial and ventricular sensitivity values are programmable independently. Selection of the AGC sensing method applies that method to all chambers and the type of sensing method used (AGC versus Fixed) must be the same for the atrial and ventricular channels.
Fixed sensitivity Atrial fixed sensitivity
Ventricular Fixed Sensitivity
Automatic Gain Control The Automatic Gain Control dynamically adjusts the sensitivity in both the atrium and the ventricle. the programmable AGC value is the minimum sensitivity value that can be reached between one beat and the next one this programmable value is not a fixe value present throughout the cardiac cycle; rather the sensitivity level begins at a higher value and decrements towards the programmed floor AGC typically reaches the programmable floor after pacing or low amplitude signals when moderate or high amplitude signals are sensed AGC will not typically reach the programmed floorThe AGC in each respective chamber processes an electrogram signal via a two-step process to optimize sensing of potentially rapidly changing cardiac signals. the device adjusts the ventricular sensitivity according to a slow or fast AGC the AGC applies a “slow” component to set an interval in search of the next QRS amplitude by calculating an “average” of the peaks of the preceding signals, the “slow” component defines a zone that is likely to contain the following peak, and sets this zone between a minimum and a maximum value
First step AGC uses a rolling average of previous signal peak to calculate a search area where the next peak will likely occur with MAX and MIN limits. if the previous beat is sensed, it is incorporated into the rolling peak average if the previous beat is paced, the peak average is calculated using the rolling average and a paced peak value; the paced peak value depends on the settings: for nominal or more sensitive settings, it is a fixed value (initial value 4.8 mV in the ventricle, 2.4 mV in the atrium); for less sensitive settings, it is higher value calculated using the programmed AGC floor value the peak average is used to bound an area with Min and Max limits
Second step The device senses the amplitude of the intrinsic beat. Full R-wave and P-wave range is available up to 32 mV. the device holds the sensitivity level at the peak (or Max) through the absolute refractory period + 15 ms at the end of the refractory period + 15 ms, the sensitivity setting decreases to 75% of the sensed peak or, if the last ventricular event is paced, to 75% of the average peak the device thereafter decreases the sensitivity setting every 35 ms for the ventricle and 25 ms for the atrium, to 7/8 of the previous setting this step-down continues until whether the MIN or the programmed sensing floor is reached, whichever is reached first after a paced beat, the AGC also steps down to 7/8 of previous value so that the MIN or programmed AGC floor is reached 150 ms from the next scheduled pace
Programmable parameter Sensing Method: AGC/Fixed atrial AGC is nominally 0.25 mV right Ventricular ACG is nominally 0.6 mV |
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