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Atrial flutter (AFl)

AFl basics

Typical AFl

When talking about typical atrial flutters, this referes to flutters which utilise the cavo tricuspid isthmus (CTI), also known as CTI dependent flutters.
CTI flutter presentations account for >90% of all atrial flutters
A CTI flutter ablation is typically a straight forward procedure with high success rate >90%, and low complication risk <1%
In the right atrium, where the circuit spins (mostly counter clockwise direction) around the tricuspid annulus.
The CTI is a small ridge between the tricuspid annulus and the IVC

Typical AFl with saw tooth appearance on ECG

Typical CTI AFl and post ablation block

Atypical AFl

Atypical atrial flutters are any flutters outside the CTI.
These flutters are often associated with scar (often post surgical (e.g., cardiac surgery, post PVI ablation, etc) or scar developed by certain conditions (e.g., sarcoid))
Can be difficult to map and ablate
Often are left sided
Multiple atrial circuits may be involved

Examples of atypical atrial flutter circuits

Atypical AFl with isoelectric segments on ECG

Atrial entrainment in atrial flutter

Atrial entrainment is a manouvre utilised during atrial flutter to determine if the pacing site is part of the atrial flutter circuit.
This is done by pacing at any point in the atrium 20-30ms faster that the TCL. The tachycardia must continue after (exact same rhythm- same activation- same rate).
The PPI-TCL can then be evaluated.
If PPI-TCl is <30ms this indicates that the pacing location is in the circuit.
The greater the PPI-TCL, the further away from the circuit the catheter is.
Other activation patterns can be viewed in terms of conceled or manifest patterns to determine if the pacing site is similar/different location to the atrial flutter.
for example: a typical atrial flutter will have concentric atrial activation across the CS (CSp to CSd). Pacing from the CTI region will show the same activation pattern in the CS (concealed fusion). However pacing from the lateral LA will result in eccentric CS activation (CSd to CSp) and will demonstrate manifest activation.

AFl ablation

Equipment

Venous access multiple sites
Often a decapolar coronary sinus catheter is used
A second decapolar or duodecapolar catheter may be utilised to sit along the lateral RA for typical CTI flutters
May need transeptal equipment if left sided (sheath and needle - multiple (2) punctures may be performed - Dr dependent)
Ablation catheter
+ / - 3D mapping catheter (almost always used for atypical AFl)

Useful 3D views

Procedure - CTI ablation

PROVING FLUTTER IS CTI WHEN IN ATRIAL FLUTTER

If patient is in atrial flutter, there a couple of ways to demonstrate CTI involvement.
Activation map using 3D mapping system. The entire circuit will be in the right atrium. The circuit will spin around the tricuspid annulus.
One atrium will be mapped at a time. If that atrium is involved in the flutter, the entire cycle length will be displayed. If not, this will reflect passive activation.
This is confirmed with atrial entrainment. Termination of arrhythmia with ablation should be expected with ACL increase prior to termination (if shorter ACL- may be ectopics terminating rhythm)

ATRIAL ENTRAINMENT

How to perform

pacing the atrium 20-30ms faster that the TCL.
The tachycardia must continue after (exact same rhythm- same activation- same rate)
Measure PPI
If PPI-TCL is <30ms this indicates that the pacing location is in the circuit
The greater the PPI-TCL, the further away from the circuit the catheter is
Other activation patterns can be viewed in terms of concealed or manifest patterns to determine if the pacing site is similar/different location to the atrial flutter.
a typical atrial flutter will have concentric atrial activation across the CS (CSp to CSd).
Pacing from the CTI region will show the same
activation pattern in CS (concealed fusion).
pacing from the lateral LA will result in eccentric CS
activation (CSd to CSp) and will demonstrate manifest activation.

TRANS ISTHMUS CONDUCTION TIME (TICT)

If a patient is in sinus rhythm on the day of the procedure, and because most atrial flutters tend to be CTI dependent, it is assumed that if a patient presented with atrial flutter with typical appearance (saw-tooth) and no prior cardiac surgery or conditions (CHD), it is assumed to be CTI dependent.

Moreover, as it is not a reliable method to induce atrial flutter (more likely to induce AF), and thus ablation is performed in sinus rhythm.

A baseline TICT maybe recorded.

A post ablation TICT will also be measured with differential

pacing to prove bidirectional block.

