What is the best approach to manage a patient with supraventricular tachycardia (SVT), considering potential underlying medical conditions such as heart disease, asthma, or chronic obstructive pulmonary disease (COPD)?

Approach to a Patient with SVT

Immediate Hemodynamic Assessment

Begin by immediately assessing hemodynamic stability—if the patient is unstable (hypotensive, altered mental status, chest pain, acute heart failure), proceed directly to synchronized cardioversion without attempting vagal maneuvers or medications. 1, 2

• Unstable patients require immediate synchronized cardioversion at 50-100 J (biphasic), with stepwise increases if initial shock fails 2
• Cardioversion equipment must be immediately available even when treating stable patients, as adenosine can precipitate atrial fibrillation with rapid ventricular response 1

Management of Hemodynamically Stable SVT

Step 1: Vagal Maneuvers (First-Line)

For stable patients, initiate treatment with the modified Valsalva maneuver, which has significantly higher success rates than standard carotid sinus massage. 1, 2, 3

• Modified Valsalva technique: Patient bears down against closed glottis for 10-30 seconds (generating 30-40 mmHg pressure) while supine, then immediately lies flat with legs elevated 1, 2
• The modified Valsalva maneuver achieved 5.47 times higher conversion rates compared to carotid sinus massage in network meta-analysis 3
• Alternative vagal maneuvers include carotid sinus massage (after confirming absence of bruit) for 5-10 seconds, or applying ice-cold wet towel to face 1
• Switching between techniques if first attempt fails increases overall success to 27.7% 1

Step 2: Adenosine (Second-Line)

If vagal maneuvers fail, administer adenosine 6 mg as rapid IV push through a large peripheral vein, followed immediately by 20 mL saline flush. 1, 2

• Adenosine terminates AVNRT and orthodromic AVRT in 90-95% of cases 1, 2
• If 6 mg fails, give 12 mg, then another 12 mg if needed 2
• Critical dosing adjustments: Reduce to 3 mg in patients taking dipyridamole, carbamazepine, or with transplanted hearts; larger doses needed with theophylline or caffeine 2

Step 3: Synchronized Cardioversion (Third-Line)

If adenosine fails or is contraindicated, proceed to synchronized cardioversion after adequate sedation in stable patients. 1, 2

Special Population Considerations

Patients with Asthma or COPD

Adenosine is absolutely contraindicated in asthma patients due to risk of severe, potentially fatal bronchospasm. 2, 4

• Severe bronchospasm can occur even in patients without known pulmonary disease 4
• For patients with severe bronchospastic disease, avoid adenosine entirely and proceed directly to synchronized cardioversion if vagal maneuvers fail 2
• Beta-blockers should be avoided in acute decompensated pulmonary disease, though metoprolol has been used cautiously after correction of hypoxia 1

Patients with Heart Disease

In patients with structural heart disease, heart failure, or low ejection fraction, avoid verapamil and diltiazem due to risk of hemodynamic collapse. 2

• These patients have 13-26% risk of proarrhythmic events with certain antiarrhythmics 5
• Synchronized cardioversion should be considered earlier in the treatment algorithm for patients with significant cardiac dysfunction 1

Wide-Complex Tachycardia

Never administer verapamil, diltiazem, or other AV nodal blocking agents if QRS >120 ms or pre-excitation is suspected—this can precipitate ventricular fibrillation. 1, 2

• Wide-complex tachycardia must be treated as ventricular tachycardia until proven otherwise 1
• If pre-excited atrial fibrillation is confirmed, use procainamide or ibutilide (if stable) or immediate cardioversion (if unstable) 1

Critical Safety Warnings

• Always have resuscitation equipment and defibrillator immediately available when administering adenosine 2
• Continuous ECG recording during adenosine administration helps distinguish drug failure from successful termination with immediate reinitiation 1
• Carotid massage must only be performed after confirming absence of carotid bruit by auscultation 1
• Never apply pressure to the eyeball—this technique is dangerous and abandoned 1

Documentation Requirements

• Obtain 12-lead ECG before and after treatment to confirm rhythm and document response 1
• Record rhythm strip during adenosine administration to capture diagnostic information about underlying rhythm 1