Initial Workup for Tachycardia
The initial workup for a patient presenting with tachycardia should include a 12-lead ECG, assessment of hemodynamic stability, and evaluation for underlying causes through focused history, physical examination, and basic laboratory tests. 1, 2
Step 1: Assess Hemodynamic Stability
Immediately evaluate for signs of instability:
- Hypotension
- Altered mental status
- Ischemic chest pain
- Acute heart failure
- Signs of shock
If unstable, proceed to immediate synchronized cardioversion while simultaneously addressing:
- Oxygen supplementation
- IV access
- Monitoring 1
Step 2: Obtain 12-Lead ECG
The ECG is essential for diagnosis and classification of tachycardia 1, 2. Analyze for:
- QRS width:
- Narrow complex (<0.12 seconds)
- Wide complex (≥0.12 seconds)
- Rhythm regularity:
- Regular
- Irregular
- P wave presence and morphology
- Relationship between P waves and QRS complexes
- Pre-excitation patterns
Step 3: Classify the Tachycardia
Narrow-Complex Tachycardias (QRS <0.12 seconds):
- Sinus tachycardia
- Atrial fibrillation
- Atrial flutter
- AV nodal reentry tachycardia (AVNRT)
- Accessory pathway-mediated tachycardia
- Atrial tachycardia
- Multifocal atrial tachycardia (MAT)
- Junctional tachycardia 1
Wide-Complex Tachycardias (QRS ≥0.12 seconds):
- Ventricular tachycardia (VT)
- Ventricular fibrillation (VF)
- Supraventricular tachycardia with aberrancy
- Pre-excited tachycardias (Wolff-Parkinson-White syndrome)
- Ventricular paced rhythms 1
Step 4: Laboratory Evaluation
Obtain basic laboratory tests to identify underlying causes:
- Complete blood count
- Basic metabolic panel (electrolytes, renal function)
- Thyroid function tests
- Cardiac biomarkers (troponin)
- Toxicology screen if indicated 1, 2
Step 5: Additional Diagnostic Testing
Based on clinical presentation and initial findings:
- Echocardiography: Recommended for all patients with new-onset AF or suspected structural heart disease to evaluate cardiac function, chamber size, and valvular abnormalities 1
- Chest radiograph: If pulmonary disease or heart failure is suspected 1
- Continuous cardiac monitoring: For paroxysmal tachycardias not captured on initial ECG 1
- Transesophageal echocardiography (TEE): If atrial fibrillation is present and cardioversion is planned 1
Special Considerations
For Regular Narrow-Complex Tachycardia:
- If hemodynamically stable, consider vagal maneuvers (Valsalva, carotid sinus massage) as first-line intervention 2
- If vagal maneuvers fail, adenosine (6 mg rapid IV push, followed by 12 mg if needed) can be both diagnostic and therapeutic 1, 2
For Irregular Narrow-Complex Tachycardia:
- Most likely atrial fibrillation or multifocal atrial tachycardia 1
- Focus on rate control and anticoagulation assessment for AF 1
For Wide-Complex Tachycardia:
- Assume ventricular tachycardia until proven otherwise 1, 2
- Avoid verapamil in undiagnosed wide-complex tachycardia due to risk of hemodynamic collapse 2
Common Pitfalls to Avoid
Misdiagnosing sinus tachycardia: Remember that sinus tachycardia is often secondary to underlying conditions (fever, anemia, dehydration, pain) and requires treatment of the primary cause rather than the tachycardia itself 1
Overlooking medication-induced tachycardia: Always obtain a complete medication history, including over-the-counter and weight loss supplements 3
Failing to recognize pre-excitation: Pre-excitation on resting ECG with history of paroxysmal palpitations suggests AVRT and requires referral to an arrhythmia specialist 1
Delaying cardioversion in unstable patients: Do not delay cardioversion for diagnostic workup in hemodynamically unstable patients 1, 2
Using inappropriate medications: Avoid verapamil, diltiazem, and adenosine in patients with suspected Wolff-Parkinson-White syndrome with atrial fibrillation 2