Unipolar & Bipolar signals

What is a bipolar electrogram?

A bipolar electrogram records the voltage difference between two nearby catheter electrodes.

What is a unipolar electrogram?

A unipolar electrogram records from one catheter electrode compared to a distant reference electrode.

Which signal is more local: bipolar or unipolar?

Bipolar is more local.

Which signal has a larger field of view?

Unipolar has a larger field of view.

What are bipolar signals best used for?

Activation mapping, voltage mapping, scar identification, and identifying fractionated signals.

Why are bipolar signals usually sharp?

Because they mostly show local near-field electrical activity.

What does a high-amplitude bipolar signal usually suggest?

Healthy tissue.

What does a low-amplitude bipolar signal usually suggest?

Scar, diseased tissue, poor contact, or catheter orientation issues.

Why can bipolar amplitude change with catheter direction?

Because bipolar signals depend on the direction of the wavefront relative to the two electrodes.

When is a bipolar signal usually largest?

When activation travels parallel to the electrode pair.

When can a bipolar signal become small or misleading?

When activation travels perpendicular to the electrode pair.

What are unipolar signals best used for?

Determining wavefront direction and confirming whether the catheter is near the site of origin.

Why do unipolar signals show more far-field activity?

Because the reference electrode is distant, so the signal captures a larger area of electrical activity.

What does a pure QS unipolar signal suggest?

The activation is moving away from the catheter, suggesting the catheter may be at or very near the site of origin.

Why does a QS pattern suggest the origin is under the catheter?

Because the wavefront begins near the electrode and spreads away from it.

What does an rS unipolar pattern suggest?

The catheter is close to the source, but activation likely reached the catheter from another nearby site first.

What does an RS unipolar pattern suggest?

The wavefront is passing by the catheter rather than starting directly underneath it.

What is near-field activity?

Electrical activity from tissue directly near the catheter.

What does near-field activity look like?

Sharp, narrow, and high-frequency.

What is far-field activity?

Electrical activity from tissue farther away from the catheter.

What does far-field activity look like?

Broader, smoother, and lower-frequency.

Why is it important to separate near-field from far-field signals?

Because far-field activity can make a site look earlier or more important than it actually is.

In PVC mapping, what does '-30 ms' mean?

The local electrogram occurs 30 milliseconds before the surface QRS.

In atrial tachycardia mapping, what timing are you looking for?

The earliest atrial electrogram before the surface P wave.

What three findings make a strong ablation target for a focal PVC?

Earliest bipolar activation, QS unipolar morphology, and a high pace-map match.

What does 'good bipolar timing but no perfect QS' suggest?

The catheter may be close to the exit site but not directly over the true origin.

What findings support a good RVOT PVC ablation target?

Early bipolar timing, pure QS unipolar signal, and a high pace-map match.

Why can papillary muscle PVCs be difficult to map?

Because catheter stability is harder, exits can shift, and the unipolar signal may not show a perfect QS.

Why might RF lesions be placed around a papillary muscle region instead of one exact point?

Because papillary PVCs may have variable exits, catheter contact changes, or preferential conduction.

What does preferential conduction mean?

The true origin may be in one location, but the arrhythmia exits to the surface from a different nearby location.

Bipolar signals are best for what?

Local timing, voltage mapping, scar, and fractionation.

Unipolar signals are best for what?

Direction of activation and confirming whether the catheter is near the origin.

Which signal is better for voltage mapping?

Bipolar.

Which signal is better for confirming a focal source?

Unipolar.

Which signal is more affected by catheter orientation?

Bipolar.

Which signal is more affected by far-field activity?

Unipolar.

How can you remember bipolar signals?

Bipolar means 'between two electrodes.'

How can you remember unipolar signals?

Unipolar means 'one electrode looking out at the bigger field.'

What should you think when you hear '-30 with a QS'?

The local signal is 30 ms early and activation is moving away from the tip, which supports a likely source site.

What should you think when the bipolar is early but the unipolar is not QS?

The catheter may be near the source but not exactly on it, or the origin may be intramural, epicardial, papillary, or using preferential conduction.