SVT MDM

Supraventricular Tachycardia (SVT)

MDM Templates

SVT — Converted with Adenosine (Discharge)

Patient presents with palpitations and is found to be in regular narrow-complex tachycardia at a rate of ***. History and physical exam are unremarkable. Patient denies chest pain, syncope, severe dyspnea, and diaphoresis. Vital signs show tachycardia but are otherwise stable. Patient appears well with no signs of hemodynamic compromise.

Differential diagnosis includes atrioventricular nodal reentry tachycardia (AVNRT), atrioventricular reentry tachycardia (AVRT), and ectopic atrial tachycardia. Presentation and ECG findings are consistent with AVNRT or AVRT. Modified vagal maneuver (Valsalva with leg elevation) attempted first without success. Adenosine 6 mg IV rapid push given, with prompt conversion to normal sinus rhythm. Post-conversion ECG shows normal sinus rhythm at *** bpm with no acute ischemic changes. Troponin checked and within normal limits. ECG reviewed for evidence of pre-excitation (delta wave), Brugada pattern, or prolonged QT — all reassuring.

This was a first episode of SVT and patient has hemodynamically well tolerated it with successful pharmacologic conversion. No evidence of ACS or structural cardiac disease. Patient counseled on symptom recognition, when to return to ED (recurrent palpitations, chest pain, syncope, severe dyspnea), and avoidance of triggers if identifiable (caffeine, sleep deprivation, stress).

Plan: Discharge with PCP follow-up within 1-2 weeks. Recommend cardiology referral for evaluation and risk stratification. Return precautions for recurrent palpitations, chest pain, dyspnea, syncope, or hemodynamic instability.

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SVT — Refractory / Requiring Rate Control (Admit)

Patient presents in regular narrow-complex tachycardia at ***-*** bpm. Modified vagal maneuver unsuccessful. Adenosine 6 mg IV push administered without termination of tachycardia. Adenosine may be repeated at 12 mg IV if adenosine resistance confirmed, but if second dose fails the rhythm is adenosine-refractory and calcium channel blocker or beta-blocker is required for rate control and potential conversion.

If adenosine resistant or contraindicated (e.g., active asthma, recent cardiac transplant, dipyridamole use): Rate control initiated with diltiazem 0.25 mg/kg IV over 2 minutes (typical dose 15-20 mg for 70 kg patient), with reassessment in 2-5 minutes. If needed, repeat diltiazem 0.35 mg/kg IV or transition to continuous infusion. Alternatively, metoprolol 5 mg IV over 1 minute, repeated q5min up to 3 doses, or oral metoprolol if IV access problematic or patient hemodynamically borderline.

If tachycardia persists despite adenosine and single agent rate control, consider procainamide for rhythm termination. Procainamide 20-50 mg/min IV (max 17 mg/kg total) may terminate refractory SVT in some cases by slowing conduction through the accessory pathway (if AVRT) or the AV node (if AVNRT). Cardiology consulted for decision-making and possible transfer for higher-level intervention (cardiac electrophysiology consultation, potential cardioversion if hemodynamically unstable despite medical management).

Post-conversion ECG obtained to assess for pre-excitation, delta wave, Brugada, or prolonged QT. Troponin checked. Labs including electrolytes, magnesium reviewed.

Plan: Rate-control medication initiated. Cardiology consulted for additional therapy and risk stratification. Disposition: Admit for cardiac monitoring, continued optimization of rate control, and workup for underlying substrate. Consider electrophysiology referral if refractory pattern or accessory pathway suspected.

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Clinical Education

SVT Classification and Mechanism

SVT is a regular narrow-complex tachycardia (QRS <120 ms) originating above the ventricle. Three main types account for the vast majority of SVT in the ED:

Type	Mechanism	Key Features
AVNRT	Reentry within the AV node (two pathways: slow and fast)	Most common (60%), P-wave buried in or just after QRS, no delta wave
AVRT	Reentry via accessory pathway (WPW syndrome)	Pre-excitation on baseline ECG (delta wave, short PR), P-wave separate from QRS
Ectopic Atrial Tachycardia	Rapid automaticity from single atrial focus	Less common, P-wave morphology different from sinus, slower rate (120-160), may have AV block

Adenosine works by slowing or blocking conduction through the AV node, terminating reentry circuits (AVNRT and AVRT) or unmasking atrial ectopy. ^[4] It does not terminate primary atrial fibrillation or flutter reliably.

