| Atrial tachyarrhythmias |
| Primary atrial tachycardias |
| Atrial ectopic tachycardia (AET)* | - AET and FAT together account for approximately 15% of pediatric SVT
- Usually idiopathic but can be associated with underlying cardiac or pulmonary disease
- Can occur at any age
- Emanates from a single atrial focus
- Often incessant
- P waves are discrete with non-sinus appearance
- PR interval is inappropriately long relative to the atrial rate
- Variable rate, influenced by the autonomic nervous system
- Mechanism: Enhanced automaticity
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| Focal atrial tachycardia (FAT)* | - FAT and AET together account for approximately 15% of pediatric SVT
- Usually idiopathic but can be associated with underlying cardiac or pulmonary disease
- Can occur at any age
- Emanates from a single atrial focus
- Paroxysmal, starting and stopping abruptly
- PR interval is inappropriately long relative to the atrial rate
- Rate is usually relatively constant within a given paroxysm
- Mechanism: Microreentry or triggered activity
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| Sinoatrial node reentry tachycardia (SANRT) | - A subtype of FAT
- Emanates from a single focus in the head of the sinoatrial node
- Paroxysmal, starting and stopping abruptly
- P waves are identical to sinus P waves
- PR interval is inappropriately long relative to the atrial rate
- Rate is usually relatively constant within a given paroxysm
- Mechanism: Reentry
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| Chaotic (or multifocal) atrial tachycardia (CAT) | - Uncommon arrhythmia in children; usually occurs as a transient disorder during infancy
- Can be associated with underlying structural heart disease, channelopathy, or RASopathy
- Emanates from a multiple atrial foci; however, cases involving a single focus have been described
- Can be paroxysmal or persistent
- P wave morphology is variable (with at least 3 non-sinus P wave morphologies)
- Characterized by irregular P-P, P-R, and R-R intervals
- Mechanism: Likely triggered activity
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| Atrial fibrillation | - Uncommon in children
- Typically emanates from pulmonary vein foci, but can arise from other sites
- Can be paroxysmal or persistent
- Atrial reentry wavelets appear on ECG as a low-amplitude irregular baseline with a variable R-R interval
- Mechanism: Reentry and triggered activity
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| Atrial flutter |
| Typical atrial flutter | - In children, atrial flutter most commonly occurs in patients with CHD; can also occur in the fetus and newborn
- Reentrant circuit traversing the right atrial tissue between the orifice of the inferior vena cava and the tricuspid valve annulus (ie, the cavo-tricuspid isthmus)
- Sawtooth pattern on ECG, usually with 2:1 AV conduction
- Mechanism: Macroreentry
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| Intraatrial reentrant tachycardia (IART) | - Usually follows surgery for CHD
- Appearance and behavior are similar to atrial flutter
- Associated with atrial scars following cardiac surgery
- Sometimes referred to as "atypical atrial flutter" or "incisional atrial tachycardia"
- Mechanism: Macroreentry
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| Tachyarrhythmias involving the AV junction |
| AV reentrant tachycardia (AVRT) | - The most common type of SVT in children, accounting for >80% of cases in infancy and 50 to 60% of cases in older children
- Reentrant rhythm involving an extranodal accessory pathway
- Usually paroxysmal
- Little to no variation in the RR interval
- Typical rate range is 220 to 280 bpm in infants; 180 to 240 bpm in older children
- ECG in sinus rhythm may show preexcitation (ie, WPW pattern) with characteristic delta wave, widening of the QRS, and short PR interval
- Mechanism: Macroreentry
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| AV nodal reentrant tachycardia (AVNRT) | - The second most common type of SVT in children, accounting for approximately 10 to 15% of cases
- Reentrant rhythm involving pathways within the AV node
- Usually paroxysmal
- ECG during SVT generally appears similar to that of AVRT; however, if P waves are visible, the RP interval is typically shorter than AVRT (ie, <100 msec); if P waves are not visible, they are usually buried in the QRS complex, which is more typical of AVNRT
- ECG in sinus rhythm is typically normal (ie, no preexcitation)
- Mechanism: Reentry
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| Permanent junctional reciprocating tachycardia (PJRT) | - A variant of orthodromic AVRT in which retrograde conduction in the accessory pathway is slow
- Typically persistent or paroxysmal and frequently recurrent (unlike AVRT, which is usually sporadically paroxysmal); thus, patients more often present with signs of heart failure
- Mechanism: Macroreentry
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| Junctional ectopic tachycardia | - Uncommon arrhythmia; usually occurs in patients with CHD immediately following surgery, though it can occur as a congenital arrhythmia
- Focal ectopic arrythmia arising from the AV node or bundle of His
- Mechanism: Enhanced automaticity
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