Factors affecting pulsus alternans in the rapidly driven heart and papillary muscle

Abstract

Driving rates at which pulsus alternans appeared ("threshold rate") in the in situ dog heart (Nembutal anesthesia) and cat papillary muscle were determined and identified. Epinephrine abolished pulsus alternans, raising threshold rates. This effect was abolished by a [beta] -blocking agent (propranolol). Calcium ion also abolished alternans and EDTA lowered threshold for alternation in mechanical responses. Calcium acted after propranolol, and epinephrine action was not prevented by EDTA. Ouabain abolished alternans at the threshold rates and this effect remained after EDTA administration and after EDTA plus propranolol. Quinldine lowered threshold for alternans as did high KC1 but not in all instances. Following KC1 injection an initial negative inotropic action was often followed by a late rise in blood pressure and abolition of existing alternation. Propranolol diminished this late action. Results obtained in papillary muscle confirmed those from the in situ heart. Mechanical alternation at threshold rates was not accompanied by an alternation in electrical response in either preparation. Multiple factors which can be affected independently are involved in cardiac excitation-contraction coupling and the maintenance of uniform mechanical responses.