Silent Myocardial Infarction Prevails Prior to Sudden Cardiac Death, Autopsy Data Suggests

Among individuals who had sudden cardiac death (SCD) due to ischemic cardiac disease, a substantial number had a previously undetected myocardial infarction at autopsy; some of them had electrocardiographic abnormalities prior to the death. The study by Vähätalo et al., published in JAMA Cardiology, revealed.

The Finnish Genetic Study of Arrhythmic Events (FinGesture) is a case-control study that included consecutive individuals with autopsy-verified SCD in Northern Finland between 1998 and 2017. Subjects who experienced coronary artery disease (CAD)-associated SCD with and without a silent myocardial infarction (SMI) were regarded as cases and controls, respectively. Incidentally recorded, premortem electrocardiography (ECG) was collected from medical records and analyzed by investigators blinded to the SMI data.

Of 5869 individuals with SCD, CAD was the cause of death in 4392 (74%) individuals. Among the individuals who experienced CAD-associated SCD, 3122 did not have a prior diagnosis of CAD, and 1322 (42.4%) of these had myocardial scarring indicative of SMI at autopsy. When compared to non-SMI controls, SMI cases were older (mean age 66.9 ± 11.1 vs. 65.5 ± 11.6 years; P<0.001), more likely to be males (83.4% vs. 75.5%; P<0.001), and had SCD more often during physical activity (18.2% vs. 12.4%; P<0.001) or outdoors (20.0% vs. 14.9%; P=0.001). Additionally, the total heart weight, heart weight-to-body surface area ratio, and the prevalence of left ventricular hypertrophy were significantly higher in SMI cases.

Overall, 187 individuals in the SMI group and 251 individuals in the non-SMI group had prior ECG recordings. At least one ECG abnormality (e.g., fragmented QRS complexes, prolonged QRS duration, pathological Q waves, or inverted T waves) was observed more frequently in subjects with SMI than those without SMI (66.8% vs. 55.4%; P=0.02), indicating the presence of myocardial scarring.

To better identify individuals with SMI, imaging modalities such as cardiac magnetic resonance or echocardiographic strain analysis may be considered after initial screening by the standard ECG. “After diagnosing previous SMI, secondary prevention strategies should be initiated, as in clinical myocardial infarction.” Dr. Vähätalo concluded.

The study has some limitations. First, the autopsy data only documented the presence but not the extent of myocardial scars. Second, a premortem ECG was not available in all individuals, and SMI that developed after the ECG recording might not be captured. Therefore, the prevalence of ECG markers among autopsy-defined myocardial scarrings could not be accurately determined.