Determinants of Premature Cardiovascular Mortality and the Role of Health System Responsiveness in South South Nigeria: A Mixed-Methods Investigation

Premature cardiovascular mortality in South South Nigeria is driven by a confluence of biological risk, structural health system weaknesses, and socioeconomic factors that remain incompletely modelled in existing epidemiological literature. This study examines the determinants of premature cardiovascular mortality and the mediating role of health system responsiveness in Edo, Rivers, and Akwa Ibom States using a mixed-methods approach. The quantitative strand applies a case-control design, recruiting 400 cases (relatives of individuals who died from cardiovascular causes before age 65 within the past five years) and 400 controls matched by age, sex, and residential area from community settings, with data collected on cardiovascular risk factor profiles, healthcare-seeking history, health facility quality, and out-of-pocket expenditure. Binary logistic regression and path analysis in R examine direct and mediated pathways to premature cardiovascular death. The qualitative strand comprises 45 in-depth interviews with bereaved relatives, survivors of cardiovascular events, and healthcare providers, analysed through Interpretive Phenomenological Analysis to examine lived experiences of cardiovascular care quality and responsiveness. The World Health Organisation Health System Responsiveness framework and Social Epidemiology Theory inform the integrated analysis. Original contributions include a tested mediation model of health system responsiveness and premature cardiovascular mortality, and cross-state comparisons novel to the South South regional literature. Findings will support the development of cardiovascular disease emergency care protocols and health system responsiveness improvement plans. Keywords: premature cardiovascular mortality, health system responsiveness, South South Nigeria, mixed methods, cardiovascular risk.