What is the management approach for a patient with Supraventricular Tachycardia (SVT), including vagal maneuvers, pharmacological interventions such as adenosine, calcium channel blockers (e.g. verapamil, diltiazem), and beta-blockers (e.g. metoprolol, propranolol), considering potential contraindications, side effects, and patient monitoring?

Management of Supraventricular Tachycardia (SVT)

Begin with immediate hemodynamic assessment, then proceed with vagal maneuvers in stable patients, followed by adenosine if vagal maneuvers fail, and move directly to synchronized cardioversion in any unstable patient. 1, 2

Initial Assessment and Stabilization

Determine hemodynamic stability immediately by assessing for hypotension (systolic BP <90 mmHg), altered mental status, signs of shock, chest pain, or acute heart failure. 1, 3 This single determination dictates your entire treatment pathway.

For Hemodynamically UNSTABLE Patients:

• Proceed directly to synchronized cardioversion without attempting vagal maneuvers or medications 1, 2
• Use initial biphasic energy of 50-100 J, increasing stepwise if initial shock fails 2
• Ensure adequate sedation/anesthesia when time permits 1
• Have resuscitation equipment immediately available 2

For Hemodynamically STABLE Patients:

Proceed through the following algorithmic sequence:

Step 1: Vagal Maneuvers (First-Line)

Vagal maneuvers terminate approximately 25-28% of SVT episodes and should always be attempted first in stable patients. 1, 3

Modified Valsalva Maneuver (Most Effective):

• Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mmHg pressure) while supine 1
• Immediately after bearing down, lay patient flat with legs elevated 2
• This modified technique has significantly higher success rates than standard carotid massage 2

Alternative Vagal Techniques:

• Carotid sinus massage: Apply steady pressure over right or left carotid sinus for 5-10 seconds after confirming absence of bruit by auscultation 1
• Diving reflex: Apply ice-cold, wet towel to face 1
• Never apply pressure to the eyeball - this is dangerous and abandoned 1

Common Pitfall: Switching between vagal techniques increases overall success to 27.7% when one method fails. 1

Step 2: Adenosine (Second-Line)

If vagal maneuvers fail, adenosine is 90-95% effective for terminating AVNRT and orthodromic AVRT. 1, 2, 3

Dosing Protocol:

• Initial dose: 6 mg rapid IV push through large peripheral vein (antecubital preferred), followed immediately by 20 mL saline flush 1, 2
• Second dose: 12 mg rapid IV push if rhythm does not convert within 1-2 minutes 1
• Reduced initial dose of 3 mg for patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 1, 2
• Larger doses may be required for patients with significant blood levels of theophylline, caffeine, or theobromine 1, 2

Critical Safety Requirements:

• Have defibrillator immediately available when administering adenosine 1, 2
• Adenosine is absolutely contraindicated in asthma patients due to risk of severe bronchoconstriction 1, 2
• Safe and effective in pregnancy 1

Expected Side Effects (Common but Transient):

• Flushing, dyspnea, and chest discomfort occur in approximately 30% of patients 1, 3
• All side effects are brief due to adenosine's extremely short half-life 1

Diagnostic Value:

• Adenosine will unmask atrial activity in atrial flutter or atrial tachycardia even when it doesn't terminate the rhythm 1
• This diagnostic information guides subsequent therapy 1

Step 3: Longer-Acting AV Nodal Blockers (Third-Line)

If adenosine fails or SVT recurs, or if adenosine unmasks atrial flutter/fibrillation requiring rate control, use calcium channel blockers or beta-blockers. 1

Intravenous Diltiazem (Preferred):

Diltiazem is more effective than beta-blockers for terminating SVT, with 80-98% success rates. 1, 4

Dosing:

• Initial bolus: 0.25 mg/kg IV (typically 20 mg for average adult) 4
• Second bolus: 0.25 mg/kg IV after 5 minutes if first dose ineffective 4
• In one study, 13 of 28 patients required the second bolus after the first failed, but ultimately all responded 4

Absolute Contraindications (FDA Label):

• Sick sinus syndrome (unless functioning ventricular pacemaker present) 5
• Second- or third-degree AV block (unless functioning ventricular pacemaker present) 5
• Severe hypotension or cardiogenic shock 5
• Atrial fibrillation/flutter with accessory bypass tract (WPW syndrome, short PR syndrome) - can cause life-threatening increase in heart rate 5
• Ventricular tachycardia or wide-complex tachycardia (QRS ≥0.12 seconds) - can cause hemodynamic deterioration and ventricular fibrillation 5
• Systolic heart failure 1
• Do not administer with IV beta-blockers together or within a few hours 5

Warnings and Monitoring:

• May cause symptomatic hypotension in 3.2% of patients 5
• Can prolong AV nodal conduction, rarely causing high-degree AV block 5
• Transient ventricular premature beats may occur on conversion (benign, no clinical significance) 5
• Use with extreme caution in patients with impaired ventricular function 5

Drug Interactions (Critical):

• Increases simvastatin levels 5-9 fold - limit simvastatin to 10 mg daily if coadministration required 5
• Increases lovastatin levels 3-4 fold 5
• Increases cyclosporine levels - may require 15-48% cyclosporine dose reduction 5
• Increases carbamazepine levels 40-72%, potentially causing toxicity 5
• Cimetidine increases diltiazem levels 58% 5
• Monitor for excessive bradycardia when combined with digoxin 5
• Avoid with clonidine - can cause severe bradycardia requiring pacemaker 5

