What are the causes and treatments of tachycardia in a young adult?

Causes of Tachycardia in a 22-Year-Old

Primary Causes to Evaluate

In a 22-year-old with tachycardia, you must first distinguish between physiological sinus tachycardia (secondary to an underlying condition) and primary cardiac arrhythmias, as the management differs completely. 1

Physiological/Secondary Causes (Most Common in Young Adults)

• Fever, infection, dehydration, anemia, pain - These are the most common causes of sinus tachycardia in young adults and should be identified and corrected first 1
• Hyperthyroidism - Must be excluded with TSH testing, as it commonly presents with persistent tachycardia 1, 2
• Anxiety and panic disorder - A critical pitfall: anxiety is frequently the actual diagnosis when SVT is suspected, but conversely, SVT is frequently misdiagnosed as panic disorder because symptoms are nearly identical (palpitations, chest discomfort, dyspnea, lightheadedness) 1, 2
• Exogenous substances - Caffeine, beta-agonists (albuterol, salmeterol), illicit stimulants (amphetamines, cocaine) 1
• Medications - Review all current medications for tachycardia-inducing effects 1

Primary Cardiac Arrhythmias

Narrow-complex tachycardias (QRS <120 ms): 1

• Supraventricular tachycardia (SVT) - Most commonly AV nodal reentry tachycardia (AVNRT) or AV reentry tachycardia (AVRT) in young adults 1, 3
• Wolff-Parkinson-White syndrome - Accessory pathway-mediated tachycardia that requires immediate cardiology referral 4, 2, 3
• Atrial fibrillation - Less common in this age group without structural heart disease 1
• Atrial flutter - Can occur with variable AV conduction 1
• Inappropriate sinus tachycardia (IST) - Defined as unexplained sinus tachycardia at rest (>100 bpm) with mean 24-hour rate >90 bpm, causing debilitating symptoms including weakness, fatigue, and lightheadedness 1, 4

Wide-complex tachycardias (QRS ≥120 ms): 1

• Ventricular tachycardia - Less common in young adults without structural heart disease but must be considered 1, 5
• SVT with aberrancy - Supraventricular rhythm conducted with bundle branch block 1, 5
• Pre-excited tachycardias - WPW syndrome with anterograde conduction down accessory pathway 1

Diagnostic Approach

Immediate Assessment

Obtain a 12-lead ECG immediately - This is the single most important diagnostic test to document the rhythm, measure QRS duration, identify P-wave morphology and relationship to QRS, and look for pre-excitation (delta waves suggesting WPW) 1, 4, 2

Key ECG features to distinguish mechanisms: 1

• Sinus tachycardia: Gradual onset/termination, P waves before each QRS, rate typically <150 bpm unless severe physiologic stress 1, 2
• SVT: Abrupt onset/termination, rate typically >150 bpm, regular rhythm, narrow QRS 1, 2, 3
• Pre-excitation (WPW): Short PR interval, delta wave, wide QRS at baseline 4, 2

Laboratory Workup

• TSH - To exclude hyperthyroidism 2
• Complete blood count - To identify anemia 2
• Basic metabolic panel - To assess for electrolyte abnormalities and dehydration 2
• Echocardiogram - To exclude structural heart disease including cardiomyopathies, valvular abnormalities, and assess for tachycardia-mediated cardiomyopathy 4, 2

Rhythm Documentation

• Ambulatory monitoring (Holter or event recorder) - Essential if episodes are paroxysmal to capture the arrhythmia and confirm diagnosis 2, 3

Critical Diagnostic Distinctions

Rate <150 bpm: Unless there is impaired ventricular function, symptoms are unlikely to be caused primarily by the tachycardia itself; look for underlying causes 1, 4

Rate ≥150 bpm: More likely that tachycardia is the primary cause of symptoms, especially if sustained 1, 4

Abrupt onset/termination: Strongly suggests SVT (AVNRT or AVRT) rather than sinus tachycardia from anxiety 2, 3

Episodes lasting hours: More consistent with SVT than simple anxiety-related sinus tachycardia 2

Mandatory Cardiology Referral Criteria

Immediate referral required for: 4, 2

• Pre-excitation (WPW syndrome) on ECG
• Wide-complex tachycardia of unknown origin
• Syncope during tachycardia or with exercise
• Documented sustained SVT
• Recurrent episodes of regular, paroxysmal palpitations with abrupt onset/termination
• Disabling symptoms despite treatment

Treatment Approach

For Physiological Sinus Tachycardia

Treat the underlying cause, not the heart rate - No specific antiarrhythmic therapy is indicated for physiologic sinus tachycardia 1, 4

• Correct fever, dehydration, anemia, hyperthyroidism, or discontinue offending medications 1
• Address anxiety with appropriate psychiatric referral if cardiac workup is negative 2

For Inappropriate Sinus Tachycardia

Treatment is for symptom reduction only, as prognosis is generally benign - Lowering heart rate may not alleviate symptoms 1

• Beta blockers or calcium channel blockers are often ineffective or not well tolerated due to hypotension 1
• Ivabradine (If channel inhibitor) reduces sinus node pacemaker activity 1
• Exercise training may be beneficial but unproven 1

For Acute SVT (Hemodynamically Stable)

Vagal maneuvers and/or IV adenosine (Class I recommendation) 1

• Adenosine dosing: First dose 6 mg rapid IV push followed by NS flush; second dose 12 mg if required 1, 6
• If ineffective or not feasible, consider IV beta blockers or calcium channel blockers 1

For Acute SVT (Hemodynamically Unstable)

Immediate synchronized cardioversion - Do not delay for IV access if patient is unstable 1, 4

• Starting dose: 50-100 J for SVT, increase stepwise if initial shock fails 4

Critical Pitfalls to Avoid

Do not assume "just anxiety" without proper cardiac evaluation - SVT and panic disorder present with nearly identical symptoms and are frequently confused 2, 3

Do not use AV nodal blocking agents if pre-excitation is present on ECG - This can be dangerous in atrial fibrillation with WPW syndrome 2

Do not "normalize" heart rate in compensatory tachycardia - When cardiac function is poor, cardiac output can depend on rapid heart rate; slowing it can be detrimental 4

Recognize tachycardia-mediated cardiomyopathy - Persistent tachycardia (weeks to months) with fast ventricular response can cause reversible cardiomyopathy requiring careful long-term follow-up 4