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Ventricular Pacing example five



 Here we see ventricular pacing spikes following native P-waves - but only every other P-wave.  The atrial native rate is 125, and the pacer is clearly sensing the P-waves.  The P-R interval is set at 0.18 seconds, and capture is good.  This pacer has been programmed to provide a ventricular rate of less than this atrial rate, so it only follows up on P-waves every other time.  Thus, it is sensing the atria and responding by both stimulation and inhibition, in alternation.  The pacer is in DDD mode.  If the pacer were turned off, the underlying rhythm would probably be third degree block.