Intravenous Verapamil:

Verapamil has similar efficacy to diltiazem (80-98% success) but was compared less favorably to adenosine in some studies. 1, 6

Dosing:

• Standard IV dosing per institutional protocol 1
• Success rate 88% in out-of-hospital setting 6

Contraindications (Same as Diltiazem):

• Identical contraindication profile to diltiazem: avoid in VT, pre-excited AF, systolic heart failure, wide-complex tachycardia of uncertain etiology 1
• Risk of hemodynamic collapse and ventricular fibrillation in these populations 1

Intravenous Beta-Blockers:

Beta-blockers have limited evidence for terminating AVNRT but possess excellent safety profiles. 1

Specific Agents:

• Esmolol: Poor efficacy at 0.5 mg/kg dosing (only 25% success rate vs 100% for diltiazem) 4
• Metoprolol: Reasonable option but less effective than diltiazem 1, 7
• Propranolol: Can be used but evidence limited 1

Key Consideration:

• Diltiazem was significantly more effective than esmolol in head-to-head comparison (100% vs 25% success) 4
• Use beta-blockers when calcium channel blockers contraindicated or in patients where beta-blockade provides additional benefit 1

Step 4: Synchronized Cardioversion (When Pharmacotherapy Fails)

Synchronized cardioversion is highly effective (near 100%) for terminating SVT when medications fail or are contraindicated in stable patients. 1

• Most stable patients respond to pharmacotherapy (80-98% success), but rare resistant cases require cardioversion 1
• Ensure adequate sedation in stable patients 1

Special Populations and Situations

Pre-Excited Atrial Fibrillation (WPW Syndrome):

Never use AV nodal blocking agents (adenosine, diltiazem, verapamil, beta-blockers, digoxin) in patients with atrial fibrillation/flutter and accessory pathways. 3, 5

• These agents can enhance conduction over the accessory pathway, causing life-threatening ventricular rates and ventricular fibrillation 3, 5
• Use IV procainamide or ibutilide instead for stable patients 3
• Use immediate cardioversion for unstable patients 3

Automatic Tachycardias (Ectopic Atrial Tachycardia, Multifocal Atrial Tachycardia, Junctional Tachycardia):

These arrhythmias are NOT responsive to cardioversion and require rate control with AV nodal blocking agents. 1, 2

• Onset and termination are gradual (not abrupt like reentrant rhythms) 1
• Focus on controlling ventricular rate rather than rhythm conversion 1

Recurrent SVT After Conversion:

Monitor for recurrence and treat with longer-acting AV nodal blocking agents. 1

• Recurrence rates similar between adenosine (23 patients) and verapamil (15 patients) requiring additional therapy 6
• Transition to oral beta-blockers, diltiazem, or verapamil for ongoing management 1

Ongoing/Long-Term Management

Oral Pharmacotherapy:

For patients declining or not candidates for catheter ablation, oral verapamil or diltiazem are first-line for ongoing management. 1

First-Line Agents:

• Oral beta-blockers, diltiazem, or verapamil for patients without ventricular pre-excitation 1
• Well-tolerated and effective alternatives to ablation 1
• Monitor for bradyarrhythmias and hypotension when initiating 1
• Avoid in systolic heart failure 1

Second-Line Agents (Patients Without Structural Heart Disease):

• Flecainide or propafenone for patients without structural or ischemic heart disease 1, 7
• Class Ic antiarrhythmics effective but require absence of structural disease 1

Third-Line Agents (When Others Ineffective/Contraindicated):

• Sotalol may be reasonable 1
• Dofetilide may be reasonable 1
• Amiodarone may be considered (last resort due to toxicity profile) 1
• Digoxin may be reasonable in patients without pre-excitation 1

All Class III antiarrhythmics should be administered in consultation with a cardiologist due to potential proarrhythmic risks. 7

Catheter Ablation (Definitive Treatment):

Catheter ablation has 94.3-98.5% success rates with <5% recurrence and <1% risk of inadvertent heart block. 3, 7

• Preferred treatment for symptomatic patients, especially those with WPW syndrome 3, 7
• Most effective therapy to prevent recurrent SVT 3
• Consider for all patients with recurrent symptomatic episodes 1

Patient Education:

Teach all patients how to perform vagal maneuvers for self-management of future episodes. 1

Critical Safety Summary

Never Use AV Nodal Blockers When:

• Wide-complex tachycardia of uncertain etiology 1, 5
• Known or suspected accessory pathway with atrial fibrillation/flutter 3, 5
• Ventricular tachycardia 5
• Systolic heart failure 1
• Severe hypotension or cardiogenic shock 5
• High-degree AV block without pacemaker 5

Always Have Available:

• Defibrillator when administering adenosine or other antiarrhythmics 1, 2, 5
• Resuscitation equipment and monitoring capabilities 5

Rhythm Misidentification:

• Remains a common issue in clinical practice - ensure accurate diagnosis before administering AV nodal blockers 6
• When in doubt, treat as wide-complex tachycardia (assume VT) until proven otherwise 5