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We read with interest the study by Tapanainen et al. (1). The researchers introduced the brain natriuretic peptide (BNP) as a good predictor of sudden cardiac death (SCD) after acute myocardial infarction (AMI). In their study, BNP level of the patients with AMI was used to predict SCD. The incidence of SCD after the mean follow-up of 43 ± 13 months was 3.1%. The mean BNP level in patients with SCD was 54.4 ± 76.1 pmol/l and it was 26.1 ± 28.0 pmol/l in survivors. They found that a BNP level of 23.0 pmol/l was the best cut-off point to predict SCD. In another new study by Wang et al. (2), higher BNP was also associated with increased risk of overall death. The investigators reported a 27% increase in the risk of death with each increment of 1 SD in log of BNP level.
We know from the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) investigators that the survival of postmyocardial infarction patients with ejection fraction (EF) <30% will improve with prophylactic implantation of a defibrillator (3). It means that irrespective of BNP level, post-AMI patients with low EF will derive benefit from defibrillator implantation. Approximately one-third of the patients with prior infarction, left ventricular EF <40%, and spontaneous nonsustained ventricular tachycardia (VT) have inducible sustained VT, predicting 6% to 9% per year risk of sustained VT or SCD. A defibrillator reduces this risk to 3% to 5% per year (3,4). An EF between 30% to 40% is a gray area for defibrillator implantation, and this is the area that needs more clarification.
The studies have shown that BNP can probably be a good predictor of death, especially SCD, after MI. If we know the value of this predictive role in post-myocardial infarction patients with EF between 30% and 40%, we may be able to use it as a guide to defibrillator implantation decision. In the study by Tapanainen et al. (1) the mean EF of patients with SCD was 39.9 ± 10.8%. It seems that most of the patients in thestudy had an EF >30%, but separate analyses for different EF levels were not shown. We believe that if the researchers could perform a separate analysis for the patients with EF between 30% and 40%, the role of BNP level in predicting SCD in non-MADIT II patients might be more clearly established.
- American College of Cardiology Foundation