Atrial Fibrillation
By the end of this post you will be able to:
- Identify and address the reversible triggers of new atrial fibrillation in a hospitalized patient.
- Apply CHADS-65 to decide whether a patient needs anticoagulation, and select an appropriate agent.
- Choose between rate and rhythm control, and recognize when cardioversion requires anticoagulation first.
TL;DR
What you need to know before seeing your first patient on your IM rotation with this condition
Estimated read time: 3 minutes
- What it is: The most common sustained arrhythmia on the wards. Irregularly irregular ventricular response. ECG: absent P waves, fibrillatory baseline, irregular R-R intervals.
- How it presents: Palpitations, dyspnea, fatigue, lightheadedness — or asymptomatic. Feel for irregularly irregular pulse, variable S1.
- If unstable (hypotension, active ischemia, severe hemodynamic compromise): call your senior — patient may need transfer to a monitored setting (critical care unit) and emergent electrical cardioversion.
- If stable — rate control: Target resting HR <100 bpm (CCS). First-line:
• Metoprolol tartrate 25–50 mg PO BID (acute: 2.5–5 mg IV q5min x3)
• Diltiazem ER 120–240 mg PO daily (acute: 0.25 mg/kg IV bolus)
• In HFrEF: beta-blockers only — avoid diltiazem/verapamil - Always ask “why now?”: e.g. infection, post-op, PE, alcohol, thyroid. Treating the cause often resolves the AF.
- When to call for help: Rapid rate does not respond to first-line agents.
Listen: The Intern at Work
Read Around the Case
Based on the 2020 CCS/CHRS Comprehensive Guidelines and the CCS AF Pocket Guide
Estimated read time: 12 minutes
Pathophysiology
AF is driven by triggers (ectopic foci, often from pulmonary veins) firing into a vulnerable substrate (atrial fibrosis, dilation, electrical remodelling). “AF begets AF” — sustained fibrillation promotes further remodelling, making sinus rhythm restoration progressively harder.
Key modifiable risk factors (CCS): hypertension, HF, obesity, OSA, diabetes, alcohol, and inactivity. The CCS emphasizes that risk factor management is as important as rate/rhythm control and anticoagulation.
Classification
- Paroxysmal: terminates within 7 days (usually <48h)
- Persistent: >7 days but <1 year
- Long-standing persistent: >1 year, rhythm control still pursued
- Permanent: rhythm control no longer pursued
- Valvular AF: mechanical valve or moderate–severe mitral stenosis
Investigations
- 12-lead ECG — confirm AF, document PR/QRS/QT, rule out pre-excitation
- Echo — LV function, LA size, valvular disease
- Labs — CBC, lytes (Ca2+, Mg2+), renal/liver function, TSH, coagulation, fasting glucose/HbA1c
Stroke Prevention: CHADS-65
CHADS-65 Algorithm
No
No
No
- DOACs > warfarin for non-valvular AF. Valvular AF (mechanical valve, mod–severe MS): warfarin only.
- ASA is NOT for stroke prevention in AF — AVERROES: apixaban superior to ASA.
- Bleeding scores (HAS-BLED) identify modifiable risk — not reasons to withhold OAC.
DOAC dosing by renal function:
*2.5 mg BID if ≥2 of: age ≥80, wt ≤60 kg, Cr ≥133 μmol/L.
†110 mg BID if ≥80 y/o, or ≥75 with bleeding risk.
‡30 mg if wt ≤60 kg or potent P-Gp inhibitor.
Rate Control
Target: resting HR <100 bpm per CCS. (The RACE II trial showed a lenient target of <110 bpm was non-inferior to strict <80 bpm — some centres use <110 for asymptomatic patients.)
HFrEF (LVEF ≤40%): bisoprolol, carvedilol, or metoprolol succinate ± digoxin. Non-dihydropyridine CCBs (diltiazem, verapamil) are contraindicated — their negative inotropic effect can acutely worsen cardiac output and precipitate decompensated heart failure. The CCS Pocket Guide explicitly lists CHF and LV dysfunction as contraindications to ND-CCBs for rate control in AF.
Rhythm Control
Consider when symptomatic despite rate control, or first-line in select patients (new-onset, highly symptomatic, tachycardia-mediated cardiomyopathy).
AAD selection by cardiac disease (CCS):
- No HF, no CAD: flecainide, propafenone, dronedarone, sotalol, amiodarone
- CAD (no HF): dronedarone, sotalol, amiodarone
- HFrEF (LVEF ≤40%): amiodarone only
Class IC agents (flecainide, propafenone) are contraindicated in structural/ischemic heart disease. Dronedarone is contraindicated in decompensated HF and permanent AF.
