What is the appropriate acute management for a hemodynamically stable patient who had supraventricular tachycardia that degenerated into atrial fibrillation, self‑terminated to sinus rhythm but remains tachycardic with a heart rate in the high 120 beats per minute?

Management of Post-Conversion Tachycardia Following SVT-to-AFib Episode

For a hemodynamically stable patient who self-converted from atrial fibrillation back to sinus rhythm but remains tachycardic at 120+ bpm, initiate rate control with intravenous diltiazem 15–20 mg over 2 minutes or intravenous metoprolol 2.5–5 mg every 2–5 minutes (maximum 15 mg), while monitoring for recurrent arrhythmia and addressing any underlying precipitants such as volume depletion, infection, or sympathetic surge. 1

Immediate Assessment and Monitoring

• Confirm hemodynamic stability by assessing blood pressure, mental status, presence of chest pain, and signs of acute heart failure; if any instability exists, proceed directly to synchronized cardioversion rather than pharmacologic therapy. 1, 2

• Obtain a 12-lead ECG to document sinus rhythm, measure QTc interval, and exclude ongoing atrial fibrillation or flutter with rapid ventricular response. 1

• Institute continuous cardiac monitoring because patients who recently converted from atrial fibrillation commonly experience premature atrial or ventricular complexes that can trigger recurrent SVT or re-entry into atrial fibrillation. 1

Rate Control Strategy

First-Line: Intravenous Calcium-Channel Blocker

• Intravenous diltiazem is the preferred agent for rate control in this clinical scenario, dosed at 15–20 mg (approximately 0.25 mg/kg) administered over 2 minutes, with clinical effect typically observed within 3–7 minutes and heart rate reduction maintained for 1–3 hours after bolus dosing. 1, 3

• Diltiazem achieves at least 20% heart rate reduction in 95% of patients with atrial fibrillation or flutter, and is equally effective for controlling ventricular response in patients who have recently converted to sinus rhythm but remain tachycardic. 3

• Administer the diltiazem infusion slowly (over up to 20 minutes rather than 2 minutes) if there is any concern about blood pressure stability, as hypotension occurs in approximately 3.2% of patients and may persist for 1–3 hours. 1, 3

Alternative: Intravenous Beta-Blocker

• Intravenous metoprolol is a reasonable alternative when calcium-channel blockers are relatively contraindicated or not preferred, dosed at 2.5–5 mg IV every 2–5 minutes with a maximum cumulative dose of 15 mg over 10–15 minutes. 1

• Intravenous esmolol is particularly useful when concurrent hypertension is present or when short-acting rate control is desired due to its ultra-short half-life. 1

• Beta-blockers have an excellent safety profile but are slightly less effective than calcium-channel blockers for acute rate control in supraventricular arrhythmias. 1

Critical Safety Contraindications

• Do NOT administer calcium-channel blockers if any of the following are present: (1) suspected systolic heart failure or acute HFrEF, (2) hemodynamic instability, (3) pre-excited atrial fibrillation (Wolff-Parkinson-White pattern), or (4) inability to exclude ventricular tachycardia as the underlying rhythm. 1, 2

• Do NOT combine intravenous calcium-channel blockers with intravenous beta-blockers due to synergistic negative inotropic effects and risk of severe hypotension and bradycardia. 1

Addressing Underlying Precipitants

• Persistent sinus tachycardia at 120+ bpm after conversion suggests an ongoing physiologic stressor such as hypovolemia, sepsis, pain, anxiety, hyperthyroidism, or sympathetic surge from the recent arrhythmia episode itself. 4

• Correct volume status with intravenous fluids if the patient is hypovolemic, as dehydration is a common precipitant of both SVT and atrial fibrillation and may explain persistent tachycardia after rhythm conversion. 3

• Screen for infection, pulmonary embolism, and acute coronary syndrome if clinical context suggests these diagnoses, as they are common triggers for both supraventricular arrhythmias and persistent sinus tachycardia. 4

• Consider thyroid function testing if the patient has risk factors for hyperthyroidism, which causes atrial fibrillation in 5–15% of cases and is associated with persistent tachycardia even after rhythm conversion. 4

Monitoring for Recurrence

• Early recurrence of SVT or atrial fibrillation is common in the first hours after conversion, particularly in patients with frequent premature complexes, and may require administration of a longer-acting AV-nodal blocker for prophylaxis. 1

• If the patient re-enters atrial fibrillation or SVT, treat the recurrent episode with adenosine (if SVT) or consider a longer-acting AV-nodal blocker such as oral diltiazem or a beta-blocker for ongoing rhythm control. 1

• Spontaneous conversion of atrial fibrillation to sinus rhythm occurs in approximately 17% of patients within 3 hours of emergency department presentation, and is most likely in patients with first-onset AF, episode duration <24 hours, lower body mass index, and normal left atrial size. 5

Anticoagulation Considerations

• For patients who develop transient atrial fibrillation as a complication of acute illness and who do not have a prior history of AF, the need for anticoagulation and its duration should be based on the patient's CHA₂DS₂-VASc score rather than the single episode of arrhythmia. 4

• Dual antiplatelet therapy alone may be considered for patients with a low CHA₂DS₂-VASc score, with reconsideration of anticoagulation indications over time as the clinical picture evolves. 4

Common Pitfalls to Avoid

• Do not assume the tachycardia is purely "sinus" without ECG confirmation, as atrial flutter with 2:1 conduction can present with a ventricular rate of 120–150 bpm and may be mistaken for sinus tachycardia. 1

• Do not delay rate control while searching for an underlying cause if the patient remains symptomatic with palpitations, dyspnea, or chest discomfort, as pharmacologic rate reduction provides immediate symptomatic relief. 3

• Do not discharge the patient without cardiology follow-up, as all patients treated for SVT or atrial fibrillation should be referred for heart rhythm specialist evaluation to discuss long-term management options including catheter ablation. 6