PRN Education · The Curbside · Cardiology

Borderline Is Not Unstable.

In AF with RVR, shock when the rhythm is causing instability. A soft number alone is not enough.

The case

Permanent AF. Rate 135–150. BP 95/59. Comfortable. Clear lungs. No ischemic pain. No altered mentation. The pads can wait while you decide what the pressure means.

Is AF causing the crash?

Attributable is the key word

Red line · synchronize now

Instability attributable to AF

Shock or persistent hypotension with hypoperfusion
Ongoing ischemic chest discomfort
Acute heart failure or pulmonary edema
Acute altered mental status

Immediate synchronized cardioversion. Sedate when feasible. Do not delay a necessary shock for anticoagulation.

Look again · treat the physiology

Soft pressure, intact patient

SBP 95 is not a diagnosis. Recheck it. Look at mentation, skin, urine output, lactate trend when useful, lungs, bedside echo, and the trajectory.

HR under 150 is a clue, not a clearance rule. AHA notes tachyarrhythmia is typically at least 150 bpm. Decide whether AF is cause, consequence, or bystander.

The four-question curbside.

Ten seconds before the syringe

Is the instability truly from AF?

Cardiovert when AF is driving shock, ischemia, acute heart failure, or altered mentation. If perfusion is intact, keep thinking.

What is driving the rate?

Hunt for infection, hypovolemia, ischemia, hypoxemia, pain, PE when plausible, electrolyte loss, thyrotoxicosis, withdrawal, and missed medication. Treat the driver in parallel.

What can this ventricle tolerate?

Know the EF. Look for decompensated HF and pre-excitation. The substrate chooses the drug.

What is the rhythm and stroke plan?

Permanent AF usually means rate control tonight. Verify anticoagulant, dose, renal function, last dose, bleeding, and the actual adherence gap.

Choose by substrate.

BP matters. EF matters more.

Agent	Acute dose	Best fit	Do not miss
Diltiazem	0.25 mg/kg IV over 2 min	Stable AF with EF >40%. Fast and effective.	Avoid with moderate or severe LV systolic dysfunction. A lower initial dose, about 0.14 mg/kg, has observational ED support when BP is marginal.
Metoprolol	2.5–5 mg IV over 2 min; up to 3 doses	Stable AF. Useful with adrenergic drive, ischemia, or when already beta-blocked.	Titrate carefully in soft BP, acute HF, or bronchospasm.
Digoxin	0.25–0.5 mg IV; then 0.25 mg q6h; max 1.5 mg/24 h	When beta-blockers and diltiazem are contraindicated or ineffective, especially with HF.	Slow. Renally cleared. The maximum is not the target. Reduce the load in older adults and renal dysfunction. Poor solo agent in a high-catecholamine state.
Amiodarone	150–300 mg IV over 1 h, then infusion	Critically ill or decompensated HF when first-line AV nodal blockers cannot be used.	Not benign rate control. It may cardiovert. Account for AF duration and stroke risk.

These are guideline doses. A fixed 10 mg diltiazem push is a cautious ED tactic, not the guideline-standard weight-based dose. Give small fluid aliquots only when hypovolemia is plausible. Reassess lungs, perfusion, rate, and pressure after every intervention.

The target

Fix symptoms and perfusion. Do not chase 80. A resting HR below 100–110 is a reasonable chronic target in AF without HF. RACE II did not study the borderline acute ED patient.

The cleanups.

Where the original script drifted

Good

Rate control is the default in permanent AF.

There is no prize for restoring sinus rhythm that the long-term plan has already abandoned.

Pitfall

Do not reflexively bridge a missed DOAC.

Verify the gap, renal function, dose, bleeding, and indication. Resume the appropriate anticoagulant when safe. Heparin does not erase missed-dose risk.

Good

Keep pads nearby, not inevitable.

Borderline can deteriorate. Continuous monitoring and a clear trigger to cardiovert are part of conservative management.

Pitfall

Never AV-node block pre-excited AF.

An irregular wide-complex tachycardia with pre-excitation is a different case. Avoid diltiazem, beta-blockers, digoxin, adenosine, and amiodarone.

Disposition follows the cause.

Rate alone does not own the bed

Home can work

Everything is clean

Symptoms resolved and perfusion is normal
Rate remains controlled after observation
No ACS, decompensated HF, sepsis, or other acute driver
Oral plan, anticoagulation, and follow-up are reliable

Observe or admit

The substrate is not clean

Persistent hypotension, symptoms, or recurrent RVR
New HF, ischemia, significant infection, or major electrolyte disorder
High-risk medication change or uncertain EF
Unsafe anticoagulation or follow-up plan

Epic note.

Document the attribution call

AF with RVR · MDM

Patient presented in chronic atrial fibrillation with ventricular rate [RATE] and BP [BP]. Despite the borderline BP, there were no clinical signs that AF was causing hemodynamic instability: no shock, ongoing ischemic discomfort, acute pulmonary edema, or altered mentation. [REVERSIBLE CAUSE ASSESSMENT]. EF/heart-failure history reviewed as [EF / HF STATUS]. Treated with [AGENT / DOSE] under continuous monitoring, with HR improving to [RATE], BP to [BP], and symptoms [RESPONSE]. Anticoagulant, last dose, renal function, and adherence reviewed: [DETAILS]. [DISPOSITION AND FOLLOW-UP].

Sources.

Guidance first. Trials second.

Guideline 2023 ACC/AHA/ACCP/HRS Atrial Fibrillation Guideline Acute rate control, cardioversion, anticoagulation, dosing. Algorithm 2025 AHA Adult Tachyarrhythmia With a Pulse Instability criteria and synchronized cardioversion. Trial RACE II Lenient versus strict chronic rate control in permanent AF. ED study Low-dose diltiazem in AF with RVR Observational evidence for a lower initial bolus strategy. ED trial Diltiazem versus metoprolol Acute rate-control efficacy and adverse events. Guideline 2024 ESC Atrial Fibrillation Guideline Contemporary AF-CARE framework and acute management.