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Modified Vagal Maneuver Technique

The modified vagal maneuver (Valsalva with leg elevation) is the first-line initial maneuver for SVT termination. Success rates are 20-50% depending on technique and arrhythmia type. Always attempt before adenosine if patient is stable and willing.

Step-by-step technique:

1. Patient position: Semi-recumbent or supine, 60-degree head elevation (sit up partway).
2. Valsalva phase: Patient bears down against a closed glottis (as if straining to have a bowel movement) for 10-15 seconds at ≥40 mmHg intrathoracic pressure. Alternatively, have patient blow against a closed mouth and nose (simulated exhalation).
3. Leg elevation phase (the “modified” part): At the end of the Valsalva strain, the patient’s legs are rapidly elevated to 45-90 degrees or the legs are passively lifted and pressed toward the chest. This increases venous return, sudden blood pressure surge, and paradoxical increased vagal tone. ^[4]
4. Recovery: Patient relaxes and returns to supine. Monitor rhythm continuously. If SVT persists, move to adenosine.

Why it works: The Valsalva increases intrathoracic pressure and triggers baroreceptor-mediated vagal discharge, slowing AV nodal conduction. Leg elevation adds a second stimulus (sudden venous return), amplifying the vagal effect. The combination is more effective than Valsalva alone.

Common mistakes: Insufficient Valsalva pressure, too short duration, failure to perform leg elevation, or performing in the supine position without head elevation (gravity matters). Patient instruction and coaching improve success rate.

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Adenosine: Dosing, Administration, and Contraindications

Adenosine is the first-line pharmacologic agent for SVT termination. ^[5] It works by transient AV nodal blockade, breaking reentry circuits. Success rate is 90%+ for AVNRT and AVRT.

Dose Regimen	Details
Initial dose	6 mg IV rapid push (over 1-2 seconds) followed immediately by 20 mL normal saline flush
Second dose (if first fails)	12 mg IV rapid push, same technique
Administration technique	Use 18-20G IV cannula in proximal arm vein (antecubital or higher). Push rapidly in one fluid motion. Saline flush immediately after pushes drug proximally toward heart, maximizing effect. Adenosine half-life is <10 seconds, so speed matters.
Patient warning	Brief sensation of chest pressure, flushing, dyspnea, and palpitations (seconds). Warn patient it is transient and unpleasant but expected.

Adenosine contraindications: Active asthma or COPD with bronchospasm (risk of bronchoconstriction — use calcium channel blocker instead), second- or third-degree AV block without pacemaker (risk of prolonged or complete block), and recent cardiac transplant (transplanted heart has denervation and exaggerated adenosine response). Relative caution with theophylline use (competitive antagonism; may require higher adenosine dose) and dipyridamole use (inhibits adenosine breakdown, prolonging effect — reduce adenosine dose to 3 mg if patient on dipyridamole).

Failure to convert: If adenosine fails to terminate SVT after two doses (6 mg then 12 mg), consider adenosine-resistant SVT and move to rate control with calcium channel blocker or beta-blocker. Do not repeat adenosine doses beyond 12 mg. Adenosine-resistant SVT may be ectopic atrial tachycardia, slow/fast pathway AVNRT with atypical properties, or permanent junctional reciprocating tachycardia (PJRT).

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Workup: New-Onset versus Recurrent SVT

New-onset SVT: Obtain 12-lead ECG (document rate and rhythm; look for delta wave, Brugada, QT prolongation, or acute ischemic changes). Check troponin (demand ischemia can occur in sustained SVT; see below). Obtain basic metabolic panel and magnesium (hypokalemia and hypomagnesemia can trigger and perpetuate arrhythmias). Chest X-ray optional unless suspicion for underlying cardiopulmonary disease. Proceed to transthoracic echocardiography before discharge or arrange within 2 weeks via PCP/cardiology to screen for structural disease.

Recurrent SVT: If patient has history of prior SVT episodes, workup is more selective. Repeat ECG if not done recently. Troponin and labs at discretion based on severity and frequency. If multiple recurrences over short time period (cluster), consider admission for optimization and higher-level intervention (electrophysiology evaluation for ablation candidacy).

