Ziad F. Issa Profile picture
Aug 20, 2021 7 tweets 3 min read Read on X
#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 Image
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.
4/
DOUBLE-WAVE REENTRY
Typical AFL circuits with a large excitable gap may allow a second excitation wave to be introduced in the same circuit by a critically timed extrastimulus. The 2 wavefronts occupy the circuit simultaneously. This rhythm rarely lasts more than a few beats.
5/
LOWER LOOP REENTRY (LLR)
In LLR, the wavefront rotates around the IVC.
6/
LLR vs Typical AFL
LLR often coexists with typical AFL. Significant RA disease and slow conduction across the lower crista terminalis to enable reentry around the IVC instead of around the TA. In contrast conduction block across the posterlateral RA is required for typical AFL ImageImage
6/
INTRA-ISTHMUS REENTRY
Small reentry circuits confined to the CTI (often the medial aspect of CTI) can develop, especially in patients with prior extensive CTI ablation for typical AFL, which provides the substrate for reentry (even in the presence of bidirectional CTI block).

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More from @ZiadIssaMD

Dec 10, 2021
#IssaTweetorials
 
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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2/9

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]).
3/9

Aberration secondary to phase 3 block tends to be in the form of RBBB when premature excitation (and Ashman phenomenon) occurs during normal baseline heart rates and in the form of LBBB when it occurs during fast heart rates.
Read 9 tweets
Nov 17, 2021
#IssaTweetorials
#EPeeps

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. Image
2/9
There are currently 2 methods to measure impedance: Generator Impedance (GI) & Local Impedance (LI).
3/9
Lack of impedance drop during RF energy application can reflect inefficient energy delivery to the tissue due to poor tissue contact, lack of catheter stability, or inadequate power delivery.
Read 8 tweets
Oct 29, 2021
#IssaTweetorials
#EPeeps

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.
3/8
IMPEDANCE OF ELECTRICAL CONDUCTORS
Currently used electrical conductors from the generator to the patient and from the ground pad back to the generator are designed to have low electrical resistance to help minimize power loss within those conductors.
Read 8 tweets
Oct 8, 2021
#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.

#EPeeps #CardioTwitter #ECG
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.
Read 8 tweets
Oct 1, 2021
#IssaTweetorials
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.

#EPeeps #CardioTwitter #ECG Image
2/4
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. ImageImage
3/4
Any pair of structures in the AV conduction system that has the appropriate EP physiological relationship can exhibit the gap phenomenon (e.g., atrium–AVN, proximal AVN–distal AVN, AVN–HPS, HB-distal HPS). Gap can occur in the anterograde or retrograde direction. Image
Read 4 tweets
Sep 24, 2021
#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."

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#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.
Read 7 tweets

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