High Pain Tolerance May Explain Many Unrecognized MIs

Marlene Busko

December 23, 2016

TROMSØ, NORWAY — A population-based, cross-sectional study suggests that people who better tolerate pain are more likely to have an unrecognized MI, including silent MI, and those less tolerant of pain are more likely to have a recognized MI[1].

This was especially true for women in a study by Dr Andrea Milde Øhrn (University of Tromsø, Norway) and colleagues, published online December 19, 2016 in the Journal of the American Heart Association.

Researchers measured pain tolerance by a cold pressor test (which involves keeping one's hand in freezing water as long as possible for up to about 2 minutes) and used ECG and hospital records to identify participants who had an unrecognized or recognized MI.

The relationship between pain and silent MI has not been studied until now, Øhrn told heartwire from Medscape in an email. "I was surprised to see that . . . pain sensitivity may be so important in the presentation and diagnosis of MI," she said. "This is obviously a factor that we need to take seriously [and study further] to eventually be able to prevent, discover, and treat [silent MI].

"Because the difference in pain tolerance between unrecognized and recognized MI was larger in women, it might be that it takes more symptoms/pain to have your heart attack recognized if you are a woman," Øhrn added.

The clinical implications are that a lack of chest pain "should not lower alertness of doctors toward ischemic heart disease. . . . It is important to think of an unrecognized myocardial infarction if a patient presents with signs such as heavy breathing and swollen legs; these can be symptoms of heart failure because of a myocardial infarction, even though there is no record of one."

Pain Tolerance and Silent MI

Silent MI is associated with a similar risk of death and recurrent MI as recognized MI, and it may be unrecognized because patients perceive pain differently, according to Øhrn and colleagues. However, the association between sensitivity to pain and recognition of MI has not been examined.

They analyzed data from 4849 people who participated in the Tromsø Study in Norway in 2007–2008 and had an ECG and cold pressor test. Participants were a mean age of 62 years.

Women were less likely than men to have had an MI (7% vs 19%, P<0.001), but a larger proportion of MIs were unrecognized in women than in men (75% vs 58%, P<0.001).

Overall, 387 participants (8%) had an unrecognized MI and 227 participants (4.7%) had a recognized MI.

Women were more likely to abort the pain test than men (38% vs 23%, P<0.0001).

Overall, men and women were 36% less likely to abort the pain test (hazard ratio [HR] 0.64; 95% CI 0.47–0.88), after adjustment for age and sex, if they had an unrecognized vs recognized MI.

A closer look revealed that women were 48% less likely to abort the test if they had an unrecognized vs recognized MI (HR 0.52; 95% CI 0.33–0.84), but this relationship was not significant for men.

After researchers also adjusted for systolic blood pressure, antihypertensive drugs, diabetes, smoking, physical distress, and physical activity, the association was attenuated and not significant.

"Unrecognized myocardial infarctions are associated with a similar bad prognosis as the recognized, chest-pain heart attacks, and we know that they constitute a larger proportion in women compared with men. And because of that, I basically consider this . . . a women's heart disease [research] project, and this condition deserves more attention," Øhrn said.

It is unknown why some people have heart attacks with little or no symptoms, she added. "Earlier studies showed that they may have no symptoms of importance, or they may experience pain in the stomach area, arm, or jaw or experience general discomfort or a flulike feeling. These symptoms are not as associated with the heart as chest pain, and they may not seek medical assistance, or if they do, they may receive a wrong diagnosis."

This study was funded by the Norwegian National Advisory Unit on Women's Health, Oslo University Hospital. The authors had no relevant financial relationships.

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