Diagnosis is Paroxysmal Supraventricular Tachycardia (SVT), Most Likely Atrioventricular Nodal Reentrant Tachycardia (AVNRT).
1. Definition
Supraventricular tachycardia (SVT) refers to tachyarrhythmias arising from or involving atrial or atrioventricular nodal tissue.
Paroxysmal SVT typically presents as a sudden-onset, regular tachycardia, usually with a narrow QRS complex <120 ms.
In this patient, the abrupt onset, regular narrow-complex tachycardia, and absent visible P waves are most consistent with AVNRT.
2. Types
Common mechanisms of paroxysmal SVT include:
1. Atrioventricular nodal reentrant tachycardia (AVNRT)
2. Atrioventricular reentrant tachycardia (AVRT) involving an accessory pathway
3. Focal atrial tachycardia
AVNRT is one of the most common forms of regular paroxysmal SVT in adults.
3. Pathophysiology
3.1 AVNRT Mechanism
1. AVNRT is caused by a reentrant circuit involving functionally distinct fast and slow AV nodal pathways
2. In typical AVNRT:
o Antegrade conduction occurs through the slow pathway
o Retrograde conduction occurs through the fast pathway
3. The atria and ventricles are activated almost simultaneously
4. Retrograde P waves are therefore often hidden within the QRS complex
5. Retrograde atrial activation may produce:
o Pseudo R' wave in lead V1
o Pseudo S waves in leads II, III, and aVF
3.2 Precipitating Factors
Episodes may occur without an identifiable trigger. Potential precipitants include:
1. Emotional or physical stress
2. Sleep deprivation
3. Stimulants
4. Certain medications, including sympathomimetic agents
Moderate caffeine intake alone does not establish the cause of SVT.
4. Clinical Features
1. Sudden onset and sudden termination of palpitations
2. Rapid, regular heartbeat
3. Lightheadedness or dizziness
4. Anxiety
5. Chest discomfort
6. Dyspnea
7. Presyncope or syncope in more severe episodes
Patients with AVNRT are often otherwise healthy between episodes.
5. Diagnostic Evaluation
5.1 ECG Findings
Typical findings during AVNRT include:
1. Regular narrow-complex tachycardia
2. QRS duration usually <120 ms
3. Heart rate commonly approximately 150 to 250 beats per minute
4. P waves absent or buried within the QRS complex
5. A short RP interval is typical
6. Pseudo R' wave in V1 or pseudo S waves in the inferior leads may be present
The ECG pattern in this patient strongly favors typical AVNRT, although orthodromic AVRT and atrial tachycardia remain part of the differential diagnosis.
5.2 Assessment of Hemodynamic Stability
Features suggesting hemodynamic instability include:
1. Hypotension
2. Acutely altered mental status
3. Signs of shock
4. Ischemic chest discomfort
5. Acute heart failure
This patient is hemodynamically stable because she is alert, has preserved blood pressure, and has no ischemic chest pain, shock, or acute heart failure.
6. Management
6.1 Hemodynamically Stable Regular Narrow-Complex Tachycardia
First step
1. Perform vagal maneuvers
2. The modified Valsalva maneuver is more effective than the standard Valsalva maneuver and is a preferred practical technique when feasible
If vagal maneuvers fail
1. Give adenosine 6 mg by rapid IV push, immediately followed by a saline flush
2. If required, give a second dose of 12 mg by rapid IV push
If adenosine is ineffective or contraindicated
1. IV diltiazem or verapamil may be used in appropriate hemodynamically stable patients
2. IV beta blockers are another option in selected patients
3. Synchronized cardioversion may be used when vagal maneuvers and pharmacologic therapy fail or are contraindicated
6.2 Hemodynamically Unstable Tachycardia
1. Perform immediate synchronized cardioversion
2. Sedation should be provided when feasible without delaying cardioversion
6.3 Important Pharmacologic Insight
1. Adenosine produces transient AV nodal blockade
2. It commonly terminates AVNRT and orthodromic AVRT because these rhythms depend on AV nodal conduction
3. Adenosine may also terminate some adenosine-sensitive atrial tachycardias
4. If it does not terminate an atrial tachycardia or atrial flutter, transient AV block may unmask the underlying atrial activity, helping establish the diagnosis
7. Definitive Treatment
Catheter ablation is the definitive treatment for symptomatic recurrent AVNRT.
For AVNRT, ablation targets the slow AV nodal pathway.
It is particularly appropriate in patients with:
1. Recurrent symptomatic episodes
2. Patient preference for definitive therapy
3. Inadequate response to or intolerance of medical therapy
Catheter ablation is highly effective and is recommended as definitive therapy for symptomatic AVNRT.
8. Complications
1. Recurrent symptomatic episodes
2. Hemodynamic instability during severe episodes
3. Syncope, uncommon
4. Tachycardia-induced cardiomyopathy, uncommon and mainly associated with frequent or incessant tachycardia
9. Key Clinical Insight
Sudden-onset, regular narrow-complex tachycardia with absent or buried P waves strongly suggests AVNRT.
In a stable patient: vagal maneuvers → adenosine → AV nodal blocking therapy if appropriate.
In an unstable patient: immediate synchronized cardioversion.
Recurrent symptomatic AVNRT can be definitively treated with catheter ablation.
References
1. Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. Circulation. 2016;133(14):e506-e574. doi:10.1161/CIR.0000000000000311.
2. Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the Management of Patients With Supraventricular Tachycardia. Eur Heart J. 2020;41(5):655-720. doi:10.1093/eurheartj/ehz467.
3. Wigginton JG, Agarwal S, Bartos JA, et al. Part 9: Adult Advanced Life Support: 2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2025;152(Suppl 2):S538-S577. doi:10.1161/CIR.0000000000001376.
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