Cardiovascular · PANCE / PANRE

Orthostatic Hypotension and Vasovagal Syncope

Common, often benign causes of transient loss of consciousness; recognize red-flag features that distinguish reflex syncope from cardiac syncope.

Also known as: orthostatic hypotension, vasovagal syncope, neurocardiogenic syncope, reflex syncope, POTS

Overview

Orthostatic hypotension (OH) is a sustained drop in blood pressure within 3 minutes of standing — ≥20 mmHg systolic or ≥10 mmHg diastolic. Vasovagal (neurocardiogenic, reflex) syncope is the most common cause of transient loss of consciousness, mediated by an inappropriate autonomic reflex that produces transient hypotension and/or bradycardia in response to a trigger.

Epidemiology

Lifetime prevalence of syncope is ~35%, with peak incidence in adolescence and again after age 70. Vasovagal syncope accounts for ~50% of all syncope episodes. OH affects ~5-30% of older adults and is increasingly common with antihypertensive use. POTS (postural orthostatic tachycardia syndrome), a related but distinct disorder, predominantly affects young women.

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Risk factors

Orthostatic hypotension: volume depletion (dehydration, GI loss, blood loss, diuretics), antihypertensives (especially alpha-blockers, beta-blockers, ACEi/ARB, diuretics), nitrates, tricyclics, autonomic neuropathy (diabetes, Parkinson disease, multiple system atrophy, pure autonomic failure, amyloidosis), adrenal insufficiency, prolonged bed rest, deconditioning
Vasovagal: prolonged standing, hot environment, emotional stress, pain, blood/needle phobia, dehydration, alcohol, instrumentation (venipuncture, defecation, micturition, swallowing, cough)
POTS: female sex, young age, history of viral illness, joint hypermobility (Ehlers-Danlos)

Pathophysiology

Orthostatic hypotension reflects failure to compensate for the venous pooling of ~500-700 mL of blood into the lower extremities and splanchnic bed on standing. Normally, baroreceptors trigger sympathetic vasoconstriction and increase heart rate. Failure can be due to absolute volume loss, medication-mediated impairment of compensation, or autonomic insufficiency. Vasovagal syncope (reflex syncope) involves activation of cardiac mechanoreceptors during venous pooling, triggering paradoxical withdrawal of sympathetic tone and increased vagal tone — producing the cardioinhibitory (bradycardia), vasodepressor (hypotension), or mixed responses on tilt-table testing.

Clinical presentation

Symptoms

Vasovagal: prodrome of lightheadedness, warmth, nausea, diaphoresis, tunnel vision over 30 seconds to minutes, often after a trigger; brief loss of consciousness with rapid recovery
Orthostatic hypotension: lightheadedness, blurred vision, neck/shoulder ache ('coat hanger' pain), syncope upon standing or after prolonged standing
POTS: lightheadedness, palpitations, brain fog, fatigue, headache on standing without true syncope; symptoms improve with recumbency

Signs / physical exam

Drop in BP ≥20/10 mmHg from supine to standing at 1-3 min (orthostatic hypotension) — measure after 5 min supine, then at 1 and 3 min standing
Pallor, sweating, bradycardia during a vasovagal episode
Findings of underlying autonomic neuropathy: diabetic features, parkinsonism, anhidrosis, fixed heart rate

Classic findings

Vasovagal syncope: young patient with prodromal symptoms, identifiable trigger, rapid full recovery without confusion. OH: positional symptoms with reproducible BP drop on bedside testing.

Differential diagnosis

Cardiac (arrhythmic) syncope — Syncope without prodrome, exertional, recumbent, or preceded by palpitations; structural heart disease; abnormal baseline ECG — red flags warranting cardiac workup
Cardiac (structural/obstructive) syncope — Severe AS, HCM, pulmonary embolism, tamponade — exertional syncope, characteristic murmurs/echo findings
Seizure — Tongue biting (lateral), prolonged confusion postictal, urinary incontinence, witnessed tonic-clonic movements; brief myoclonic jerks can also occur in syncope and do not equal seizure
Hypoglycemia — Diabetic on insulin/sulfonylurea; sweating, tremor, confusion; fingerstick glucose diagnostic
Carotid sinus hypersensitivity — Older patient with syncope on neck turning or tight collars; >3 sec asystole or >50 mmHg BP drop on carotid massage
POTS (postural orthostatic tachycardia syndrome) — Sustained HR increase of ≥30 bpm (≥40 in adolescents) within 10 min of standing WITHOUT meeting OH criteria; symptoms of orthostatic intolerance
Pulmonary embolism — Syncope can be the presenting feature; concurrent dyspnea, tachycardia, hypoxia
Psychogenic pseudosyncope — Frequent events with preserved color and vital signs; eyes closed during episode; tilt table provokes typical event with normal hemodynamics

