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Ziad F. Issa

8 Oct, 8 tweets, 4 min read

#IssaTweetorials

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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2/8
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.

3/8
Early PACs can arrive at the AVN during the refractory period and conduct with long PRI or block (physiologic rather than pathologic block) and can mimic Mobitz I or Mobitz II 2°AVB.

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Atrial bigeminy, with failure of conduction of the PACs, can be misinterpreted as 2:1 AVB.

5/8
Atrial trigeminy, with failure of conduction of the PACs, can be misinterpreted as Mobitz II AVB.

6/8
PACs can partially penetrate the AV conduction system (concealed conduction) precipitating AVB during subsequent atrial complexes.

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The mere occurrence of PACs (even when conducted) in a trigeminal or quadrigeminal pattern can produce group-beating patterns mimicking Wenckebach periodicity.

8/8
Apparent Mobitz type II AV block can also be caused by concealed junctional extrasystoles (confined to the specialized conduction system and not propagated to the myocardium) and junctional parasystole.

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More from @ZiadIssaMD

Ziad F. Issa

@ZiadIssaMD

24 Sep

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What is Concealed Conduction?

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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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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.

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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.

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Ziad F. Issa

@ZiadIssaMD

10 Sep

#IssaTweetorials
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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)

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

Ziad F. Issa

@ZiadIssaMD

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

Ziad F. Issa

@ZiadIssaMD

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).