Clinical and experimental pain perception is attenuated in patients with painless myocardial infarction

The lack of pain alarm in painless myocardial infarction (MI) leads to increased morbidity and mortality, since patients do not seek medical treatment in a timely manner. We aimed to explore whether reduced systemic pain perception in response to experimental stimuli and pain related personality variables characterizes painless MI patients.

Level of chest pain intensity was assessed by numerical scale, range from 0 (no pain) to 100 (maximal pain). Heat pain threshold, magnitude estimation of supra-threshold phasic and tonic painful stimuli as well as anxiety and pain catastrophizing scores were assessed in 92 acute MI patients; 67 with and 25 without chest pain, respectively. All experimental stimuli were performed by Thermal Sensory Analysis (TSA) and applied to the right forearm.

Greater intensity of chest pain scores was inversely correlated with lower pain threshold (r=-0.417, p<0.001), and directly associated with higher pain scores in response to the heat pain (r=0.354, p=0.002). Patients with painful MI demonstrated lower pain threshold (41.9+/-3.6 degrees C vs. 44.9+/-3.8 degrees C, p=0.001) and higher catastrophizing level (10.6+/-12.0 vs. 5.4+/-8.8, p=0.032). Logistic regression analysis revealed that older age and lower pain scores in response to supra-threshold painful stimuli were associated with greater risk for painless MI. The demographic variables, history of ischemic heart, risk factors for coronary artery disease, ST-T segment changes on ECG and troponin levels were similar in both groups.

This study suggests that reduced systemic pain perception as well as cognitive personality variables play an important role in the etiology of painless MI.