From the Journals

Almost half of sudden cardiac deaths linked to prior silent MI



Almost half of individuals who died of sudden cardiac death (SCD) had a myocardial scar at autopsy, indicating a prior silent myocardial infarction (SMI), in a case-controlled study.

The research team led by Juha H. Vähätalo, MD, from the University of Oulu (Finland), compared autopsy findings, clinical characteristics, and ECG markers associated with SMI in 5,869 people in Northern Finland who had sudden cardiac deaths during 1998-2017.

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Overall, 75% of the deaths were caused by coronary artery disease (CAD), and of them, 71% had no previous diagnosis of CAD. Of these latter individuals, 42% had a myocardial scar at autopsy (detected by macroscopic and microscopic evaluation of myocardium), a finding that the authors said indicated a previous, unrecognized MI.

The analysis showed that individuals with SMI were slightly older, at 69.9 years, than were those with no SMI, at 65.5 years, and were more likely to be male (83.4% vs. 75.5%).

The group with prior SMI also died during physical activity at a greater rate than did those without (18.2% vs. 12.4%), the study authors reported in their paper published in JAMA Cardiology.

The research team obtained 438 ECGs prior to SCD; 187 in individuals with SMI and 251 in the group previously diagnosed with CAD.

Of the premortem ECGs in the individuals who had had an SCD after an SMI, 67% were abnormal, the researchers reported.

The SMI group had more frequently inverted T waves (16.6% vs. 8.4%) and pathologic Q waves (12.8% vs. 6.8%), compared with the non-SMI group. Both differences were statistically significant.

Fragmented QRS was the most common marker of a scar in the SMI group, however the authors noted that the fQRS complex was “probably a sensitive marker of myocardial scarring, but its specificity is not very high”.

Overall, having at least one of the following ECG abnormalities – fQRS, Q wave, T-wave inversion, or QRS of at least 110 msec – was more common in the SMI group (66.8%) compared with the non-SMI group (55.4%).

“Among patients in whom SCD without a prior MI is the first sign of cardiac disease, a previous ECG result is likely to be normal. ... ECGs were available only in 187 individuals with SMI, so the data are not sufficient to draw definite conclusions. Rather, they support motivation for further studies on this question,” the study authors noted.

“In the future, other, more efficient methods might be useful for diagnosing SMI, in addition to standard ECGs,” such as cardiac magnetic resonance imaging, but the cost-effectiveness “is likely to be unreasonable. Therefore, screening high-risk populations with ECG to identify individuals for further examinations would probably be reasonable,” they wrote.

The research team noted some limitations of the study such as the autopsy data not revealing the size of the scar detected in the myocardium and not all individuals had an ECG recorded prior to death.

SOURCE: JAMA Cardiol. 2019 Jul 10; doi: 10.1001/jamacardio.2019.2210

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