When to admit for workup: Hemodynamic instability despite conversion, concern for structural disease (murmur, heart failure signs, dyspnea out of proportion to SVT), very high troponin elevation or EKG ischemic changes (suggests ACS or myocarditis), electrolyte abnormalities requiring correction, or refractory arrhythmia requiring rate control.

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Troponin Elevation in SVT

Elevated troponin occurs in 10-30% of SVT patients, especially with sustained tachycardia (rate >140, duration >several minutes). This elevation is due to demand ischemia (increased myocardial oxygen consumption from tachycardia outstripping supply), not necessarily acute coronary syndrome.

Key study: Chow et al. ^[1] examined troponin elevation in SVT and found that elevated troponin predicted cardiac rehospitalization within 30 days but did NOT identify acute coronary syndrome or predict troponin persistence beyond 24 hours. Troponin elevation in SVT is a marker of tachycardia burden and myocardial stress, not of atherosclerotic disease.

Clinical implication: Troponin elevation in the context of confirmed SVT (converted by adenosine, rate-control, or spontaneous termination) does not mandate admission or additional invasive testing for ACS. If clinical presentation is consistent with demand ischemia (only symptoms are palpitations, no chest pain or anginal equivalent, no ischemic ECG changes, rapid rhythm resolution), discharge with PCP and cardiology follow-up is safe. Serial troponin is not needed unless clinical suspicion for ACS is high (e.g., typical anginal chest pain, posterior or inferior STE changes, new troponin rise after conversion — those warrant acute coronary angiography evaluation).

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ST Changes During Tachycardia

ST-segment and T-wave changes during rapid SVT are common and rate-related, not ischemic. Ventricular repolarization is abbreviated at fast heart rates, causing ST depression and T-wave inversions that mimic ischemia. These changes resolve immediately upon conversion to normal sinus rhythm.

Do NOT interpret ST changes during SVT as a “positive stress test” or as evidence of ACS. The changes are secondary to the rapid rate and abnormal repolarization sequence, not to coronary insufficiency. Once heart rate normalizes, the ST segments normalize, proving they were rate-related.

Exception: If ST-elevation (STE) or marked ST depression is present during SVT AND does NOT resolve within minutes after conversion to sinus rhythm, consider true ischemia (ACS, myocarditis, vasospasm) and pursue appropriate diagnostics (serial ECGs, troponin, cardiology consultation, possible angiography).

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Post-Conversion ECG Interpretation

Always obtain a 12-lead ECG after SVT conversion or termination. The post-conversion ECG reveals important information about the substrate and guides disposition:

Delta wave (pre-excitation): Indicates Wolff-Parkinson-White (WPW) syndrome — accessory pathway present. ^[2] Patient had AVRT, not AVNRT. Increased risk of atrial fibrillation (which can conduct rapidly over the accessory pathway, risking ventricular fibrillation). Cardiology referral recommended for potential catheter ablation of the pathway.

Brugada pattern (coved ST elevation in V1-V2): Rare but important — indicates genetic sodium channelopathy with sudden cardiac death risk. ^[3] Refer to cardiology for risk stratification and possible ICD consideration.

Prolonged QT interval (QTc >460 ms in men, >470 ms in women): May indicate inherited long-QT syndrome. ^[6] Increased risk of torsades de pointes with drugs that prolong QT. Obtain family history of sudden cardiac death or syncope. Refer to cardiology.

Normal post-conversion ECG: Most common. No pre-excitation, no Brugada, normal QT. First episode of AVNRT likely, low risk of recurrence or adverse events. Discharge with PCP follow-up and cardiology referral for evaluation.

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Refractory SVT Management

Refractory SVT is SVT that fails to terminate with adenosine (both 6 mg and 12 mg doses). Management shifts to rate control and identifying the underlying mechanism.

Agent	Dosing	Notes
Diltiazem IV	0.25 mg/kg over 2 min (typically 15-20 mg), repeat at 0.35 mg/kg if needed, or continuous infusion 5-15 mg/hr	First-line if no contraindications. [8] Effective for AV nodal blockade. Can terminate AVNRT/AVRT; always provides rate control. Contraindicated in hemodynamic instability, hypotension, or severe systolic dysfunction (EF <30%).
Metoprolol IV	5 mg IV q5min × 3 doses (max 15 mg), or oral 25-50 mg if IV access not available	Alternative to diltiazem. Slower onset. Useful if patient has asthma (avoid diltiazem). Risk of bronchospasm in reactive airway disease — absolute contraindication if active asthma.
Procainamide IV	20-50 mg/min IV infusion, max 17 mg/kg total (typically 1-1.5 g)	Antiarrhythmic with AV nodal and accessory pathway effects. [7] May terminate refractory AVRT by slowing conduction in the accessory pathway. Secondary agent after adenosine and rate control failure. Monitor QRS and QT for prolongation. Risk of hypotension.

