The antiarrhythmic effects of Leonurus cardiaca on cardiac electrophysiology
Although several antiarrhythmic drugs of chemical origin are in clinical use since decades, their application is often limited by their adverse effects and especially by their inherited proarrhythmic risk, which can lead to a significantly increased mortality in patients receiving these compounds . On the other hand, aqueous extracts from the central European Lamiaceae Leonurus cardiaca have been used for centuries as a remedy against tachyarrhythmia and other cardiac disorders. Nevertheless, a scientific basis for the claim of a direct cardiac electrophysiological or antiarrhythmic effect of Leonurus preparations has not been established up to now . In order to concentrate the active compounds from the raw decoct and to eliminate undesired substances, a bioassay guided fractionation procedure was applied, resulting in a refined extract the reproducibility of which was controlled by TLC and HPLC. This refined extract was applied intracoronarily in isolated rabbit hearts perfused according to the Langendorff technique. Mapping experiments with 256 electrodes on the heart surface (HAL4) showed a reduction of left ventricular pressure and an increase of relative coronary flow at a concentration of 2.0mg refined extract per ml. Furthermore, the PQ-interval was prolonged and both the basic cycle length and the activation recovery interval were increased. In addition, patch-clamp-investigations were performed on several cell models demonstrating that the refined extract exerted calcium-antagonistic activity (ICa.L blockade) and prolonged the AP-duration, possibly explaining the old traditional use of Leonurus cardiaca, described in German herbals  as „fürtrefflich gut zu dem Zittern und Klopfen des Herzens“.
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