7. Atypical AFL

CTI, atrial depolarization wave must propagate caudocephalically up the septum and travel down to the lateral RA to arrive at distal poles of halo catheter. So the distal poles of halo catheter are the last poles which record the atrial potentials (Figure 8b). In order to assess the lateral to medial block across CTI, pacing from lateral to the ablation line is performed (e.g. halo distal poles or tip of ablation catheter at 8:00 o'clock). In case of lateral to medial block, atrial depolarization wave will propagate superiorly up the lateral RA and travel down the interatrial septum to reach the CS ostium, recorded at proximal CS (Figure 8a). Figure 8c shows the atrial activation during CS proximal pacing prior to medial to lateral isthmus block which demonstrates the collision of the cranial and caudal right atrial wave fronts in the mid-

CS proximal or low lateral RA is usually paced in order to measure conduction interval across CTI. Obviously, the interval is the time from the stimulus pacing artifact from one side of the isthmus (e.g. CS proximal) to the atrial electrogram recorded on the other side (e.g. distal halo poles). More than 50% prolongation of this interval or an absolute interval time of 150 ms or

This maneuver is used to assess CW and CCW block across CTI. At first, pacing is performed close to the ablation line, then pacing site is moved away from first pacing spot (Figure 9). For example, to check CCW (lateral to medial) block, the pacing is done from halo distal poles (Halo 1,2) and the time from stimulus artifact to the atrial electrogram recorded on the proximal CS is measured. Then pacing site is done farther from ablation line (Halo 3,4). If there is CCW, the measured interval will be shortened on the latter spot (Halo 3,4). When CTI conduction is intact, conduction occurs via a counterclockwise wavefront across the CTI to reach proximal CS, so the measured interval will be longer once it is paced from Halo 3,4

Electroanatomical 3D mapping can also be used to confirm conduction block across CTI. For example, when CCW block is present, Halo 1,2 pacing results in an activation wavefront directing in a CW pattern and CTI immediately medial to the ablation line will be the last part in the circuit which will be activated. If CTI is intact, with pacing from Halo 1,2 the activation wavefront travels rapidly through the CTI, with the upper septum will be the last part of

RF ablation of the typical AFL is relatively safe, with an average complication rate of 3% which includes mostly peripheral vascular injury (0.5%). The risk of serious complication is very low which include complete heart block (0.3%), tamponade, myocardial infarction due to damage to the right coronary artery, stroke and pulmonary embolism (0.1%). The recurrence

lateral RA (RA 5–6).

34 Cardiac Arrhythmias

6.4.5. Differential pacing

compared to Halo 1,2 [24].

activation.

6.5. Complication

6.4.6. Electroanatomical mapping

6.4.4. Trans CTI conduction time

more is in favor of CTI block [22, 23].

Atypical AFL frequently demonstrates attenuated flutter waves which help to distinguish from typical flutter. They are classified as atypical right or left atrial flutter [27] (Figure 10). Prompt identification of these AFL types will maximize the success rate of ablation.

#### 7.1. Atypical right atrial isthmus-dependent flutter

#### 7.1.1. Lower loop reentry

Lower loop reentry is a form of CTI-dependent AFL in which the circuit is around IVC. The eustachian ridge and lower crista terminalis usually cause a breakdown in wavefront

7.2.3. Dual-loop reentry

other circuit [27].

7.3. Atypical left atrial flutter

7.3.1. ECG characteristics of left atrial flutter

the negative flutter waves in typical AFL [30, 31].

circuit. Most of the patients have a past history of AF ablation [29].

