A Man With Two Pacemakers: The Mystery of the Electrocardiogram

Figures

• 

  FIGURE 1. Cabrera sequence recording. The above pacing ECG shows sequential capture of the atrium and ventricle, with dominant spikes at the beginning of the P wave and an aberrant QRS complex, maintaining a basic cycle of 1000 ms. The ECG reveals right atrial appendage pacing with a positive P wave in leads I, II, III, and aVF, a negative P wave in lead aVR, and a biphasic P wave in lead V1, with a PtfV1 of 0.05 mm/s. The ventricular electrode is positioned in the right ventricular outflow tract, indicated by a left bundle branch morphology in lead V1, a QS complex in leads I and aVL, and a tall R wave in leads II, III, and aVF. Additionally, three spike signals are observed during stable pacing periods, with fixed spikes occurring during the AV delay at 180 ms intervals, excluding other operation types such as CRT and His bundle pacing. Upon encountering this ECG, a pacemaker interrogation was performed immediately. AV, atrioventricular; CRT, cardiac resynchronization therapy; ECG, electrocardiogram.

• 

  FIGURE 2. (a, b) X‐ray contrast images before and after pacemaker extraction. The two X‐rays above show the contrast images taken before and after pacemaker extraction. The left image (a) displays two pacemaker generators positioned below the bilateral clavicles. The pacemaker on the right side is a 15‐year‐old single‐chamber pacemaker, with its electrode lead located at the right ventricular apex. The pacemaker on the left side is a 1‐week‐old dual‐chamber pacemaker with pacing electrodes situated in the right atrial appendage and the proximal septum. The right image (b) shows the single‐chamber pacemaker generator extraction with the passive electrode remaining in place.

• 

  FIGURE 3. Cabrera sequence recording. The above ECG characterized by two pacemakers indicates the following: Firstly, the patient has a dual‐chamber pacemaker operating in DDD or VAT mode, with both sensing and pacing functions being normal. Secondly, the pacemaker is in the stage of battery depletion and has automatically switched to VOO mode. Additionally, the pacing rate alternates between 30 bpm and 60 bpm, with a few unipolar pacing spikes successfully capturing the ventricle (as seen in the second and last aberrant QRS complexes). Lastly, the QS complexes in the inferior and precordial leads, as well as the R wave in leads I and aVL, align with the pacing characteristics of the right ventricular apex. Meanwhile, a chest X‐ray confirms the anatomical locations of the electrodes. This ECG demonstrates the characteristics of both pacemakers, leading us to recommend extracting the old pacemaker generator (Figure 2b). DDD, dual mode, dual sensing, dual pacing; ECG, electrocardiogram; VAT, ventricular pacing, atrial sensing, tracking; bpm, beats per minute; VOO, ventricular pacing, no sensing.

• 

  FIGURE 4. Prolonged recording of lead II for 60 s. The above ECG characterized by two pacemakers indicates the following: Firstly, the patient has a dual‐chamber pacemaker operating normally in DDD or VAT mode. Secondly, the pacemaker is in the stage of battery depletion and has automatically switched to VOO mode. Additionally, the pacing rate alternates between 30 and 60 bpm, with intermittent ventricle capture observed. In summary, the ventricle capture is not related to whether the pacing spikes are odd or even, thus eliminating the possibility that the pacemaker is reserving power for a minute due to battery depletion. Instead, ventricular capture is associated with the supernormal phase of myocardial activity, which can respond to subthreshold stimuli. The ventricular supernormal interval is determined to range from 440 ms to 520 ms. DDD, dual mode, dual sensing, dual pacing; ECG, electrocardiogram; VAT, ventricular pacing, atrial sensing, tracking; bpm, beats per minute; VOO, ventricular pacing, no sensing.