Pacing failure to capture verification#

This adjustment can only be made in an output range defined by a programmable lower limit (Adjusted Minimum Amplitude parameter) and the upper threshold limit of 5.0 V and 1.0 ms. After a successful pacing threshold search, the device calculates a target amplitude by multiplying the RV amplitude safety margin by the amplitude threshold measured at a pulse duration of 0.4 ms. The amplitude delivered for these 24 hours is dependent on the programmed values for the « RV amplitude safety margin » and « RV minimum adjusted amplitude » parameters.

Pacing failure to capture verification#

Once the threshold has been measured, the pacing amplitude is automatically adjusted for the next 24 hours without cycle to cycle verification of capture efficiency. The backup pacing is emitted 100 ms after the test pacing it is performed at the programmed amplitude and at a pulse duration of 1.0 ms. During the threshold measurement procedure, a back-up pacing automatically follows each test pacing (whether captured or not), which prevents the possibility of a ventricular pause during this procedure. It then increases the amplitude in incremental 0.125 V steps until it regains a capture 3 times in succession (corresponds to the new threshold value). The device continues to decrease the amplitude in decremental 0.125 V steps until loss of capture. In the absence of a previous search, the search starts at 0.75 V. The search for pacing threshold begins at an amplitude of less than 0.125 V from the last measured threshold. The device evaluates the capture by sensing the signal of the evoked response following each test pacing (differentiation between polarization and evoked response). In practice, every day at 1 a.m., the pacemaker performs an amplitude measurement of the ventricular pacing threshold for a fixed pulse duration of 0.4 ms. For Medtronic TM pacemakers, the Auto-threshold model has been favored, with the ventricular pacing threshold being measured periodically (a single daily measurement) with adjustment of the amplitude as a function of this measurement without cycle to cycle verification of capture efficiency, which requires sufficient safety margins. Indeed, it is now possible to program in all contemporary pacemakers an automatic measurement function of the ventricular threshold more or less associated with an automatic adjustment of the pacing amplitude. In this setting, the Capture Management function must be discussed.

In dialysis patients, electrolyte conditions (serum sodium, serum calcium, serum potassium, blood glucose) constantly change with possible variations in pacing thresholds, requiring that the pacing outputs be regularly monitored and modified accordingly in order to efficiently capture the myocardium. This patient was programmed with a pacing amplitude of 2.5 Volts for 0.4 ms. This safety margin is designed to take into account the circadian variations in the pacing threshold which is influenced in variable manner from one subject to another by sleep, meals, physical activity, fever, etc. It is generally recommended to set a safety margin of 100% which corresponds to a double threshold voltage. The determination of the pacing threshold is of major importance since the programming of the voltage and the duration of the pulse defines the safety margin and determines the energy consumption of the prosthesis and therefore the rate of battery wear. It can be measured in voltage (Volts) or in pulse width (milliseconds). The pacing threshold corresponds to the smallest electrical pulse, delivered outside of all natural refractory periods, capable of generating the propagation of a depolarization. continued absence of ventricular capture.

ineffective ventricular pacing the ensuing QRS is not detected this does not correspond to a sensing defect this QRS falls into the post-ventricular pacing ventricular blanking period, an absolute ventricular refractory period and is therefore not detected.new atrial sensing sequence - ineffective ventricular pacing (AS-VP) blocked P wave the base rhythm corresponds to a Wenckebach-type second-degree atrioventricular block (prolongation of the PR interval followed by blocked P wave).the spontaneous ventricle following the previous P wave is properly detected (VS).proper atrial sensing resulting in an AV delay and ventricular pacing (AS-VP) the ventricular EGMs and the 2 leads show the absence of ventricular capture (no ventricular signal after the stimulus).The first line corresponds to lead I with the superimposed markers, the second line to the atrial EGM, the third and fourth lines to the ventricular EGM and the last line to lead III