Difference in degree of A-V block and QS2 abbreviation of ouabain digoxin and digitoxin in cats.

Six trained domestic cats received a spectrum of polar to nonpolar cardiac glycosides: ouabain, digoxin or digitoxin with medication free intervals of four weeks. Significant (P less than 0.01) rate reduction (-19 +/- 8%) and prolongation of PR interval (+13 +/- 5%) occurred with ouabain and with digoxin (-18 +/- 5% and +13 +/- 3%) but not with digitoxin (-6 +/- 4% and +6 +/- 5%). However, rate corrected QS2 abbreviation was greater with digitoxin (-13 +/- 3%) than with ouabain (-8 +/- 3%) or digoxin (-10 +/- 5%). The findings indicate that in cats the polar cardiac glycosides ouabain and digoxin produce greater prolongation of A-V conduction while the nonpolar glycoside digitoxin produces greater abbreviation of QS2. Previously this finding was reported by the authors in guinea-pigs and in rabbits and has since been reported in intact rats, dogs, and in man by other authors. Investigators using nonintact subjects have not been able to demonstrate the finding. The differences may have clinical significance and suggest new insight into structural/activity relationships within the cardiac glycoside family.