Paroxysmal Supraventricular Tachycardias¶
Chapter 256 | Part 6: Disorders of the Cardiovascular System
KEY CLINICAL POINTS¶
- AVNRT (atrioventricular nodal reentry tachycardia) is the most common PSVT, accounting for ~60% of cases.
- Accessory pathways (APs) cause preexcited tachycardias (e.g., WPW syndrome) with delta waves and wide QRS complexes.
- Catheter ablation is curative in >95% of patients with recurrent or severe PSVT.
- Adenosine is first-line for acute management of narrow QRS PSVT, with success rates >90%.
- Preexcited AF with APs <250 ms R-R intervals carries high risk of ventricular fibrillation and sudden death.
1. DEFINITION & OVERVIEW¶
Paroxysmal supraventricular tachycardias (PSVT) are rapid, regular tachycardias originating above the ventricles. Includes AV nodal reentry tachycardia (AVNRT), AV reciprocating tachycardia (AVRT), and preexcited tachycardias via accessory pathways (APs). PSVT is characterized by sudden onset, often terminating with vagal maneuvers or AV nodal blockers.
Classification of PSVT¶
| Type | Mechanism | ECG Features |
|---|---|---|
| AVNRT | Reentry through AV node and perinodal tissue | Narrow QRS, retrograde P waves |
| AVRT | Reentry via accessory pathway | Narrow or wide QRS with delta waves |
| Preexcited Tachycardia | Antegrade conduction over AP | Wide QRS with delta waves |
1.1 Classification¶
PSVT is classified into AV nodal-dependent (AVNRT, orthodromic AVRT) and AV node-independent (preexcited tachycardias via APs). Preexcited tachycardias include WPW syndrome and junctional reciprocating tachycardia.
1.2 ECG Features¶
Narrow QRS complex (AVNRT/AVRT) or wide QRS with delta waves (preexcited tachycardias). P waves may be buried in QRS or appear after it (retrograde P waves).
2. EPIDEMIOLOGY¶
AVNRT is most common in adults (60% of catheter ablation cases), more prevalent in women. WPW syndrome occurs in 1 in 1500–2000 individuals. Preexcited AF with APs <250 ms R-R intervals occurs in ~25% of APs.
2.1 Risk Factors¶
Family history of arrhythmias, congenital heart disease (Ebstein’s anomaly, hypertrophic cardiomyopathy), and prior catheter ablation.
2.2 Demographics¶
AVNRT peaks in 2nd–4th decades, more common in women. WPW is rare in adults but frequent in children (especially post-surgery for congenital heart disease).
3. ETIOLOGY & PATHOPHYSIOLOGY¶
AVNRT: Reentry through AV node and perinodal tissue. AVRT: Reentry via accessory pathway (orthodromic or antidromic). Preexcited tachycardias: Antegrade conduction over APs causes preexcitation with delta waves. WPW syndrome: Preexcitation due to APs with variable conduction properties.
Accessory Pathway Locations and ECG Features¶
| Location | ECG Features | Associated Conditions |
|---|---|---|
| Anteroseptal | Short P-R interval, delta waves | WPW syndrome |
| Posteroseptal | Negative P waves in leads II, III, aVF | WPW syndrome |
| Left Free Wall | Negative delta waves in aVL | WPW syndrome |
3.1 AVNRT Mechanism¶
Reentry through slow AV nodal pathway (right inferior extension) and fast pathway (top of AV node). P waves are inscribed during or after QRS.
4. CLINICAL FEATURES¶
Symptoms include palpitations, chest discomfort, syncope, and dyspnea. Physical exam may reveal tachycardia, elevated JVP, and cannon A waves. Complications include tachycardia-induced cardiomyopathy and sudden cardiac death in preexcited AF.
4.1 Presentation¶
Sudden onset of rapid, regular tachycardia (150–250 bpm). May be associated with syncope, angina, or pulmonary edema in elderly.
4.2 Complications¶
Tachycardia-induced cardiomyopathy, sudden cardiac death (especially in preexcited AF with APs <250 ms R-R intervals).
