What is the recommended workup for a patient presenting with tachycardia?

Workup for Tachycardia

Immediately attach a cardiac monitor, obtain vital signs, establish IV access, assess oxygen saturation, and obtain a 12-lead ECG to define rhythm characteristics—but do not delay cardioversion if the patient is unstable. 1, 2

Initial Assessment and Stabilization

Immediate Actions

• Attach cardiac monitor/defibrillator and obtain continuous vital signs monitoring 3, 1
• Establish IV or IO access 3, 2
• Assess oxygen saturation and respiratory status (look for tachypnea, retractions, paradoxical breathing—hypoxemia is a common reversible cause) 1, 2
• Administer supplemental oxygen 3

Critical Decision Point: Hemodynamic Stability

Assess immediately for signs of hemodynamic instability: 1, 2

• Acute altered mental status
• Ischemic chest discomfort or pain
• Acute heart failure
• Hypotension or shock

If any of these are present, proceed directly to treatment without delay—do not wait for 12-lead ECG completion. 1, 2

Diagnostic Workup

12-Lead ECG Analysis

Obtain a 12-lead ECG during tachycardia if possible (this is the cornerstone of diagnosis, but only after stabilization in unstable patients) 3, 1, 2

Classify the rhythm by two key variables: 3, 4

1. Regularity: Is the ventricular rate regular or irregular?
2. QRS width: Is the QRS narrow (<0.09 seconds or <120 ms) or wide (≥0.09 seconds or ≥120 ms)?

Narrow-Complex Tachycardia (<0.09 seconds)

Evaluate for: 3

• Sinus tachycardia: Search for and treat reversible causes (fever, dehydration, anemia, hypoxemia, pain, anxiety, medication effects) 3, 1
• Supraventricular tachycardia (SVT): Look for P wave location relative to QRS
  • Short RP interval suggests AVNRT or orthodromic AVRT 3
  • Pseudo S waves in inferior leads or pseudo R' in V1 suggest AVNRT 3
  • P wave in early ST segment suggests orthodromic AVRT 3
• Irregular rhythm: Consider atrial fibrillation, multifocal atrial tachycardia, or atrial flutter with variable AV conduction 3

Wide-Complex Tachycardia (≥0.09 seconds)

This is ventricular tachycardia until proven otherwise—misdiagnosis can be life-threatening. 3

Look for diagnostic features of VT: 3

• AV dissociation (ventricular rate faster than atrial rate)—diagnostic of VT
• Fusion complexes—diagnostic of VT
• Concordance of precordial QRS complexes (all positive or all negative)—suggests VT or pre-excitation
• Apply Brugada criteria or Vereckei algorithm for systematic differentiation 3, 5

If wide-complex tachycardia origin is uncertain, consult cardiology urgently—even if self-terminated. 1, 2

Additional Workup Based on Clinical Context

Laboratory Studies

Check for reversible causes: 1

• Electrolytes (potassium, magnesium, calcium)
• Complete blood count (anemia)
• Thyroid function tests (if clinically indicated)
• Troponin (if ischemia suspected)
• Blood cultures (if sepsis suspected)

Obtain 12-Lead ECG in Sinus Rhythm

If tachycardia has resolved, obtain ECG in sinus rhythm to look for: 3, 1

• Pre-excitation pattern (delta waves)—indicates Wolff-Parkinson-White syndrome and requires urgent electrophysiology referral 3, 6
• Baseline conduction abnormalities
• Evidence of structural heart disease

Cardiac Monitoring for Intermittent Symptoms

If tachycardia not captured but history is suspicious: 2, 6

• Holter monitor for frequent daily symptoms
• Event recorder for less frequent episodes
• Consider implantable loop recorder for rare but significant episodes

Special Populations and Situations

Pediatric Considerations

Age-specific heart rate thresholds: 1

• First week of life: upper normal limit is 166 bpm
• First month: upper normal limit is 179 bpm
• After 6 months: upper normal limit is approximately 160 bpm

Work up pediatric sinus tachycardia when associated with: fever, infection, anemia, pain, dehydration, hyperthyroidism, or myocarditis 1

Patients with Ventricular Dysfunction

Lower threshold for workup (<150 bpm) in patients with known ventricular dysfunction, as they are more vulnerable to hemodynamic compromise 1, 2

Suspected Ventricular Tachycardia

Even if self-terminated, urgent workup includes: 7, 1

• Urgent cardiology consultation
• Echocardiography to evaluate for structural heart disease
• Consider cardiac MRI if etiology unclear

Critical Pitfalls to Avoid

• Never delay cardioversion in unstable patients while obtaining 12-lead ECG 1
• Never use AV nodal blocking agents (adenosine, calcium channel blockers, beta blockers) in pre-excited atrial fibrillation—this accelerates ventricular response and can be lethal 1
• Never give adenosine for irregular or polymorphic wide-complex tachycardia—may cause degeneration to ventricular fibrillation 1
• Never assume wide-complex tachycardia is SVT with aberrancy—treat as VT until proven otherwise 3

Indications for Cardiology/Electrophysiology Referral

Refer when: 1

• Wide-complex tachycardia of unknown origin
• Any suspected or confirmed ventricular tachycardia (even if self-terminated)
• Pre-excitation on resting ECG with history of paroxysmal palpitations
• Drug-resistant or drug-intolerant narrow-complex tachycardia
• Patients desiring freedom from long-term drug therapy (catheter ablation candidates)
• Recurrent symptomatic SVT