“Pill-in-the-Pocket”: For infrequent paroxysmal AF without structural heart disease. AV nodal blocker (e.g., diltiazem 60 mg PO) 30 min before flecainide 200–300 mg PO or propafenone 450–600 mg PO (dose by weight). First dose must be monitored.
Cardioversion & Anticoagulation
- Can cardiovert without prior OAC: NVAF <12h (no prior stroke/TIA), or NVAF 12–48h without stroke risk factors (no HTN, HF, DM, prior stroke/TIA, age ≥65)
- Needs OAC ≥3 weeks first (or TEE to rule out LAA thrombus): NVAF >48h, NVAF 12–48h with any stroke risk factor, or valvular AF
- Post-cardioversion: OAC for ≥4 weeks regardless; long-term OAC per CHADS-65
Lifestyle & Risk Factor Modification
- Weight loss: Target ≥10% weight loss to BMI <27. The LEGACY trial showed that sustained weight loss of ≥10% was associated with a six-fold greater probability of AF freedom compared to <3% loss.
- Obstructive sleep apnea: Screen AF patients for OSA. Untreated OSA increases AF recurrence after cardioversion and ablation. The CCS recommends CPAP for AHI ≥15.
- Alcohol: The ALCOHOL-AF trial showed that abstinence in regular drinkers (≥10 drinks/week) with paroxysmal/persistent AF reduced AF recurrence. CCS recommends ≤1 standard drink/day.
- Exercise: Moderate exercise (e.g., 150 min/week) reduces AF risk. However, extreme endurance exercise (marathon running, competitive cycling) may paradoxically increase AF risk.
- Other: Optimize BP (<130/80), diabetes (HbA1c ≤7%), and smoking cessation.
When to Involve Cardiology/Electrophysiology
- AF with pre-excitation (WPW) — avoid AV nodal blockers
- Failed ≥1 AAD — catheter ablation referral
- AF with HFrEF — consider ablation
- Diagnostic uncertainty (flutter vs. AF vs. other SVT)
Before reaching for metoprolol, always ask: why is this patient in AF right now? The CCS lists reversible causes: surgery, acute cardiac/pulmonary pathology, infection, thyrotoxicosis, alcohol, medications (e.g., ibrutinib), SVT, and ventricular pacing. “New AF” in an acutely ill patient often resolves once the trigger is addressed.
Related Trial Files
Rate vs Rhythm Control for AF (AFFIRM)Trial Files Throwback →Dual Cardioversion for AFDoes dual-pad placement improve conversion? →Left Atrial Appendage Closure after Ablation for AFConcomitant LAA closure at the time of ablation →Edoxaban Monotherapy in AF + Stable CAD (EPIC-CAD)Dropping antiplatelets ≥12 months post-PCI →
Why Do We Use Apixaban Over Aspirin in AFib? (AVERROES)
Trial Files Throwback →
Stroke Management in AFib with Prior DOAC
Trial Files →
How Long Should We Monitor for AFib Post Cryptogenic Stroke?
Trial Files Throwback →
Listen: Deep Dives
Test Yourself
MCQ 1 for medical students · MCQ 2 for residents
You are called overnight about a 68-year-old man who is post-op day 2 from a hip replacement. The nurse reports a new irregularly irregular rhythm on telemetry at 148 bpm. His BP is 112/72 mmHg, he is alert and comfortable, and his oxygen saturation is 96%. You have assessed for and addressed reversible triggers (electrolytes are normal, no signs of infection or PE). What is the most appropriate next step?
A 74-year-old woman admitted with community-acquired pneumonia develops new AF with rapid ventricular response (HR 156 bpm). Her known history includes HFrEF with LVEF 35%. She has received metoprolol 5 mg IV x2 without significant improvement. What is the most appropriate next agent to add?
Reflect
Before reading this post, would you have given diltiazem to a patient in AF with an EF of 30%? What would you do now — and why does it matter?
Please do not include patient identifying details — no names, initials, dates, medical record numbers, or any detail that could identify a specific patient or encounter. Write about your reasoning, not about a real person.
Further Reading
-
Canadian Guideline
2020 CCS/CHRS Comprehensive Guidelines for the Management of AF — Andrade et al. CJC 2020. -
Pocket Guide
CCS Atrial Fibrillation Pocket Guide -
International Guideline
2023 ACC/AHA/ACCP/HRS AF Guideline — Joglar et al. Circulation 2024. -
Clinical Resource
Thrombosis Canada: Stroke Prevention in AF