Evaluation of heart rate variability (HRV) has been shown to be a valuable tool for measuring autonomic dysfunction associated with depression and with cardiac disease. Low HRV is a marker of increased risk of cardiac mortality, and is observed in depressed coronary artery disease patients and in anxious patients post-MI. Treatment with sympathomimetic antidepressants, such as MAO inhibitors and tricyclics, reduce HRV further, and have been associated with elevated heart rate, orthostatic hypotension, and with adverse cardiac events. Although there is increasing evidence that the selective serotonin reuptake inhibitor (SSRI) class of antidepressants have minimal effects on the cardiovascular system, the case is less clear with the SNRI antidepressants which block the reuptake of both serotonin and norepinephrine. It is possible that measures of the extent of norepinephrine transporter blockade or inhibition may relate to the HRV reduction seen with noradrenergic drugs. Given these considerations, we propose a study to compare the cardiovascular profile of the SSRI escitalopram (Lexapro), with the most recently available SNRI, duloxetine, in outpatients with depression. Using HRV methodology, we will test the hypothesis that greater reduction in HRV will be associated with duloxetine than escitalopram. In addition, we will measure the magnitude of serotonin and norepinephrine transporter occupancy produced by each drug. This will allow us to examine the relationship between changes in HRV to the magnitude of transporter inhibiting effects of each drug.
Low heart rate variability is a marker of increased risk of cardiac mortality, and is observed in depressed coronary artery disease patients. Some antidepressants may themselves, however, decrease heart rate variability. We will test the hypothesis that greater reduction in heart rate variability will be associated with duloxetine (which has noradrenergic activity) than escitalopram (a selective serotonin reuptake inhibitor). We will also test the hypothesis that changes in heart rate variability are related to the magnitude of norepinephrine transporter occupancy.