Some Actions of Mercury Compounds on the Heart. ∗

Discussion and Summary

The various mercurials studied show both quantitative and qualitative differences in their cardiac action. In the case of the mercurial diuretics the aminophylline containing compounds produce an increase in the sinus rate as well as ventricular tachycardia while the free mercurials produce only a ventricular tachycardia (Fig. 2). The evidence presented makes it probable that the differences in response of the heart rate are due to the theophylline content of these preparations.

The ST and T wave changes described occurred somewhat prior to the QRS changes. ST and T wave changes are probably related to alterations in the process of repolarization of cardiac muscle while the QRS changes probably indicate mainly changes in intraventricular conduction. The mercurials studied are powerful inhibitors of enzymes containing essential SH groups( 4 , 5 ). Thus the biochemical processes responsible for repolarization of cardiac muscle seem to be more sensitive to these SH inhibitors than the processes involved in intraventricular conduction.

The action of p-chloromercuribenzoate is of interest. It affects only the ST and T wave and thus probably interferes mainly with repolarization of the muscle but has no effect on intraventricular conduction processes. However; it does interfere with atrioventricular conduction and thus, with this enzyme poison it seems possible to inhibit selectively atrioventricular conduction. Differences in the histology and staining qualities of the atrioventricular and intraventricular conductile system have been described by Robb et al.( 6 ) and pharmacological differences are thus not surprising.