What investigations, differential diagnosis, assessment, and management plan are appropriate for a patient presenting to the emergency department with symptomatic tachycardia?

Emergency Department Approach to Symptomatic Tachycardia

Immediate Assessment and Stabilization

The first priority is determining hemodynamic stability—if the patient shows acute altered mental status, ischemic chest pain, acute heart failure, hypotension, or shock, proceed immediately to synchronized cardioversion. 1

Initial Actions (Perform Simultaneously)

• Attach cardiac monitor and obtain continuous vital signs 1, 2
• Establish IV access 1, 2
• Check pulse oximetry—hypoxemia is a common driver of tachycardia 1
• Provide supplemental oxygen if oxygen saturation is low or signs of respiratory distress present 1
• Obtain 12-lead ECG without delaying cardioversion if unstable 1, 2

Critical Decision: Stable vs. Unstable

For unstable patients (altered mental status, chest pain suggesting ischemia, acute heart failure, hypotension/shock): perform immediate synchronized cardioversion with sedation if conscious and time permits. 1, 2

For stable patients: obtain 12-lead ECG and proceed with algorithmic evaluation. 1, 2

Differential Diagnosis Based on ECG Characteristics

Narrow-Complex Tachycardia (QRS <0.12 seconds)

Primary differential:

• Sinus tachycardia (most common in ED)—physiologic response to fever, dehydration, anemia, hypotension, pain, anxiety 1
• Supraventricular tachycardia (SVT)—AV nodal reentry, accessory pathway-mediated, atrial tachycardia 2, 3
• Atrial fibrillation with rapid ventricular response 1
• Atrial flutter 1, 2

Key distinguishing feature: If heart rate <150 bpm, symptoms are unlikely caused primarily by the tachycardia unless ventricular dysfunction is present—search for underlying cause. 1

Wide-Complex Tachycardia (QRS ≥0.12 seconds)

Assume ventricular tachycardia (VT) until proven otherwise—misdiagnosis can be fatal. 4

Primary differential:

• Ventricular tachycardia (most common) 1
• SVT with aberrancy 1
• Pre-excited tachycardia (accessory pathway conduction, e.g., WPW) 1
• Ventricular paced rhythm 1

Assess regularity:

• Regular wide-complex: likely VT or SVT with aberrancy 1
• Irregular wide-complex: atrial fibrillation with aberrancy, pre-excited atrial fibrillation, or polymorphic VT/torsades 1

Investigations

Essential Initial Workup

• 12-lead ECG—defines rhythm, QRS width, regularity, P-wave relationship 1, 2
• Continuous cardiac monitoring 1
• Vital signs including blood pressure 1, 2
• Pulse oximetry 1

Laboratory Investigations

• Electrolytes (potassium, magnesium, calcium)—critical for arrhythmia management 4
• Troponin—assess for acute myocardial infarction (AMI present in 21% of stable VT, 65% of unstable VT) 5
• Complete blood count—evaluate for anemia 1
• Thyroid function—if atrial fibrillation or unexplained sinus tachycardia 6
• Toxicology screen—if suspected drug-induced arrhythmia 1

Additional Diagnostic Studies

• Echocardiography—evaluate for structural heart disease, particularly in VT patients 2
• Chest X-ray—assess for heart failure, pulmonary pathology 6

Assessment and Management Plan

For Sinus Tachycardia

No specific antiarrhythmic treatment required—identify and treat underlying cause (fever, dehydration, anemia, hypotension, pain, sepsis, pulmonary embolism, hyperthyroidism). 1

Critical pitfall: Do not "normalize" heart rate in patients with poor cardiac function where cardiac output depends on compensatory tachycardia—this can be detrimental. 1

For Stable Narrow-Complex SVT

First-line: Attempt vagal maneuvers (Valsalva maneuver preferred—safer and more efficacious than carotid massage, especially in elderly). 1, 3

Second-line: Adenosine 6 mg rapid IV bolus; if no response, give 12 mg (may repeat 12 mg once). 1, 3

• Adenosine is first-line pharmacologic agent with minimal transient side effects 1
• Contraindications: severe asthma, second/third-degree AV block 3
• May precipitate atrial fibrillation in 1-15% of cases 4

Third-line: AV nodal blocking agents:

• Beta-blockers (metoprolol, esmolol) or calcium channel blockers (diltiazem, verapamil) for rate control 1
• Use caution in obstructive pulmonary disease or heart failure 1

Critical contraindication: Do NOT use AV nodal blocking agents (adenosine, calcium blockers, beta-blockers, digoxin) in pre-excited atrial fibrillation/flutter (WPW syndrome)—may accelerate ventricular response and cause hemodynamic collapse. 1, 7

For Stable Wide-Complex Tachycardia

Assume VT and treat accordingly unless definitively proven otherwise. 4

First-line pharmacologic options:

• Procainamide 15 mg/kg IV over 30-60 minutes—preferred for stable monomorphic VT without severe heart failure or acute MI 1, 4
• Amiodarone 150 mg IV over 10 minutes—preferred if severe heart failure, acute MI, or impaired LV function present 1, 4

Diagnostic/therapeutic consideration: Adenosine may be used for undifferentiated regular stable wide-complex tachycardia—relatively safe and helps diagnose rhythm. 1, 4

• If rhythm terminates, suggests SVT with aberrancy rather than VT 4
• Do NOT use adenosine for unstable, irregular, or polymorphic wide-complex tachycardia 1

Absolute contraindication: Calcium channel blockers (verapamil, diltiazem) are contraindicated for wide-complex tachycardia of unknown origin—can cause hemodynamic collapse if rhythm is VT. 1, 4, 7

For Polymorphic VT (Torsades de Pointes)

If prolonged QT present: IV magnesium sulfate 2 g over 1-2 minutes is primary treatment. 4, 6

If accompanied by bradycardia or pauses: consider overdrive pacing or IV isoproterenol. 4

If normal QT (ischemic polymorphic VT): treat as monomorphic VT with amiodarone. 1

For Unstable Tachycardia (Any Type)

Immediate synchronized cardioversion without delay for pharmacologic therapy. 1, 2, 4

• Sedate if conscious and time permits 1
• Do not delay cardioversion to obtain additional diagnostic studies 4

Disposition and Follow-up

Admission Criteria

• All patients with VT require ICU/CCU admission and immediate cardiology/electrophysiology consultation 4
• Patients with persistent tachycardia or tachypnea have increased mortality risk (5.7% vs 3.1% for persistent tachycardia) 8
• Hemodynamically unstable patients 1
• Patients requiring antiarrhythmic drug initiation 1

Cardiology/Electrophysiology Referral Indications

• Wide-complex tachycardia of unknown origin 2, 4
• Clear history of paroxysmal regular palpitations 2
• Drug-resistant or drug-intolerant narrow-complex tachycardia 2
• Pre-excited atrial arrhythmias (WPW)—ablation is potentially curative 9
• Recurrent SVT in patients desiring freedom from long-term drug therapy 2

Common Pitfalls to Avoid

• Do not assume wide-complex tachycardia is SVT with aberrancy—treat as VT 4
• Do not use calcium channel blockers for undifferentiated wide-complex tachycardia 1, 4, 7
• Do not use AV nodal blockers in pre-excited atrial fibrillation 1, 7
• Do not delay cardioversion in unstable patients 4
• Do not normalize heart rate in compensatory tachycardia with poor cardiac function 1
• Do not combine IV calcium channel blockers and beta-blockers—risk of profound bradycardia and hypotension 1, 4
• Do not give adenosine for irregular or polymorphic wide-complex tachycardia 1