MCC DEEP Dive: Atrial Fibrillation

Definition: Atrial fibrillation is a type of arrhythmia caused by extremely fast and irregular beats from the atria (300-500 beats per minute) that are asynchronous with the ventricles.  

Risk Factors/Causes: Sleep apnea, cardiac ischemia, heart valve disorders, heart failure,  hypertension, lung disease, thyroid disease, infections, advanced age, alcohol abuse, smoking, stimulant use (Illegal or legal), electrolyte imbalance, cardiac surgery, obesity, sedentary lifestyle, increased height, diabetes, sepsis, family history. 

See MCCICUTrainer.com for quick mnemonic reference for new onset afib in critical care 

Sub-classes: Paroxysmal (comes and goes), persistent atrial fibrillation (lasts longer than 7 days), long standing persistent atrial fibrillation (lasts long than one year), permanent atrial fibrillation, 

atrial fibrillation with rapid ventricular response (atrial fibrillation with heart rates > 100) 

Symptoms: Irregular heart beat, fatigue, palpitations, chest pain or pressure, dyspnea, sweating

Pharmacologic Treatment: Beta blockers (Metoprolol, Atenolol, Labetalol, Carvedilol) , Non-dihydropyridine Calcium Channel Blockers (Diltiazem, Verapamil), Antiarrhythmics (Amiodarone, Sotalol, Tikosyn), or Cardiac Glycosides (Digoxin)  

Nonpharmacologic: Electricity (Synchronized cardioversion), Atrial Fibrillation Ablation, Watchman Procedure

   Just a heads up, the December 2023 guideline is a monster of a read and much of it applies to patients that are not critically ill. The following is a summary of the recommendations that are more in line with ICU patients rather than a summary of the entire guideline. 

Guidelines: American Heart Association 2023

• New onset atrial fibrillation should be evaluated with an echocardiogram and labs including CBC, bmp, and thyroid function. For critically ill patients, this probably makes some sense unless you already know why they are in afib, for example, the patient just had a major cardiac surgery. 
• Do not routinely look for acute coronary syndrome, pulmonary embolism, or cardiac ischemia unless the patient has symptoms of these. Again, this is referring to general work up and apply this to ICU patients when appropriate. 
• For patients who have had a systemic thromboembolic event without a known history of AF and in whom maximum sensitivity to detect AF is sought, an implantable cardiac monitor is reasonable. 
• Patients with AF should be evaluated for their annual risk of thromboembolic events using a validated clinical risk score such as CHADS-VASC. Bleeding risk should be evaluated in all patients. Patients with intermediate risk (Score of 1 for men and 2 for women) can consider modification of stroke risk factors if they are uncertain about the use of anticoagulation. 

Risk was explained as <1% per year as low, 1-2% per year as intermediate, and > 2% as high.

