#IssaTweetorials
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."

#EPeeps
#CardioTwitter
#ECG
2/7
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.
3/7
Irregular Ventricular Response During AF:
AVN is expected to conduct at regular intervals when its RP expires after each conducted AF impulse. Irregular response is caused by incomplete penetration of some AF impulses into AVN, variably resetting its refractoriness.
4/7
Unexpected Prolongation of Conduction:
When a PAC or PVC incompletely penetrates the AV conduction system, it can render it partially refractory at the time of the next sinus beat, which may then conduct with longer PRI.
5/7
Unexpected Failure of Conduction:
When a PAC or PVC incompletely penetrates the AV conduction system, it can render it fully refractory at the time of the next impulse, which may then be blocked.
6/7
Perpetuation of Aberrant Conduction During SVTs:
Concealed trans-septal conduction of an impulse into one bundle branch can perpetuate bundle branch block during subsequently conducted impulse.
7/7
Unexpected Facilitation of Conduction:
When PAC or PVC incompletely penetrates the conduction system, it can normalize conduction of a previously present AVB or BBB by preexciting the conduction system and ending its RP earlier than expected or by CL-dependent RP shortening

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More from @ZiadIssaMD

10 Sep
#IssaTweetorials
#EPeeps

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)
3/10
According to Ohm’s law, the amount of power per unit volume (resistive heating) equals the square of current density times the impedance (resistance) of the tissue, which in turn, is a function of the square of RF current density.
Read 10 tweets
20 Aug
#IssaTweetorials
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.
#EPeeps
2/
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.
3/
PERITRICUSPID REENTRY
In typical AFL the wavefront rotates around the tricuspid annulus. A line of conduction block in the RA free wall is usually required to as a critical lateral boundary that prevents short-circuiting of the flutter wavefront around the IVC.
Read 7 tweets
13 Aug
#IssaTweetorials
#EPEEPS
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.
3/
Key to the development of typical AFL is formation of a line of transverse conduction block in the RA free wall, which acts as a critical lateral boundary that prevents short-circuiting of the flutter wavefront around the IVC and, hence, extinguishes (see video).
Read 9 tweets

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