Effects of diltiazem on hemodynamic variables and ventricular function in healthy horses.
Authors: Schwarzwald Colin C, Bonagura John D, Luis-Fuentes Virginia
Journal: Journal of veterinary internal medicine
Summary
Diltiazem, a calcium channel blocker, has shown promise for controlling ventricular rate in atrial fibrillation across multiple species, yet its safety profile and optimal dosing in horses remained undefined. Schwarzwald and colleagues administered intravenous diltiazem to eight healthy, conscious horses in escalating cumulative doses (0–2 mg/kg), measuring cardiac electrophysiology, ventricular function via catheterisation and echocardiography, and peripheral haemodynamics throughout treatment. The drug reliably suppressed sinus and atrioventricular nodal activity whilst producing peripheral vasodilation and increased forelimb blood flow, though it modestly impaired both systolic and diastolic left ventricular function; however, compensatory sympathetic activation from baroreceptor reflexes partially offset these negative inotropic effects in most horses. Two animals developed significant sinus arrests with severe hypotension, indicating that dosing must be carefully titrated and that systemic vascular collapse represents a genuine risk, particularly at cumulative doses approaching 2 mg/kg. For practitioners considering diltiazem in cases of equine atrial fibrillation, the drug's AV nodal effects make it mechanistically suitable for rate control, but close cardiovascular monitoring—including blood pressure surveillance—is essential, and conservative dosing protocols should be established before clinical application becomes routine.
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Practical Takeaways
- •Diltiazem shows promise for controlling heart rate in equine atrial fibrillation through AV nodal inhibition, but dosing must be carefully individualized due to variable plasma concentrations
- •Hypotension from vasodilation and direct sinus node suppression are the primary dose-limiting factors; monitor blood pressure and cardiac rhythm closely during administration
- •Baroreceptor reflex-mediated sympathetic activation may partially offset diltiazem's negative effects on the heart, suggesting careful monitoring is needed to distinguish true cardiac depression from compensatory mechanisms
Key Findings
- •Diltiazem achieved plasma concentrations of 390-910 ng/mL with considerable inter-individual variation among horses
- •Diltiazem caused intermittent depression of sinus and AV nodes with mild impairment of systolic and diastolic LV function
- •Diltiazem produced arterial vasodilatation, increased limb blood flow, and decreased systemic vascular resistance
- •Two horses developed transient high-grade sinus arrest with severe systemic hypotension, limiting safe dosage