Catheter Ablation

Question 1

At what tissue temperature does permanent thermal injury occur causing un-excitable scar formation?

Answer 1

50 degrees C (122 degrees F)

Question 2

How can the impedance reading on the tip of the ablation catheter tell you about tissue contact even before you start an ablation lesion?

Answer 2

In an ex-vivo pig study by Thiagalingam (JCE 2007), She found that the impedance measured with the catheter in the blood pool (65.6 ± 3.0 ) was significantly lower than when the catheter was in contact with tissue (110.5 ± 11.7 ). In addition, there was little or no impedance drop when ablation was conducted in the blood pool.

Question 3

To what physical phenomenon does the impedance drop during RF ablation correlate?

Answer 3

In an ex-vivo pig heart study by Thiagalingam (JCE 2007), repeated ablations at the same site had similar
impedance profiles, suggesting that the impedance drop
such is related to reversible changes such as tissue temperature rather than an irreversible changes secondary to destruction of myocardial tissue.

Question 4

What is the effect of irrigation on impedance measured at the tip of the catheter prior to turning on ablation?

Answer 4

When the catheter was in contact with myocardium,
starting irrigation flow significantly increased the
impedance (110.5 ± 11.7 with flow compared with 106.8 ±
11.6 P < 0.01 without flow). When the catheter was in the
blood pool, the impedance was not significantly affected by flow within the catheter tip (65.5 ± 3.0 compared with 65.1 ± 2.9 P = 0.138). From Thiagalingam A (JCE 2007)

Question 5

An RF lesion is created in the power controlled mode delivering 30 W for 30 seconds to a 4 mm and 8 mm tip catheter. Maximum temperature is set at 60 degrees and is not reached using either catheter. Blood flow and tissue contact force are the same. The lesion size will be: 
A) larger with the 4 mm tip
B) larger with the 8 mm tip
C) no different
D) depends on the starting impedance

Answer 5

Answer: A.

A larger tip (non-irrigated catheter) simply allows more cooling allowing higher powers with safe temperatures. If you deliver the same amount of power to a large tip catheter, the energy is distributed over a larger surface area and the lesion size is actually SMALLER than the more concentrated energy delivery of a 4 mm tip catheter.

Question 6

An RF lesion is created in the power controlled mode delivering 30 W for 30 seconds using a non irrigated 4 mm tip catheter and an irrigated 4mm tip catheter. Blood flow and tissue contact force are the same. The lesion size will be 
A) larger with the 4mm tip non-irrigated
B) larger with the 4mm tip non-irrigated
C) no different
D) depends on the starting impedance

Answer 6

Answer: C

Same size tip, same power delivered, same lesion size. Irrigation allows you delivery more power safely by controlling temperature rise but if you can deliver the same power the lesion size should be the same.

Question 7

Which of the following correlate with RF ablation lesion size?
A. contact force
B. Initial impedance
C. Impedance drop
D. Unipolar injury current amplitude
E. amplitude of the bipolar or unipolar ventricular electrogram
F. Electrode temperature

Answer 7

Answer: A and C

Based on a study from Sonny Jackman’s lab using SJM Tacticath, first author Atsushi Ikeda, MD. Published in Circ Arrhythm Electrophysiol. 2014;7:1174-1180.

Question 8

Contact force and impedance drop I’ve been shown to correlate with RF lesion effectiveness. What attribute of the atrial electrogram can also correlate with transmurality of an ablation lesion?

Answer 8

According to a study from Aug Circ A & E, elimination of the negative component of the unipolar atrial electrogram (R morphology completion) during radiofrequency applications reflects transmural lesions creation