Diagnostic workup

Labs

BMP including glucose, magnesium
CBC for anemia or occult blood loss
Cortisol, ACTH stimulation if adrenal insufficiency suspected
Hemoglobin A1c if diabetic autonomic neuropathy suspected
Pregnancy test in women of reproductive age

Imaging

Orthostatic vital signs (supine and standing at 1 and 3 min)
12-lead ECG in ALL syncope patients — rule out high-risk arrhythmic substrates (Brugada, LQTS, AV block, WPW, ischemia, hypertrophy)
Echocardiography if structural heart disease suspected or there are exertional symptoms / abnormal ECG
Holter monitor, event monitor, or implantable loop recorder for recurrent unexplained syncope
Tilt-table testing for recurrent reflex syncope when diagnosis is uncertain — provokes characteristic cardioinhibitory, vasodepressor, or mixed responses
Active stand test or tilt-table for POTS evaluation

Diagnostic algorithm

Feature	Reflex (Vasovagal)	Orthostatic Hypotension	Cardiac Syncope (RED FLAG)
Typical age	Younger adults	Older adults	Any age, more common >60
Prodrome	Yes — nausea, warmth, lightheadedness	Lightheadedness on standing	Often absent or palpitations
Trigger	Pain, sight of blood, prolonged standing, heat	Position change (lying → standing)	Exertion, recumbent, none
Recovery	Rapid, no confusion	Improves supine	May be prolonged; injury common
ECG / structural disease	Normal	Normal (unless from autonomic cause)	Often abnormal
First-line therapy	Trigger avoidance, hydration, counterpressure	Salt/fluid, compression, taper offending drugs	Treat underlying arrhythmia/structural disease

Distinguishing reflex syncope, orthostatic hypotension, and cardiac syncope.

Treatment

First-line

Vasovagal syncope: reassurance and education about the benign nature, trigger avoidance, adequate hydration (2-3 L/day) and salt intake (≥150 mEq/day if no contraindication), physical counterpressure maneuvers (leg crossing with tension, handgrip, arm tensing) at prodrome onset
Orthostatic hypotension: review and reduce offending medications (alpha-blockers, antihypertensives, tricyclics, nitrates), hydration (2-3 L/day), sodium liberalization, slow position changes, raise head of bed 4-6 inches, compression stockings (thigh-high or abdominal binder), small frequent meals, avoid alcohol and large carbohydrate loads

Second-line / adjunct

Refractory orthostatic hypotension: fludrocortisone 0.1-0.2 mg daily (volume expansion; monitor potassium and supine HTN), midodrine 2.5-10 mg TID (alpha-1 agonist; avoid late dosing to limit supine HTN), droxidopa 100-600 mg TID (norepinephrine prodrug, approved for neurogenic OH), pyridostigmine for autonomic failure
Refractory vasovagal syncope: midodrine, fludrocortisone, beta-blockers in older patients (data mixed), or SSRIs in selected cases; permanent pacing for older patients (>40) with documented severe cardioinhibitory pacemaker-indicated form (asystolic vasovagal syncope on tilt or implantable loop recorder)
POTS: same lifestyle measures plus ivabradine, propranolol low-dose, or fludrocortisone/midodrine; structured exercise reconditioning program is highly effective

Complications

Falls and traumatic injury (especially elderly with OH)
Motor vehicle collisions
Anxiety, restricted lifestyle, depression with recurrent events
Supine hypertension as a complication of OH pharmacotherapy
Failure to identify a serious underlying cardiac cause if workup is inadequate

PANCE pearls

Always measure orthostatic vitals at 1 AND 3 minutes standing — many cases of OH are missed if only the 1-minute reading is obtained.
Red flags suggesting cardiac syncope (NOT reflex): syncope during exertion, recumbent syncope, no prodrome, syncope preceded by palpitations, structural heart disease, abnormal ECG, family history of sudden cardiac death, age >60 with new-onset syncope — workup with echo, ambulatory monitoring, and possibly EP referral.
POTS is defined by an increase in HR ≥30 bpm within 10 minutes of standing without meeting OH criteria — distinguishes from orthostatic hypotension.
First-line therapy for both vasovagal and orthostatic hypotension is non-pharmacologic: hydration, salt, counterpressure maneuvers, and medication review.
Pacing for vasovagal syncope is only effective for the cardioinhibitory subtype documented on tilt or ILR, typically in older patients (>40) with recurrent severe events.

References

ACC/AHA/HRS 2017 — 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Syncope (Shen et al., JACC 2017)
ESC 2018 — 2018 ESC Guidelines for the Diagnosis and Management of Syncope (Brignole et al., Eur Heart J 2018)
Consensus Definition — Consensus Statement on the Definition of Orthostatic Hypotension, Neurally Mediated Syncope and the POTS (Freeman et al., Auton Neurosci 2011)

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