A clinically utilized intravenous continuous rate infusion of diltiazem does not significantly decrease systolic function in healthy dogs.

Objective: To determine if left ventricular systolic function on echocardiography, systemic blood pressure, and electrocardiography change with a clinically accepted intravenous (IV) diltiazem constant rate infusion (CRI) compared to a control.

Animals: 10 healthy client-owned adult dogs.

Procedures: Prospective, masked, crossover study from May 27, 2021, to August 22, 2021. Dogs were randomized to receive diltiazem (loading dose of 240 μg/kg, IV followed by a CRI of 6 μg/kg/min for 300 minutes) or the same volume of 5% dextrose in water (D5W) administered IV followed by the opposite intervention after a 7-day washout. Blood pressure was monitored during each CRI, and echocardiographic and electrocardiographic studies were performed immediately before the CRI and during the last hour of the CRI.

Results: Postdiltiazem systolic time interval (STI) (median, 0.30; range, 0.16 to 0.34) was significantly lower than post-D5W STI (median, 0.32; range, 0.22 to 0.40; P = .046). All other echocardiographic parameters did not differ significantly between each of the groups after receiving diltiazem or D5W. Systemic blood pressure did not change significantly with either diltiazem (P = .450) or D5W (P = .940), and none of the dogs became hypotensive at any point in the study. Expectedly, negative dromotropy was observed with diltiazem.

Clinical Relevance: A significant decrease in left ventricular systolic function was not appreciated in healthy dogs receiving diltiazem at a clinically accepted intravenous infusion rate at this dosing regimen. Further studies are needed in dogs with cardiac disease.