Unravelling pain in Göttingen Minipigs undergoing experimentally induced closed-chest myocardial infarction: a prospective cohort study

The pain associated with experimental myocardial infarction in pigs has never been investigated. We aimed at assessing pain and its correlation with myocardial damage. Twenty-four Göttingen minipigs undergoing closed chest myocardial infarction followed by coronary reperfusion under general balanced anaesthesia were included in the trial. Pain was assessed through mechanical and thermal thresholds, sensitivity to Von Frey filaments and behavioural indicators before (Pre MI), the day after (Post MI) and at the study endpoint (Post MI-endpoint). Over time differences in mechanical thresholds (MT) and thermal thresholds (TT) were assessed using one-sample t-test and their correlations with troponin I/cytokines using logistic regression. In four minipigs at Post MI acute pain requiring analgesia was identified. Pain thresholds decreased significantly at Post MI (MT: 51 [35.6; 74] TT: 44.8 [42.7; 48.7]) and Post MI-endpoint (MT: 47.5 [35; 64.3]; TT: 44.3 [43.1; 48.6]) compared to Pre MI (MT: 72 [53.4; 84], TT: 46.3 [43.8; 53.8]). The response to von Frey filaments remained sporadic. Troponin I highly increased at Post MI, but no correlations with pain thresholds were found. Following balanced anaesthesia, acute pain had low incidence and mild to moderate intensity. Somatic hyperalgesia remained until the study endpoint, but its relevance remains to be unravelled.