• Re-entry and Supraventricular Tachycardia
• Anatomy of the Right Atrium
• Atrial Flutter
• Typical Flutter (Isthmus-Dependent)
• Reverse Typical Flutter (Isthmus-Dependent)
• Atypical Flutter (Isthmus-Independent)
• ECG and Atrial Flutter
• How Flutter (F) Waves (Sawtooth Waves) Are Formed
• ECG and Typical Flutter (Isthmus-Dependent)
• Reverse Typical Flutter (Isthmus Dependent)
• Conduction to the Ventricles
• Laddergram and Atrial Flutter
• Rapid Diagnosis - Atrial Flutter
• Atrial Flutter (2:1)

Re-entry and Supraventricular Tachycardia

• In supraventricular tachycardia (SVT), impulses originate in the atria or in the AV junction
• Re-entry is one of the mechanisms of tachycardia
• where the impulse circulates in a loop, most often around an anatomical obstacle (scar)
• Sinoatrial Nodal Re-entry Tachycardia
• Re-entry is in the SA node
• or re-entry passes through the SA node
• Intra-atrial Re-entry Tachycardia
• Re-entry is somewhere in the atria
• most commonly around a scar (post myocardial infarction)
• or re-entry occurs without an obstacle
• AV Nodal Re-entry Tachycardia
• Re-entry is in the AV node
• AV Re-entry Tachycardia
• It is macro re-entry, the impulse circulates between:
• the atria and ventricles through the AV node and an accessory pathway
• There are 3 accessory pathways:
• Kent bundle (WPW syndrome)
• James bundle (LGL syndrome)
• Mahaim bundle (Mahaim syndrome)
• Atrial Flutter
• It is macro re-entry, the impulse circulates
• through the entire most commonly right atrium

Atrial Flutter

• It almost always occurs in a structurally altered right atrium
• P pulmonale (right atrial hypertrophy)
• In the right atrium, there is a macro re-entry circuit
• Through which the impulse circulates at a frequency of approximately 300/min (200 - 400/min)
• The impulse passes through the AV node to the ventricles most commonly in a ratio of 2:1
• The impulse circulates twice in the macro re-entry (in the right atrium)
• and passes once to the ventricles
• The atria beat at 300/min, and the ventricles at 150/min
• This is a protective mechanism of the AV node (through the refractory period)
• Atrial flutter with 1:1 conduction can occur in WPW syndrome
• If the patient receives medications to slow the AV node
• Impulses from the atrium then reach the ventricles through an accessory pathway
• Which does not have the protective mechanism of the AV node
• The ventricles are activated at 300/min and ventricular fibrillation occurs
  
  
• Atrial flutter and atrial fibrillation
• Can cause embolic stroke
• At high atrial frequencies, blood stagnates in the atria
• and thrombi (blood clots) form
• Atrial flutter (300/min - atrial frequency)
• Atrial fibrillation (350-600/min - atrial frequency)

Reverse Typical Flutter (Isthmus-Dependent)

Reverse Typical Atrial Flutter, Clockwise Atrial Flutter

• Sometimes referred to as Reverse Type I atrial flutter
• It is very rare (< 10% of cases)
• Macro re-entry occurs through the cavotricuspid isthmus
• The impulse circulates through the re-entry circuit at a frequency of 240-340/min
• The impulse circulates clockwise (Clockwise re-entry)
• Characteristic sawtooth waves (F-waves) are seen on the ECG, instead of P waves

ECG and Atrial Flutter

• Narrow QRS complexes (because impulses are conducted to the ventricles through the AV node)
• Atrial frequency is approximately 300/min
• Isthmus-dependent flutter: 240-340/min (90% of cases)
• Isthmus-independent flutter: 340-440/min (< 10% of cases)
• In the inferior leads (II, III, aVF) there are "sawtooth waves"
• An isoelectric line is not present
• Flutter (F) waves (sawtooth waves) may resemble P waves in V1

ECG and Typical Flutter (Isthmus-Dependent)

• This is the most common atrial flutter (90% of cases)
• The impulse circles through re-entry across the isthmus around the AV node with a frequency of approximately 300/min
• The impulse circles through re-entry in a direction AWAY FROM the inferior leads
• In the inferior leads (II, III, aVF)
• negative flutter waves (sawtooth waves) appear
• Positive waves appear in V1
• Because the V1 lead is "opposite" the inferior leads

Conduction to the Ventricles

• Isthmus-dependent flutter has a re-entry frequency of approximately 300/min.
• The AV node blocks the conduction of impulses to the ventricles
• This is a functional block - a protective mechanism of the AV node, protecting the ventricles from extreme tachycardia
• This is not an organic AV block (due to damage to the AV node)
• The functional AV block or conduction to the ventricles can have varying degrees
• Ventricular frequency (QRS) with atrial flutter at a frequency of 300/min. will depend on the conduction ratio:
• Conduction 2:1 = ventricles at 150/min.
• Conduction 3:1 = ventricles at 100/min.
• Conduction 4:1 = ventricles at 75/min.
• Atrial flutter can also have variable AV block (conduction to the ventricles)
• On the ECG, this results in a varying conduction ratio of 2:1, 3:1, 4:1
• Flutter then resembles atrial fibrillation because the heart action (QRS) is irregular

Atrial Flutter (4:1)

• Frequency: 68/min.
• Atrial frequency: 272/min.
• Ventricular frequency: 68/min.
• Note that this is not a 3:1 block; the block to the ventricles is 4:1
• Notice the peaks of the flutter waves, which are oriented downward
• This is again istmus-dependent flutter (frequency is 240-340/min.)

