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ECG fails to diagnose many heart attacks reports new study

Robin Wulffson MD's picture
heart attack, myocardial infarction, MI, diagnosis, MRI, ECG

Heart disease is the leading cause of death in the United States, according to the Centers for Disease Control and Prevention (CDC). When an individual suffers a myocardial infarction (MI), a correct diagnosis is imperative. Electrocardiography (ECG) is a common diagnostic tool; however, it does not diagnose all MIs. The situation is known as an unrecognized MI (UMI).

Researcher in Reykjavik Iceland conducted a study, comparing the diagnostic ability of an ECG to that of magnetic resonance imaging (MRI). They published their findings on September 5 in the Journal of the American Medical Association (JAMA).

The objective of the study was to determine the prevalence and mortality risk for UMI detected by cardiac magnetic resonance (CMR) imaging or ECG among older individuals. The researchers reviewed data from the ICELAND MI, which was at sub-study of the Age, Gene/Environment Susceptibility–Reykjavik Study (enrollment: January 2004-January 2007) using ECG or cardiac MRI (CMR) to detect UMI. Data from 963 seniors in Iceland aged 67 to 93 years were analyzed, including 670 who were randomly selected and 266 with diabetes.

The main outcome measures were the prevalence and mortality of MI through September 1, 2011. The researchers found that of 936 participants, 91 had recognized MI (RMI; 9.7%) and 157 had UMI detected by CMR (17%), which was more prevalent than the 46 UMI detected by ECG (5%). Participants with diabetes (337 participants) had more UMI detected by CMR than by ECG (CMR: 72 (21%); ECG: 15 (4%)). Unrecognized MI by CMR was associated with atherosclerosis risk factors, coronary calcium, coronary revascularization, and peripheral vascular disease. Over an average follow-up period of 6.4 years, 30 of 91 participants (33%) with RMI died, and 44 of 157 participants (28%) with UMI died; both of these rates were higher than that of the 119 of 688 participants (17%) with no MI who died. Unrecognized MI by CMR improved risk stratification for mortality over RMI, meaning that these individuals were identified as being at higher risk of death. Adjusting for age, sex, diabetes, and RMI, UMI by CMR remained associated with mortality, absolute risk increase, and significantly improved risk stratification for mortality; however, UMI by ECG did not. Being unaware of a MI resulted in less attention to medical treatment that could reduce the risk of death. Compared with those with RMI, participants with UMI by CMR used cardiac medications such as statins less often (UMI: 36%; RMI: 73%).

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The authors concluded: “In a community-based cohort of older individuals, the prevalence of UMI by CMR was higher than the prevalence of RMI and was associated with increased mortality risk. In contrast, UMI by ECG prevalence was lower than that of RMI and was not associated with increased mortality risk.”

Take home message:
This study notes the superiority of a MRI over an ECG for diagnosing a myocardial infarction. An ECG is a simple, inexpensive diagnostic procedure whereas a MRI is expensive and more involved. Thus, it is important for an individual to be aware of the signs of a myocardial infarction and ask his or her healthcare provider to consider ordering a MRI if the ECG is negative. The following symptoms are associated with a myocardial infarction:

  • Chest pain is a major symptom of heart attack. You may feel the pain in only one part of your body, or it may move from your chest to your arms, shoulder, neck, teeth, jaw, belly area, or back.
  • The pain can be severe or mild. It can feel like: a tight band around the chest; bad indigestion; something heavy sitting on your chest; or squeezing or heavy pressure
  • The pain usually lasts longer than 20 minutes. Rest and a medicine called nitroglycerin do not completely relieve the pain of a heart attack. Symptoms may also go away and come back.

Other symptoms of a heart attack include:

  • Anxiety
  • Cough
  • Fainting
  • Light-headedness, dizziness
  • Nausea or vomiting
  • Palpitations (feeling like your heart is beating too fast)
  • Shortness of breath
  • Sweating, which may be extreme

Some people (seniors, individuals with diabetes, and women) may have little or no chest pain. Or, they may experience unusual symptoms (shortness of breath, fatigue, weakness). A “silent heart attack” is a heart attack with no symptoms.

Reference: JAMA

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