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What is the mechanism of aberrant conduction?
 
1/9

“Aberration” describes transient bundle branch block (BBB) and does not include persistent QRS abnormalities caused by persistent BBB, preexcitation, or the effect of drugs.

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Acceleration-dependent BBB (aka “phase 3 block” or “voltage-dependent block”) occurs when an impulse arrives at tissues that are still refractory due to incomplete repolarization (during phase 3 of the action potential [AP]).

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Impedance and RF ablation:
Part 2: How does RF ablation affect impedance?
 
1/9
As tissue temperature rises during RF energy application, ions within the tissue being heated become more mobile, resulting in a decrease in impedance to current flow. 2/9
There are currently 2 methods to measure impedance: Generator Impedance (GI) & Local Impedance (LI).

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Impedance & RF ablation:
Part 1: How does impedance affect RF lesion formation?

1/8
During RF ablation, system impedance = impedance of genera¬tor + transmission lines + catheter + electrode-tissue interface + skin patch interface + interposed tissues. 2/8
IMPEDANCE & POWER
The magnitude of RF current delivered by the generator is determined by impedance btwn ABL electrode and ground pad. Ablation at lower impedance yields higher current output (and tissue heating) compared with ablation at a similar power & higher impedance.

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The mimicry of second-degree AV block (2°AVB)

1/8
ECG patterns that mimic 2°AVB are often related to atrial ectopy, concealed junctional ectopy, or AVN echo beats. Distinguishing physiologic from pathologic AVB is important.

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In 2°AVB, sinus P-P interval is fairly constant (except for some variation caused by ventriculophasic arrhythmia), the nonconducted P wave occurs on time as expected, and P wave morphology is constant. With ectopy, P waves occur prematurely & often have different morphology.

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What Is the Gap Phenomenon?
1/4
“PROXIMAL DELAY ALLOWS DISTAL RECOVERY” is the fundamental concept of gap phenomenon. This requires a distal site with a long effective refractory period (ERP) and a proximal site with a shorter ERP.

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During gap phenomenon, initial block occurs distally (due to longer ERP). Earlier impulses encroach on the relative refractory period (RRP) of proximal site where conduction delay is encountered, which allows for expiration of the ERP of the distal site, enabling conduction.

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What is Concealed Conduction?

1/7
Concealed conduction can be defined as "the propagation of an impulse within the conduction system that can be recognized only from its effect on the subsequent impulse, interval, or cycle."

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Impulse propagation in the conduction system generates too small electrical current to be recorded on ECG. If this impulse travels only a limited distance (incomplete penetration) in the conduction system, it can interfere with formation or propagation of another impulse.

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1/9
How reliable is ablation electrode temperature to monitor RF lesion formation?

RF lesion creation is thermally mediated; hence, monitoring tissue temp is the most reliable approach to achieve effective (temp >50°C) & safe (temp <100°C) ablation.

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Temp measurements relevant to RF lesion formation include:

1- Intramural temp.
2- Endocardial surface temp.
3- Abl electrode temp.

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1/10

Q: If you could deliver 30 W of RF energy for 30 sec using any of the ablation (abl) electrodes shown in the figure, which RF ablation catheter creates larger ablation lesion size?

A: Let’s talk about how the RF abl lesion is formed. 2/10
The size of the lesion created by RF is determined by the amount of tissue heated to >>50°C.

Heat is generated when charged ions in tissue oscillate rapidly (following the alternating RF current) converting RF energy to kinetic/thermal energy (Ohmic/Resistive Heating)

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How does drug therapy affect atrial flutter (AFL)?

1/8
- Typical AFL is an intra-atrial peritricuspid macroreentry that is independent of the AVN.
- Drugs used in AFL affect the atrial action potential, the AVN action potential, or both.

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For AFL reentry to sustain, the wavelength of the reentrant wavefront (conduction velocity x ERP) should be shorter than the reentry pathlength.

This can be achieved by:
- Slowing wavefront velocity.
- Shortening ERP
- Enlarging anatomic length of the reentry circuit.

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1/
What are the types of CTI-dependent atrial macroreentry?

CTI-dependent macroreentrant atrial tachycardias (MRATs) are confined to the RA & incorporate the CTI as a critical part of the circuit. All these MRATs can be eliminated by CTI ablation.
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CTI-dependent MRATs include:
(1) peritricuspid reentry (clockwise and counterclockwise typical atrial flutter [AFL])
(2) peritricuspid double-wave reentry
(3) lower loop reentry
(4) intra-isthmus reentry.

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Do you know the mechanism of typical atrial flutter (AFL)?
1/
Typical AFL is a macroreentrant circuit with the activation wavefront rotating clockwise or counterclockwise around the tricuspid annulus and using the CTI as an essential part of the circuit. 2/
Conduction across the CTI is relatively slower than the rest of the atrium (likely due to the anisotropic fiber orientation), which provides the protected zone of relatively slow conduction necessary for the flutter reentry circuit.

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Biophysics of RF Energy
RF refers to the portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. Electrosurgery (coagulation, cauterization, and ablation) uses wavelengths found in band 6 (300-3000 kHz). which are similar to those used for broadcast radio. However, the RF energy is electrically conducted, not radiated, during catheter ablation.