A recent observational longitudinal study published in the Journal of American College of Cardiology showed that previous silent myocardial infarction (MI) was found in 8.2% of patients presenting with first acute myocardial infarction (AMI). Previous silent MI was detected by late gadolinium enhancement- cardiac magnetic resonance (LGE-CMR).
Dr. Amier et al reports that this is the first study in patients with acute myocardial infarction (AMI) to investigate silent MI using LGE-CMR and to assess its long-term prognostic implications. Previous silent MI was proven to be a strong independent predictor for adverse long-term clinical outcome. Electrocardiogram (ECG) showed limited sensitivity for detection of silent MI and was not associated with long-term clinical outcome in the study cohort.
“Silent MI occurred in 8.2% of patients presenting with first AMI and was independently related to poorer long-term clinical outcome, with a more than 3-fold risk of mortality and MACE.” – Raquel Amier et al
The study reports, silent MI constitutes up to 54% of all MIs in the general population and more than 60% in the elderly population older than 60 years, with increasing prevalence in presence of cardiovascular risk factors. Silent MI is usually discovered by routine ECG examination. Although ECG seems to be an appropriate screening tool in the general population, smaller infarctions can be missed and not all patients develop Q waves after infarction, thereby limiting the sensitivity of the ECG. The preferred method for silent MI detection is late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR), which provides the unique possibility of tissue characterization.
The 2-center observational longitudinal study is representative of 405 patients presenting with AMI between 2003 and 2013, without a history of prior MI, who underwent LGE-CMR within 14 days of AMI. Patients with silent MI tended to be older than patients without silent MI, although this was not statistically significant. Patients with silent MI who used medication before hospitalization more often (p=0.021), presented with ST-elevation myocardial infarction (STEMI) less often (p=0.023), and had deferred or no reperfusion more often (p=0.002). Cardiovascular risk factors, medical history, infarct-related artery, and the number of coronary vessel disease were comparable between the groups.
The author noted the following important limitations associated with this study: One limitation is that no causal relations can be assumed between silent MI and long-term prognosis. Although it is conceivable that silent MI increases the risk of cardiovascular complications through increased myocardial damage and LV dysfunction, it might be that the occurrence of silent MI is an indication of more severe comorbidity, poor disease management, or tendency of patients to avoid medical care. Also, the association of silent MI and greater risk of major adverse cardiac events (MACE) occurrence was mainly driven by increased mortality.