Using a unipolar EGM, a signal with the absence of an R wave and a steep negative deflection indicates the catheter tip (anode) is likely over the signal origin.

Using a unipolar EGM, a signal with the absence of an R wave and a steep negative deflection indicates the catheter tip (anode) is likely over the signal origin.

• A. True
• B. False
• C. Not determinable
• D. Indeterminate

Answer: (A)

In a unipolar electrogram, the local activation timing and location are inferred from how the waveform appears relative to the electrode’s position. When the catheter tip is directly over the origin of activation, the wavefront propagates away from the tip in all directions, producing a QS pattern: a single, steep negative deflection with no positive (R) deflection. The sharp downward plunge reflects abrupt near-field activation as the wavefront passes beneath the tip. Therefore, a recording showing no R wave and a pronounced negative deflection is most consistent with the tip being at the signal’s origin. If the tip were not at the origin, activation would often move toward the electrode at some point, yielding an R wave or a different morphology instead.

In a unipolar electrogram, the local activation timing and location are inferred from how the waveform appears relative to the electrode’s position. When the catheter tip is directly over the origin of activation, the wavefront propagates away from the tip in all directions, producing a QS pattern: a single, steep negative deflection with no positive (R) deflection. The sharp downward plunge reflects abrupt near-field activation as the wavefront passes beneath the tip. Therefore, a recording showing no R wave and a pronounced negative deflection is most consistent with the tip being at the signal’s origin. If the tip were not at the origin, activation would often move toward the electrode at some point, yielding an R wave or a different morphology instead.