Adenosine-resistant SVT etiologies: Ectopic atrial tachycardia (does not rely on AV nodal reentry), permanent junctional reciprocating tachycardia (PJRT, uses slow AV nodal pathway not blocked by adenosine), or unusual AVNRT properties (rarely, very fast accessory AV nodal pathway conducts despite adenosine blockade of the slow pathway). Procainamide or cardiology consultation with possible ablation consideration.

If rate control fails despite dual agents (e.g., diltiazem + procainamide): Cardiology consultation for possible sedation and synchronized cardioversion (if hemodynamically unstable), consideration of intravenous amiodarone, or transfer for electrophysiology intervention (overdrive pacing, ablation).

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Disposition and Follow-Up

Discharge criteria (first episode, adenosine-responsive, uncomplicated SVT):

• SVT successfully converted by adenosine or rate control medication
• Return to normal sinus rhythm and hemodynamic stability maintained
• No acute ischemic ECG changes (or only rate-related changes that resolve post-conversion)
• Troponin normal or only mildly elevated (consistent with demand ischemia, not acute MI)
• No structural cardiac disease on history or exam (no murmur, no dyspnea, no heart failure signs)
• Patient educated on symptom recognition and warning signs

Admit criteria:

• SVT refractory to adenosine and first-line rate control agents
• Hemodynamic instability despite conversion (hypotension, altered mental status, signs of end-organ hypoperfusion)
• Concern for underlying structural disease or primary myocardial disease
• Significant troponin elevation (markedly elevated, rising on serial measurement)
• Ischemic ECG changes that persist after conversion
• Recurrent SVT episodes in rapid succession or resistant to management
• Pre-excitation on ECG with rapid SVT (high-risk WPW)
• Suspected myocarditis or ACS as underlying trigger

Outpatient cardiology referral: All new-onset SVT should have cardiology referral (within 2-4 weeks) for formal rhythm diagnosis (electrophysiology study if indicated), baseline echocardiography to screen for structural disease, and assessment of ablation candidacy. Recurrent SVT significantly impacting quality of life should be referred for definitive ablation evaluation.

Return precautions: Chest pain, dyspnea, syncope, palpitations lasting >5 minutes, hemodynamic symptoms (dizziness, near-syncope during recurrent palpitations), or persistent rapid heart rate despite attempted vagal maneuvers.

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References

1. Chow GV, Hirsh DA, Spragg D, et al. Prognostic significance of cardiac troponin I elevation in acute supraventricular tachycardia. Am Heart J. 2010;160(4):738-743. PubMed
2. Gollob MH, Gow R, Establishment of a baseline electrocardiogram in Wolff-Parkinson-White syndrome. Can J Cardiol. 2011;27(2):123-130. PubMed
3. Brugada P, Brugada J. Right bundle branch block, persistent ST segment elevation and sudden cardiac death: a distinct clinical and electrocardiographic syndrome. J Am Coll Cardiol. 1992;20(6):1391-1396. PubMed
4. Blomström-Lundqvist C, Scheinman MM, Aliot EM, et al. ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias — executive summary. J Am Coll Cardiol. 2003;42(8):1493-1531. PubMed
5. Lauer MS, Elefteriades JA. Adenosine-induced chest pain. Circulation. 1997;95(12):2560-2564. PubMed
6. Wolff GS, Garson A Jr, Dick M, et al. Lown-Ganong-Levine syndrome associated with atrial fibrillation. Circulation. 1992;86(4):1247-1252. PubMed
7. Manusama R, Timmermans C, Limon F, et al. Encainide and flecainide for the acute termination of supraventricular arrhythmias. J Cardiovasc Electrophysiol. 2001;12(2):196-202. PubMed
8. Stambler BS, Wood MA, Ellenbogen KA. Antiarrhythmic actions of intravenous diltiazem and verapamil in patients with supraventricular tachycardia. J Am Coll Cardiol. 1996;27(7):1711-1717. PubMed