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Atrial fibrillation (AF) is the most common form of cardiac arrhythmia, so a review of the role imaging in AF is a natural topic to include in this book. Further motivation comes from the fact that the treatment of AF probably includes more different forms of imaging, often merged or combined in a variety of ways, than perhaps any other clinical intervention. A typical clinical electrophysiology lab for the treatment of AF usually contains no less than six and often more than eight individual monitors, each rendering some form of image-based information about the patient undergoing therapy. There is naturally great motivation to merge different images and different imaging modalities in the setting of AF, but this is also very challenging as a result of a host of factors, including the small size, extremely thin walls, large natural variation in atrial shape, and the fact that fibrillation is occurring so atrial shape is changing rapidly and irregularly. Thus, the use of multimodal imaging has recently become a very active and challenging area of image processing and analysis research and development, driven by an enormous clinical need to understand and treat a disease that affects approximately five million Americans alone, a number that is predicted to increase to almost 16 million by 2050.1
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In this chapter, we attempt to provide an overview of the large variety of imaging modalities and their uses in the management and understanding of AF, with special emphasis on the most novel applications of magnetic resonance imaging (MRI) technology. To provide clinical and biomedical motivation, we outline the basics of the disease together with some contemporary hypotheses about its etiology and management. We then describe briefly the imaging modalities in common use in the management and research of AF, and then focus on the use of MRI for all phases of the management of patients with AF and indicate some of the major engineering challenges that can motivate further progress.
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Clinical Profile of AF
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AF is a growing problem in modern societies, with an enormous impact on both short-term quality of life and long-term survival.2 Approximately 0.5% of people age 50 to 59 years have AF, and 9% of people age 80 to 89 years have AF, and these prevalences are increasing.1,3 Although many people with the condition go untreated, AF is associated with an almost two-fold increase in the risk of mortality. AF patients experience a dramatically increased rate of stroke (from 1.5% for those aged 50 to 59 years to 23.5% for those between age 80 and 89),4 a risk that, by contrast, decreases with age in the normal population. Treatment of AF represents a significant health care burden, with the annual costs estimated at approximately seven billion US dollars.5
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Restoring and maintaining normal sinus rhythm remains one of the major goals in treating patients with AF. One treatment modality is ...