Cardiology
Core concepts
Cardiology questions reward a disciplined approach: distinguish anatomy/physiology (pressure-volume loops, Frank-Starling, excitation-contraction coupling) from pathophysiology (volume overload vs. pressure overload, forward vs. backward failure) and from therapeutics (when to use diuretics, ACE inhibitors, pimobendan, antiarrhythmics). Know the ACVIM consensus staging of myxomatous mitral valve disease (MMVD): stage A (at risk), B1 (asymptomatic, no remodeling), B2 (asymptomatic with cardiomegaly), C (symptomatic/CHF), D (refractory CHF). Understand that pimobendan is indicated in stage B2 and C/D, and that the EPIC trial established its benefit in preclinical cardiomegaly. For feline cardiomyopathy, distinguish HCM (concentric hypertrophy, diastolic dysfunction, dynamic outflow obstruction), restrictive, and unclassified; DCM is now rare and taurine-related in cats.
Common traps
- Assuming a murmur grade predicts severity-grade correlates poorly with hemodynamic significance.
- Confusing S3 gallop (volume overload/CHF in dogs) with physiologic findings.
- Forgetting that cats with HCM often present with respiratory signs or thromboembolism, not a murmur.
- Mixing up which arrhythmias are vagally mediated (sinus arrhythmia, 1st/2nd-degree AV block) vs. pathologic.
- Applying human heartworm or DCM guidelines to veterinary patients.
Worked rule of thumb
A small-breed dog with a left apical systolic murmur and a vertebral heart score of 12.5 (normal ≤10.5) but no clinical signs is stage B2 and should receive pimobendan; a dog with the same murmur, VHS 11.0, and no remodeling is B1 and is monitored, not treated. Vertebral heart score and LA:Ao ratio are the practical remodeling markers.