What are the exact doses of anticoagulants (AntiCoagulants) such as apixaban (Apixaban), rivaroxaban (Rivaroxaban), and dabigatran (Dabigatran) in Atrial Fibrillation (AFib) versus other conditions, and how do you differentiate AFib with aberrant conduction from Ventricular Tachycardia (VTach) in patients with conditions like cirrhosis?

Anticoagulation Dosing in Atrial Fibrillation and Distinguishing AFib with Aberrancy from VTach

Exact DOAC Doses for Atrial Fibrillation

For stroke prevention in nonvalvular atrial fibrillation, use apixaban 5 mg twice daily, dabigatran 150 mg twice daily, rivaroxaban 20 mg once daily, or edoxaban 60 mg once daily as standard dosing, with specific dose reductions based on renal function, age, and weight criteria. 1

Standard Dosing by Agent

• Apixaban: 5 mg orally twice daily is the standard dose 1, 2

  • Reduce to 2.5 mg twice daily if patient has ≥2 of: age ≥80 years, body weight ≤60 kg, or serum creatinine ≥1.5 mg/dL 1, 2

• Dabigatran: 150 mg orally twice daily is the standard dose 1

  • Reduce to 110 mg twice daily (not FDA-approved in US, but used in Europe) for patients at higher bleeding risk 1
  • Reduce to 75 mg twice daily if CrCl 15-30 mL/min 1
  • Contraindicated if CrCl <15 mL/min or on dialysis 1

• Rivaroxaban: 20 mg orally once daily with the evening meal 1

  • Reduce to 15 mg once daily if CrCl 15-50 mL/min 1

• Edoxaban: 60 mg orally once daily 1

  • Reduce to 30 mg once daily if CrCl 15-50 mL/min, body weight ≤60 kg, or concomitant use of P-glycoprotein inhibitors 1
  • Contraindicated if CrCl >95 mL/min (increased stroke risk) 1
  • Contraindicated if CrCl <15 mL/min or on dialysis 1, 3

Critical Renal Function Considerations

Apixaban has the lowest renal clearance (27%) among all DOACs, making it the preferred agent in advanced renal impairment including dialysis. 4, 3

• Dabigatran: 80% renal excretion 1, 4
• Rivaroxaban: 66% renal excretion 1, 4
• Edoxaban: 50% renal excretion 1, 3
• Apixaban: 27% renal excretion 1, 4

Special Population: Dialysis and ESRD

In patients with ESRD on hemodialysis, apixaban 5 mg twice daily is the only DOAC with FDA approval, with dose reduction to 2.5 mg twice daily if age ≥80 years or weight ≤60 kg. 4, 3, 2

• Observational data from 25,523 dialysis patients showed standard-dose apixaban (5 mg twice daily) was associated with lower risk of stroke/embolism and death compared to reduced-dose apixaban (2.5 mg twice daily) and warfarin 4, 3
• Dabigatran and edoxaban are absolutely contraindicated in dialysis patients 1, 3
• Rivaroxaban is not recommended for dialysis patients 1

Cirrhosis Dosing Considerations

All DOACs should be avoided in Child-Pugh B (moderate) and C (severe) cirrhosis due to increased bleeding risk and unpredictable drug metabolism. 1

• Child-Pugh A (mild): Use with caution; no dose adjustment needed for apixaban, rivaroxaban, or edoxaban 1
• Child-Pugh B (moderate): Avoid all DOACs 1
• Child-Pugh C (severe): Avoid all DOACs 1
• Warfarin should also be avoided in Child-Pugh B and C cirrhosis 1

DOAC Dosing for Other Indications vs. Atrial Fibrillation

DVT/PE Treatment (Different from AFib Dosing)

For acute DVT/PE treatment, apixaban and rivaroxaban require higher initial loading doses compared to their AFib dosing, while dabigatran requires parenteral anticoagulation bridging. 5, 2

• Apixaban for DVT/PE: 10 mg twice daily for 7 days, then 5 mg twice daily (vs. 5 mg twice daily for AFib) 5, 2
• Rivaroxaban for DVT/PE: 15 mg twice daily for 21 days, then 20 mg once daily (vs. 20 mg once daily for AFib) 1
• Dabigatran for DVT/PE: Requires 5-10 days of parenteral anticoagulation first, then 150 mg twice daily (same as AFib dose but different initiation) 1

Extended VTE Prevention (Lower Doses)

• Apixaban: 2.5 mg twice daily after completing 6 months of treatment for DVT/PE 5, 2
• Rivaroxaban: 10 mg once daily for extended VTE prevention 1

