At times, reasons for the loss of capture are reversible, but, if the causes cannot be reversed, the lead(s) might need revision/repositioning/replacement or the generator might need to be changed. Reaching the end of the pacemaker or ICD battery can cause loss of capture. The table also delineates cardiogenic versus noncardiac causes of noncapture in the long-term period postimplant. In general, the categories can be subdivided by the acuity of the loss of capture, which is usually cardiac in nature. Table 1 summarizes the causes by breaking them down into these categories. There are many causes for the loss of capture, with the timing of the implant having a high correlation with specific causes (especially immediately postimplantation). During the device interrogation, there may be an indication of pacing on the near- or far-field electrocardiogram without an appropriate capture of the chamber being paced. 6 An example is shown in Figure 1, where the atrial pacing stimuli do not capture the atrial tissue and, therefore, there is no atrial depolarization with P waves following the pacing stimuli. On the electrocardiogram or rhythm strip, a pacing spike can be seen with no P or QRS complex subsequently following the pacing spike. Loss of capture, also known as noncapture, is when the myocardium does not respond to the electrical stimuli from the pacemaker or ICD. It is common to encounter some of these issues, with failure to capture being an important factor that requires assessment and therapy. 3, 4 Pacemaker and ICD lead malfunctions can be classified based on the electrocardiogram signs into the following groups: loss of capture, inadequate output, undersensing or oversensing, inappropriate pacing, pacemaker-mediated tachycardia, and issues with battery life. 2, 3 Although it is important to be able to assess arrhythmias and perform device management, physicians should also be aware of device and lead malfunctions and failures. There is a frequent need for the evaluation of these devices for the clinical benefit of monitoring the patient’s rhythm abnormalities and events that have occurred, along with the need for therapy. Therefore, a basic understanding of normal device function, device malfunction, and troubleshooting has become an essential thing to have. 1, 2 Health-care providers have frequent interactions with patients with pacemakers and implantable cardioverter-defibrillators (ICDs). The number of patients with implantable cardiac devices is continuously increasing. A knowledge of these factors is essential for health care providers, given the morbidity and mortality that can potentially be associated with device-related issues, especially in patients who are dependent on the included pacing function. Further, there are also potential noncardiac causes, such as medications, electrolyte imbalance, and acidemia. Loss of capture can also occur from external electrical stimuli and inappropriate pacemaker or ICD settings. This change can be due to a cardiomyopathy, fibrosis medications, metabolic imbalance, lead fracture, or an exit block. In comparison, an increase in the required threshold promoting a loss of capture can happen after months to years of insertion of the pacemaker or ICD. The most common acute cause just after the insertion procedure is lead dislodgement or malposition. There are many causes for a loss of capture, with the timing of the implant having a high correlation with certain causes over others. Loss of capture can be an emergent presentation for an unstable patient and can be encountered intermittently in hospitalized patients. As more pacemakers and implantable cardioverter-defibrillators (ICDs) are being placed, a basic understanding of some troubleshooting for devices is becoming essential. The number of patients with implantable electronic cardiac devices is continuously increasing.
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