Low heart rate variability and the effect of depression on post-myocardial infarction mortality.
BACKGROUND
Depression is associated with an increased risk for mortality after acute myocardial infarction (MI). The purpose of this study was to determine whether low heart rate variability (HRV) mediates the effect of depression on mortality.


METHODS
Twenty-four-hour ambulatory electrocardiograms were obtained from 311 depressed patients with a recent acute MI who were enrolled in the Enhancing Recovery in Coronary Heart Disease (ENRICHD) clinical trial and from 367 nondepressed patients who met the ENRICHD medical inclusion criteria. Standard HRV indexes were extracted from the recordings.


RESULTS
The log of very low-frequency (LnVLF) power, an index of HRV derived from power spectral analysis of the electrocardiogram signal (0.0033-0.04 Hz [in milliseconds squared]), was lower in the depressed than in the nondepressed patients (P<.001). There were 47 deaths (6.1%) during a 30-month follow-up. After adjusting for potential confounders, the depressed patients remained at higher risk for all-cause mortality compared with the nondepressed patients (hazard ratio, 2.8; 95% confidence interval [CI], 1.4-5.4; P<.003). When LnVLF power was entered into the model, the hazard ratio for depression dropped to 2.1 (95% CI, 1.1-4.2; P = .03). The proportion of the risk for depression attributable to LnVLF power was 0.27 (95% CI, 0.23-0.31; P<.001).


CONCLUSIONS
Low HRV partially mediates the effect of depression on survival after acute MI. This finding helps to clarify the physiological mechanisms underlying depression's role as a risk factor for mortality in patients with coronary heart disease. It also raises the possibility that treatments that improve both depression and HRV might also improve survival in these patients.
Carney
Robert M
RM
Department of Psychiatry, Washington University School of Medicine, St Louis, MO, USA. carneyr@bmc.wustl.edu
Blumenthal
James A
JA
Freedland
Kenneth E
KE
Stein
Phyllis K
PK
Howells
William B
WB
Berkman
Lisa F
LF
Watkins
Lana L
LL
Czajkowski
Susan M
SM
Hayano
Junichiro
J
Domitrovich
Peter P
PP
Jaffe
Allan S
AS
D002940:Circadian Rhythm / Q000502:physiology*; D003863:Depression / Q000150:complications* / Q000503:physiopathology; D015716:Electrocardiography, Ambulatory; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000150:complications / Q000401:mortality* / Q000503:physiopathology; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index; D015996:Survival Rate; D014481:United States / Q000453:epidemiology