The electrocardiogram is a valuable diagnostic method providing insight into pathologies of the heart, especially rhythm disorders or insufficient myocardial blood supply (myocardial ischemia). The commonly used surface ECG is, however, limited in detecting short-lasting myocardial ischemia, in particular in the territory of the left circumflex coronary artery supplying the postero-lateral wall of the left ventricle. Conversely, an ECG recorded in close vicinity to the myocardium, i.e., within a coronary artery (intracoronary ECG, icECG) has been thought to overcome these limitations. Since its first implementation during cardiac catheterization in 1985, icECG has shown ample evidence for its diagnostic value given the higher sensitivity for myocardial ischemia detection when compared to the surface ECG. In addition, icECG has been demonstrated to be a direct measure of myocardial ischemia in real-time, thus, providing valuable information during percutaneous coronary diagnostics and interventions. However, a lack of analysing systems to obtain and quantify icECG in real-time discourages routine use.

The goals of this MD-PhD thesis are two-fold: First, to determine the diagnostic accuracy of icECG ST-segment shift during pharmacologic inotropic stress in comparison to established indices for coronary lesion severity assessment using quantitative angiographic percent diameter stenosis as reference (Project I). Second, to determine the optimal icECG parameter for myocardial ischemia detection and quantification (Project II and III).

In essence, this thesis demonstrates that the icECG is an easy available diagnostic method providing highly accurate information on the amount of myocardial ischemia in real-time. Quantitative assessment of acute, transmural myocardial ischemia by icECG is most accurately performed by measuring ST-segment shift at the J-point, while the quantitative assessment during physical exercise, respectively its pharmacologic simulation, is most accurately performed by measuring ST-segment shift 60ms after the J-point.