Is This Pacemaker Functioning Abnormally?

An 85-year-old man with a history of ischemic heart disease and a single-chamber pacemaker implanted 6 months earlier because of atrial fibrillation with slow ventricular response was admitted to the emergency department with complaints of lightheadedness. A 12-lead ECG was obtained to assess pacemaker function as part of the initial diagnostic evaluation (Figure 1). Pacing stimuli follow an irregular pattern, as can be observed in the ECG tracing. Some pacing outputs are delivered right after the QRS complex. As a result, concerns about pacemaker malfunction arose. What is the current pacing mode in this case?Figure Twelve-lead ECG obtained at the emergency department. 1. Normal VVI function with true fusion and pseudofusion complexes, or2. Normal VVT functionPlease turn the page to read the diagnosis.The rhythm is irregular without any evidence of P wave consistent with underlying atrial fibrillation. Pacing stimuli can be seen (annotated …