What causes dizziness during exertion in the absence of hypertension?

Dizziness During Exertion Without Hypertension

Dizziness during exertion in the absence of hypertension is most commonly caused by post-exertional orthostatic hypotension due to autonomic dysregulation, though cardiac causes (structural heart disease, arrhythmias) and exercise-induced bronchoconstriction must be ruled out first given their life-threatening potential.

Immediate Diagnostic Priorities

The evaluation must systematically exclude life-threatening cardiac etiologies before attributing symptoms to benign autonomic causes:

Rule Out Cardiac Causes First

• Structural heart disease including hypertrophic cardiomyopathy, aortic stenosis, anomalous coronary arteries, and pulmonary arterial hypertension can all present with exertional dizziness and carry risk of sudden death 1
• Exercise-induced arrhythmias such as catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT syndrome type 1, supraventricular tachycardia, or complete heart block must be excluded 1
• Exercise stress testing is indicated when syncope or presyncope occurs during or shortly after exertion to reproduce symptoms and evaluate hemodynamic response 1
• During stress testing, monitor for: failure of heart rate to increase appropriately, progressive fall in systolic blood pressure with increasing workload, or development of high-grade AV block 1

Critical Assessment During Exercise Testing

Do not terminate testing prematurely - if dizziness occurs but blood pressure is rising appropriately with normal heart rhythm and normal rise in heart rate/oxygen pulse, the dizziness is unlikely due to cardiac output failure and further exercise may clarify the origin 1

Testing should be terminated only if 1:

• Decrease in ventricular rate with increasing workload plus extreme fatigue or dizziness
• Failure of heart rate to increase with exercise plus symptoms of insufficient cardiac output
• Progressive fall in systolic blood pressure with increasing workload
• Severe hypertension (>250 mmHg systolic or >125 mmHg diastolic)

Most Likely Diagnosis: Post-Exertional Orthostatic Hypotension

Pathophysiology

Post-exertional syncope is almost invariably due to autonomic failure or neurally-mediated mechanisms characterized by hypotension that can be associated with marked bradycardia or asystole, typically occurring in subjects without structural heart disease 1

The mechanism involves 2, 3, 4:

• Transient postural hypotension from lower extremity blood pooling once exercise stops
• Failure of peripheral vascular resistance to increase appropriately
• Impaired cardiac baroreflexes
• Reflex vasodilatation rather than vasoconstriction

Clinical Pattern Recognition

Symptoms characteristically 2:

• Develop upon standing after exertion (not during)
• Include dizziness, lightheadedness, weakness, visual disturbances
• Are relieved by sitting or lying down
• Worsen in morning hours, after meals, with heat exposure, and after exertion

Diagnostic Confirmation

Orthostatic vital signs are essential 2, 3:

• Measure blood pressure after 5 minutes lying/sitting
• Remeasure at 1 and 3 minutes after standing
• Positive if systolic BP drops ≥20 mmHg or diastolic BP drops ≥10 mmHg
• In hypertensive patients, systolic drop ≥30 mmHg is diagnostic 3

Tilt table testing can diagnose neurally-mediated syncope manifesting as post-exertional symptoms 1, 5

Contributing Factors to Evaluate

Medication Review

The most common reversible cause is medication-induced orthostatic hypotension 3:

• Diuretics (volume depletion)
• Vasodilators including nitrates
• Alpha-adrenergic blockers
• Beta-blockers 6
• Any vasoactive drugs

Volume Status

Assess for 3:

• Excessive diuresis
• Dehydration
• Inadequate fluid intake around exercise

Age-Related Changes

Older patients are predisposed through 3:

• Stiffer hearts less responsive to preload changes
• Impaired compensatory vasoconstrictor reflexes
• Baroreflex dysfunction
• Reduced cerebral autoregulation

Underlying Autonomic Dysfunction

Consider screening for 3, 7:

• Diabetes mellitus with autonomic neuropathy
• Parkinson's disease
• Multiple system atrophy
• Pure autonomic failure
• Amyloidosis

Important caveat: Post-exertion dizziness may be the sole presenting symptom of evolving autonomic failure before other classic symptoms (postural dizziness at rest, urinary abnormalities, erectile dysfunction) develop 7

Management Algorithm

If Cardiac Causes Excluded and Orthostatic Hypotension Confirmed

1. Reduce or eliminate offending medications if possible 1, 3

   • Cautiously decrease diuretics if no signs of congestion present
   • Consider alternatives to alpha-blockers or vasodilators

2. Non-pharmacologic interventions 2, 4:

   • Patient education about transient nature of symptoms
   • Trendelenburg position (legs elevated) immediately post-exercise
   • Gradual cool-down period rather than abrupt cessation of activity
   • Adequate hydration before and after exercise
   • Avoid prolonged standing immediately after exertion
   • Compression stockings to reduce venous pooling

3. Modify exercise regimen 1, 5:

   • Interval training allows high peripheral exercise stimulus without significant heart rate increase
   • Keep training heart rate as low as possible
   • Multiple short sessions may be better tolerated than single prolonged sessions

4. Pharmacologic treatment for autonomic dysregulation if symptoms persist 8:

   • Medications targeting autonomic nervous system function
   • Seven of nine patients in one series improved substantially and resumed all activities with such treatment

If Neurally-Mediated (Vasovagal) Post-Exertional Bradycardia

Consider permanent pacing only if symptoms are severe, recurrent, and refractory to conservative measures 5

Common Pitfalls to Avoid

• Do not assume benign cause without cardiac evaluation - structural heart disease and arrhythmias can be fatal and must be excluded first 1
• Do not attribute to dehydration reflexively - while contributing, the primary mechanism is autonomic dysregulation, not simple volume depletion 4
• Do not discontinue essential cardiac medications (like beta-blockers in heart failure) without considering pacemaker placement as alternative 5
• Do not overlook medication review - this is the most common and most easily reversible cause 3
• Recognize this may herald progressive autonomic failure - arrange appropriate follow-up even if initial symptoms seem benign 7