Find the gap or go home

• how to spot a gap in your line
• what are the pitfalls that can lead to a gap
• how you can validate your line

Providing a continues leaner lesion across CTI is crucial for successful procedure. Nevertheless, it is sometimes challenging to accomplish this task in one pull back of the catheter (even for most experienced operator). Please note that even a successful termination by ablation do not necessarily means a complete block without gaps.
The reasons for gaps can differ from the anatomical nature (pouch, extreme thickness, prominent Eustachian valve) or procedural dependent (catheter stability, power settings).    
Here are some methods for spotting a gap in the ablation line of CTI:

• Look for high voltage potential indicating non-ablated regions. Repeat the pullback movement of the catheter and pay close attention to the amplitude and characteristics of the atrial component of the signals. Mind the far-field signals and only ablate near-field signals (you can check out the differences in Lesson 4). Look for irregularity in the catheter movement that can indicate you jumped from one side of a pouch to another, thus missed the critical region
• Find the near spaced double potential during pacing from one side of the CTI. Again, move slowly along the ablation line and measure (observe) the interval between first atrial signal and the one following it. You should target the region where you see the closes spacing between those two signals. If you see only far-field signals (blurred and low amplitude) of closely spaced potentials you are probably in good region but you are missing contact or something is blocking it (pouch, Eustachian valve or other catheter). Sometimes you will have problems with distinguishing between second potential and the far-field ventricular signal. To distinguish those to stop the pacing for a 2-3 beats and look at the characteristic of ventricle signal.
• Activation mapping of CTI with the use of 3D-mapping system. For that approach you can use CS pacing and collect signals along ablation line on at least lateral side. Mapping both sides will give you better understanding but it is not necessary. Remember that this technique works better with small tip or multipolar catheters providing you with more detailed map. Also, some experience with annotation of the potential. In order to close the gap, you should ablate the earliest activation “breaking out” from CTI line.