In a dog diagnosed with hypertrophic cardiomyopathy (HCM), which drug should be avoided?

In a dog diagnosed with hypertrophic cardiomyopathy (HCM), which drug should be avoided?

• A. Enalapril
• B. Pimobendan
• C. Furosemide
• D. Digoxin

Answer: (D)

In hypertrophic cardiomyopathy with left ventricular outflow tract obstruction, the heart’s outflow is narrowed during systole, and anything that increases the force of contraction can worsen that obstruction. Digoxin is a positive inotrope: it increases intracellular calcium, boosting contractility and potentially intensifying the dynamic obstruction. It also carries a risk of arrhythmias and interacts with preload and electrolyte status, which can complicate HCM further. Because of these effects, digoxin should be avoided. Other drugs in the list don’t have the same direct contractility-boosting issue, so they’re not chosen for avoidance on this basis, though their use in HCM can require cautious consideration depending on the specific clinical scenario.

In hypertrophic cardiomyopathy with left ventricular outflow tract obstruction, the heart’s outflow is narrowed during systole, and anything that increases the force of contraction can worsen that obstruction. Digoxin is a positive inotrope: it increases intracellular calcium, boosting contractility and potentially intensifying the dynamic obstruction. It also carries a risk of arrhythmias and interacts with preload and electrolyte status, which can complicate HCM further. Because of these effects, digoxin should be avoided.

Other drugs in the list don’t have the same direct contractility-boosting issue, so they’re not chosen for avoidance on this basis, though their use in HCM can require cautious consideration depending on the specific clinical scenario.