Immediate Synchronized Cardioversion for Hemodynamically Unstable AVNRT
Perform immediate synchronized cardioversion for hemodynamically unstable AVNRT—this is a Class I recommendation with the highest priority when the patient shows signs of hemodynamic compromise. 1, 2
Treatment Algorithm for Hemodynamically Unstable AVNRT
First-Line: Immediate Cardioversion
- Synchronized cardioversion should be performed immediately as the definitive treatment when a patient with AVNRT demonstrates hemodynamic instability 1
- This intervention takes precedence over all pharmacological approaches in the unstable patient 2
- Cardioversion must be performed promptly to restore sinus rhythm and prevent potential deterioration to more dangerous rhythms 2
When Cardioversion May Be Briefly Delayed
If the patient is not yet critically unstable and you have seconds to attempt rapid interventions:
- Vagal maneuvers can be attempted first if immediately feasible and the patient remains conscious, but do not delay cardioversion if the patient is truly unstable 1
- Adenosine IV may be considered if immediately available and can be administered within seconds, but again, do not delay cardioversion for drug preparation if the patient is deteriorating 1
Critical caveat: The guidelines explicitly state that cardioversion should be performed "when adenosine and vagal maneuvers do not terminate the tachycardia or are not feasible"—the key phrase being "not feasible" in the unstable patient 1
What Defines Hemodynamic Instability
Look for these specific signs that mandate immediate cardioversion 2:
- Hypotension with altered mental status
- Signs of shock (cool extremities, delayed capillary refill)
- Acute heart failure or pulmonary edema
- Ongoing chest pain suggesting ischemia
- Syncope or near-syncope
Critical Pitfalls to Avoid
Do NOT Use These Medications in Unstable Patients
- Avoid IV calcium channel blockers (verapamil, diltiazem) in hemodynamically unstable patients—these are only reasonable for stable patients 1
- Avoid IV beta blockers in unstable patients—again, these are only for stable patients 1
- These medications can worsen hypotension and cause further hemodynamic deterioration in unstable patients 2
Ensure Correct Rhythm Diagnosis
- Confirm the rhythm is truly AVNRT before considering any AV nodal blocking agents, as these drugs can be catastrophic in ventricular tachycardia or pre-excited atrial fibrillation 2
- In the unstable patient where rhythm diagnosis is uncertain, synchronized cardioversion remains safe and appropriate for any wide or narrow complex tachycardia 1
Post-Cardioversion Management
- Monitor closely for immediate recurrence of tachycardia after successful cardioversion 2
- Consider prophylactic antiarrhythmic therapy to prevent reinitiation if multiple cardioversion attempts are needed 2
- Once stabilized, the patient should be evaluated for definitive management with catheter ablation 1
Evidence Strength
The recommendation for immediate cardioversion in hemodynamically unstable AVNRT carries a Class I, Level of Evidence B-NR designation from the 2015 ACC/AHA/HRS guidelines, representing the strongest possible recommendation 1. This means there is uniform consensus that cardioversion is beneficial, useful, and effective, with evidence derived from well-designed non-randomized studies and clinical experience 1.