How is failure to capture typically identified on an ECG strip?

Failure to capture is identified on an electrocardiogram (ECG) strip by observing spikes that do not correlate with the QRS complexes. In the context of pacing, "capture" refers to the pacemaker successfully stimulating the heart to contract in response to its electrical signals. When there is failure to capture, the pacemaker's electrical spike does not result in depolarization of the myocardium, and thus, there is no corresponding QRS complex following the pacemaker spike. This absence of a QRS complex indicates that the heart did not respond to the pacing impulse, which is a critical sign of malfunctioning in a paced setting.

The presence of spikes without corresponding QRS complexes is a clear indicator that the pacing pulse is ineffective, which could be due to various factors such as lead displacement, electrode malposition, or underlying heart condition that prevents successful stimulation. Recognizing this pattern is essential for clinicians monitoring patients with pacemakers to make timely interventions if pacing is ineffective.