Atrial Flutter (AFL)

Typical flutter

• saw-tooth pattern P-waves in leads II, III, aVF (inverted w/ CC and positive w/ C rotation)

• AV ratio ranges from 2:1 - 4:1 with atrial rates commonly 150-250 ms

• The circuit includes the CTI and tricuspid valve

Atypical flutter

• Saw-tooth pattern P-waves, but different morphology than typical flutter

• A:V ratio ranges from 2:1-4:1 with the atrial rate varying depending on circuit and substrate properties

• Often occurs as a result of substrate from atrial myopathies and prior surgeries or ablation procedures

Atrial flutter (rate, p-wave, pr interval, qrs, rhythm)

Rate: fast 250-350 BPM for atrial, but ventricular rate is often slower

P-wave: saw-toothed morphology

PR interval: not measurable

QRS: Narrow (<120ms)

Rhythm: regular atrial and ventricular rates can vary

Prerequisites for reentry

1. Two pathways- separated by an anatomical structure

2. Different conduction/refractory velocities

3. Unidirectional block in one pathway

Types of atypical atrial flutter

Peri-mitral annulus → uses mitral annulus and left atrial isthmus and occurs post-Afib

Roof-dependent → uses PV ablation lines (commonly between RSPV and LSPV ablation lines, occurs post Afib ablation

Scar dependent → uses surgical scars and occurs post left atrial atriotomy

Entrainment mapping

• Burst atrial pacing during tachycardia

• location: HRA or prox CS

• Confirms CTI dependence

1. acceleration of tachycardia to PCL

2. continuation of TCL upon cessation of pacing

3. measuring PPI

4. if PPI-TCL is <30ms, entrainment within reentrant circuit confirmed

Activation sequence mapping

Continuously compare atrial electrograms against a reference signal to the progression of the activation sequence around a defined macro-reentrant circuit

For typical flutter:

1. initial atrial wave deflection is observed on CS ostium EGM

2. timed with initial downstroke of flutter p wave in inferior ECG leads

3. followed by HIS atrial EGM

4. then RA free wall EGM

Concealed entrainment

• Fusion of the paced stimulus with the tachycardia activation wavefront, typically near the circuit

• Confirmed via acceleration of tachycardia during pacing without change in activation pattern

Manifest entrainment

Paced stimulation causes a change in the tachycardia activation wavefront because the stimulus is outside of the circuit

Crista terminalis

• During typical AFlutter, the CT serves as an electrical barrier, channeling the wavefront to propagate the flutter circuit

• placement location for multi-electrode catheters to evaluate signal propagation, timing, and differential pacing to determine CCW vs CW, typical vs atypical AFL, and bi-directional block post AFL ablation

Trans-isthmus interval

• the time it takes from the onset of CSd simulation to the ablation to the ablation catheter

• baseline is 79 ms, and the goal is to achieve an increase in the trans-isthmus interval by 50% or greater

• TII post-ablation should be > 160 ms to indicate a successful line of conduction block across the CTI because the paced stimulation has to travel the long way around to the lateral side of the ablation line