What are the non-cardiac causes of tachycardia and how are they managed, particularly in patients with a history of anxiety, stress, or substance use?

Non-Cardiac Causes of Tachycardia

The primary non-cardiac causes of tachycardia include infection with fever, dehydration, anemia, hyperthyroidism, exogenous substances (caffeine, alcohol, nicotine, illicit stimulants, beta-agonist medications), anxiety disorders, autonomic dysfunction, and acid-base disturbances. 1

Physiological and Metabolic Causes

Infection and Fever

• Fever from any infectious source triggers compensatory sinus tachycardia as a normal physiological response 1
• When resting sinus tachycardia >120 bpm is detected, repeat the ECG after a rest period to exclude recent exercise or anxiety as the cause 2

Volume and Hematologic Disturbances

• Dehydration reduces preload and triggers compensatory tachycardia to maintain cardiac output 1
• Anemia decreases oxygen-carrying capacity, requiring increased heart rate to meet tissue oxygen demands 1
• These conditions represent appropriate physiological responses rather than primary cardiac pathology 1

Endocrine Disorders

• Hyperthyroidism is a critical reversible cause that must be systematically excluded 1, 3
• Thyrotoxicosis-induced tachycardia responds to beta-blockade while definitive treatment with carbimazole or propylthiouracil takes effect 2
• Non-dihydropyridine calcium channel blockers (diltiazem or verapamil) serve as alternatives when beta-blockers are contraindicated 2

Acid-Base Disturbances

• Metabolic acidosis and alkalosis can precipitate tachycardia through direct effects on cardiac automaticity 1

Exogenous Substances and Medications

Stimulants and Recreational Drugs

• Caffeine, alcohol, nicotine, and illicit stimulants (cocaine, amphetamines, methamphetamine) induce hyperadrenergic states causing vasoconstriction and tachycardia 1, 4
• Cannabis can trigger tachycardia through autonomic effects 1
• Stimulant drugs evoke life-threatening complications including acute coronary syndrome, arrhythmias, and aortic dissection, particularly in young patients without traditional cardiovascular risk factors 4

Prescription Medications

• Beta-agonist medications (albuterol, terbutaline) directly stimulate cardiac beta-receptors 1
• Aminophylline and theophylline reduce the sedative effects of benzodiazepines and can precipitate tachycardia 2, 5
• Atropine and catecholamines have direct chronotropic effects 1
• Anthracycline chemotherapy agents cause cardiotoxicity that may manifest as tachycardia 1
• Numerous antiarrhythmic agents, antimicrobial drugs, psychotropic medications, methadone, neurological drugs, and anticancer agents can induce various arrhythmias 6

Psychological and Autonomic Causes

Anxiety and Stress Disorders

• Emotional stress and anxiety-related disorders are extremely common non-cardiac causes of tachycardia, often misdiagnosed, leading to extensive unnecessary cardiac testing 2, 1
• Beta-blockade is highly effective for physiological symptomatic sinus tachycardia triggered by emotional stress and anxiety disorders 2
• In patients with recurrent chest pain and tachycardia despite negative cardiac workup, cognitive-behavioral therapy reduces symptom frequency by 32% over 3 months 2
• For patients with multiple presentations of tachycardia and palpitations with consistently negative cardiac evaluations, referral to a cognitive-behavioral therapist is reasonable rather than repeating cardiac testing 2

Inappropriate Sinus Tachycardia (IST)

• IST is defined as persistent resting heart rate >100 bpm with average 24-hour heart rate >90 bpm, unexplained by physiological demands 3, 7
• The condition predominantly affects young females (approximately 90%), with mean presentation age of 38 years, and disproportionately affects healthcare professionals 2
• Mechanisms include dysautonomia, neurohormonal dysregulation, intrinsic sinus node hyperactivity, enhanced automaticity, and abnormal autonomic regulation with excess sympathetic and reduced parasympathetic tone 1, 3, 7
• Beta-blockers should be prescribed as first-line therapy; non-dihydropyridine calcium channel blockers (verapamil, diltiazem) are effective alternatives 2

Postural Orthostatic Tachycardia Syndrome (POTS)

• POTS is diagnosed by sustained heart rate increase ≥30 bpm in adults (≥40 bpm in adolescents) within 10 minutes of standing, or heart rate ≥120 bpm, without orthostatic hypotension 3
• Symptoms include lightheadedness, dizziness, nausea, dyspnea, diaphoresis, headache, and fatigue that appear or worsen in upright position with relief when sitting or lying down 3
• Deconditioning triggers a vicious cycle: reduced physical activity → plasma volume reduction → secondary cardiac atrophy → compensatory tachycardia to maintain cardiac output 3

Pain and Physical Stress

• Acute pain from any source triggers sympathetic activation and compensatory tachycardia 1
• Physical activity and exercise represent normal physiological causes that must be distinguished from pathological tachycardia 1, 3

Diagnostic Approach Algorithm

Initial Evaluation

1. Obtain 12-lead ECG during tachycardia when possible to distinguish supraventricular from ventricular origins and assess QRS width 2
2. If resting sinus tachycardia >120 bpm, repeat ECG after rest period to exclude recent exercise or anxiety 2
3. Systematically exclude secondary causes before diagnosing primary dysautonomia or inappropriate sinus tachycardia 3

Laboratory and Clinical Assessment

• Check thyroid function tests (TSH, free T4) to exclude hyperthyroidism 1, 3
• Obtain complete blood count to identify anemia 1, 3
• Assess volume status and electrolytes to detect dehydration and acid-base disturbances 1, 3
• Screen for infection with fever 1, 3
• Obtain detailed substance use history including caffeine, alcohol, nicotine, prescription medications (beta-agonists, aminophylline, atropine), and illicit stimulants 1, 3

Cardiac Evaluation

• Echocardiogram to exclude structural heart disease 2
• 24-hour Holter monitor for frequent arrhythmias (several episodes per week) 2
• Event or loop recorder for less frequent symptoms 2
• Exercise stress testing if arrhythmia is triggered by exertion 2

Management Principles

Treat Underlying Cause

• The mainstay of management involves identifying and eliminating or treating the underlying cause 2
• Correct dehydration with volume replacement 1
• Treat anemia appropriately 1
• Manage hyperthyroidism with antithyroid medications 2
• Eliminate offending substances and medications when possible 1, 6
• Address infection and fever 1

Pharmacologic Management

• Beta-blockers are first-line for anxiety-related tachycardia, inappropriate sinus tachycardia, and symptomatic thyrotoxicosis 2
• Non-dihydropyridine calcium channel blockers (diltiazem, verapamil) serve as alternatives when beta-blockers are contraindicated 2
• For anxiety disorders with recurrent tachycardia, antidepressants and anxiolytics have mixed evidence, but cognitive-behavioral therapy demonstrates clear benefit 2
• Benzodiazepines like lorazepam can be used cautiously for acute anxiety-related tachycardia, but carry risks of abuse, dependence, and withdrawal reactions 5

Critical Pitfalls to Avoid

• Do not initiate class I or III antiarrhythmic drugs without documented arrhythmia due to proarrhythmic risk 2
• Avoid misdiagnosing anxiety or panic disorder when organic causes have not been adequately excluded 8
• In young patients with tachycardia and no traditional cardiovascular risk factors, maintain high suspicion for illicit stimulant use 4
• Do not repeatedly order cardiac testing in patients with multiple negative evaluations; instead refer for cognitive-behavioral therapy 2
• When using benzodiazepines, avoid concomitant opioids due to risk of fatal respiratory depression 5