Why No DAPT in Atrial Fibrillation Alone

Dual antiplatelet therapy (DAPT) with aspirin plus clopidogrel is inferior to oral anticoagulation for stroke prevention in atrial fibrillation and should not be used unless there is a separate indication requiring antiplatelet therapy. 1

When DAPT is Avoided in AFib

• AFib patients without coronary artery disease or recent PCI should receive oral anticoagulation monotherapy only 1
• DAPT (aspirin + clopidogrel) provides inadequate stroke protection compared to anticoagulation in AFib 1
• Adding aspirin to anticoagulation significantly increases bleeding risk without improving outcomes in stable AFib 1

When Triple Therapy or Dual Therapy is Required

In AFib patients undergoing PCI or with ACS, use time-limited triple therapy (OAC + aspirin + P2Y12 inhibitor) or dual therapy (OAC + P2Y12 inhibitor) based on bleeding risk, then transition to OAC monotherapy. 1

Elective PCI in AFib (Low Bleeding Risk, HAS-BLED 0-2)

• Triple therapy (OAC + aspirin + clopidogrel) for 1 month 1
• Then dual therapy (OAC + clopidogrel) for 6 months 1
• Then OAC monotherapy 1

Elective PCI in AFib (High Bleeding Risk, HAS-BLED ≥3)

• Triple therapy for 1 month only 1
• Then dual therapy (OAC + clopidogrel) for 6 months 1
• Then OAC monotherapy 1

ACS with PCI in AFib (High Bleeding Risk, HAS-BLED ≥3)

• Triple therapy for 1-3 months 1
• Then dual therapy (OAC + clopidogrel) up to 12 months 1
• Then OAC monotherapy 1

Stable CAD in AFib (>1 year post-ACS)

• OAC monotherapy only (no aspirin or clopidogrel) 1

Distinguishing AFib with Aberrant Conduction from Ventricular Tachycardia

Wide complex tachycardia in a patient with known atrial fibrillation should be presumed to be ventricular tachycardia until proven otherwise, as this assumption is correct in approximately 80% of cases and prevents dangerous treatment errors. 1

Key Diagnostic Approach

When faced with wide complex tachycardia, use the following algorithm:

1. Assume VTach first - This is the safest approach as treating VTach as SVT with aberrancy can be fatal, while the reverse is safer 1

2. Look for AV dissociation - Independent P waves marching through the QRS complexes strongly favor VTach 1

3. Assess QRS morphology:

   • RBBB pattern: Look at V1 and V6
     • VTach: Monophasic R wave or qR in V1; R/S ratio <1 in V6 1
     • Aberrancy: Triphasic rSR' in V1; R/S ratio >1 in V6 1
   • LBBB pattern: Look at V1 and V6
     • VTach: R wave >30 ms in V1; any Q wave in V6; notched downstroke of S wave in V1 1
     • Aberrancy: Narrow R wave in V1; no Q in V6; smooth rapid downstroke in V1 1

4. Check for fusion or capture beats - These are pathognomonic for VTach 1

5. Assess QRS axis - Extreme axis deviation (northwest axis) strongly favors VTach 1

6. Consider clinical context:

   • History of structural heart disease (MI, cardiomyopathy) strongly favors VTach 1
   • Hemodynamic stability does NOT rule out VTach 1

Critical Pitfall to Avoid

Never give calcium channel blockers or beta-blockers to wide complex tachycardia of uncertain etiology, as this can cause cardiovascular collapse if the rhythm is VTach. 1

• If VTach is suspected: Use amiodarone or procainamide, or proceed directly to cardioversion if unstable 1
• If truly uncertain: Treat as VTach with electrical cardioversion 1

Role of Electrophysiology Study

An electrophysiology study can definitively establish the diagnosis when wide complex tachycardia is recurrent and the surface ECG diagnosis remains uncertain despite careful analysis. 1

• EP study can distinguish between VTach, SVT with aberrancy, and antidromic AVRT 1
• This is particularly useful when the rhythm is recurrent and treatment decisions depend on accurate diagnosis 1

Special Consideration in Cirrhosis

Patients with cirrhosis and atrial fibrillation who develop wide complex tachycardia require the same diagnostic approach, but treatment options are limited by liver dysfunction and bleeding risk. 1

• Avoid antiarrhythmics metabolized by the liver in Child-Pugh B or C cirrhosis 1
• Electrical cardioversion is preferred for hemodynamically significant arrhythmias 1
• Anticoagulation decisions must account for both thrombotic risk from AFib and bleeding risk from cirrhosis 1