What is the management for an adult patient with a suspected overdose that may cause ventricular tachycardia, potentially due to pre-existing cardiac conditions or medications such as certain antipsychotics or antibiotics that can lead to QT (Prolonged QT Interval) prolongation?

Management of Overdose with Potential for Ventricular Tachycardia

For suspected drug overdoses that may cause ventricular tachycardia, immediately administer sodium bicarbonate (1 mEq/kg IV bolus) for wide-complex tachycardia from sodium channel blockers (tricyclic antidepressants, cocaine, class Ic antiarrhythmics), correct all electrolyte abnormalities urgently (potassium >4.5 mEq/L, normalize magnesium), and discontinue all QT-prolonging medications. 1, 2

Immediate Assessment and Stabilization

ECG Evaluation

• Obtain 12-lead ECG immediately to assess for QRS widening (>120 ms) and QTc prolongation 1
• Measure QTc using Fridericia formula: critical thresholds are QTc >500 ms or increase >60 ms from baseline 1, 2
• Look specifically for signs of impending torsades de pointes: QT-U distortion, T-wave alternans, and polymorphic ventricular ectopy 1

Electrolyte Correction (Priority Action)

• Check and aggressively correct potassium to >4.5 mEq/L (ideally 4.5-5.0 mEq/L) 1, 2
• Normalize magnesium levels immediately, as hypokalemia and hypomagnesemia exponentially increase torsades risk 1, 2
• These corrections must occur before any antiarrhythmic therapy 1, 2

Drug-Specific Management Algorithms

Sodium Channel Blocker Overdose (TCAs, Cocaine, Class Ic Antiarrhythmics)

Wide-complex tachycardia from these agents requires immediate sodium bicarbonate therapy 1, 3

• Administer sodium bicarbonate 8.4% solution (1 mEq/mL) at 1 mL/kg IV bolus 1
• Repeat boluses until hemodynamic stability restored and QRS narrows to <120 ms 1
• Target serum pH of 7.45-7.55 to maximize sodium channel unblocking 1
• This approach extrapolates from strong evidence in tricyclic antidepressant and flecainide toxicity 1, 3

Common pitfall: Do not use lidocaine for cocaine-induced wide-complex tachycardia, as current evidence neither supports nor refutes its role 1

QT-Prolonging Drug Overdose (Antipsychotics, Antibiotics, Antiarrhythmics)

Management stratified by QTc severity 1, 2:

QTc 481-500 ms:

• Discontinue all QT-prolonging agents 1, 2
• Correct electrolytes aggressively (potassium >4.5 mEq/L, normalize magnesium) 1, 2
• Implement continuous ECG monitoring 2
• Consider dose reduction if drug cannot be stopped 2

QTc >500 ms or ΔQTc >60 ms:

• Immediately discontinue all causative medications 1, 2
• Correct electrolyte abnormalities urgently 1, 2
• Continue ECG monitoring until QTc normalizes 2
• Prepare for potential torsades de pointes management 1, 2

High-Risk Antipsychotic Overdoses

The American Academy of Pediatrics and European Heart Journal provide specific QTc prolongation data 4:

Highest risk agents to identify:

• Thioridazine: 25-30 ms prolongation (FDA black box warning) 4
• Ziprasidone: 5-22 ms prolongation 4
• Pimozide: 13 ms prolongation 4
• Haloperidol: 7 ms prolongation (higher with IV route) 4

Critical caveat: IV haloperidol carries substantially higher risk than oral or IM administration for both QTc prolongation and torsades de pointes 4

Management of Active Ventricular Tachycardia

Hemodynamically Unstable VT

• Perform immediate electrical cardioversion 1, 5
• If recurrent after cardioversion, administer class I antiarrhythmics (lidocaine, ajmaline) or amiodarone 5

Torsades de Pointes (Polymorphic VT with Prolonged QT)

First-line therapy regardless of serum magnesium level 1, 2:

