For a patient with supraventricular tachycardia (SVT) and stable blood pressure, do you give adenosine or diltiazem?

Adenosine for Hemodynamically Stable SVT

Give adenosine first for this hemodynamically stable patient with regular narrow-complex SVT. While this patient has mild chest pain, she maintains a stable blood pressure (138/90) and does not meet criteria for hemodynamic instability requiring immediate cardioversion.

Treatment Algorithm for Stable SVT

First-Line: Adenosine

• Adenosine is the preferred initial pharmacologic agent for acute termination of regular narrow-complex SVT in hemodynamically stable patients, with success rates of approximately 90-95% 1, 2
• The 2015 ACC/AHA/HRS guidelines recommend adenosine be considered first when the tachycardia is regular and has a narrow QRS complex 1
• Adenosine works rapidly with median time to conversion of 3 minutes 3
• Should be preceded by vagal maneuvers (Valsalva maneuver preferred), which have a 27.7% success rate 2

Second-Line: Diltiazem

• Diltiazem is highly effective as rescue therapy if adenosine fails, with conversion rates of 64-98% 1, 2
• Diltiazem receives a Class IIa recommendation (can be effective) for hemodynamically stable SVT, compared to adenosine's implicit first-line status 1
• In one study, diltiazem successfully rescued 35% of cases that failed adenosine monotherapy 3
• Dosing: 0.25 mg/kg IV bolus over 2 minutes; if first bolus fails, a second bolus often succeeds 2, 4, 5
• Median time to conversion is 6 minutes, slightly longer than adenosine 3

Why Adenosine First in This Case

The presence of mild chest pain does NOT constitute hemodynamic instability. The ACLS guidelines define hemodynamic instability as hypotension, acutely altered mental status, signs of shock, or acute heart failure symptoms 1. This patient's BP of 138/90 indicates she is hemodynamically stable.

Recent Comparative Evidence

A 2025 multicenter study showed similar conversion rates between adenosine (66.8%) and diltiazem (82.4%), though the difference was not statistically significant (p=0.08) 3. However, this does not override guideline recommendations that prioritize adenosine as first-line therapy.

Critical Safety Considerations

Contraindications to Diltiazem

• Must exclude pre-excited atrial fibrillation/flutter (Wolff-Parkinson-White syndrome) before giving diltiazem, as it can cause hemodynamic collapse and ventricular fibrillation 1, 2
• Avoid in systolic heart failure or suspected ventricular dysfunction 1, 2
• Contraindicated in AV block greater than first degree, SA node dysfunction without pacemaker, hypotension, decompensated heart failure, and cardiogenic shock 2, 6

Adenosine Safety Profile

• Safer initial choice when SVT mechanism is uncertain 1
• Ultra-short half-life (seconds) limits duration of adverse effects
• Can be used diagnostically to help differentiate SVT from other wide-complex tachycardias

Common Pitfalls to Avoid

1. Do not give diltiazem first without ensuring the rhythm is not pre-excited AF - this is the most dangerous error, as calcium channel blockers can precipitate ventricular fibrillation in WPW with AF 1, 2
2. Do not mistake mild chest pain for hemodynamic instability - chest pain alone with stable vital signs does not warrant immediate cardioversion 1
3. If adenosine fails, diltiazem is an excellent rescue agent - approximately 77% of adenosine failures respond to diltiazem 3
4. Slow infusion of diltiazem (over 2 minutes) reduces hypotension risk compared to rapid bolus 2, 5, 7