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Chapter 7: Catheter Ablation

CASE 7—1A

The patient had electrophysiologic assessment for WPW and recurrent SVT. AVRT over a posteroseptal AP was found with earliest atrial activation during tachycardia at the proximal coronary sinus (PCS) electrode. Ablation adjacent to the CS os was performed and posteroseptal preexcitation was abolished with no inducible tachycardia. Fifteen minutes later, SVT was again induced, and a PVC was introduced into the cycle as in the Case. The ablation catheter is near the previous site and the coronary sinus catheter has not moved. Where would one ablate now?

An illustration of an intracardiac electrogram presents 9 different lines. The line labeled I starts with a curved horizontal line followed by a positive spike then between each spike there is a slightly elevated horizontal line. Line labeled II starts with a small positive spike followed by a horizontal line which repeats until the end except in the middle there is a negative dip. The line labeled ABL d starts with an irregular line followed by a dip, spike, and deep sharp dip and this pattern continues until the end. The line labeled RVa p starts with a dip and spike with flat tips and this continues until the end with small variations. The line labeled CS 9-10 is almost horizontal with minimal spikes. Line CS 7-8 has a bunch of small dips and spikes in the group followed by a flat line and this pattern repeats until the end. The line labeled CS 5-6 has repeated small spikes and dips. The line labeled CS 3-4 is almost straight with a few small bidirectional spikes. The line labeled CS 1-2 is almost straight with a spike initially and followed by minimal spikes.
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CASE 7–1B

An illustration of an intracardiac electrogram presents 9 different lines. The line labeled I starts with a curved horizontal line followed by a positive spike then between each spike there is a slightly elevated horizontal line. Line labeled II starts with a small positive spike followed by a horizontal line which repeats until the end except in the middle there is a negative dip. The line labeled ABL d starts with an irregular line followed by a dip, spike, and deep sharp dip and this pattern continues until the end. A star is marked on one of the spikes. The line labeled RVa p starts with a dip and spike with flat tips and this continues until the end with small variations. The line labeled CS 9-10 is almost horizontal with minimal spikes. The line CS 7-8 has a bunch of small dips and spikes in the group followed by a flat line and this pattern repeats until the end. The line labeled CS 5-6 has repeated small spikes and dips. The line labeled CS 3-4 is almost straight with a few small bidirectional spikes. The line labeled CS 1-2 is almost straight with a spike initially and followed by minimal spikes. An arrow from the line CS 1-2 points to line CS 5-6.
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Explanation:

The PVC programmed into the cardiac cycle is relatively late coupled with minimal fusion and yet preexcites the next atrial cycle, so it is clearly AVRT. Earliest atrial activation is still near the CS os as identified on the ABL atrial electrogram, but now the atrial activation in the coronary sinus has shifted (long arrow) from distal to proximal, although the far-field PCS EGM is relatively earlier (short arrow). One may speculate that there is a now a left pathway but the atrial activation at the CS os (ABL catheter) is still very early. Ablation at this site terminated tachycardia and this was no longer inducible. The initial ablation at the CS os region likely resulted in interatrial block over the CS interatrial connection. Although AVRT was still occurring over a posteroseptal accessory pathway, there was a change in atrial activation of the LA resulting in a distal to proximal CS activation in spite of the origin of preexcitation near the CS os. This is infrequently seen with minimal ablation in the CS os region but is an interpretative issue that has consequences for successful ablation.

CASE 7–2A

The patient was undergoing PVI ablation, and the left upper PV had just been completed. The CS electrograms are shown in lower part and the circular mapping catheter electrodes are shown in the middle of the tracing. Pacing is attempted from the circular mapping catheter within the left pulmonary vein. How would one interpret the observations?

An illustration of an intracardiac electrogram presents 18 different lines. The line labeled I and II is almost flat with three small spikes. The line labeled V1 has three negative dips and micro spikes in otherwise flat lines. The next eight lines are labeled as 20 A 19, 20; 20 A 17, 18; 20 A 15, 16; 20 A 13, 14; 20 A 11, 12; 20 A 9, 10; 20 A 7, 8; and 20 A 5, 6 has tall spikes overlapping with the adjacent lines in 5 places. Each has a different variation at the beginning and the end in the horizontal line. Line 20 A 3, 4 is similar to the previous lines with five spikes overlapping the adjacent lines but there are smaller spikes between the larger spikes in the horizontal line. The lines labeled 20 A 1, 2 are similar to the previous lines with five spikes overlapping the adjacent lines. The five lines labeled Pr CS 9, 10; Pr CS 7, 8; Pr CS 5, 6; Pr CS 3, 4; and Pr CS 1, 2 are similar lines with small spikes in three places.
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CASE 7–2B

An illustration of an intracardiac electrogram presents 18 different lines. The line labeled I and II is almost flat with three small spikes. The line labeled V1 has three negative dips and micro spikes in otherwise flat lines. The lines between the two dips are labeled CL 890 and 890. The next eight lines are labeled as 20 A 19, 20; 20 A 17, 18; 20 A 15, 16; 20 A 13, 14; 20 A 11, 12; 20 A 9, 10; 20 A 7, 8; and 20 A 5, 6 has tall spikes overlapping with the adjacent lines in five places. Each has a different variation at the beginning and the end in the horizontal line. The third and fourth spikes are labeled S1 and S2. An arrow points to the initial part of the line and a small spike after the last spike in the line labeled 20 A 17, 18. A star is present near the second spike between the lines 20 A 13, 14 and 20 A 11, 12. Line 20 A 3, 4 is similar to the previous lines with five spikes overlapping the adjacent lines but there are smaller spikes between the larger spikes in the horizontal line. The lines labeled 20 A 1, 2 are similar to the previous lines with five spikes overlapping the adjacent lines. The five lines labeled Pr CS 9, 10; Pr CS 7, 8; Pr CS 5, 6; Pr CS 3, 4; and Pr CS 1, 2 are similar lines with small spikes in three places.
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Explanation:

The first observation is that there is some local activation after each pacing spike (asterisk) so that the spike is capturing the PV. The second is that the underlying rhythm is sinus (CL 890 milliseconds) and is dissociated from the paced activity inside the PV. The potentials in the pulmonary vein are “far field” coming from the left atrial appendage and this characteristically shows the biggest far-field potentials in the anterior part of the circumferential mapping catheter ...

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