• For any patient with a thromboembolic risk of over 2% per year with atrial fibrillation, anticoagulation is recommended regardless if the patient was in paroxysmal, persistent, or long standing atrial fibrillation 
• For patients with patients who do not have a history of rheumatic moderate to severe mitral stenosis or mechanical valve, DOACs are recommended over warfarin for thromboembolic event prevention
• Do not use aspirin or dual antiplatelets for prevention of thromboembolism in patients eligible for AC; this is associated with harm. 
• In patients with TIA or cryptogenic stroke, implantation of a loop recorder is reasonable. 
• In patients with moderate to high risk of stroke and contraindication to AC or high risk for bleeding with AC, performing a left atrial appendage occlusion is reasonable
• For patients with AF who are at very high risk for stroke (>5%) and have active ICH, waiting 1-2 weeks prior to AC resumption is reasonable. (Think mechanical valve, active PE patient with ICH) 
• For patients with AF and ICH, consider waiting 4-8 weeks while balancing stroke risk VS bleeding risk 
• In high risk bleeding patients (cerebral amyloid for example) and atrial fibrillation, consider left atrial appendage occlusion to reduce both stroke risk and risk of intracerebral hemorrhage 
• For patients in AF with high risk for thromboembolic event and undergoing surgery while on AC, holding of AC is dependent on the surgical risk of bleeding, renal function, and depends on the specific agent being used for AC 
• Post surgery, if the risk of bleeding of the procedure is low, AC should resume the next day. For surgery with a high risk of bleeding, AC should resume between the evening of Day 2 after surgery and the evening of Day 3. 
• For patients undergoing surgery and are using warfarin as AC, DO NOT bridge with lovenox as this has been associated with harm. 
• In patients with PAD and AF, solo anticoagulation is preferred over dual therapy (AC + aspirin or plavix)
• For patients in AF with rheumatic mitral stenosis or mitral stenosis of moderate or worse degree or patients with mechanical valve, warfarin is the preferred method of AC. 
• Rate control for AF is consider resting heart rate less than 110
• For patients in AF with RVR and a known EF of > 40%, beta blockers or nondihydropyridine calcium channel blockers are recommended to achieve target heart rate. 
• For patients in AF with RVR, digoxin should be considered if the patient is not responsive to beta blocker or  nondihydropyridine calcium channel blockers
• Consider high dose magnesium infusion in addition to standard treatments for AF with RVR 
• For patients in AF with RVR who are critically ill or in decompensated heart failure and in whom CCB or BB are either contraindicated or not effective, amiodarone may be considered for acute rate control. 
• For patients in AF with RVR and have a known moderate to severe LV systolic dysfunction, DO NOT use nondihydropyridine calcium channel blockers for rate control. 
• For long term rate control of patients with known EF of < 40%, nondihydropyridine calcium channel blockers are not recommended
• For patients in AF for > 48 hours, 3 weeks of AC or a TEE to rule out cardiac thrombus prior to cardioversion is recommended. 
• AC should continue 4 weeks post cardioversion 
• If cardiac thrombus is present on imaging, full AC for 3-6 weeks with follow up imaging prior to cardioversion is recommended 
• For patients with previous left atrial appendage closure, cardiac imaging is recommended prior to cardioversion to ensure there is no device related thrombus 
• If the patient is in AF for < 48 hours prior to cardioversion and has a CHADS-VASc score of 2 or greater, pre-cardioversion imaging is of consideration 
• For patients in AF < 12 hours with CHADS-VASc score of 1 or less, pre-cardioversion imaging is uncertain 
• In patients with AF and hemodynamic instability, synchronized cardioversion is recommended 
• In patients with AF and hemodynamic stability, synchronized cardioversion should be considered if pharmacological cardioversion has failed. 
• For synchronized cardioversion, 200J is the recommended charge. 
• In patients with obesity, manual compression of the cardioversion pads may be beneficial. 
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Pharmacology: For our purposes, I am focusing more on IV options for rate control

Beta Blockers: 

Metoprolol: 2.5 to 5 mg IV over 2 minutes. May repeat up to 3 doses. Selective activity on beta 1 adrenoreceptors. Maximum effect in about 20 minutes after administration with a mean half life of 2-4 hours. First line for atrial fibrillation rate control regardless of ejection fraction. 

Esmolol: 500 mcg/kg IV bolus over 1 minute followed by 50-300 mcg/kg/min IV infusion. Activity on beta 1 adrenoceptors with minor beta 2 blockade at higher doses. Onset of action within 60 seconds with steady state obtained 5-10 minutes after infusion initiation. Mean half life is about 9 minutes. 

Calcium Channel Blockers (Non-dihydropyridine) : 

Diltiazem: IV bolus of 0/25 mg/kg (Or 20 mg) IV over 2 minutes followed by IV infusion of 10 mg per hour. May be titrated as high as 15 mg per hour. Causes inhibition of calcium ion inflow to cardiac muscle during depolarization, resulting in cardiac relaxation. Onset of action occurs in 15-30 minutes with peak effect in 1-2 hours. Half life is 3.0 to 4.5 hours. Not recommended for patients with atrial fibrillation with EF < 40% due to increased risk of decompensated heart failure. 

