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A large study of cardiovascular risk in HCM and healthy cats, Part Two

Fox PR, Keene BW, Lamb K, Schober KA, Chetboul V, et al. International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study. J Vet Intern Med. 2018 Apr 16. (Winn Funded Study, W09-017)

This post continues from the previous blog regarding long term outcomes in subclinical hypertrophic cardiomyopathy. Make sure you’ve read the previous blog first to get the full context of the paper.

30.5% of cats diagnosed with hypertrophic cardiomyopathy (HCM) experienced some type of cardiovascular morbidity over the course of the study. Only 0.97% of healthy cats experienced a cardiac event. 24.2% of HCM cats experienced CHF, and 11.6 ATE. Only 2.2% experienced sudden death. As previously mentioned, there was no significant difference in any measured outcome for HCM vs obstructive (HOCM) groups.

The risk of cardiovascular morbidity and mortality increased at 1, 5, and 10 years after recruitment to the study. Risk of cardiac death was 1 in 15, 1 in 4.4, and 1 in 3.5 at 1, 5, and 10 year points for HCM cats. Risk of cardiac death for healthy cats remained stable at 1 in 100 throughout the study period. Interestingly, the use of cardiovascular medications had no effect on survival through the duration of the study.

30.5% of cats with HCM experienced congestive heart failure (CHF), arterial thromboembolism (ATE), or both, and 27.9% experienced cardiovascular death. This suggests that most cat who experience clinical signs of HCM will die of their disease. Risk for cardiovascular morbidity (CHF/ATE) assessed at 1, 5, and 10 years after study entry was 7.0%/3.5%, 19.9%/9.7%, and 23.9%/11.3%. This suggests that the risk for CHF is consistently ~2x the risk of ATE, though it is important to remember that many cats may experience both CHF and ATE. Risk of cardiac death was 6.7%, 22.8%, and 28.3% respectively at these time points. While risk of CHF increased steadily with age, the risk of ATE has largely plateaued by the third quartile.

One graph is a Kaplan-Meir survival curve in the study showing the survival of cats with HCM compared to healthy cats. It shows a steady decrease in the survival of cats with HCM over the course of time, and suggests that the median survival for a cat with subclinical HCM is 10.9 years.

Graphs from the study show the survival of cats experiencing cardiovascular events. A large portion of cats who have cardiovascular events die within the first few months, however cats that survive a year are likely to have a more prolonged survival. Survival curves for CHF and ATE are similar. The average survival for cats that survived >1 day after diagnosis of HCM or CHF was 1.3 years.

This study reached several significant conclusions based on the data collected from this population. These include clear incidence and risk statistics, indication of the survival times after the onset of clinical signs, and demographic information regarding the effected population.

Perhaps the most interesting conclusion reached was that HCM and HOCM have no difference in survival or morbidity at any point in the study, contrary to data in the human literature. Another significant finding was that the use of cardiovascular medications had no apparent effect on survival in the pre-clinical stage.

While this study was well designed and has significant power due to its large sample size and breadth of recruitment, it also has several drawbacks. The retrospective nature of the study presents some limitations and sources of potential bias that could be minimized with a prospective design. The lack of standardization of treatment protocols also presents a potential source of error, as even though there was no overall benefit to survival, stratification into specific therapies was not performed. Lastly, the large number of individual investigators may have led to varying classifications of disease.

Overall, this study provides valuable high level survival and morbidity data on cats with naturally occurring HCM. Its large enrollment numbers and multinational scope allow for valuable epidemiologic data to be collected. (MRK)

See also:

Paige CF, Abbott JA, Elvinger F, Pyle RL. Prevalence of cardiomyopathy in apparently healthy cats. J Am Vet Med Assoc. 2009;234:1398–1403.