Over time, how deadly is the combination of depression and heart attacks? A recent study that received attention in the media found no connection, in the long term, between depression and death in heart attack victims. But that study was followed almost immediately by another that found the combination of heart attack and depression to be especially lethal.
We know that cardiovascular disease and mood disorder are intertwined. By middle age, depression is a powerful risk factor for heart disease. In the elderly, depression increases the risk of death from cardiac causes. One way of understanding depression is to see it as a multisystem disease, active in heart and blood vessels as much as brain.
In the wake of heart attacks, depression is dangerous. People found to be depressed in the days after a myocardial infarction have a greatly increased risk of further cardiac events. Research suggests that depression accompanying heart attacks leads to high mortality in the short run—most studies have looked at deaths in the first year after the MI. But the issue of long-term mortality is complex.
The first recent report, published in the American Journal of Cardiology, examined elderly patients hospitalized for heart attacks. These patients had been studied four months after their hospital discharge; the depressed patients were almost four times as likely to have died. Now, eight years out, only 45% of the patients with depressive disorders were alive, as opposed to 54% of those with no depression, but the difference was no longer statistically significant. The contrasting report, in the Journal of Affective Disorders, found that patients who had major depression at the time of a heat attack were almost twice as likely to die in the next five years, when compared to patients with a heart attack alone. Even minor depression conferred a substantial risk.
So, over the long term, for patients with heart attacks, does depression kill? The study that found no demonstrable risk looked at sicker, older patients, with had high levels of hypertension and diabetes. In an especially ill population, the effect on mortality of any particular contributor—here, depression—may be hard to discern. But this study is important because its subjects may be representative of all heart attack sufferers.
The report that found a strong link between depression and death was looking at heart attack victims healthy enough to be included in research on interventions to ameliorate isolation and mood disorder, so it enrolled younger patients with fewer medical complications. Arguably, this study was especially thoughtful in its methods for diagnosing depression—more weight was given to the past history of depressive episodes.
For now, it seems safest to say that in the wake of an MI, depression puts patients at risk for death in the first year. For (slightly) healthier, younger patients, the elevated mortality rate persists for at least half a decade. For older and sicker patients, the increase in risk of death in the “out years” is less clear. There may be none.
This last result should hardly be enough to make us complacent about depression in cardiac patients. But it will make researchers yet more curious. We just don’t know enough about how heart attacks and depression are related and how any risk is conveyed. All sorts of links are possible. For instance, depression in the wake of heart attacks might be a marker for blood vessel disease or some other pathology that leads to both cardiac and neurological dysfunction. Stress is intriguing common factor. Some scientists believe that much of the risk attaches to “incident” episodes of depression, those that are not ongoing but arise in the wake of the heart attack. Perhaps it is best to say that this field, the study of the overlap between cardiology and psychiatry, is in its infancy.
One side note, regarding a controversial topic, whether doctors prescribe antidepressants inappropriately: In the five-year follow-up study (patients were enrolled between 1997 and 2000), one per cent of the non-depressed patients and 15% of the depressed patients had been using antidepressants. Among the depressed patients, it was the more severely depressed who had been medicated. In the eight-year study (of heart attacks occurring in 1995 and 1996), of 284 patients, only 14 were found to have been on antidepressants at the time of the heart attack; 13 of these met criteria for major depression. Overall, 17% of those diagnosed depressed after the heart attack had been on antidepressants; fewer than half of one per cent of the subsequently non-depressed patients (i.e., the one patient) was on an antidepressant. These figures hardly suggest over-prescribing or mis-prescribing.