FAILURE TO CAPTURE DEFINITION GENERATOR

Modern pacemakers often include algorithms that detect and terminate PMT. PMT may be terminated by placing a magnet on the pulse generator. This may result in an endless loop tachycardia, also called pacemaker mediated tachyarrhythmia / tachycardia (PMT). If the ventricular impulse manages to travel in retrograde direction back to the atria, via the bundle of His, then it may trigger another ventricular stimulation.A supraventricular tachyarrhythmia (e.g atrial fibrillation) can be transmitted to the ventricles.If ventricular pacing is triggered by atrial activity, then tachyarrhythmias may occur in the following situations: Signs of overpacing should always lead to suspicion of undersensing.

Undersensing can lead to overpacing, because the pacemaker does not sense ongoing activity. This is an appropriate form of undersensing, and was discussed previously (refer to PVARP). It may also be due to the low amplitude (voltage) of the potentials generated by activated myocardium.įunctional undersensing occurs when the pacemaker does not sense intrinsic activity during the period when sensing is disabled. This may be due to lead dislodgement, lead fracture or inadequate myocardial contact. Undersensing occurs when the pacemaker fails to detect cardiac activity. In DDI pacing, atrial oversensing leads to ventricular underpacing. In DDD pacing, atrial oversensing leads to rapid ventricular pacing. Oversensing may also occur when the ventricular lead interprets the T-wave as an R-wave. This type of oversensing is referred to as pacemaker crosstalk. Oversensing may also occur when electrical events in one chamber is sensed by the lead in the other chamber, resulting in inappropriate inhibition of the pacemaker in the latter chamber. The signals causing oversensing may not be visible on surface ECG. Oversensing occurs when the pacemaker detects electrical activity that it incorrectly interprets as atrial (P-wave) or ventricular activity (R-wave). Most pacemakers perform such calibrations several times daily, and they include a backup algorithm that delivers a stimulus when failure to capture is confirmed. The pacemaker is then set to the minimum energy needed to activate myocardium (a safety margin is often used). This is done by repeatedly stimulating with gradually decreasing amounts of energy until the stimulus no longer yields an activation. Modern pacemakers have built-in functions to calibrate the stimulus amplitude and width according to myocardial excitability. The most common cause of failure to capture is insufficient stimulus energy. A stimulus delivered during the refractory period should not result in activation because the myocardium is refractory. Functional failure to capture occurs when a stimulus is delivered during the myocardial refractory period.This may be due to insufficient stimulus energy, or lead dislodgement/fracture. Genuine failure to capture occurs when a stimulus that is expected to result in activation fails to do so.Two types of failure to capture should be distinguished: Failure to captureĭefinition: pacing does not result in myocardial activation. Failure to capture during the refractory period. The pacemaker paces in the atrium but P-waves are not visible, suggesting that the atria are not depolarized.

Atrial pacing occurs after the intrinsic P-wave. External causes are less common and include electrolyte disorders, metabolic disorders, hypoxemia, antiarrhythmic drugs, or electromagnetic disturbance caused by other machines/devices.īelow follows ECG tracings demonstrating each type of failure.

FAILURE TO CAPTURE DEFINITION GENERATOR

Most cases of malfunction are associated with the electronics in the pulse generator or dislodgement or fracture of the leads. These failures typically result in missing stimulation artifacts, misplaced stimulation artifacts, irregular pacing, etc. This is only relevant in rate responsive pacemakers. Failure to rate adjust, which means that the pacemaker fails to adjust its rate according to haemodynamic needs.Failure to sense (undersensing), which means that it fails to sense true P-waves or R-waves.Sensing of such signals normally inhibits the pacemaker. Oversensing, which means that the pacemaker senses signals that are not true P-waves or R-waves.Failure to pace (FTP), which means that the pacemaker does not stimulate as expected.Failure to capture (FTC), which means that the pacemaker stimulations do not result in myocardial activation.Pacemaker malfunction, troubleshooting and ECGĬonventional surface ECG can reveal the following types of pacemaker dysfunction:

Failure to capture definition