Immunohistological findings
Myocardial infiltration with large amounts of macrophages and T-cells is regularly observed in ICM [8] and was also present in ICM patients in our group. Patients fulfilling the criteria of TCM had a distinct pattern compared to ICM patients. The presence of macrophages and T-cells was significantly lower in the TCM group and more comparable to alterations seen in DCM patients. These findings are in some contrast to a study of EMB results in TCM patients, where the authors demonstrated a macrophage-dominated myocardial inflammation [8], which has been described in animal studies as well [20]. These differences to our results might be, at least in part, explained by the relatively short duration of tachycardia in our cohort, which was 25 % shorter compared to the animal studies; Mueller and colleagues did not report the duration of symptoms [8]. However, the relationship between arrhythmia to cardiomyopathy and the development of symptoms is difficult to determine because an arrhythmia could exist for a long time before its recognition and before TCM develops [18]. A study of 24 patients with TCM and HF, the median time from onset of arrhythmia to cardiomyopathy, and the development of HF was 4.2 years [21]. Also, in animal rapid atrial pacing TCM-models, there is a compensatory phase whereby LV dilatation, extracellular matrix remodeling, and neurohumoral activation occurs, but severe LV dysfunction does not. This phase is followed by a phase in which LV dysfunction becomes manifest and associated with defects in excitation-contraction coupling and LV myocyte remodeling and dysfunction [18]. So, the time point of EMB during the disease course will most probably have a significant impact on the results of the immunohistochemical analysis.