Does a patient with atrial fibrillation (AF) who is not on anticoagulation have an increased risk for cerebral vascular accident (CVA)?

Atrial Fibrillation Without Anticoagulation Significantly Increases Stroke Risk

Patients with atrial fibrillation who are not on anticoagulation therapy have a substantially increased risk for cerebrovascular accident (CVA). 1 This risk is well-established in multiple guidelines and clinical studies, with stroke rates increasing proportionally with additional risk factors.

Stroke Risk in Non-Anticoagulated AF Patients

• The CHADS2 and CHA2DS2-VASc scoring systems quantify stroke risk in AF patients, with higher scores correlating with progressively increased stroke rates 1
• Even patients with a CHADS2 score of 0 (considered lowest risk) have an adjusted stroke rate of 1.9% per year when not anticoagulated 1
• As CHADS2 scores increase, annual stroke rates rise dramatically:
  • Score 1: 2.8% per year
  • Score 2: 4.0% per year
  • Score 3: 5.9% per year
  • Score 4: 8.5% per year
  • Score 5: 12.5% per year
  • Score 6: 18.2% per year 1

Mechanisms and Evidence

• AF promotes thrombus formation primarily in the left atrial appendage due to blood stasis, which can embolize to the cerebral circulation 1
• In the ROCKET-AF trial, patients with AF not receiving anticoagulation had a stroke rate of 2.4 per 100 patient-years 2
• A real-world study of AF patients with contraindications to anticoagulation showed a 4.1% incidence of ischemic stroke, with rates increasing with higher CHA2DS2-VASc scores 3
• Patients with AF who cannot take anticoagulants due to bleeding risk remain at considerable risk for both ischemic and hemorrhagic events 3, 4

Impact of Anticoagulation on Stroke Risk

• Adjusted-dose oral anticoagulation reduces stroke risk by approximately 61% compared to placebo in patients with nonvalvular AF 1
• When anticoagulation is used in AF patients with contraindications, there is still a reduction in mortality (adjusted HR: 0.79), stroke (adjusted HR: 0.90), and all-cause hospitalization (adjusted HR: 0.93), though with increased risk of intracranial hemorrhage (adjusted HR: 1.42) 4
• Even suboptimal anticoagulation or antiplatelet therapy provides some protection compared to no antithrombotic therapy, with less severe neurologic deficits and better functional outcomes at 3 months 5

Risk Stratification and Treatment Decisions

• The CHA2DS2-VASc score is recommended for stroke risk assessment in AF patients, with scores ≥2 (or ≥3 for females) generally warranting anticoagulation 1
• For patients with a CHA2DS2-VASc score of 1, careful consideration of individual bleeding risk versus stroke risk is needed 1
• Age is a powerful independent risk factor - patients ≥65 years with AF have significantly higher event rates even without other risk factors:
  • Age <65 years with no risk factors: 0.23 events per 100 person-years
  • Age 65-74 years with no risk factors: 2.05 events per 100 person-years
  • Age ≥75 years with no risk factors: 3.99 events per 100 person-years 6

Common Pitfalls and Caveats

• Many AF patients who would benefit from anticoagulation do not receive it due to:
  • Overestimation of bleeding risk 4
  • Cognitive impairment affecting compliance 7
  • Monitoring difficulties, especially for vitamin K antagonists 7
  • Social factors including distance from monitoring facilities 7
• The risk of thromboembolism in atrial flutter is generally considered lower than in AF but still elevated compared to sinus rhythm; similar risk stratification criteria are recommended 1
• Silent (asymptomatic) AF carries similar stroke risk as symptomatic AF, and should not be considered lower risk 1
• The threshold for anticoagulation may be lower with NOACs than with warfarin (stroke rate of 0.9% vs 1.7% per year) 1

In summary, the evidence clearly demonstrates that AF patients not receiving anticoagulation have a significantly increased risk of stroke, with the magnitude of risk determined by additional clinical factors that are captured in risk stratification tools like CHA2DS2-VASc.