What labs should be ordered for a patient with ventricular tachycardia (VTach)?

Laboratory Workup for Ventricular Tachycardia

Order serum electrolytes (potassium, magnesium, calcium), complete blood count, renal function tests, thyroid-stimulating hormone, and cardiac biomarkers (troponin, CK-MB) immediately for any patient with documented ventricular tachycardia. 1

Core Laboratory Panel (Order Immediately)

Electrolytes - Critical Priority

• Serum potassium is essential because hypokalemia is present in 35.7% of patients with ventricular arrhythmias, with severe hypokalemia (<3.0 mmol/L) occurring in 13.6% of cases 1
• Magnesium levels must be checked as hypomagnesemia can precipitate or perpetuate ventricular arrhythmias and is frequently overlooked 1
• Calcium levels should be measured as both hypocalcemia and hypercalcemia can affect cardiac repolarization and trigger arrhythmias 1

Cardiac Biomarkers

• Troponin and CK-MB should be measured to assess for acute myocardial injury or ongoing ischemia, as coronary artery disease with prior myocardial infarction is the most common substrate for sustained VT 2, 3

Complete Blood Count

• CBC is mandatory to exclude anemia, which can mimic or aggravate tachycardia and reduce the threshold for arrhythmias 1

Renal Function

• Creatinine and BUN are essential because renal dysfunction affects electrolyte balance and drug metabolism, both critical in VT management 1

Thyroid Function

• TSH should be measured routinely as both hyperthyroidism and hypothyroidism can be primary causes of ventricular arrhythmias 1

Additional Testing Based on Clinical Context

Toxicology Screen

• Urine drug screen is reasonable in younger patients as illicit drugs (cocaine, amphetamines, ephedra) are common reversible causes of ventricular tachycardia 1
• Obtain detailed history about energy drinks, supplements, and over-the-counter stimulants 1

Medication Review

• Review all medications for QT-prolonging drugs (www.crediblemeds.org) as various antiarrhythmic and other medications can cause torsades de pointes 4
• Check for drugs that can induce Brugada pattern (www.brugadadrugs.org) 4

Critical Diagnostic Considerations

ECG Documentation

• A 12-lead ECG in sinus rhythm must be obtained to look for evidence of structural heart disease, prior MI, chamber enlargement, inherited arrhythmia disorders (long QT, Brugada, ARVC), or bundle branch blocks 4
• The ECG may reveal Q waves indicating ischemic heart disease, ventricular hypertrophy, or repolarization abnormalities from electrolyte disturbances 4

Structural Heart Disease Assessment

• Echocardiography is mandatory in all patients with ventricular arrhythmias to assess left and right ventricular function and detect structural heart disease 4
• This is particularly critical as most sustained VT occurs in the setting of structural heart disease, especially prior myocardial infarction 3

Common Pitfalls to Avoid

• Do not assume normal electrolytes - hypokalemia is present in over one-third of VT patients and must be actively excluded 1
• Do not overlook magnesium - it is frequently deficient even when potassium appears normal and requires separate measurement 1
• Do not skip thyroid testing - thyroid dysfunction can be the primary driver of arrhythmias and is easily treatable 1
• Do not forget to check renal function - it affects both electrolyte homeostasis and antiarrhythmic drug dosing 1

Urgent Cardiology Referral Indications

• Any documented wide-complex tachycardia requires urgent cardiology consultation 1
• Hemodynamic instability, syncope, or heart rate persistently >150 bpm mandate immediate specialist involvement 1
• Elevated troponin suggesting acute ischemia as the VT trigger requires emergent cardiology evaluation 2