Evolution of Mapping and Anatomic Imaging of Cardiac Arrhythmias

Progress in the understanding of cardiac arrhythmias has emerged from a number of insightful studies elucidating the activation of and resulting impulse propagation through cardiac tissue. The identification of specific patterns of sequential depolarization have enabled electrophysiologists to recognize macroreentrant or microreentrant, automatic, and triggered tachycardias and have also characterized the contribution of repolarization to those same arrhythmias. This progress has been driven, to a large degree, by available technology designed for the detection of electrical signals originating in the heart. The successful recording of the surface electrocardiogram (ECG) by Einthoven, in a sense, marked the beginning of cardiac mapping. Although important observations were made from those original surface tracings and subsequent refinements of the ECG, further progress had to await more sophisticated technology enabling detailed point to point epicardial and intracardiac recordings. Innovative deciphering of the underlying physiology subsequently proceeded to the edge of the resolution of those techniques. Further progress required yet higher levels of technology in the form of multichannel recording devices, and later electroanatomic, voltage, and noncontact mapping techniques with computer-assisted, three-dimensional displays. Each of these clarified further the role of fundamental electrophysiologic properties in arrhythmogenesis. The more recent development of charge-coupled and photodiode-based optical mapping systems and the accompanying application to ex situ myocardium have permitted an even more careful examination of the recovery of cardiac tissue, in addition to its activation. Clearly, progress in technology has led to the disclosure of progressively more mysteries of arrhythmogenesis. Nevertheless, rather than focusing on mapping technology, per se, this article considers a limited number of sentinel observations enabled by that evolving technology and the resulting emerging understanding of cardiac arrhythmias. This article focuses exclusively on reentry. In so doing, only a limited number of the many meritorious studies will be reviewed.