Multimorbidity and myocardial infarction: an investigation using linked, routinely collected health record data

Multimorbidity, defined as the co-occurrence of two or more long-term conditions (LTCs), is recognised as a key factor influencing patient management and prognosis in a number of contexts. This thesis sought to examine patterns of pre-existing multimorbidity in individuals with acute myocardial infarction (MI) and evaluate their impact on the receipt of guideline-directed care and long-term clinical outcomes.

Firstly, a systematic review and meta-analysis summarised the existing literature, highlighting the need for comprehensive ascertainment of LTCs. Subsequently, an algorithm was developed to ascertain 321 LTCs (aggregated into 116 clinical phenotypes), guided by multidisciplinary clinical, patient and public input – the Inclusive Multimorbidity Phenotyping Algorithm and Codelist Tool (IMPACT). A nationally representative, retrospective cohort study of individuals presenting with an index MI was conducted using linked primary and secondary care data. Latent class analysis (LCA) identified clusters of co-occurring LTCs (‘multimorbidity endotypes’). Flexible parametric survival models estimated 10-year cause-specific cumulative incidence ratios (CIRs) and corresponding 95% confidence intervals (CI) for each endotype, adjusting for covariates and accounting for competing risks.

Among 272,344 patients with MI (171,042 with non-ST-elevation MI [NSTEMI] and 101,302 with ST-elevation MI [STEMI]), 91.1% had ≥ 2 pre-existing LTCs (median: 7; interquartile range: 4 to 12). A greater number of LTCs were observed with female sex, increasing age, socioeconomic deprivation and NSTEMI. The number of pre-existing LTCs at MI presentation increased substantially over the study period. There was significant heterogeneity in receipt of guideline-directed care by multimorbidity endotype. The most adverse endotype (‘diabetes-related multimorbidity’) was associated with greatest 10-year mortality (NSTEMI: CIR 1.54, 95% CI: 1.48 – 1.60, and STEMI: CIR 1.60, 95% CI: 1.49 – 1.71), compared with the most favourable endotype (‘background low-impact disease’). In older adults with NSTEMI, benefits of invasive treatment strategy on clinical outcomes were observed among some endotypes (‘background low-impact disease’, ‘mental and behavioural health-related multimorbidity’), but not others.

This study demonstrated that individuals with MI had a high burden of pre-existing multimorbidity, which determined their clinical management and outcomes. This underscores the need to consider the full spectrum of pre-existing long-term conditions: a ‘whole patient’ approach to the management of MI is required.