7.3.2. Perimitral atrial flutter

7.4. EPS and mapping in atypical AFL

The coexistence of two circuits is known as dual-loop reentry. The activation wavefront can propagate through both circuits intermittently. In practice, they are identified when the ablation of one circuit leads to change in atrial activation sequence suggesting a transition to the

Atrial Flutter: Diagnosis and Management Strategies http://dx.doi.org/10.5772/intechopen.74850 37

LA flutter often coexists with AF. It is usually secondary to AF ablation (up to 50%) or open heart surgery for the valvular disease. The central obstacle of the AFL circuits is low-voltage or

Whenever the flutter wave morphology in ECG is not characteristic of typical AFL, left atrial flutter must be considered. A characteristic finding in LA flutter is a dominantly positive broad deflection in lead V1. The combination of attenuated deflections in the frontal leads with a dominantly positive deflection in V1 also suggests that origin of flutter is probably in LA. Uncommonly, negative flutter deflections in the inferior leads might be seen in left AFL mimicking typical AFL (pseudo-typical flutter). However, typical AFL demonstrates positive overshoot immediately following the negative deflection. This positive deflection is as a result of inferiorly down activation of the lateral RA. Lack of this sharp positive deflection raises suspicion of atypical AFL. In the presence of low voltage areas, the electrical impulse traversing the isthmus (protected within scar) might generate low voltage potentials, demonstrated on the surface ECG as an iso-electric interval. In addition, a small portion of the atria is being activated during the silent isoelectric period. Therefore, the isoelectric interval strongly supports the presence of a slow conducting isthmus, although its absence does not exclude it. For example, if intracardiac CS electrograms coincide with an isoelectric interval, it suggests CS region may be involved in the reentrant circuit, indirectly implies the flutter might be left sided in origin. Likewise, the electrograms of CTI region coincide with the isoelectric period between

In this type of AFL, the reentrant circuit arises around the mitral annulus. 3D voltage mapping often shows low-voltage or scar areas on the posterior LA which act as a boundary of this

In addition to CS and Halo catheter, the transseptal puncture is performed to insert a catheter in LA (usually irrigated tip ablation catheter) for the full study. In order to confirm LA flutter, a systematic approach is used. The first step is the exclusion of CTI dependent AFL. Coronary sinus activation from proximal to distal can suggest that AFL origin is from the RA; however, CS activation sequences are not very valuable in LA flutter diagnosis. If EGMs recorded

scar areas in the LA detected by electroanatomic 3D mapping [29].

Figure 10. Types of atypical flutter. Top left, Intraisthmus reentry. Top right, lower loop reentry. Bottom left, perimitral reentry. Bottom right, incisional (around ASD patch) reentry.

conduction across CTI; consequently, impulse revolves around the IVC instead of the tricuspid annulus. It is mostly identified during 3D activation mapping [28].

#### 7.1.2. Intraisthmus reentry

The circuit of intraisthmus reentry is bounded by the medial side of CTI and CS ostium. The previous ablation at the CTI might predispose and perpetuate this reentry. The EGMs are usually similar to typical AFL but entrainment shows the lateral CTI is not inside the circuit (long PPI) whereas the medial side of CTI presents in the circuit (short PPI). The mapping of the region between proximal CS and medial CTI usually shows fractionated or double potentials which are a good target for ablation. A linear lesion across the medial CTI usually breaks the circuit [27, 28].

#### 7.2. Atypical right atrial non-isthmus dependent flutter

#### 7.2.1. Lesional right atrial flutter

These circuits arise around a low-voltage area, incision, patch or scar in the lateral or posterolateral RA. These areas usually develop after the atriotomy and surgery for the congenital disease. 3D activation mapping is an excellent modality to identify this type of AFL circuits [28].

#### 7.2.2. Upper loop reentry

In this type of AFL, the wavefront activation propagates around the superior vena cava (SVC) and travels through a conduction gap in the crista terminalis.

#### 7.2.3. Dual-loop reentry

The coexistence of two circuits is known as dual-loop reentry. The activation wavefront can propagate through both circuits intermittently. In practice, they are identified when the ablation of one circuit leads to change in atrial activation sequence suggesting a transition to the other circuit [27].

#### 7.3. Atypical left atrial flutter

LA flutter often coexists with AF. It is usually secondary to AF ablation (up to 50%) or open heart surgery for the valvular disease. The central obstacle of the AFL circuits is low-voltage or scar areas in the LA detected by electroanatomic 3D mapping [29].

