Types of Atrial Arrhythmias
The main types of atrial arrhythmias are focal atrial tachycardia, macroreentrant atrial tachycardia (including typical and atypical atrial flutter), and atrial fibrillation, each with distinct electrophysiological mechanisms and anatomical bases. 1
Major Categories of Atrial Arrhythmias
Focal Atrial Tachycardia
- Characterized by origin of activation from a circumscribed area with centrifugal spread to both atria 1
- Mechanisms include enhanced automaticity, triggered activity, or microreentry (very small reentry circuits) 1
- Typically arises from preferential sites such as valve annuli, crista terminalis, and pulmonary veins 2
- May occur in both structurally normal hearts and in patients with structural heart disease 2
Macroreentrant Atrial Tachycardia
- Due to a reentry circuit of large size with fixed and/or functional barriers 1
- Can be entrained during atrial pacing 1
- Well-characterized subtypes include:
- Typical atrial flutter - most common form with counterclockwise rotation in the right atrium 1
- Reverse typical atrial flutter - clockwise rotation in the right atrium 1
- Lesion macroreentrant tachycardia - occurs around surgical scars 1
- Lower loop flutter 1
- Double wave reentry 1
- Right atrial free wall macroreentry without atriotomy 1
- Left atrial macroreentrant tachycardia 1
Atrial Flutter
- Classically defined as a regular tachycardia with rate ≥240 beats/min (cycle length ≤250 ms) lacking an isoelectric baseline between deflections 1
- ECG typically shows a "saw-tooth" pattern, particularly visible in leads II, III, and aVF 1
- May degenerate into atrial fibrillation or convert from atrial fibrillation 1
Atrial Fibrillation
- Most common sustained arrhythmia in clinical practice 3, 4
- Characterized by irregular, rapid electrical activity in the atria with resultant deterioration of atrial mechanical function 1
- ECG shows replacement of P waves with fibrillatory waves and completely irregular ventricular response 1
- Classified based on pattern and duration:
Less Well-Characterized Atrial Arrhythmias
- Atypical atrial flutter - ECG shows continuous undulation of atrial complex different from typical flutter patterns 1
- Type II atrial flutter - characterized by short cycle lengths producing fibrillatory conduction 1
- Inappropriate sinus tachycardia - originates along the superior aspect of the crista terminalis at rates above physiological range without relationship to metabolic demands 1
- Reentrant sinus tachycardia - can be induced and terminated by programmed stimulation with P wave morphology similar to spontaneous P waves 1
- Fibrillatory conduction - regular left atrial tachycardia with irregular conduction to the right atrium 1
Clinical Implications
- The identification of specific atrial arrhythmia mechanisms guides therapeutic approaches, particularly for ablation procedures 2
- Advances in mapping techniques (non-contact mapping system and electro-anatomical contact mapping) have enhanced the precision of diagnosis 1
- Transient entrainment studies help diagnose reentrant mechanisms as a complement to activation mapping 1
- Different arrhythmia types require different approaches to antiarrhythmic medication use 5
Common Pitfalls in Diagnosis
- Atrial flutter may be misdiagnosed as atrial fibrillation when atrial activity is prominent on ECG in more than one lead 1
- The ECG pattern may fluctuate between atrial flutter and atrial fibrillation, reflecting changing activation patterns of the atria 1
- Some atrial tachycardias cannot be well classified due to inadequate understanding of mechanisms or rhythm instability 1
- Left atrial activation sequence is not well characterized in many atrial tachycardias, limiting precise diagnosis 1