This week’s electrogram interpretation:
What is observed in the following electrogram?
Answer
Unable to interpret – repeat extrastimulus testing.
In this example, there are two RV catheters displayed. The physician is performing a VT study with one catheter positioned in the RV and one located in the RV outflow tract. The RV catheter is not at the RV apex as a large A is observed on the channel.
The first two impulses capture the ventricular myocardium and conduct to the atrium. The last impulse of the drive train came in after the atrium already depolarized (via either SA node); therefore, a fusion beat is observed. This QRS complex is a fusion of the ventricular depolarization initiated by the normal conduction system (from the SA node) and the depolarization initiated by ventricular pacing. Notice the QRS complex is a blend of the pacing morphology and the final displayed beat which is via the normal conduction system. Therefore, even though the extrastimulus did not capture the ventricular myocardium, this is not VERP. It is unable to be interpreted and should be repeated due to the fusion at the end of the drive train. If the sinus rate continues to come through, the drive train rate should be increased to 500 ms.
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For more information: EP Essentials – Understanding EP: A Comprehensive Approach – section on ERP.
