Page 2412 - Hematology_ Basic Principles and Practice ( PDFDrive )

C H A P T E R 147

ATRIAL FIBRILLATION

Dipak Kotecha, Keitaro Senoo, and Gregory Y.H. Lip

Atrial fibrillation (AF) is the most common cardiac rhythm distur- CLINICAL MANIFESTATIONS
bance. Patients with AF have impaired prognosis, with increased risk
of death, stroke, and hospital admission, in addition to poor quality Symptoms
1,2
of life. The impact of AF on numerous specialties is set to increase
further, as the number of patients with AF escalates to epidemic Symptoms are a major reason that patients with AF seek medical
proportions and the populations that are susceptible to AF increase advice. The most common symptoms include lethargy, dyspnea, and
in prevalence. Most notably, this includes older adults and those with palpitations, associated with a reduction in exercise capacity. AF and
heart failure, both in themselves potent risk factors for stroke and its related symptoms therefore represent a major therapeutic challenge
systemic thromboembolism (SSE). Cardiologists and general physi- and burden to health care systems. However, the relationship between
cians will often manage those patients with straightforward indica- symptoms and the onset or recurrence of AF is not always obvious,
tions (and a lack of contraindications) for anticoagulation, leaving and these symptoms may reflect other comorbidities. Given the lack
hematologists to face more difficult decisions regarding anticoagula- of a standardized symptom classification, the European Heart Rhythm
tion in patients with high bleeding risk and the consequences of Association (EHRA) score has recently been modified for use as a
therapy. clinical adjunct to classify symptoms of AF (Table 147.1). As yet,
In this chapter, we provide a brief overview and background there are no outcome data supporting its use to determine manage-
to the overall management of AF, with a focus on issues relating ment, although the modified EHRA score correlates well with more
to SSE. detailed quality of life assessments. 8

EPIDEMIOLOGY Stroke and Thromboembolism

There have been progressive increases in the incidence and prevalence The Framingham Study has clearly shown that AF is associated with
of AF, and the burden of this condition is expected to increase an increased risk of stroke (both ischemic and hemorrhagic). It is
3
further. From 2010 to 2060, the number of older adults with estimated that 20% of all strokes occur in the setting of AF; this rate
4
AF in the European Union is expected to more than double. increases to 25% in patients aged ≥80 years. Patients with AF have
Given that AF is a growing epidemic, the societal impact and an age-adjusted risk of stroke that is fivefold higher than the normal
5
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cost of this condition will continue to increase. AF is commonly population, regardless of the type of AF. Strokes in AF patients
accompanied by other comorbidities, including cardiovascular (CV) are associated with greater neurologic disability, reduced functional
diseases such as coronary artery disease and valvular heart disease, outcomes, and higher mortality than strokes in patients with sinus
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in addition to non-CV conditions affecting the lungs, kidneys, and rhythm. Cognitive dysfunction, including vascular dementia, is
liver. 6 present in 10%–15% of patients with AF, twice the rate in patients
without AF. Cognitive disturbances can occur in the absence of an
obvious stroke, as a consequence of multiple asymptomatic cerebral
PATHOBIOLOGY emboli. 11
In patients with AF, thrombi have a predilection to form within
AF can be classified based on etiology, depending on whether it the left atrial appendage (LAA) due to stagnant flow and reduced
occurs in patients without structural heart disease or whether it emptying of this blind-ended structure (See box on Concomitant
complicates other cardiac conditions. AF episodes are defined as Atrial Fibrillation and Risk of Stroke, and Fig. 147.1). The vast
paroxysmal if they terminate spontaneously (usually within 7 days) majority of atrial thrombi in nonvalvular AF (approximately 90%)
or persistent if they continue and require electrical or pharmacologic are formed within the LAA. Thrombus formation in AF is consistent
termination. Where cardioversion to sinus rhythm is not part of the with the fulfillment of the Virchow triad of thrombogenesis, with
management plan, AF is considered permanent. intraatrial stasis, endothelial dysfunction, and a prothrombotic or
The pathogenesis of AF is now thought to involve an interaction hypercoagulable state due to elevated levels of D-dimer, P-selectin,
between initiating triggers, often in the form of rapidly firing ectopic and von Willebrand factor.
foci located inside a pulmonary vein, and an abnormal atrial tissue
substrate capable of maintaining the arrhythmia. Although there is
considerable overlap, pulmonary vein triggers may play a dominant Heart Failure, Other Consequences, and Death
role in younger patients with relatively normal hearts and short
paroxysms of AF, and an abnormal atrial tissue substrate may play Beyond stroke, AF is associated with a range of CV and non-CV
a more important role in patients with structural heart disease and outcomes. Heart failure and AF are convergent disorders that are
7
persistent/permanent AF. After a period of continuous AF, electrical associated with substantial morbidity, and each of these conditions
remodeling occurs, further facilitating the continuance of AF (“AF strongly predisposes to the other. AF directly leading to acute heart
begets AF”). These changes are initially reversible if sinus rhythm is failure is termed tachycardiomyopathy, and is a direct result of
restored, but may become permanent and associated with structural the rapid heart rate that often responds to cardioversion to sinus
changes if AF continues (left atrial dilatation, cardiac fibrosis, and rhythm. However, in the vast majority of patients, the link between
impairment of systolic/diastolic function). AF and heart failure is less clear. The occurrence of new AF in

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