DGM : Directed-Graph Mapping as a novel tool to analyze cardiac arrhythmias

Cardiac arrhythmias and related diseases are the leading cause of death in the Western world. The management thereof currently accounts for about 9\% of the total health-care expenditure across the EU. Research on the mechanisms of arrhythmia and optimizations of diagnostic tools remain important. The normal rhythm of the heart results in about 60 to 100 beats per minute, which accumulate roughly to about 3 billion beats in a lifetime. It is likely for this rhythm to get disturbed once in a while. Naturally, the heart rate increases with exercise or slows down during sleep. Drugs, alcohol, nicotine and the general health condition of a person may also affect the heart's condition. However, persistent abnormality of the heart rhythm can indicate cardiac arrhythmia and the associated complications will depend on the type of arrhythmia. In general, complications and symptoms of cardiac arrhythmias may include a racing or slow heartbeat, chest pain, shortness of breath or even anxiety and fatigue. In more severe cases cardiac arrhythmia can induce stroke, heart failure and sudden cardiac death. Treatment of arrhythmia may include medication, specific therapies such as vagal maneuvers and cardioversion, surgery like ablation and maze procedures or the placement of implantable devices lika a pacemaker or defibrillator. For this work, mainly ablation therapy is of interest. During ablation the electrophysiologist (EP) inserts a catheter (a measuring device with electrodes) into the heart and records the electrical activity. These electrical signals are presented on a color-coded map. Based on an educated interpretation of these color maps and corresponding signals the EP will gather knowledge about the mechanism maintaining the arrhythmia. Once the mechanism is understood and located, the EP will ablate or scar the heart tissue in order to stop electrical propagation in that specific region. This will stop the arrhythmia restoring the normal heart rhythm or convert the excitation pattern to a (usually) slower arrhythmia. It can be very challenging to determine the mechanism of an arrhythmia and wrong ablation lines can make the heart prone to new arrhythmias and limits the myocardial contractility. Analysis of these electrical maps can be difficult and prone interpretation. Therefore, there is a need for automated and operator independent interpretations and strategies. My dissertation is devoted to the development, applicability and accuracy of Directed-Graph Mapping or DGM on analysis of cardiac arrhythmia mechanisms. DGM is a mathematical approach based on concepts of network theory describing the properties of cardiac excitation waves. DGM takes as input the spatial coordinates of the electrodes and the Local Activation Time (LAT) of the signals. With this data, a directed graph is created. Based on validated algorithms of graph theory and new algorithms I designed, DGM automatically analyzes these graphs and presents the rotational circuit or focal sources of the arrhythmia under study