5. DIFFERENTIAL DIAGNOSIS¶
Atrial flutter, atrial fibrillation, sinus tachycardia, ventricular tachycardia, and junctional ectopic tachycardia (JET). Preexcited AF must be differentiated from ventricular tachycardia.
5.1 Key Differentiators¶
Delta waves in preexcited tachycardias vs. normal QRS in ventricular tachycardia. Retrograde P waves in AVNRT vs. absent P waves in ventricular tachycardia.
6. INVESTIGATIONS & DIAGNOSIS¶
12-lead ECG is essential for diagnosis. Holter monitoring for intermittent episodes. Electrophysiology study for complex cases. Criteria: Narrow QRS (AVNRT/AVRT) vs. wide QRS with delta waves (preexcited tachycardia).
ECG Findings in PSVT¶
| Tachycardia Type | QRS Width | P Wave Morphology | Delta Waves |
|---|---|---|---|
| AVNRT | Narrow | Retrograde | Absent |
| AVRT | Narrow or Wide | Retrograde | Present in preexcited cases |
| Preexcited Tachycardia | Wide | Retrograde | Present |
6.1 Diagnostic Criteria¶
Narrow QRS tachycardia with retrograde P waves (AVNRT). Wide QRS with delta waves (preexcited tachycardia).
6.2 Imaging¶
Echocardiogram to exclude structural heart disease (e.g., Ebstein’s anomaly, hypertrophic cardiomyopathy).
7. MANAGEMENT & TREATMENT¶
Acute management: Adenosine (6–12 mg IV), vagal maneuvers (Valsalva, carotid sinus). Chronic therapy: Beta-blockers, calcium channel blockers, or flecainide. Catheter ablation is curative for recurrent cases. Avoid AV nodal blockers in preexcited AF.
Acute Management Algorithm for PSVT¶
| Step | Action | Indication |
|---|---|---|
| 1 | Adenosine (6–12 mg IV) | Narrow QRS PSVT |
| 2 | Vagal maneuvers | Attempt to terminate tachycardia |
| 3 | Cardioversion | Unstable patient (hypotension, syncope) |
| 4 | Avoid AV nodal blockers | Preexcited AF with APs |
7.1 Acute Treatment Algorithm¶
- Adenosine (6 mg IV) for narrow QRS PSVT. 2. Vagal maneuvers if ineffective. 3. Cardioversion for unstable patients. 4. Avoid AV nodal blockers in preexcited AF.
7.2 Chronic Therapy¶
Beta-blockers (e.g., metoprolol), calcium channel blockers (diltiazem, verapamil), or flecainide for prophylaxis. Catheter ablation for recurrent episodes.
8. PROGNOSIS & COMPLICATIONS¶
AVNRT is generally benign but may cause symptoms. Preexcited AF with APs <250 ms R-R intervals has 2 per 1000 patient-year risk of sudden death. Tachycardia-induced cardiomyopathy may occur with prolonged episodes.
8.1 Complications¶
Sudden cardiac death in preexcited AF, tachycardia-induced cardiomyopathy, and AV block after ablation.
8.2 Long-Term Outcomes¶
Catheter ablation is curative in >95% of cases. Mortality is low for AVNRT but higher in preexcited AF with high-risk APs.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid AV nodal blockers; consider ablation. Pediatrics: JET is common in children post-congenital heart surgery. Elderly: Monitor for hemodynamic instability. WPW in children has higher sudden death risk (~2 per 1000 patient-years).
9.1 Pregnancy¶
Avoid AV nodal blockers; use beta-blockers cautiously. Consider ablation if symptoms persist.
9.2 Pediatrics¶
JET is common in children post-congenital heart surgery. Preexcited AF with APs <250 ms R-R intervals has higher sudden death risk.
10. KEY POINTS & CLINICAL PEARLS¶
- Adenosine is first-line for narrow QRS PSVT. 2. Catheter ablation is curative for AVNRT and preexcited tachycardias. 3. Avoid AV nodal blockers in preexcited AF. 4. Preexcited AF with APs <250 ms R-R intervals has high sudden death risk. 5. JET is common in children post-congenital heart surgery.