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The 12-lead standard electrocardiogram (ECG) is a 10 second recording of human myocytes electrical activity. Filters and oversampling are necessary in order to acquire a smooth signal without distortion. ECG recordings may display ongoing arrhythmias, and some leads may be helpful in formulating the diagnosis. Advanced modalities of baseline ECG recording can be used to extract additional information with significant prognostic value. Ambulatory ECG (AECG) recording is a long-term and low-cost external recording obtained with 1 to 12 leads lasting from 24 to 30 days. For patient comfort, longer AECG recordings use fewer leads.

Surface electrocardiograms, both resting 12-lead electrocardiographs and ambulatory electrocardiograph monitoring, play an essential role in establishing indications for cardiac implantable electronic devices (pacemakers, cardiac implantable defibrillators, and cardiac resynchronization therapies), and in the evaluation of patients already implanted. Current devices have prolonged memory capabilities (defined as Holter functions) and remote monitoring functions, to evaluate the electrical properties and the automatic detection of arrhythmias. Nonetheless, surface electrocardiography remains the critical tool to detect device malfunction, evaluate programming and function, verify the automatic arrhythmia analysis and the delivered electric therapy, and prevent inappropriate intervention.

The common arrhythmia atrial fibrillation (AF) is incompletely understood. The mechanism of initiation and the perpetuation of AF remain speculative. This article summarizes current knowledge of the complex relationship between arrhythmias triggering AF and their long-term effects on atrial tissue, leading to perpetuation of tachycardia. It focuses on the role of the electrocardiogram (ECG) from AF diagnosis to identification of sinus P wave abnormalities predicting future occurrences. The role of ambulatory ECG recordings in managing AF and the use of frequency analysis determining degree of organization and identification of AF triggers are discussed.

The main role of ambulatory electrocardiography (AECG) in clinical practice is to detect and characterize the behavior of cardiac electrical activity during ordinary daily life activities. Because certain rhythm abnormalities may be infrequent and paroxysmal, and may occur only during sleep or in association with mental, emotional, or exercise-induced perturbation in cardiac function, AECG needs to be recorded over a long period of time, originally lasting 24h and now expanding up to several weeks and even to months. New technologies for continuous prolonged AECG monitoring, and new algorithms for automatic arrhythmia detection and wireless data transmission in near real-time, have significantly improved the ECG signals quality for long-term recordings and the diagnostic yield for infrequent cardiac arrhythmias. New wireless electrode systems, such as patches, vests or belts have greatly increased the tolerability, quality and feasibility of prolonged AECG, which is particularly useful for the diagnosis of infrequent symptoms, such as unexplained syncope, palpitations or cryptogenic stroke.

The QT interval on surface electrocardiogram represents the sum of depolarization and repolarization process of the ventricles. The ventricular recovery process, reflected by ST segment and T wave, mainly depends on the transmembrane outward transport of potassium ions to reestablish the endocellular electronegativity. Outward potassium channels represent a heterogeneous family of ionic carriers, whose global kinetics is modulated by heart rate and autonomic nervous activity. Several cardiac and noncardiac drugs and disease conditions, and several mutations of genes encoding ionic channels, generating distinct genetic channellopathies, may affect the ventricular repolarization, provoke QT interval prolongation and shortening, and increase the susceptibility to ventricular arrhythmias.

Almost 50 years after the first description of congenital long QT syndrome (LQTS), where QT interval prolongation was recognized as the hallmark of a new pathologic entity associated with sudden cardiac death ([1][1]), the simple linear measurement of QT interval still stands as the strongest