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J Am Coll Cardiol, 2007; 49:1824, doi:10.1016/j.jacc.2007.02.022
(Published online 13 April 2007). © 2007 by the American College of Cardiology Foundation |
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* John Hopkins University School of Medicine, Department of Medicine/Cardiology, 4940 Eastern Avenue, Baltimore, Maryland 21224-2780 (Email: rziegel{at}jhmi.edu).
Studies on the prognostic significance of depression after MI have viewed measures of MI severity like Killip class as confounders. Indeed, de Jonge et al. (1) noted that incident post-MI depression "may be confounded by the severity and consequences of the MI." However, considering a variable only as a confounder may produce misleading results if there is an interaction present (4). In the study by de Jonge et al. (1), patients with incident depression were somewhat more likely to have Killip class >1 than patients without depression. In the previous study from this group (3), patients with significant and increasing symptoms of depression were significantly more likely to have a high Killip class (odds ratio [OR] 4.57).
We re-examined data from the MI patients in the study by Grace et al. (2) to assess whether an interaction between Killip class and BDI scores predicts mortality. Of 443 patients, 58 (13.1%) had only a Killip class >1, and 96 (21.7%) had only a BDI score 
10; 29 patients (6.5%) had both. The 1-year all-cause mortality of all patients was 5.6% and was similar for patients with neither (4.6%), with only a Killip class >1 (5.2%), or with only a BDI score 10 (5.2%). The mortality rate of patients with both was significantly higher (5 of 29, 17.2%, odds ratio 4.31, 95% confidence interval 1.40 to 13.25, p = 0.01), even after controlling for age and gender (odds ratio 3.79, 95% confidence interval 1.16 to 12.41, p = 0.03).
Higher Killip class is associated with left ventricular diastolic dysfunction (5) that may make patients particularly intolerant of the effects of even mild ischemia or arrhythmia on left ventricular compliance. The increased platelet reactivity and increased sympathetic and diminished parasympathetic neural activity in patients with depression (6) may make them more likely to develop ischemia or arrhythmia after an MI, resulting in the interaction effects observed here. Higher Killip class is also significantly related to the persistence of depression at 1 year (7). It would be interesting to explore whether such an interaction, particularly one between Killip class and incident depression, might explain some of the findings reported by de Jonge et al. (1).
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