Feline hypertrophic cardiomyopathy (HCM) management is stratified by disease stage: preclinical cats with left atrial enlargement (LAE) receive clopidogrel for arterial thromboembolism (ATE) prevention, while cats in congestive heart failure (CHF) require loop diuretics as the cornerstone of treatment.

Prognosis and risk stratification should anchor every monitoring conversation with owners. In preclinical HCM cats, CHF or ATE occurred in 30.5% and cardiovascular death in 27.9% over the study period. Risk of CHF at 1, 5, and 10 years was 7.0%, 19.9%, and 23.9%, respectively; risk of ATE at those same intervals was 3.5%, 9.7%, and 11.3%. Cardiovascular death risk at 1, 5, and 10 years was 6.7%, 22.8%, and 28.3%, respectively. Once cardiovascular morbidity develops, mean survival is 1.3 ± 1.7 years. Only 10% of preclinical HCM cats reach 9–15 years. Journal of Vete… All-cause mortality is significantly greater in preclinical HCM cats than apparently healthy cats (65% vs. 40%) due to the cardiovascular death burden superimposed on noncardiovascular causes. Journal of Vete… Cats with HCM and a concurrent arrhythmia at diagnosis carry approximately 3 times the risk of death compared to HCM cats without an arrhythmia. Journal of the…

Echocardiography is the definitive diagnostic and monitoring tool. Mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion — hyperthyroidism, systemic hypertension, acromegaly, and dehydration must be ruled out before attributing LV hypertrophy to HCM. Journal of Feli… LAE on echocardiography identifies high-risk cats who may have no murmur on physical examination. Veterinary Clin… Dynamic left ventricular outflow tract obstruction (DLVOTO) from systolic anterior motion (SAM) of the mitral valve is the most common cause of a murmur in HCM cats; severe DLVOTO warrants treatment, while lesser degrees do not. Journal of Feli… Advanced echocardiographic techniques including speckle tracking echocardiography (STE) and tissue motion annular displacement (TMAD) can detect longitudinal systolic dysfunction even when conventional parameters are within normal limits, and may aid in monitoring disease progression. Journal of Feli…

Plasma NT-proBNP is the recommended initial biomarker screen; echocardiography is indicated when NT-proBNP exceeds 100 pmol/L. Biomarkers alone are insufficient to diagnose HCM and should not replace echocardiography. Journal of Feli…+1 Newer biomarkers such as galectin-3 are under investigation but not yet established in clinical practice. Veterinary Clin…

Clopidogrel is the recommended antithrombotic agent for high-risk preclinical HCM cats — those with LAE, spontaneous echocardiographic contrast, or poor left atrial function. Veterinary Clin…+1 The ACVIM consensus guidelines recommend clopidogrel for cats at increased ATE risk whether or not a prior ATE event has occurred. Journal of the… Approximately 10% of HCM cats will develop ATE over a 10-year period. Journal of the… Clopidogrel is the most difficult medication for owners to administer consistently, cited by 24% of owners in one adherence survey, with taste being the most common barrier. Journal of Vete… Most owners (66.7%) report twice-daily dosing as the maximum frequency they can reliably achieve, which is relevant when structuring the overall medication regimen. Journal of Vete…

Atenolol is used for rate control and management of severe DLVOTO. A dose of 6.25 mg per cat PO q12h has been used in clinical practice. Journal of Vete… Atenolol provides indirect positive lusitropic effects and potential neuroendocrine modulation in HCM cats. Journal of the… A critical drug interaction exists: concurrent mirtazapine and atenolol can produce severe bradyarrhythmia, including junctional escape rhythm with ventriculoatrial conduction. In a reported case, bradyarrhythmia resolved after mirtazapine discontinuation and atenolol dose reduction by half, with sinus rhythm returning within 10 days. Journal of Vete… If mirtazapine is needed for appetite stimulation in an atenolol-treated HCM cat, close ECG monitoring is mandatory.

Loop diuretics are the cornerstone of CHF management. Furosemide at 1 mg/kg PO q12h has been used in the clinical setting alongside clopidogrel and atenolol for cats with pulmonary edema secondary to obstructive HCM. Journal of Vete… Diastolic dysfunction with elevated atrial pressure is the primary driver of CHF signs, and treatment is directed at reducing that pressure. Journal of Feli…

Obstructive (HOCM) and nonobstructive (HCM) forms carry equivalent cardiovascular risk. There is no statistically significant difference between HOCM and HCM for cardiovascular morbidity, mortality, time to morbidity, or cardiovascular survival, making the distinction of limited clinical importance for prognosis. Journal of Vete…+1

Noncardiovascular causes of death — cancer, chronic kidney disease, and chronic gastrointestinal disease — are equally prevalent in HCM and apparently healthy cats and should not be overlooked during monitoring visits. Median survival to noncardiovascular death did not differ significantly between preclinical HCM cats (8.6 years) and apparently healthy cats (9.8 years), confirming that all-cause survival is shortened in HCM cats specifically because of the added cardiovascular mortality burden. Journal of Vete…

Would you like guidance on how to use left atrial size thresholds or specific echocardiographic measurements to decide when to start clopidogrel in a preclinical HCM cat?