#### 7.3.1. ECG characteristics of left atrial flutter

Whenever the flutter wave morphology in ECG is not characteristic of typical AFL, left atrial flutter must be considered. A characteristic finding in LA flutter is a dominantly positive broad deflection in lead V1. The combination of attenuated deflections in the frontal leads with a dominantly positive deflection in V1 also suggests that origin of flutter is probably in LA. Uncommonly, negative flutter deflections in the inferior leads might be seen in left AFL mimicking typical AFL (pseudo-typical flutter). However, typical AFL demonstrates positive overshoot immediately following the negative deflection. This positive deflection is as a result of inferiorly down activation of the lateral RA. Lack of this sharp positive deflection raises suspicion of atypical AFL. In the presence of low voltage areas, the electrical impulse traversing the isthmus (protected within scar) might generate low voltage potentials, demonstrated on the surface ECG as an iso-electric interval. In addition, a small portion of the atria is being activated during the silent isoelectric period. Therefore, the isoelectric interval strongly supports the presence of a slow conducting isthmus, although its absence does not exclude it. For example, if intracardiac CS electrograms coincide with an isoelectric interval, it suggests CS region may be involved in the reentrant circuit, indirectly implies the flutter might be left sided in origin. Likewise, the electrograms of CTI region coincide with the isoelectric period between the negative flutter waves in typical AFL [30, 31].

#### 7.3.2. Perimitral atrial flutter

conduction across CTI; consequently, impulse revolves around the IVC instead of the tricuspid

Figure 10. Types of atypical flutter. Top left, Intraisthmus reentry. Top right, lower loop reentry. Bottom left, perimitral

The circuit of intraisthmus reentry is bounded by the medial side of CTI and CS ostium. The previous ablation at the CTI might predispose and perpetuate this reentry. The EGMs are usually similar to typical AFL but entrainment shows the lateral CTI is not inside the circuit (long PPI) whereas the medial side of CTI presents in the circuit (short PPI). The mapping of the region between proximal CS and medial CTI usually shows fractionated or double potentials which are a good target for ablation. A linear lesion across the medial CTI usually breaks

These circuits arise around a low-voltage area, incision, patch or scar in the lateral or posterolateral RA. These areas usually develop after the atriotomy and surgery for the congenital disease. 3D activation mapping is an excellent modality to identify this type of AFL circuits [28].

In this type of AFL, the wavefront activation propagates around the superior vena cava (SVC)

annulus. It is mostly identified during 3D activation mapping [28].

reentry. Bottom right, incisional (around ASD patch) reentry.

7.2. Atypical right atrial non-isthmus dependent flutter

and travels through a conduction gap in the crista terminalis.

7.1.2. Intraisthmus reentry

36 Cardiac Arrhythmias

the circuit [27, 28].

7.2.1. Lesional right atrial flutter

7.2.2. Upper loop reentry

In this type of AFL, the reentrant circuit arises around the mitral annulus. 3D voltage mapping often shows low-voltage or scar areas on the posterior LA which act as a boundary of this circuit. Most of the patients have a past history of AF ablation [29].

#### 7.4. EPS and mapping in atypical AFL

In addition to CS and Halo catheter, the transseptal puncture is performed to insert a catheter in LA (usually irrigated tip ablation catheter) for the full study. In order to confirm LA flutter, a systematic approach is used. The first step is the exclusion of CTI dependent AFL. Coronary sinus activation from proximal to distal can suggest that AFL origin is from the RA; however, CS activation sequences are not very valuable in LA flutter diagnosis. If EGMs recorded throughout RA (i.e. atrial electrograms recorded on all Halo poles) covers more than 50% of the TCL, it is another clue for RA AFL. Another helpful maneuver is entrainment at multiple sites in the RA and comparison of their PPIs. For instance, if PPI is shorter in septum compared to lateral RA or CTI, it might be suggestive for LA flutter. In fact, the gradient of PPI in LA flutter typically is longest (more than 30 ms) in the lateral RA and remarkably shorter in the mid and distal coronary sinus. However, roof or anterior LA flutter might show long PPI in mid to distal CS [28, 29, 32]. The 3D mapping system is often necessary to perform the full activation and voltage mapping for localization and effective ablation of the reentrant circuit [33].

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