Keywords

Introduction

The most common complication of atrial fibrillation is arterial thromboembolism, which can lead to ischemic stroke [1–3]. Thus, it is important to determine which patients would benefit from antithrombotic therapy to help lower the risk of thromboembolic events. As detailed in the chapter on anticoagulation therapy, there are various Federal Drug Administration (FDA)-approved options for stroke prevention in atrial fibrillation that are endorsed by current guidelines [4]. These would include both oral and parenteral treatments, including low molecular weight heparin, unfractionated heparin, vitamin K antagonists, direct thrombin inhibitors, and factor Xa inhibitors [4]. The initiation of these medications may occur in the outpatient, emergency department (ED), observation unit (OU), or inpatient setting and will depend on the patient’s presentation and risk for thromboembolic events, which will be discussed in this chapter. Furthermore, risk stratification for entry into the OU will be discussed as a means to identify a select number of patients who may be appropriate for a short hospital stay and continued evaluation and management of atrial fibrillation.

Stroke Risk Stratification Scores

As previously discussed, anticoagulation decreases the risk of stroke and other embolic events. Several decision schemes have been validated to guide practitioners on what patients with non-valvular atrial fibrillation would benefit most from anticoagulant therapy. The decision to initiate anticoagulation therapy should be a shared decision between the patient and provider, and a discussion of the benefits of stroke prevention and the risks of bleeding, along with the patient’s values and preferences, needs to be considered.

The two most commonly used stroke risk assessment tools are the CHADS2 and the CHA2DS2-VASc [5, 6]. The acronym CHADS2 represents congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, and stroke/TIA/thromboembolism. Each risk factor is assigned a point of either 1 or 2 and added together for a maximum of 6 (Table 12.1). The listed risk factors have previously been shown to increase the risk of stroke in patients with atrial fibrillation [7–13]. In general, patients with a CHADS2 score of ≥2 should be on oral anticoagulation with warfarin, dabigatran, rivaroxaban, or, apixaban.

Table 12.1 CHADS2 and CHA2DS2-VASc scoring system
Full size table

The American College of Cardiology, American Heart Association, and Heart Rhythm Society Guidelines recently published that the CHA2DS2-VASc risk score is the preferred tool to assess stroke risk in patients with non-valvular atrial fibrillation, and it has widely become accepted by clinicians [4]. The scoring system is also detailed in Table 12.1. Evidence for the utilization of this tool for risk stratification has come from studies showing that several other factors are known to increase stroke risk, and this tool helps identify patients who are high risk for stroke who otherwise would have been considered low or moderate risk with other stratification schemas. Patients with non-valvular atrial fibrillation and a CHA2DS2-VASc score of 0 can be omitted from antithrombotic therapy. Patients with a CHA2DS2-VASc score of 1 may have consideration of no treatment or treatment with an oral anticoagulant or aspirin. Patients with a CHA2DS2-VASc score of ≥2 should be considered for oral anticoagulation with warfarin, dabigatran, rivaroxaban, or apixaban [4]. In this tool, vascular disease, such as prior myocardial infarction, peripheral artery disease, or aortic plaque, is included in the acronym. Vascular diseases have been shown to increase thromboembolic risk in atrial fibrillation [14–16]. Also, a second age category is part of the acronym, as patients with atrial fibrillation who are aged 65 or greater are known to have an increased stroke risk [17]. Additionally, as published in the Birmingham Atrial Fibrillation Treatment of the Aged Study (BAFTA) trial, it was shown that vitamin K antagonists were clearly superior to aspirin in stroke prevention in patients aged ≥75 years in the primary care setting, hence why this age group receives an extra point in the scoring tool [18]. Lastly, the scoring tool adds a sex category, as female gender is known to increase the risk of stroke and thromboembolism [19–21]. Table 12.2 outlines the adjusted stroke rates per year based on CHADS2 and CHA2DS2-VASc scores.

