March 19, 2016

A frequently asked question

The machine says: Wide QRS rhythm, left axis deviation. Do you have a different interpretation?

Figure 1

This is a paced-rhythm (60 per minute). Pacer artifacts are best seen in v4 and V5. Bipolar pacing will generate tiny artifacts unlike unipolar pacing. We can also see P waves in V1 and V2 (intrinsic SR with CHB).

A frequently asked question:

“I don’t see pacemaker spikes”

1. The pacemaker may not be pacing… usually due to inhibition by the patient’s intrinsic heart rate (which may be faster than the lower limit of the pacemaker).

2. The pacemaker may be pacing, BUT the stimulus artifacts (spikes) are not visible:

UNIPOLAR PACING STIMULUS ARTIFACTS are large and nearly always visible. BIPOLAR PACING STIMULUS ARTIFACTS may be too small in amplitude to see. In unipolar leads, the current flows between the pulse generator and the tip of the lead (large area). So it creates a large stimulus artifact. For bipolar pacing, the distance is only between the tip and the ring which is only about a cm. So, the pacing stimulus may be very difficult to see on surface ecg.

Chow AC and Buxton AE. 2006. Defibrillators: All You Wanted to Know. Malden, MA, Blackwell Pub Inc


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