Abstract Body (Do not enter title and authors here): Introduction
Cardiothoracic diseases remain a leading cause of mortality globally, with a significant proportion amenable to surgical intervention.
Research Question
Can we quantify and compare national health system capacity to meet the burden of cardiovascular disease amenable to cardiac surgery using publicly available proxy indicators?

Methods
We developed the Cardiothoracic Surgery System Pulse Index (CSSPI), a standardized index ranging from 0 to 100 to assess national capacity for cardiac surgical care. The index incorporates proxies of cardiothoracic disease burden, workforce, infrastructure, service delivery, information management, funding, and governance obtained from open access databases. Indicators were normalized using min-max scaling. Two scenarios were created using weighted and unweighted composite scores. Pearson’s correlation was used to measure the correlation between the two scenarios, regional and country income variations were assessed using ANOVA, and a linear regression model was constructed. A p-value <0.05 was considered statistically significant.

Results
The mean unweighted CSSPI was 31.4 (SD = 10.3) while the mean weighted CSSPI was 28.9 (SD = 14.8) [median difference = 3.0, (IQR: -2.0, 9.0); correlation coefficient = 0.75, p < 0.001]. Comparison of the unweighted (F (6, 210) = 9.135, p < 0.001) and weighted (F(6, 210) = 16.569, p < 0.001) CSSPI revealed significant regional variations. North America had the highest CSSPI values (mean unweighted = 40.7, SD = 25.6; mean weighted = 50.3, SD = 25.5) followed by Europe and Central Asia (mean unweighted = 36.5, SD = 10.0; mean weighted = 37.8, SD = 15.0). However, sub-Saharan Africa had the lowest regional values (mean unweighted = 24.9, SD = 7.9; mean weighted = 17.7, SD = 7.6). Similarly, disparities were observed between income categories with low-income countries ranking lower consistently (mean unweighted = 24.4, SD = 8.2; mean weighted = 16.0, SD = 6.0). World Bank income category (B = 2.600, p < 0.001) and regional (B = -1.059, p = 0.004) disparities persisted in the regression model.

Conclusion
The CSSPI suggests that income level positively influences surgical system capacity, while regional disparities may reflect structural or geographic inequities.