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Ambulatory ECG (AECG) is very commonly employed in a variety of clinical contexts to detect cardiac arrhythmias and/or arrhythmia patterns which are not readily obtained from the standard ECG. Accurate and timely characterization of arrhythmias is crucial to direct therapies that can have an important impact on diagnosis, prognosis or patient symptom status. The rhythm information derived from the large variety of AECG recording systems can often lead to appropriate and patient-specific medical and interventional management. The details in this document provide background and framework from which to apply AECG techniques in clinical practice, as well as clinical research.

Torsade de pointes ventricular tachyarrhythmia in the long QT syndrome is a prime example of how molecular biology, ion channel, and cellular and organ physiology, coupled with clinical observations, promise to be the future paradigm for advancement of medical knowledge. Both the congenital and the acquired long QT syndrome are caused by abnormalities (intrinsic, acquired, or both) of the ionic currents underlying ventricular repolarization. In this review, the continually unraveling molecular biology of congenital long QT syndrome is discussed. The various pharmacologic agents associated with the acquired long QT syndrome are listed. Although it is difficult to predict which patients are at risk for torsade de pointes, careful assessment of the risk to benefit ratio is important before prescribing drugs known to cause QT prolongation. The in vivo electrophysiologic mechanism of torsade de pointes in the long QT syndrome is described, using as a paradigm the anthopleurin-A canine model, a surrogate for LQT3. The characteristic association of torsade de pointes with T-wave alternans and short-long cardiac sequences is discussed, with emphasis on electrophysiologic mechanisms. Finally, the expanding knowledge of genetic mutations other than long QT syndrome associated with polymorphic ventricular tachyarrhythmia is emphasized.