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A recent study examined the confounding effect of mortality on the frequency of CV-related hospitalization in patients in the Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT). The impact of tafamidis on CV-related hospitalization was underestimated in the ATTR-ACT, according to researchers.

Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressive disease caused by the buildup of amyloid deposits in the heart muscle, which can lead to heart failure. Tafamidis, also known by the brand names Tindamax and Vyndaqel, is a prescription drug used to delay progression of certain types of transthyretin amyloidosis in adults.

Tafamidis was shown to be an effective treatment for patients with ATTR-CM in the international and multicenter clinical trial, Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT). Tafamadis has since been approved for wild-type cardiomyopathy or hereditary transthyretin-mediated amyloidosis in adults for reducing cardiovascular-related hospitalization and mortality and is recommended in heart failure treatment guidelines.

The New York Heart Association (NYHA) classification system places patients in one of four categories based on how much they are limited during physical activity. In ATTR-ACT, while the cardiovascular-related hospitalizations were reduced for most ATTR-CM patients who received tafamidis, in the NYHA class III subgroup, there was still a greater incidence of cardiovascular-related hospitalization.

This was unexpected because tafamidis was found to improve not only mortality but also functional capacity and quality of life in the same group of patients. According to a recent secondary analysis, the initial ATTR-ACT data likely underestimated the effect of tafamidis on cardiovascular-related hospitalizations due to the confounding effect of death post- randomization.

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When the survivor average causal effect was used to adjust for survivor bias, researchers discovered a 24% reduction in the frequency of cardiovascular-related hospitalization in NYHA class III patients treated with tafamidis. This finding suggests that tafamidis improves outcomes in patients with ATTR-CM regardless of NYHA class.

Li, H., Rozenbaum, M., Casey, M., & Sultan, M. B. (2022). Estimating the Effect of Tafamidis on Cardiovascular-Related Hospitalization in NYHA Class III Patients with Transthyretin Amyloid Cardiomyopathy in the Presence of Death. Cardiology, 147(4), 398-405. doi:10.1159/000525883