A catheter is placed in the coronary sinus and one at laterally

to the CTI. Pacing is performed at the CS ostium and timing

to the lateral RA is measured (TICT). This is then done in

the reversal (RA to CS ostium timing).

During ablation - typical CTI

Atrial signal

Attenuation of atrial signal during ablation
Tight doubles on local catheter (ablator) will reflect delayed atrial activation across the lesion
Wide doubles on local catheter reflects block

Atrial flutter
Increase in cycle length is usually seen followed by termination to sinus rhythm
CTI flutter may terminate, but switch to a different atrial flutter

Sinus rhythm
Increase in TICT will be observed (during pacing manoeuvres)
Bidirectional block is proven with differential pacing. This involves pacing from the CS ostium and measuring the time it takes to get to the lateral RA at 2 points (low lateral RA or closer to the CTI line and higher laterally, or further away from the CTI line) and measuring the TICT. Although closer to the line is physically closer to the CS ostium, it should take a longer time to reach here due to the block across the CTI line. This will prove unidirectional block. This is then repeated in the opposite direction to prove bidirectional block (from low RA to CS and high RA to CS).

Procedure - atypical atrial flutter ablation

Patient must be in the atrial flutter to determine location
Activation map using 3D mapping system.
One atrium mapped at a time à circuit seen or is it passive activation
This is confirmed with atrial entrainment.
Eccentric CS activation consistent with left sided arrhythmia
However, midline CS activation may be either right or left sided

Where to ablate

To interrupt a flutter an ablation line is performed between two areas of inactive conduction (e.g., annulus, isolated veins, other sources of scar (e.g., atriotomy scar)
Ideally, the shortest line is the best line.

Roof dependent flutter

roof +/- floor line (posterior wall isolation)

PERI-MITRAL

Lateral line (shorter line, but thick tissue)

– may perform Ligament of Marshall alcohol ablation, and complete line with traditional ablation

Anterior line (usually diagonal type line from antero-lateral mitral annulus to RSPV

Of anterior line was performed from mitral annulus (MA) to LPV, the flutter would likely become roof dependent – thus why a diagonal line is performed (see image below)

ATRIOTO MY SCAR

Flutter spinning around the atriotomy scar on the ridge of the
SVC and lateral wall. Ablation can be performed from the bottom of
the atriotomy scar to the IVC.

DUAL LOOP

Dual loop flutters can be seen in the LA for example, involving
the roof and the mitral annulus. It may give a bigeminal pattern.
(seen below). In this instance, both a roof and anterior or lateral line will need to be performed.

PROVING BLOCK

Posterior wall isolation

No signals entering/exiting (similar to PVI)

Single line of block

Trickier to prove bidirectional block

Ideally 2 catheters on either side of the line (often only 1 transeptal – 1 catheter)

Can sometimes get away with having a HD / multipolar catheter across both sides of the line with pacing from one side and EGM analysis on the other

WHAT ARE EPICARDIAL CONNECTIONS

Muscular bridges/pathways) outside the endocardium connecting parts of the atrium to others which are not necessarily directly next to each other

“Achilles' heel in endocardial ablation strategies

Key fibres include

Ligament/vein of Marshall
fibres connecting posterior LA wall to PV antrum
coronary sinus
septo-pulmonary bundle
Bachmann’s bundle

CASE STUDY SHOWING SEPTOPULMONARY EPICARDIAL CONNECTIONS

Clear line of block, however signal umping across line (earliest spot where red pin is)

LIGAMENT OF MARSHALL (LOM)

A vestigial fold of the pericardium, containing fibrous bands, small blood vessels and nervous filaments enveloped in fat.

It contains the oblique vein of marshall (VOM) that drains into the coronary sinus.

Positioned obliquely above the LAA and lateral to the LSPV

Source of rapid conduction believed to play a role in atrial arrhythmias

BACHMANS BUNDLE

Muscular bundle of parallel myocardial strands

Runs sub-epicardially from the RAA to the LAA across the interatrial groove (septal raphe) which is filled with epicardial fat*

Rightward superior extension arises in the region of the cavoatrial junction (close to sinus node) & in the vicinity of the sagittal bundle

Rightward inferior extension arises in the subepicardium of the right atrial vestibule.

Leftward superior extension traverses in the infolding of the atrial wall (arrhythmologists as the left lateral ridge) to pass in front of the orifices of the left PVs.

Leftward inferior extension descends toward the atrial vestibule to combine with the circumferentially aligned myocardial strands in the subepicardium of the inferior wall.