Table 12.2 Adjusted stroke rate per year
Full size table

While the CHADS2 scoring system is simpler to use than the CHA2DS2-VASc, there are notable limitations due to it not including the previously stated common risk factors. It is noted that patients classified as low risk by CHADS2 in its original validation study still had a stroke rate of 1.9 % per year, as listed in Table 12.2 [5]. A recent meta-analysis by Olesen et al. showed that many patients with a CHADS2 score of 0 were not all at low risk for stroke [22]. By instead utilizing the CHA2DS2-VASc score, one would better classify the risk of stroke in atrial fibrillation patients and guide decision-making for anticoagulation therapy more appropriately.

Bleeding Risk Scores

Patients with atrial fibrillation also need evaluation for bleeding risk prior to the initiation of oral anticoagulation for stroke prevention. While identifying bleeding risk should not exclude physicians from initiating oral anticoagulation, it is important to correct any modifiable bleeding risk factors if possible. It is known that physicians overestimate bleeding risk, especially in the elderly, and this is a barrier to prescribing oral anticoagulants in patients with atrial fibrillation [25, 26]. This is important to note because as demonstrated in an analysis by van Walraven et al., oral anticoagulation was significantly protective against ischemic stroke regardless of the patient’s age. Their study showed that while the protective benefit of antiplatelet therapy decreased significantly as the patient aged, the benefit for oral anticoagulation increased as they aged. Additionally, while there was an increased risk of serious hemorrhage as patient’s aged, there were no significant differences between patients on aspirin versus those on warfarin [27].

While there are several bleeding scores available [28–30], the HAS-BLED score is a simple tool that allows for evaluation of bleeding risk in patients with atrial fibrillation [31]. HAS-BLED has several risk factors that are also known to be risk factors for stroke. The acronym stands for hypertension >160 systolic, abnormal liver or renal function (defined as dialysis, renal transplant, creatinine >2.6, cirrhosis, bilirubin >2 X’s normal, alanine transaminase, aspartate aminotransferase, or alkaline phosphatase >3 X’s normal), history of stroke, predisposition to or prior major bleeding, labile international normalized ratio (INR), elderly age >65, and, drugs, including medications that predispose to bleeding, along with excessive alcohol usage. The HAS-BLED score ranges from 0 to 9 with scores ≥3 indicate a high risk of bleeding. It is important to reiterate that HAS-BLED should not be used as a tool to exclude patients from receiving oral anticoagulation but rather to help physicians identify modifiable risk factors as they proceed cautiously and regularly review treatment plans. Table 12.3 illustrates the scoring system.

Table 12.3 HAS-BLED risk score
Full size table

Observation Unit Inclusion and Exclusion Criteria

There are often scenarios where patients with atrial fibrillation may not require inpatient admission, but a short stay in the OU could be appropriate for stable patients that are not ready for discharge from the ED and warrant further management. As detailed in other chapters, the OU can serve to utilize pharmacologic treatments in attempts to achieve rate control or chemical cardioversion, electrical cardioversion if indicated, and initiation of parenteral and/or oral anticoagulation, provide patient education and consultation with cardiologists, and have appropriate discharge planning.

OU treatment protocols for atrial fibrillation have previously been described in the literature as a means to provide an alternative method to prolonged inpatient management of uncomplicated atrial fibrillation [32–35]. More recently, the Society for Cardiovascular Patient Care (SCPC) published a white paper on observation services, which included recommendations for the management of atrial fibrillation in the OU [36]. Included in those recommendations were the following inclusion and exclusion criteria:

Inclusion Criteria

  • Hemodynamically stable patient

  • Heart rate less than 110–120 after initial rate control

  • Patient able to assist in follow-up and treatment plan

Exclusion Criteria

  • Evidence of comorbidities requiring inpatient hospitalization

  • Concerns for ischemia: positive initial troponins or presence of ischemic ECG changes

  • Signs of CHF

  • Ongoing significant tachycardia or hypoxia

The criteria above provide only framework for OU entry. There are several ways to treat atrial fibrillation, and an OU protocol may be best identified on an individual facility basis, as long as guideline and evidence-based medicine are practiced. This may depend on several factors including the availability of certain pharmacologic agents, diagnostic testing, and cardiology consultation. Either way, the OU is a viable destination for the uncomplicated patient with atrial fibrillation to receive further management to determine the need for inpatient admission or outpatient follow-up.