Uncertainty of the electrocardiogram: Old and new ideas for assessment andinterpretation

The electrocardiogram (ECG) is a highly complex, dynamic and stochastic phe nomenon. Although it provides a valuable, noninvasive and rapid means of as sessing cardiac state and its change, uncertainties in its measurement and variation in the underlying electrophysiology that generates the ECG make d ifficult further improvement in its reliability for detecting and monitorin g cardiac pathologies and conditions. This article reviews the sources of v ariability and uncertainty in ECG measurement and interpretation, revisits some old ideas for dealing with them, and proposes some novel directions fo r improving accuracy of ECG assessment and interpretation. We shall explore relative information content of lead systems, representation of ECG signal s and patterns, and estimation of ECG distributions from limited lead syste ms. In addition, we will compare strategies for measuring ECG information a nd suggest new paradigms for feature extraction that reduce the sensitivity of assessment accuracy to intrinsic and extrinsic measurement errors. Fina lly, we review the importance of including dynamic information in ECG asses sment, both for interpreting current cardiac state as well as for monitorin g its change and significance.