Atrial Flutter (with variable AV block of 7:1, 8:1, and 5:1)

• Frequency (QRS): 40/min. (6-second method)
• Flutter wave frequency: 300/min.
• This is istmus-dependent flutter with variable AV block (7:1, 8:1, 5:1)

Rapid Diagnosis - Atrial Flutter

• Atrial Flutter is likely if:
• There is supraventricular tachycardia with a frequency of 130-170/min.
• Sawtooth waves (Flutter waves) are present in the inferior leads (II, III, aVF)
• QRS complexes are regularly irregular
• The patient has minimal subjective symptoms (not feeling faint, no fever, breathing well, etc.)
• Increase in AV node block
• Vagal maneuvers and Adenosine increase the AV node block
• Block of 2:1 can change to, for example, 4:1 and flutter waves can be unmasked
• With a 2:1 AV block, flutter waves might not be visible
• Differential diagnosis of SVT
• RR Interval
• Atrial flutter with variable AV block can resemble atrial fibrillation
• Because the RR interval changes irregularly but is regularly irregular
• Because the RR interval in flutter is always X times the FF interval

Atrial Flutter (2:1)

• Typical Isthmus-dependent flutter
• The impulse circles counterclockwise through the isthmus
• Inverted flutter waves in the inferior leads (II, III, aVF) with a frequency of 300/min.
• Positive flutter waves in V1 (resembling a P wave)
• Conduction to the ventricles is 2:1 (or AV block is 2:1)
• Ventricular frequency 150/min.
• Irregularity of QRS (V1-V3)
• Caused by intermittently variable conduction to the ventricles 3:1
• This is a flutter with 2:1 conduction
• because a 3:1 conduction is very rare in this ECG

Atrial Flutter (2:1)

• Flutter waves can sometimes be difficult to differentiate in flutter with 2:1 conduction
• Atrial Flutter (2:1)
• Has extremely regular QRS complexes with a frequency of about 150/min.
• Other supraventricular tachycardias do not have such extreme regularity of QRS
• AVNRT and AVRT have frequencies of 170-250/min.
• Vagal maneuvers, or adenosine (slow conduction through the AV node)
• AVNRT / AVRT often revert to sinus rhythm
• Atrial Flutter (2:1) increases AV block, for example, to 3:1 and unveils flutter waves
• Sinus tachycardia slows down and P waves become visible

AVNRT and Conversion to Sinus Rhythm After Adenosine

• Initially, there is supraventricular tachycardia with a frequency of 150/min.
• There is a high suspicion that it is atrial flutter with 2:1 conduction
• However, flutter waves could not be differentiated even on a 12-lead EKG
• After administering Adenosine
• Ventricular extrasystoles occurred
• Conversion to sinus rhythm
• Adenosine slowed and terminated the micro re-entry circuit in the AV node AVNRT
• Conversion to sinus rhythm can also be induced by vagal maneuvers
• However, they have a less pronounced effect compared to adenosine

Atrial Flutter (4:1)

• Typical Isthmus-Dependent Flutter
• The impulse circulates counterclockwise through the isthmus
• Inverted flutter waves in the inferior leads (II, III, aVF) with a frequency of 260/min
• Positive flutter waves in V1 and V2 (resembling P waves)
• Conduction to the ventricles is 4:1
• Frequency of the ventricles: 65/min

Atrial Flutter (with High Degree AV Block)

• Typical Isthmus-Dependent Flutter
• The impulse circulates counterclockwise through the isthmus
• Inverted flutter waves in the inferior leads (II, III, aVF) with a frequency of 260/min
• Positive flutter waves in V1 and V2 (resembling P waves)
• Conduction to the ventricles alternates between 7:1, 8:1, and 5:1
• Such a high-degree AV block often indicates:
• Digoxin intoxication (digoxin slows conduction through the AV node)
• Beta-blocker intoxication (which can also slow conduction through the AV node)
• Hyperkalemia
• Organic (pre-existing) AV node dysfunction
• This means the patient has AV block even with sinus rhythm

Atrial Flutter (3:1)

• Typical Isthmus-dependent atrial flutter
• The impulse circulates counterclockwise through the isthmus
• Inverted flutter waves in the inferior leads (II, III, aVF) with a frequency of 300/min
• Positive flutter waves in V1
• Every 3rd flutter wave deforms the lower part of the T wave
• Ventricular conduction is 3:1
• Ventricular rate: 100/min (QRS complexes)