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INTRODUCTION

Atrial fibrillation (AF) is a very common arrhythmia that has been the subject of an enormous amount of research into its mechanism and treatment over the past 20 years. Nonetheless, treatment decisions can be nuanced and complicated regarding whom to treat and how to treat with choices of pharmacologic versus nonpharmacologic therapies. This new chapter has been added to our second edition that will explore these areas leaving ablation of AF to be detailed in Chapter 17.

CLASSIFICATION

AF is characterized by rapid, typically more than 400/min, disorganized atrial activation that varies both spatially and temporally. On the surface electrogram this can appear as a wavy baseline without any distinct P waves (Figure 9-1A) or as a tracing that at times gives the appearance of a flutterlike rhythm (Figure 9-1B). However, true atrial flutter has an atrial rate like a metronome with clocklike regularity, and careful measurement of the flutterlike appearance in the AF tracing shows the atrial rate is irregular. With rare exception of dissociated atria, AF and true atrial flutter do not coexist. The ventricular rate is usually irregularly irregular unless the patient has heart block.

FIGURE 9-1

ECG rhythm strips of atrial fibrillation. Panel A, minimal if any atrial activity noted; Panel B, coarse atrial activity at times with a flutterlike appearance. (See text for details.)

  • A widely accepted classification follows:1-3

  • Paroxysmal—Self-terminating episodes usually lasting less than 12-24 hours but up to 7 days;

  • Persistent—episodes lasting more than 7 days and often requiring pharmacologic or electrical cardioversion;

  • Long-standing persistent—continuous AF for at least a year;

  • Permanent—AF that could not be cardioverted into sinus rhythm or a decision made by the patient and physician not to pursue sinus rhythm as a treatment option.

This classification system has problems since many patients have had episodes of both paroxysmal and persistent AF. In such cases, we tend to characterize patients by their dominant presentation. So, for patients who typically have self-terminating episodes but over the years have had an occasional cardioversion, we would designate them as paroxysmal. Further, the use of paroxysmal as a monolithic category is likely too simplistic. Some patients almost never have episodes lasing more than 6-12 hours, while others often have them for days. It is possible that triggers and substrate mechanisms differ between such patients.

EPIDEMIOLOGY

AF is estimated to affect up to 5 million Americans and 4.5 million Europeans.1-4 Its incidence and prevalence increase with age. Approximately 1% of the population less than 60 years of age has AF, but more than one-third of AF patients are at least 80 years old. A family history of AF is not uncommon, but ...

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