• Administer 2g IV magnesium sulfate immediately 1, 2
• This suppresses torsades episodes even with normal magnesium levels 1, 2

If torsades persists or recurs 2:

• Implement temporary overdrive pacing (target heart rate >90 bpm) 2
• Alternative: IV isoproterenol titrated to heart rate >90 bpm if pacing unavailable 2
• Perform non-synchronized defibrillation for hemodynamically unstable sustained episodes 2

Do NOT use: Class Ia or Ic antiarrhythmics (procainamide, quinidine, flecainide) or sotalol in patients with prolonged QT, as these will worsen the arrhythmia 1

Polymorphic VT with Normal QT (Ischemia-Related)

• IV amiodarone may reduce arrhythmia recurrence 1
• Beta-blockers may be effective 1
• Magnesium is unlikely to be effective when QT interval is normal 1

Antiarrhythmic Drug Selection in Overdose Context

When Antiarrhythmic Therapy is Needed

For regular wide-complex tachycardia of uncertain etiology 1:

• Procainamide (Class IIa) is preferred first-line agent 1
• Amiodarone (Class IIb) is alternative 1
• Sotalol (Class IIb) is third option 1
• Avoid procainamide and sotalol if QT is prolonged 1
• Never give a second antiarrhythmic without expert consultation 1

Critical warning about amiodarone: Although amiodarone markedly prolongs QT interval, it rarely causes torsades de pointes due to uniform repolarization delay across all myocardial layers 1, 6. However, co-administration with other QT-prolonging drugs increases torsades risk 6

Drugs to Absolutely Avoid

• Verapamil is contraindicated for wide-complex tachycardia unless proven supraventricular origin 1
• Adenosine should not be given for unstable, irregular, or polymorphic wide-complex tachycardia as it may precipitate ventricular fibrillation 1

Special Considerations for Specific Overdoses

Cocaine Toxicity

• Benzodiazepines (lorazepam, diazepam) are beneficial for cocaine-induced hypertension and chest discomfort 1
• Nitroglycerin and morphine can also be used 1
• For wide-complex tachycardia: sodium bicarbonate as described above 1
• Choose drug doses carefully as cocaine effects are transient and hypotension may develop after metabolism 1

Methadone Overdose

• High doses and recent dose increases are common features of methadone-related torsades 1
• Multiple drug interactions can increase methadone levels and QTc prolongation risk 1
• Follow QTc prolongation management algorithm above 1, 2

Citalopram and Other SSRI Overdoses

• Torsades de pointes has been reported with citalopram overdose 1
• Manage according to QTc prolongation severity as outlined above 1, 2

Monitoring Requirements

Continuous Monitoring Needed For:

• All patients with QTc >480 ms 2
• Any patient receiving IV antiarrhythmics 6
• Patients with recurrent ventricular arrhythmias 2
• High-risk patients: females, age >65, baseline cardiac disease, congenital long QT 1, 4

Serial ECG Timing:

• Baseline immediately upon presentation 1, 2
• After each intervention (sodium bicarbonate, electrolyte correction, antiarrhythmic administration) 2
• Every 2-4 hours until QTc normalizes and patient stabilizes 2

Critical Pitfalls to Avoid

1. Do not delay sodium bicarbonate for wide-complex tachycardia while waiting for toxicology results—treat empirically if sodium channel blocker suspected 1

2. Do not assume normal magnesium level means magnesium won't help torsades—give 2g IV regardless 1, 2

3. Do not combine multiple QT-prolonging antiarrhythmics without expert consultation, as this exponentially increases torsades risk 1, 6

4. Do not use class Ia/Ic antiarrhythmics or sotalol if QT is already prolonged 1

5. Do not forget that IV haloperidol (often used for agitation) has higher arrhythmia risk than oral/IM routes 4

6. Do not measure QT intervals in paced rhythms or bundle branch blocks without recognizing the artificial prolongation from widened QRS 7