Pain Perception is Attenuated in Patients With Painless Myocardial Infarction

Objective: Silent myocardial infarction (MI) is an event of severe myocardial ischemia without pain experience. The lack of pain alarm leads to increased morbidity and mortality, because the patients do not sick timely medical treatment. This study aims to explore whether reduced systemic pain perception in response to painful stimuli and personality pain related variables characterizes silent MI patients.

Methods: Level of chest pain intensity was assessed by visual analogue scale (VAS), range from 0 (no pain) to 100 (maximal pain). Heat pain threshold, magnitude estimation of supra-threshold painful stimuli at 47ºC as well as pain catastrophizing scores were assessed in 90 acute MI patients (mean age 66±12.1, range 33-79) with chest pain (n=65) and without pain symptoms(n=25). All stimuli were performed by Thermal Sensory Analysis (TSA) and applied to the right forearm.

Results: 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. Greater intensity of chest pain VAS 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 vs. 44.9±3.8, p=0.001), higher VAS scores in response to the supra-threshold painful stimuli (50.2 ±21.8 vs. 27.0±25.2, p=0.002), and higher catastrophizing level (10.6±12.0 vs. 5.4±8.8, p=0.032). Chest pain complaint was not related to ST-T changes as well as concomitant diseases.

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