Figure 3. 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.
ECG, electrocardiogram; VOO, ventricular pacing, no sensing; DDD, dual mode, dual sensing, dual pacing; VAT, ventricular pacing, atrial sensing, tracking; bpm, beats per minute