Local myocardial and global ventricular function compared during positive inotropic medication

Abstract

The assessment of the pharmacological efficiency of cardiotonic drugs interferes with the complex force generation within the spatially netted myocardial meshwork. By multifocal local force and distance measurements we distinguished "afterloaded" from "unloading" force types, which essentially differ in their transient behaviour during changes in ventricular shape. Histologically we found the "afterloaded" force type in oblique fibre populations whereas the "unloading" force curve is generated in surface parallel fibres. Amrinon reduces pre- and afterload, thus inducing ventricular shrinkage. The resulting rearrangement of the intramural force pattern modifies the transmission of fibre tension to ventricular ejection in a way that contractility indices, derived from left ventricular pressure, become inapplicable. However, direct intracoronary drug injection, monitored by segmental force and distance measurements within the irrigated myocardial area, characterizes Amrinon as a potent positive inotropic drug.