Verapamil: 5 to 10 mg IV bolus over at least 2 minutes. May follow with an additional 10 mg IV bolus after 30 minutes if response is not adequate. Causes inhibition of calcium ion inflow to cardiac muscle during depolarization, resulting in cardiac relaxation. Onset of action occurs within 1-2 minutes with peak effect at 10-15 minutes. Half life 2.5 to 5 hours. Not recommended for patients with atrial fibrillation with EF < 40% due to increased risk of decompensated heart failure. 

Cardiac Glycosides:

Digoxin: IV 8-12 mcg/kg ideal body weight or IV 6-10 mcg/kg with renal insufficiency. Causes an increase in intracellular sodium that drives an influx of calcium into cardiac cells, resulting in increased contractility as well as slowing conduction and prolonging AV node refractory period. Initial onset of action is as soon as 30 minutes after IV dose, but takes 2-4 hours to reach peak effect. Half life is 1-2 days and decreased renal function will lengthen this. This medication does have an inotropic effect and may be used in patients with reduced ejection fraction. 

Antiarrhythmics 

Amiodarone: 150 mg IV bolus over 10 minutes followed by IV infusion followed by continuous infusion of 1 mg/min for 6 hours and the 0.5 mg/min for 18 hours. Causes blockade of potassium channels with some sodium and calcium channel blockade effect as well as mild alpha and beta blockade. Onset of action 30-60 minutes after IV dose. Extremely variable half life (25 to 100 days). May cause QT prolongation. This is not FDA approved for treatment of atrial fibrillation outside of a CV Surgery prophylactic use. 

Ibutilide: 1 mg IV over 10 minutes if your patient is 60 kg or more. If arrhythmia has not terminated in that 10 minutes, a second 1 mg infusion over 10 minutes may be repeated. If your patient is less than 60 kg, us 0.01 mg per kg over 10 minutes. Causes blockade of cardiac potassium channels. Onset of action 30-90 minutes after infusion and half life 4-8 hours. 

Electrolytes

Magnesium: IV infusion to target a serum magnesium of 3-4 mg/dl. Studies for this inclusion in the guidelines show potential for use as augmentation of the above agents rather than as a solo agent. 

Medications to avoid: 

Beta agonists (dobutamine, epinephrine,) 

Random Dan Advice: 

• Atrial fibrillation is very common in the ICU. Depending on what study you read, critically ill patients develop new onset atrial fibrillation anywhere from 15-45% of all ICU admissions. There is usually an underlying cause (See MCCICUTrainer.com for causes mnemonic) and I tend to think of a-fib more as a symptom of illness rather than a diagnosis. Conversion to NSR may depend more on treating the patient’s underlying cause rather than picking the right meds. 
• Don’t get obsessed with rate control right off of the bat. That heart rate of 130 might be for very good reason (Patient is hypovolemic, patient is anemic, etc). Tune your patient up before worrying about why your rate isn’t that picture perfect less than 110. 
• If the patient is hemodynamically stable, be patient. Everyone loves seeing someone convert with that amio bolus, but most of the medications listed above take some time. Consider a big magnesium (4mg IV) load to help things along. 
• If your patient is not stable, use electricity. The only amount of joules you should ever use is “all of the joules”. The guidelines also recommend for obese patients, there may be some benefit to pushing down on the pads with your gloved hand. I have never personally tried this, but….noted. 
• You have 48 hours to convert your patient to NSR. After that, you are on the hook for ruling out left atrial thrombus as the chance of stroke increases significantly. Don’t convert you patient into NSR + an acute CVA. Documenting the timing of a-fib might be something we should all consider doing. 
• After that first run of atrial fibrillation, do a CHADsVASc. If your patient is in the intermediate risk category, and that is going to be almost everyone, you are officially on the hook for anticoagulation, even in cases of paroxysmal atrial fibrillation. 
• Consider placing an EP follow up right away so this does not get forgotten. While I generally do not consult EP for a-fib while the patient is in ICU, they really should be followed up as outpatients. For those of you who have worked with me, I am generally against consulting other providers for problems we can manage, but a quick ambulatory referral for discharge follow up is a reasonable plan. 
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Recent evidence for/against some of the above: 

I…..just can’t. The December 2023 guidelines are absolutely packed with studies (Over 1500 separate studies) were cited in the new guidelines. I am going to ask that we just take their word for it on this one.