Initial Treatment for AVNRT
Begin with vagal maneuvers immediately, followed by IV adenosine if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients. 1
Treatment Algorithm for Hemodynamically Stable Patients
First-Line: Vagal Maneuvers (Class I Recommendation)
- Perform vagal maneuvers as the immediate first-line intervention with the patient in the supine position 1
- Modified Valsalva technique: Have the patient bear down against a closed glottis for 10-30 seconds, generating at least 30-40 mm Hg of intrathoracic pressure 1
- Carotid sinus massage: After confirming absence of carotid bruit by auscultation, apply steady pressure over the right or left carotid sinus for 5-10 seconds 1
- Ice-cold wet towel to the face (diving reflex): Apply directly to the face as an alternative vagal maneuver 1
- Success rate is approximately 27.7% when switching between different vagal techniques 1
- Never apply pressure to the eyeball—this practice is dangerous and has been abandoned 1
Second-Line: IV Adenosine (Class I Recommendation)
- Administer adenosine 6 mg as a rapid IV push through a large vein, followed immediately by saline flush 1, 2
- If no response after 1-2 minutes, give a second dose of 12 mg rapid IV push 3, 2
- Adenosine terminates AVNRT in approximately 90-95% of patients 1, 4
- Have resuscitative equipment immediately available during administration, as adenosine can cause transient AV block, bronchoconstriction, and rarely cardiac arrest 2
Third-Line: IV Calcium Channel Blockers or Beta-Blockers (Class IIa Recommendation)
- IV diltiazem or verapamil are reasonable for hemodynamically stable patients with success rates of 80-98% 1, 4, 5
- IV beta-blockers (such as esmolol or metoprolol) are less effective than calcium channel blockers but have an excellent safety profile 1, 4
- Critical safety warning: Ensure the rhythm is truly AVNRT before administering calcium channel blockers or beta-blockers, as these agents can cause ventricular fibrillation or hemodynamic collapse in pre-excited atrial fibrillation or ventricular tachycardia 1, 3
- Avoid calcium channel blockers in patients with suspected systolic heart failure 1, 3
- Avoid beta-blockers in patients with severe conduction abnormalities or sinus node dysfunction 1
Fourth-Line: Synchronized Cardioversion (Class I Recommendation)
- Perform synchronized cardioversion when pharmacological therapy fails or is contraindicated in stable patients 1
- Initial energy: 50-100 joules for SVT 3
Treatment Algorithm for Hemodynamically Unstable Patients
Immediate Synchronized Cardioversion (Class I Recommendation)
- Proceed immediately to synchronized cardioversion without delay when the patient demonstrates hypotension with altered mental status, signs of shock, acute heart failure, pulmonary edema, or ongoing chest pain suggesting ischemia 1, 6
- Vagal maneuvers may be attempted first only if immediately feasible and the patient remains conscious, but do not delay cardioversion 6
- Do not administer IV calcium channel blockers or beta-blockers to hemodynamically unstable patients, as these can worsen hypotension and cause further deterioration 6
Critical Pitfalls to Avoid
- Never give verapamil, diltiazem, or adenosine to patients with pre-excited atrial fibrillation, as this can precipitate ventricular fibrillation 3
- Avoid calcium channel blockers in patients with severe conduction abnormalities, sinus node dysfunction, or acute decompensated heart failure 1
- Avoid beta-blockers in patients with severe bronchospastic pulmonary disease 1
- Do not use adenosine in patients with second- or third-degree AV block (except those with functioning pacemakers), sick sinus syndrome, or known bronchoconstrictive lung disease 2