Moscow, Russia Purpose: Understanding of the basic mechanisms of atrial fibrillation (AF) maintenance and termination may help to optimise AF treatment. The objective of this study was to analyse the process of AF termination in humans. Method: Six patients with paroxysmal AF (48.7 + 2.8 y.o.) underwent noninvasive ECG imaging (ECGI) procedure (EP Solution SA, Switzerland). Up to 224 special unipolar electrodes were placed onto the patient's torso followed by ECG-gated computed tomography (CT)

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... canning of the torso and heart. A CT data was processed by the ECGI system to reconstruct 3-dimensional models of the torso and heart. Body surface electrodes were connected to the ECGI system and ECG recordings up to 30 min in duration during AF were performed. The phase of the unipolar electrogram at each point was calculated using the Hilbert transform and a phase map was reconstructed to analyse the patterns of AF termination. Results: During AF we registered 1 or 2 pairs of rotors. In 3 cases AF terminated spontaneously and in 3 other cases during propafenone administration. The mechanism of the AF termination was the movement towards each other, connection and mutual annihilation of the rotors with opposite chirality. Two types of AF termination patterns were observed: by closing in the ring and by reduction of the wave front (Figure) . The most of rotors annihilation events did not lead to AF termination because the second wave front was maintaining AF. Propafenone administration led to decreasing of rotors stability and increasing of the number of collision events. Conclusion: The understanding and further investigation of the AF mechanisms is crucial to improve medical treatment and may add some new targets to interventional procedure. Conflict of interest: Alexey Tsyganov consults EP Solutions SA. Vitaly Kalinin holds equity in EP Solutions SA. Purpose: Sudden cardiac death in young athlete is always tragic. Some international guidelines recommend the realization of an electrocardiogram before practising competitive sports to carry out the risk of sudden cardiac death due to genetic cardiopathy like QT long syndrome. Unfortunately, the diagnosis can be difficult because intensive sport can increase the QT interval over normal recognized values for sedentary people. Using a QT correction formula free of heart rate appears essential. Patients and methods: 446 young athletes (aged 10 to 18) had an electrocardiogram. QT intervals were measured and four methods were used to correct the QT interval for heart rate. Results: The Bazett formula performed the worst in terms of rate adjustment success. Hodges and Fridericia formulas are the best both in males and females, independently of age. Female had longer QTc intervals than males. Conclusion: The most widely used Bazett formula should be surrendered whereas Hodges and Fridericia formulas should be prefered, particularly in young athletes.