Is ASA as Good as Warfarin in the Treatment of Atrial Fibrillation?

Findings of a Provocative New Meta-Analysis

Jason M. Burstein, MD
Internal Medicine Resident,
University of Toronto,
Toronto, ON.

Shabbir M.H. Alibhai, MD, MSc, FRCP(C)
Clinical Assistant, Internal
Medicine & Geriatrics,
University Health Network, Toronto, ON.

Introduction
Atrial fibrillation is a common cardiac condition that challenges many physicians, including primary care and emergency doctors, general internists, geriatricians and cardiologists. One of the best-understood and most studied complications is cardio-embolic stroke. While management of atrial fibrillation may seem straightforward, it is interesting to note that there are still large variations in practice patterns, and a recent meta-analysis was contradictory to many previous studies and guidelines. This paper will focus on the epidemiology and treatment of atrial fibrillation in the older population and will examine both the reasons for variations in practice pattern and the conflicting evidence in major medical journals.

Epidemiology and Causes of Atrial Fibrillation
Age is perhaps the most important influence on the incidence and prevalence of disease. The prevalence rate of atrial fibrillation is 2-3% at age 60 to 65 and 8-10% at age 80. Up to 70% of all affected patients are at least 65 years old. The incidence of atrial fibrillation before age 50 is 0.5 per 1,000 person-years and increases to 9.7 per 1,000 person-years after age 70.^1,2

The relation of atrial fibrillation to age is in part captured by the underlying causes of atrial fibrillation, which are more common in the geriatric population (see Table 1). Any cause of structural heart disease that results in changes to atrial size and pressure can lead to atrial fibrillation. In developed countries, hypertensive heart disease is the most common cause of atrial fibrillation.³ Importantly, some patients have a structurally normal heart with no other identifiable non-cardiac cause. This entity is referred to as lone atrial fibrillation and has important prognostic and therapeutic implications, as will be discussed.

Complications of Atrial Fibrillation
Atrial fibrillation results in a number of complications, both acute and chronic in nature. The loss of atrial contribution to cardiac output may result in a 20% decrease in left ventricular stroke volume.⁴ Therefore, new onset atrial fibrillation can result in cardiac ischemia, congestive heart failure and hemodynamic instability. Pre-existing left ventricular dysfunction, mitral stenosis, diastolic dysfunction, and rapid ventricular responses all predispose to more serious presentations of atrial fibrillation.

In many patients with atrial fibrillation there is no acute medical instability but more chronic issues at hand. The most common symptoms include palpitations, fatigue and decrease in exercise tolerance. Quality of life in patients with chronic atrial fibrillation is also reduced. It has also been demonstrated that elderly patients with chronic atrial fibrillation more often have impaired cognitive function as compared to age-matched controls.^5,6,7 Moreover, atrial fibrillation adversely affects survival. Data from the Framingham Heart Study demonstrated a relative risk of dying of 1.5 for men with atrial fibrillation and 1.9 for women, after adjustment for other risk factors.⁸

One of the most well studied risks of chronic atrial