Autonomic dysfunction and serotonin
For many years, the majority of cases of hypertension were classified as “essential hypertension,” which simply means of unknown etiology. Because there is substantial evidence for autonomic dysfunction in both hypertension and panic, a parsimonious explanation for the association between these 2 conditions in at least some cases of essential hypertension is common autonomic dysfunction.21 Davies and colleagues22 tested this hypothesis by considering panic attack symptom profiles in people who had experienced a panic attack. Hypertensive participants (with resting blood pressure greater than 160/90 mm Hg) were more likely to report experiencing sweating (64.6% vs 46.2%) and flushing (54.9% vs 39.7%) during their worst attack than were normotensive patients. In addition, factor analysis revealed a 4-factor solution with a dominant autonomic symptom factor containing sweating, flushes, and shaking—and only this factor was significantly associated with hypertension.

An explanation of these data may be that experiencing panic attacks with autonomic symptoms is a marker for a specific kind of hypertension in these people—one in which there is a dysregulated central 5-HT system. A range of diverse data relates to this assertion, including the clinical utility of SSRI antidepressant medications in patients with cardiovascular conditions. The Sertraline Antidepressant Heart Attack Randomized Trial (SADHART) group reported that sertraline was a safe and somewhat effective antidepressant in subjects with ischemic heart disease and major depression, and a post hoc analysis hinted at an improvement in severe cardiac events.23 The Enhancing Recovery in Coronary Heart Disease Patients (ENRICHD) investigators demonstrated a psychological benefit in post–myocardial infarction patients with cognitive therapy (plus sertraline for some patients) with no impact on cardiovascular morbidity or mortality.24

Depression rather than anxiety was examined in these studies and neither study reported a significant improvement in blood pressure. SSRI-induced inhibition of platelet 5-HT uptake is known to reduce platelet plug formation, which could be of additional benefit. Animal data also exist that support putative 5-HT (ie, sympathethic) anxiety circuits and provide a plausible preclinical biological model.25

Using the ATD procedure, we demonstrated that people with SSRI-remitted anxiety disorders—including panic disorder—show an increased cardiovascular (independent of anxiety measures) and psychological response to a disorder-specific stressor when depleted of tryptophan in comparison with a control (nondepleted) condition.10,12,26,27 Healthy volunteers, however, do not show an increased response to a single-breath 35% carbon dioxide stress challenge when they are tryptophan-depleted, which suggests that they have a more robust 5-HT system.28 The integrity of the 5-HT system in people with dysregulated blood pressure control, as determined by the ability to buffer the stress response under the tryptophan-depleted versus nondepleted condition, has yet to be assessed.

SSRIs as antihypertensives
If patients with hypertension and autonomic symptoms of panic are susceptible to a pressor effect by acutely depleting central 5-HT, might not the addition of SSRIs improve their blood pressure control? We already have some intriguing early data that suggest that this may indeed be true. Polyák29 has presented the results of a study of 107 adults with both hypertension and anxiety who were taking a range of antihypertensive medications. Low-dose (mean, 39 mg/d) sertraline was added to their diverse antihypertensive regimens, and the effects on blood pressure was checked at 1 month and at 6 months. At both points, a significant improvement in systolic blood pressure of about 10 mm Hg and diastolic blood pressure of about 5 mm Hg were seen. Although this case series has not been replicated and subjects with autonomic panic were not specifically identified, these data cannot easily be ignored.

We propose conducting a series of follow-up studies to explore the utility of SSRI therapy in people with hypertension and the related condition of prehypertension, and to evaluate the evidence for serotonergic dysfunction and altered blood pressure response to stress in people with prehypertension and panic attacks via serotonergic manipulation. Until such work is undertaken, this interesting therapeutic option will remain largely a research interest.

Conclusions
An association between 5-HT, panic, and hypertension has long been noted and is now the subject of active research interests. Manipulating 5-HT may have clinical implications for blood pressure control in people with panic attacks and anxiety. Our data suggest that panic attacks comorbid with hypertension may be distinct from panic attacks uncomplicated by hypertension—and it may be that hypertension complicated by panic attacks has specific biological features compared with hypertension uncomplicated by panic. Serotonergic manipulation of hypertension has largely been ignored or dismissed since the isolation of serotonin in 1948; however, we believe that by focusing on patients with key autonomic panic symptoms such as sweating and flushing, we may clarify this issue with potential therapeutic benefits.

 
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