Cardiac Actions of a Myocardial Depressant Factor Isolated from Shock Plasma 1

Summary

A myocardial depressant factor (MDF) which appears in the plasma during a variety of forms of shock was tested on the isolated perfused cat heart (Langendorff preparation) for cardiotoxic properties, MDF exerted a marked negative inotropic effect (83% decrease in cardiac contractile force) under conditions of controlled heart rate, coronary perfusion pressure, and resting tension. Coronary flow increased an average of 35% during this rapid decline in contractile force. Cardiac arrest occurred in 88% of the experiments within 1 to 2 min after addition of the plasma extract containing MDF to the perfusate. As contractile activity reappeared following cardiac arrest, A-V blocks frequently occurred. These results indicate that MDF has a direct negative inotropic effect on the isolated cat heart. This cardiotoxic effect is not a result of restriction of coronary flow, since coronary flow increased during the negative inotropic effect, nor of the induction of arrhythmias, since the arrhythmias (e.g., A-V block and premature ventricular contractions) occurred after the negative inotropic effect had occurred.